Fantastic and all your clips are outstanding John this is the best way to prepare for an upgrade, if you are taking a Electrical course. Dont know why I wasted money on costly Electrical DVDS. Thanks John.
The French have a DNO supplied 500ma RCBO on the supply which acts as the main switch as well. This solves it. But it is plastic. It is fitted outside of the Consumer Unit which are plastic in France. But usually in a metal cupboard (which is legal in the UK). The French usually have TT earthing.
Actually the cable glands are made of plastic, the inlet (the things with the two holes shown aside) is made of rubber. Actually they are used to offer some protection against dust or water (IP54) and providing some strain-relief if mounted correctly.
Previous to these ammendments metal cased consumer units were a no no on TT systems unless additional rcd protection was provided in an all insulated enclosure prior to the consumer unit. Now it seems using PVC/PVC supply conductors to such an enclosure is acceptable because they have suddenly become double insulated, they are not as they are merely PVC/PVC insulated. A few years ago I would have been pulled for doing this.
Great educational video again. I will not just test for voltage between live and earth on these systems as the earth may be at 230 Volts and not trip anythings. Result = Meter reads 0 volts even if Line at 230 volts !!!!
I wouldn't mind betting that someone within the powers that be,was personally affected by this matter,perhaps had a consumer unit fire or similar,the thing that pisses me off about this kind of thing is that the people who make these changes almost always have no idea about the subject he/she is making changes to.GO FIGURE!!
It was my understanding and that of technical is that the RCD prior to the new 3rd Amendment consumer units is enclosed in a self extinguishing insulated material such as Wylex's supply authority isolated enclosures.
Dale Goodrum The problem with that is the regulation specifies 'non-combustible' rather than self extinguishing, yet does not have any definition for 'non-combustible' other than the suggested example of ferrous metal/steel. A single RCD for the whole installation would not comply with 314.2 either.
*****. Sorry with regards to the RCD I was referring to the 100mA type S RCD not the 30mA located within the main consumer unit. the IET website states not readily combustable, so with that in mind if you do not consider self extinguishing as not readily combustable how would the self extinguishing plastic stuffing gland for the tails comply or any other cable enter for that matter?
Dale Goodrum Common sense would suggest self extinguishing and not readily combustible would be suitable - but the reg specifically states non-combustible which is entirely different. This is probably why all of the consumer unit manufacturers have gone for the steel option. The reg does not say anything about glands or anything other than the enclosure itself so plastic ones could be used, whether they are self extinguishing or not. As you may have guessed by now, the new reg is exceptionally poorly worded and will probably be revised in the fairly near future.
Stainless Steel CU's would be ideal for the many damp cellars around these parts. Still waiting to see MK actually produce any 3rd amendment metal boards ...
There could easily be a technical, if not very elegant fix to this problem. What would be required is a device that monitored the earth voltage relative to neutral. It would be installed in the CU and if a threshold voltage between neutral and earth was exceeded (say 60v) if would create a live-to-neutral path and blow the supplier fuse (and no doubt make a big bang too). Of course the device would probably be destroyed in the process by passing such a big current, but as this ought to be a very rare event, then it's a price worth paying to keep the installation safe (especially as such a fault wouldn't have made just the electrical systems earth live, but also any metal parts bonded to it - like the gas and water pipes). So there's my solution - effectively a device that connects Earth to Neutral within the CU and which goes closed circuit if there's a potential of more than (say) 50v. The very simplest sort of device would work like a souped-up diac and be connected between neutral and earth. Of course, that's a very simple element, but if necessary a more complicated one could be created that created a closed circuit between Live/Line and Neutral, which would be more positive in operation. So how do I file a patent, or have I got the principle wrong?
And if the fuse doesn't blow for some reason you get a fire, and also with that dead short you will probably trip protections on the supplier side that act faster than the fuse, leaving without power an entire block. The solution would be integrating RCD protection on the supplier side, of course time delayed protection to avoid that it trips before the RCD that you have inside you home.
it seems that the problem cannot be solved entirely as at some point in the dwelling the meter tails have to enter the consumers switchgear, and that switchgear now must been metalic i would suggest that a) consumer units should be positioned as close to the REC supply (reg 531.4.1 indicates this) to reduce potential of tails being damaged and a high impedance fault occuring b) cable manufaturers should look at increasing insulation resistance on meter tails or providing insulated sleeving to be fitted on installation c) consumer units need to be more spacious for accomodating larger size cables due to suggested insulation increase and so reducing strain on connections due to bending and tensioning of meter tails inside the consumer unit.
Curious, as there is , as it looks, an unavoidable problem with TT systems, wouldnt it be beneficial to get the power networks to change earth rods to a TNCS PME connection. Everybody worries about fires and not considering death by electrocution on these types of earthing systems, Surely they could just cut the main earth and put it in with the neutral to avoid this problem?
+matt filmer Where TNCS is available it would usually be a better option than TT. However it is not available everywhere as it depends on the design of the electricity network in the area.
there is an option to use ceramic, which can be moulded to any shape, and fits both fireproof and non conductive, or carbon fibre which is used for sports car brakes, so must be hard to set fire to, but maybe this is way too expensive!
a) if you've never seen F1 carbon brakes on fire you've not lived b) carbon fibre is VERY conductive and causes havoc for F1 engineers where for structural integrity reasons they have to maintain that integrity whilst cutting a hole in bulkheads etc AND insulate the cut hole as the carbon fibres are VERY abrasive and after chafing through insulation provide a shorting path for signals and power. My youngest brother has worked as an engineer with one of the top F1 teams for over 25 years and both these issues have the bane of his life for pretty much all that time.
Much older fuse boards did in fact have a porcelain chassis housing the onto which the metal connecting and switching parts were fixed. The porcelain chassis usually had an outer shell-type cover that was either metal or plastic, I guess that JW has some in his museum - check his Flameport site.
I've hit this exact problem with a TT consumer board install. If you check out Crabtree they are suggesting an external 100ma RCD which just moves the problem as JW says. Why don't the manufacturers just put in a simple phase separator or non flammable & conductive sleeve.
+Evil Knievel i work for one of the scottish suppliers, if we get a bad Ze, standard practice now is to fit a 100ma RCD after the meter. the tails are at this point not enclosed, or passing through any metal enclosure, so this does fix the earth problem.
+ben kerr thanks for your response,I think that is the answer but the job I have to do is my own C/U for my first registration with Napit,I'm sure you'll be aware they're one of England's registration bodies. One of their assessors advised me that adding a separate RCD was a possibility but he felt that this would just move the problem as JW suggests. I think you are right as this would be similar to the isolation switch that we've just paid to have installed before continuing with the job. Yes it's got mechanical parts but other than that it's a joint,like a Henley block and the cables aren't really enclosed within it. There's so many opinions,one bloke always thinks he's wiser than the next,I have my opinions,on & on.... I bet they never have a fire start from a cutout switch or a meter so perhaps it is only within C/U's that were poorly installed, had a faulty MCB as someone else suggested or have been tampered with by the consumer or another trade. Let's face it we all have different standards. When will be the first shock from a metal C/U ? Sorry I'm just opinionating , is that a word ? Does anyone have an opinion ?
So if I were to enclose an existing plastic cu in a ferrous cabinet should the cabinet comply to a standard or ip rating ect? Or as long as the cabinet is earthed it would comply?...confusing stuff as usual..think we need an amendment4 to confirm3
Hi John.... This business of the meter tails passing through one hole in the new metal consumer units via a special gland. Now...I watched your video when you tested the theory out....inductance etc.. Why does this not apply to ...say...twin and earth entering a metal back box of a socket etc..
With T&E you have both line and neutral in the cable, current in each wire is in opposite directions so any magnetic effects are cancelled out. The same applies with those plastic glands, as both line and neutral wires pass through the same hole. The problem only occurs with a single wire through one hole.
This amendment was put forward and proposed by the Fire Brigade due to the increase in Consumer Unit fires in the last 5-6 years. It was about 5-6 years ago that there was a recall issued on certain Wylex, Crabtree and Volex MCB's due to them possibly being faulty. Could these MCB's be the root cause of the fires and NOT sub-standard work by Sparkies???
ToonandBBfan Could well be. Not entirely convinced that the Fire Brigade actually proposed this either - the data about the increase in fires certainly came from them, but that may have just been used by others to get metal consumer units as a requirement.
+ToonandBBfan I cant help thinking this is just to create income by legislative obsolescence, there is no reason not to have an RCD mounted in a fireproof fibreglass box ouside the property as they are here in Bulgaria.
Robert Szasz Not done in the UK because it's not permitted - only the electricity supplier can do that, and when they do it, it's done before the meter.
***** that seems like a good way to have the neutral leg floating at some significantly non zero voltage compared to a local ground rod. Do I understand correctly that in the UK earth can/is bonded to the actual local ground? I would expect standing on wet soil and touching the earth conductor (or the shield of a coax connector) to be near totally safe. Thanks for all your informative videos.
Robert Szasz In the US the neutral (white) is attached via a common bus bar in the breaker box with the earth grounds (green) which in turn runs to a grounding rod. Your two hot legs are run across a pair of buses that breakers attach to and for 120 volts the wires are black, for 220 - 240 volts they are usually red and blue with the bare ground for 30 amp, 50 amp has the 4th white neutral added to the cable. The systems in the UK are somewhat dangerous in comparison to the US due to the numerous hazards that can happen just like the one in this video.
ElfNet Gaming thanks for the reply. I know just enough to do hobbiest electronics safely and not blast rf out the power lines when I do ham stuff. Proper premises safety I leave to paid professionals.
Oh yes of course. I work on commercial 2-way radio, cellular, and IT systems. I had to get certified to do electrical work and such. buy yeah leave the premises safety to the guys getting paid for it.
I think that would be the best solution Pat well thought of. I think there would only be a slight increase in cost but it definetly solves the issue. There is plenty PVC coated flat 0.7mm gauge metal around, you could probably get LSF if you look hard enough.
***** They would, but that relies on such things actually being available. Manufacturers who have released new catalogues so far have gone for the 100% metal option, no plastic to be found.
@@jwflame I read recently in ESQCR that the DNO has to abide by BS7671 as soon as their service enters a dwelling. This would include their DP isolator. I'm trying to decide what exactly 421.1.201 applies to when it mentions 'consumer units and similar switchgear assemblies'. I'd say an isolator or stand-alone RCD is an item of switchgear, but lacks similarity to a consumer unit so the non-combustible requirement doesn't apply. I'm looking for an enclosure for an S100 mA RCD at a TT job next week and I think I'm going with plastic.
@@westinthewest Like many things it's not clearly defined, but several manufacturers still make isolators in plastic enclosures, and they are often installed. A metal enclosure on TT direct from the supply is something to be avoided - go with the plastic enclosure and RCD.
Out in 'the sticks' we have many properties on PME and TT's earthing arrangements and I have experienced a broken neutral on an overhead transformer on a property, feeding a farmhouse. The kitchen sink and copper metal pipework were at 250v potential. Not nice and very dangerous..I can see also why the new EV regulation on local earth rod's (TT) has come in, as an EV Car can become live too, hence them upgrading the RCD. PME is not all it's cracked up to be..
Hi, John. I think your presentations are brill!! I'm hoping that you have time to help me with a dilemma I have concerning metal consumer units. My home is on a TT system and is currently being rewired. A 17 way British General Electrical metal consumer unit is being fitted and after viewing your video I am concerned about cables inside the unit creating a fault to the metal case. The unit is fitted with a cable gland. I looked at the Wylex site and they recommend that a 100 milliamp time delay S type RCCB device be fitted between their metal consumer unit and the supply unit. Will this prevent the metal case from ever becoming live and is the Wylex device above compatible with the BG Electrical unit that is being fitted in my home? Thanking you, in anticipation.
Couple of questions: If Neutral is effectively the same as Earth why do we need both cables ? Is there any argument for having any circuits NOT protected by RCDs ? (as seems to be the case in my consumer unit)
+David Graeme-Baker It's an additional safety feature. A system which uses a single conductor for neutral and earth throughout the installation is called TNC, and has the disadvantage that if that conductor is broken, exposed metalwork of appliances will have dangerous voltages, as the combined neutral & earth carries current in normal operation.
When you apply earth bonding to a TT system you could have some worker cut through the main earth wire from the earth rod. If a live wire happens to touch any metal part that is connected to the bonded system then all metallic items become live even with a plastic consumer unit. Unlikely but not impossible?
@@jwflame Initially, I thought the same as you John where I included a failed RCD in my original post (reason for edited) but when you consider that there is no earthing means then a working RCD will be ineffective. I attended a NICEIC talk regarding new regulations and queried the reason for earth bonding and was informed that other countries, such as the USA, do not employ this practice. A short plastic pipe connection between isolating valves and outlets (taps, washing machine valves....) would deem this practice redundant.
@@od5699 "no earthing means then a working RCD will be ineffective" - why do you say that (taking you mean no earth at the consumer rather than the supplier)? A person in contact with an exposed conductive part and earth will pass current that will imbalance the L/N currents so the RCD should operate.
Why not just produce a CU enclosure with a plastic internal case ( similar to what we already had) inside a metal outer case with the plastic entry grommet fitting? These people are just trying to justify their positions by making up stuff as they go. Nonsense...🙄
Can you build some kind of CT arrangenent over the Main TT Earth conductor for it to operate some kind of shunt trip when significant current is detected?
But the trip unit (100A contactor say) would HAVE to be mounted in a metal enclosure OUTSIDE of the CU and as John explained, you are then back to square one! My understanding though (and it's now 7 years later) is that a BAKELITE switch cover is acceptable for an external isolator as bakelite is essentially fireproof (not so much as steel clearly). At least to the necessary extent of preventing fire egress sufficiently well and long enough. Certainly far longer than the MCB materials in the CU. One possibility to reduce risk would be a low current warning lamp fitted between its own external ground and the chassis of the CU. That way any current path via the chassis not large enough, due to earth loop impedance, to blow the incoming fuse, but large enough to produce 5 to 12 volts potential drop would light the bulb (and could sound a low volt alarm). Voltage drops greater than 12 volts can easily be catered for by a suitable buck/boost circuit producing constant voltage and limited DC current. The latter is a trivial task and in fact most LED switching circuit supplies have the (isolating) electronics required, but need some minor component tweaks.
Hey John you said at 2.29 you said another connection the supply would provide so can we see that earthing connection or is it that's not. In a house I mean is that near the consumer unit or is it away.
The transformer on the left hand side of the drawing represents the electricity supply company's transformer, that transformer could be a considerable distance from a house depending on location. The supply company will connect the neutral of THEIR transformer output to earth using a large deep rod, conductive mat, or similar. In the diagram the house has its own separate rod (right hand side)
Would a 100amp 100ma time delayed double pole RCD in a ceramic enclosure do the trick ? I know all ( most anyway ) final circuits have to be protected with 30ma RCDs, but do the meter tails need 30ma protection ?
Would not be surprised that all the Fuses / RCD / Mains switch will have to be made out of metal. Surely they will burn and then the metal case could become live.
Allegedly because of an increase in fires involving consumer units - although the exact cause of those fires was never revealed and it would have been far better to deal with the actual cause of the fires rather than just making the box non-flammable.
what about the bakelite fuse board remember those we ripped them out to make way for the "new plastic consumer units" to be honest i have been a spark my hole life its now becoming a joke new reg = more money
Hi john I have been looking at this and came across it saying only rcbo consumer units to be installed on tt not split load rcd boards is this true thanks
Did you ever find a good solution to this j.w If you where installing a metal c.u on a tt system would you install 30ma rcds in the consumer unit and a main switch 100amp 100ma time delayed rcd before the consumer unit Thanks
The solution provided by manufacturers is to use a specific plastic grommet where the wires enter the consumer unit, and to maintain the outer covering of the wires inside the consumer unit. Some have suggested using a plastic enclosure with another RCD (such as the 100mA time delayed type) before the CU, and have stated that is not under the same requirements for metal as the main CU. In many cases the supply can be changed to TN-C-S which avoids the problem entirely.
@@jwflame sound jw. On a tt system would you say 10mm main earth and 6mm main bonding is ok . Or should it be upgraded to 16mm main earth and 10mm binding. What are the lowest values allowed
@@jwflame You said 'Some have suggested using a plastic enclosure with another RCD (such as the 100mA time delayed type) before the CU, and have stated that is not under the same requirements for metal as the main CU'. You said on this video it wouldn't comply, so is this based on new information as your comment was made 4 years after this video?
pcuser80 T=Terre (French) or Terra (Latin) meaning earth. TT as there are two connections directly to the earth, one at the supply and one at the installation.
Fantastic and all your clips are outstanding John this is the best way to prepare for an upgrade, if you are taking a Electrical course. Dont know why I wasted money on costly Electrical DVDS. Thanks John.
....... "sizzling away in the ground", some of your dialogue is priceless, you're quite funny John. :-)
The French have a DNO supplied 500ma RCBO on the supply which acts as the main switch as well. This solves it. But it is plastic. It is fitted outside of the Consumer Unit which are plastic in France. But usually in a metal cupboard (which is legal in the UK).
The French usually have TT earthing.
Actually the cable glands are made of plastic, the inlet (the things with the two holes shown aside) is made of rubber. Actually they are used to offer some protection against dust or water (IP54) and providing some strain-relief if mounted correctly.
Perfect tuition John and 2 years later still holds current (no pun intended) thank you!
wylex shows a RCCB Time Delay 100mA between meter and consumer unit to deal with that fault and that RCCB does not have to go into a metal box.
Previous to these ammendments metal cased consumer units were a no no on TT systems unless additional rcd protection was provided in an all insulated enclosure prior to the consumer unit. Now it seems using PVC/PVC supply conductors to such an enclosure is acceptable because they have suddenly become double insulated, they are not as they are merely PVC/PVC insulated. A few years ago I would have been pulled for doing this.
Id take a plastic consumer unit and a smoke alarm any day. Some of the old TNS earthing I see out and about **shudders**
You can use plastic con unit if you put a non combustible surrounding it
Great educational video again. I will not just test for voltage between live and earth on these systems as the earth may be at 230 Volts and not trip anythings. Result = Meter reads 0 volts even if Line at 230 volts !!!!
Good video John but you have not given a solution to the final part of the cables within the metal consumer unit.
the solution was the gland, but just not 'ideal'
I wouldn't mind betting that someone within the powers that be,was personally affected by this matter,perhaps had a consumer unit fire or similar,the thing that pisses me off about this kind of thing is that the people who make these changes almost always have no idea about the subject he/she is making changes to.GO FIGURE!!
It was my understanding and that of technical is that the RCD prior to the new 3rd Amendment consumer units is enclosed in a self extinguishing insulated material such as Wylex's supply authority isolated enclosures.
Dale Goodrum The problem with that is the regulation specifies 'non-combustible' rather than self extinguishing, yet does not have any definition for 'non-combustible' other than the suggested example of ferrous metal/steel.
A single RCD for the whole installation would not comply with 314.2 either.
*****. Sorry with regards to the RCD I was referring to the 100mA type S RCD not the 30mA located within the main consumer unit. the IET website states not readily combustable, so with that in mind if you do not consider self extinguishing as not readily combustable how would the self extinguishing plastic stuffing gland for the tails comply or any other cable enter for that matter?
Dale Goodrum Common sense would suggest self extinguishing and not readily combustible would be suitable - but the reg specifically states non-combustible which is entirely different. This is probably why all of the consumer unit manufacturers have gone for the steel option.
The reg does not say anything about glands or anything other than the enclosure itself so plastic ones could be used, whether they are self extinguishing or not.
As you may have guessed by now, the new reg is exceptionally poorly worded and will probably be revised in the fairly near future.
Stainless Steel CU's would be ideal for the many damp cellars around these parts. Still waiting to see MK actually produce any 3rd amendment metal boards ...
There could easily be a technical, if not very elegant fix to this problem. What would be required is a device that monitored the earth voltage relative to neutral. It would be installed in the CU and if a threshold voltage between neutral and earth was exceeded (say 60v) if would create a live-to-neutral path and blow the supplier fuse (and no doubt make a big bang too).
Of course the device would probably be destroyed in the process by passing such a big current, but as this ought to be a very rare event, then it's a price worth paying to keep the installation safe (especially as such a fault wouldn't have made just the electrical systems earth live, but also any metal parts bonded to it - like the gas and water pipes).
So there's my solution - effectively a device that connects Earth to Neutral within the CU and which goes closed circuit if there's a potential of more than (say) 50v. The very simplest sort of device would work like a souped-up diac and be connected between neutral and earth. Of course, that's a very simple element, but if necessary a more complicated one could be created that created a closed circuit between Live/Line and Neutral, which would be more positive in operation.
So how do I file a patent, or have I got the principle wrong?
And if the fuse doesn't blow for some reason you get a fire, and also with that dead short you will probably trip protections on the supplier side that act faster than the fuse, leaving without power an entire block.
The solution would be integrating RCD protection on the supplier side, of course time delayed protection to avoid that it trips before the RCD that you have inside you home.
it seems that the problem cannot be solved entirely as at some point in the dwelling the meter tails have to enter the consumers switchgear, and that switchgear now must been metalic
i would suggest that
a) consumer units should be positioned as close to the REC supply (reg 531.4.1 indicates this) to reduce potential of tails being damaged and a high impedance fault occuring
b) cable manufaturers should look at increasing insulation resistance on meter tails or providing insulated sleeving to be fitted on installation
c) consumer units need to be more spacious for accomodating larger size cables due to suggested insulation increase and so reducing strain on connections due to bending and tensioning of meter tails inside the consumer unit.
Curious, as there is , as it looks, an unavoidable problem with TT systems, wouldnt it be beneficial to get the power networks to change earth rods to a TNCS PME connection.
Everybody worries about fires and not considering death by electrocution on these types of earthing systems,
Surely they could just cut the main earth and put it in with the neutral to avoid this problem?
+matt filmer Where TNCS is available it would usually be a better option than TT. However it is not available everywhere as it depends on the design of the electricity network in the area.
And that is why in finland we tie earth and neutral with a wire in between their "bus" bars in the CONSUMER unit aswell
there is an option to use ceramic, which can be moulded to any shape, and fits both fireproof and non conductive, or carbon fibre which is used for sports car brakes, so must be hard to set fire to, but maybe this is way too expensive!
a) if you've never seen F1 carbon brakes on fire you've not lived
b) carbon fibre is VERY conductive and causes havoc for F1 engineers where for structural integrity reasons they have to maintain that integrity whilst cutting a hole in bulkheads etc AND insulate the cut hole as the carbon fibres are VERY abrasive and after chafing through insulation provide a shorting path for signals and power.
My youngest brother has worked as an engineer with one of the top F1 teams for over 25 years and both these issues have the bane of his life for pretty much all that time.
how about some sort of ceramic or porcelain consumer unit?
Much older fuse boards did in fact have a porcelain chassis housing the onto which the metal connecting and switching parts were fixed. The porcelain chassis usually had an outer shell-type cover
that was either metal or plastic, I guess that JW has some in his museum - check his Flameport site.
I've hit this exact problem with a TT consumer board install. If you check out Crabtree they are suggesting an external 100ma RCD which just moves the problem as JW says.
Why don't the manufacturers just put in a simple phase separator or non flammable & conductive sleeve.
+Evil Knievel i work for one of the scottish suppliers, if we get a bad Ze, standard practice now is to fit a 100ma RCD after the meter. the tails are at this point not enclosed, or passing through any metal enclosure, so this does fix the earth problem.
+ben kerr thanks for your response,I think that is the answer but the job I have to do is my own C/U for my first registration with Napit,I'm sure you'll be aware they're one of England's registration bodies.
One of their assessors advised me that adding a separate RCD was a possibility but he felt that this would just move the problem as JW suggests.
I think you are right as this would be similar to the isolation switch that we've just paid to have installed before continuing with the job.
Yes it's got mechanical parts but other than that it's a joint,like a Henley block and the cables aren't really enclosed within it.
There's so many opinions,one bloke always thinks he's wiser than the next,I have my opinions,on & on....
I bet they never have a fire start from a cutout switch or a meter so perhaps it is only within C/U's that were poorly installed, had a faulty MCB as someone else suggested or have been tampered with by the consumer or another trade.
Let's face it we all have different standards.
When will be the first shock from a metal C/U ?
Sorry I'm just opinionating , is that a word ?
Does anyone have an opinion ?
how about plastic or ceramic inserts that fit inside the consumer unit enclosing all pre RCD cables?
That's exactly what was used years ago, ceramic grommets - some had to be quite large to allow entry of supply cable cores.
So if I were to enclose an existing plastic cu in a ferrous cabinet should the cabinet comply to a standard or ip rating ect? Or as long as the cabinet is earthed it would comply?...confusing stuff as usual..think we need an amendment4 to confirm3
Hi John.... This business of the meter tails passing through one hole in the new metal consumer units via a special gland. Now...I watched your video when you tested the theory out....inductance etc..
Why does this not apply to ...say...twin and earth entering a metal back box of a socket etc..
With T&E you have both line and neutral in the cable, current in each wire is in opposite directions so any magnetic effects are cancelled out. The same applies with those plastic glands, as both line and neutral wires pass through the same hole.
The problem only occurs with a single wire through one hole.
This amendment was put forward and proposed by the Fire Brigade due to the increase in Consumer Unit fires in the last 5-6 years.
It was about 5-6 years ago that there was a recall issued on certain Wylex, Crabtree and Volex MCB's due to them possibly being faulty.
Could these MCB's be the root cause of the fires and NOT sub-standard work by Sparkies???
ToonandBBfan Could well be. Not entirely convinced that the Fire Brigade actually proposed this either - the data about the increase in fires certainly came from them, but that may have just been used by others to get metal consumer units as a requirement.
*****
Thanks.
My company had its annual NIC inspection this week and our NIC Inspector is livid about the Metal CU's being brought in.
+ToonandBBfan I cant help thinking this is just to create income by legislative obsolescence, there is no reason not to have an RCD mounted in a fireproof fibreglass box ouside the property as they are here in Bulgaria.
Excellent & very helpful as usual.
Cheers John
I think that in the US neutral is bonded to earth at the entrance to the consumer unit. Is there a reason that isn't done in the UK?
Robert Szasz Not done in the UK because it's not permitted - only the electricity supplier can do that, and when they do it, it's done before the meter.
***** that seems like a good way to have the neutral leg floating at some significantly non zero voltage compared to a local ground rod. Do I understand correctly that in the UK earth can/is bonded to the actual local ground? I would expect standing on wet soil and touching the earth conductor (or the shield of a coax connector) to be near totally safe.
Thanks for all your informative videos.
Robert Szasz In the US the neutral (white) is attached via a common bus bar in the breaker box with the earth grounds (green) which in turn runs to a grounding rod.
Your two hot legs are run across a pair of buses that breakers attach to and for 120 volts the wires are black, for 220 - 240 volts they are usually red and blue with the bare ground for 30 amp, 50 amp has the 4th white neutral added to the cable.
The systems in the UK are somewhat dangerous in comparison to the US due to the numerous hazards that can happen just like the one in this video.
ElfNet Gaming thanks for the reply. I know just enough to do hobbiest electronics safely and not blast rf out the power lines when I do ham stuff. Proper premises safety I leave to paid professionals.
Oh yes of course. I work on commercial 2-way radio, cellular, and IT systems. I had to get certified to do electrical work and such. buy yeah leave the premises safety to the guys getting paid for it.
Plastic coating on the inside of the new metallic consumer units?
I think that would be the best solution Pat well thought of. I think there would only be a slight increase in cost but it definetly solves the issue. There is plenty PVC coated flat 0.7mm gauge metal around, you could probably get LSF if you look hard enough.
Moving the problem of course, but reducing the risk
Would not non-flammable plastic enclosures be permitted still?
***** They would, but that relies on such things actually being available. Manufacturers who have released new catalogues so far have gone for the 100% metal option, no plastic to be found.
I heard that Hager went to court and lost their appeal on the production of their non combustible plastic to be used to make fuse boards
Why can we not have a plastic enclosure for an upfront RCD yet when the DNO installs a DP isolator its plastic..?
DNOs do not work to BS7671.
@@jwflame I read recently in ESQCR that the DNO has to abide by BS7671 as soon as their service enters a dwelling. This would include their DP isolator. I'm trying to decide what exactly 421.1.201 applies to when it mentions 'consumer units and similar switchgear assemblies'. I'd say an isolator or stand-alone RCD is an item of switchgear, but lacks similarity to a consumer unit so the non-combustible requirement doesn't apply. I'm looking for an enclosure for an S100 mA RCD at a TT job next week and I think I'm going with plastic.
@@westinthewest Like many things it's not clearly defined, but several manufacturers still make isolators in plastic enclosures, and they are often installed. A metal enclosure on TT direct from the supply is something to be avoided - go with the plastic enclosure and RCD.
As an electrician in London I have very little experience with TT systems. Why do they not make it a PME system?
londontrada Great question. Why isn’t every tt a Tncs
Because most TT systems use overhead lines, a broken Neutral on a TNCS makes the system dangerous. The same applies to a PME System.
Out in 'the sticks' we have many properties on PME and TT's earthing arrangements and I have experienced a broken neutral on an overhead transformer on a property, feeding a farmhouse. The kitchen sink and copper metal pipework were at 250v potential. Not nice and very dangerous..I can see also why the new EV regulation on local earth rod's (TT) has come in, as an EV Car can become live too, hence them upgrading the RCD. PME is not all it's cracked up to be..
Hi, John. I think your presentations are brill!!
I'm hoping that you have time to help me with a dilemma I have concerning metal consumer units. My home is on a TT system and is currently being rewired. A 17 way British General Electrical metal consumer unit is being fitted and after viewing your video I am concerned about cables inside the unit creating a fault to the metal case. The unit is fitted with a cable gland. I looked at the Wylex site and they recommend that a 100 milliamp time delay S type RCCB device be fitted between their metal consumer unit and the supply unit. Will this prevent the metal case from ever becoming live and is the Wylex device above compatible with the BG Electrical unit that is being fitted in my home? Thanking you, in anticipation.
Couple of questions:
If Neutral is effectively the same as Earth why do we need both cables ?
Is there any argument for having any circuits NOT protected by RCDs ? (as seems to be the case in my consumer unit)
+David Graeme-Baker It's an additional safety feature. A system which uses a single conductor for neutral and earth throughout the installation is called TNC, and has the disadvantage that if that conductor is broken, exposed metalwork of appliances will have dangerous voltages, as the combined neutral & earth carries current in normal operation.
When you apply earth bonding to a TT system you could have some worker cut through the main earth wire from the earth rod. If a live wire happens to touch any metal part that is connected to the bonded system then all metallic items become live even with a plastic consumer unit. Unlikely but not impossible?
Theoretically possible, assuming the RCD is also not working. Even with the rod connected, a failed RCD still causes the same dangerous result.
@@jwflame Initially, I thought the same as you John where I included a failed RCD in my original post (reason for edited) but when you consider that there is no earthing means then a working RCD will be ineffective. I attended a NICEIC talk regarding new regulations and queried the reason for earth bonding and was informed that other countries, such as the USA, do not employ this practice. A short plastic pipe connection between isolating valves and outlets (taps, washing machine valves....) would deem this practice redundant.
@@od5699 "no earthing means then a working RCD will be ineffective" - why do you say that (taking you mean no earth at the consumer rather than the supplier)? A person in contact with an exposed conductive part and earth will pass current that will imbalance the L/N currents so the RCD should operate.
Why not just produce a CU enclosure with a plastic internal case ( similar to what we already had) inside a metal outer case with the plastic entry grommet fitting? These people are just trying to justify their positions by making up stuff as they go. Nonsense...🙄
Can you build some kind of CT arrangenent over the Main TT Earth conductor for it to operate some kind of shunt trip when significant current is detected?
But the trip unit (100A contactor say) would HAVE to be mounted in a metal enclosure OUTSIDE of the CU and as John explained, you are then back to square one!
My understanding though (and it's now 7 years later) is that a BAKELITE switch cover is acceptable for an external isolator as bakelite is essentially fireproof (not so much as steel clearly). At least to the necessary extent of preventing fire egress sufficiently well and long enough. Certainly far longer than the MCB materials in the CU.
One possibility to reduce risk would be a low current warning lamp fitted between its own external ground and the chassis of the CU.
That way any current path via the chassis not large enough, due to earth loop impedance, to blow the incoming fuse, but large enough to produce 5 to 12 volts potential drop would light the bulb (and could sound a low volt alarm). Voltage drops greater than 12 volts can easily be catered for by a suitable buck/boost circuit producing constant voltage and limited DC current.
The latter is a trivial task and in fact most LED switching circuit supplies have the (isolating) electronics required, but need some minor component tweaks.
Hey John you said at 2.29 you said another connection the supply would provide so can we see that earthing connection or is it that's not. In a house I mean is that near the consumer unit or is it away.
The transformer on the left hand side of the drawing represents the electricity supply company's transformer, that transformer could be a considerable distance from a house depending on location. The supply company will connect the neutral of THEIR transformer output to earth using a large deep rod, conductive mat, or similar. In the diagram the house has its own separate rod (right hand side)
And surely the manufacturers could develop and non-conductive non-combustible solutions
Hager lost their appeal in the recent years for their non combustible plastic material to make fuse boards with
Is the simple solution just to put the pre consumer unit RCD in a ceramic enclosure ? Non conductive and fireproof
That would do - the only problem is finding a ceramic enclosure..
Would a 100amp 100ma time delayed double pole RCD in a ceramic enclosure do the trick ? I know all ( most anyway ) final circuits have to be protected with 30ma RCDs, but do the meter tails need 30ma protection ?
Would not be surprised that all the Fuses / RCD / Mains switch will have to be made out of metal. Surely they will burn and then the metal case could become live.
Justin Oh Justin some arsehole higher up is thinking what good idea metal RCDs don't give em anymore ammunition.
If this is such a potential problem (no pun intended) what is the rationale behind the move in the first place ??
Allegedly because of an increase in fires involving consumer units - although the exact cause of those fires was never revealed and it would have been far better to deal with the actual cause of the fires rather than just making the box non-flammable.
what about the bakelite fuse board remember those we ripped them out to make way for the "new plastic consumer units" to be honest i have been a spark my hole life its now becoming a joke new reg = more money
Hi john I have been looking at this and came across it saying only rcbo consumer units to be installed on tt not split load rcd boards is this true thanks
No, the dual RCD types can be fitted.
@@jwflame thanks j.w
In UK each house has its own transformer from high voltages to 230 V?
No. Typically there will be a transformer serving a district and distributed fro here to each dwelling with a 100, 80 or 63 amp fuse
Did you ever find a good solution to this j.w
If you where installing a metal c.u on a tt system would you install 30ma rcds in the consumer unit and a main switch 100amp 100ma time delayed rcd before the consumer unit
Thanks
The solution provided by manufacturers is to use a specific plastic grommet where the wires enter the consumer unit, and to maintain the outer covering of the wires inside the consumer unit. Some have suggested using a plastic enclosure with another RCD (such as the 100mA time delayed type) before the CU, and have stated that is not under the same requirements for metal as the main CU.
In many cases the supply can be changed to TN-C-S which avoids the problem entirely.
@@jwflame sound jw. On a tt system would you say 10mm main earth and 6mm main bonding is ok . Or should it be upgraded to 16mm main earth and 10mm binding. What are the lowest values allowed
@@jwflame You said 'Some have suggested using a plastic enclosure with another RCD (such as the 100mA time delayed type) before the CU, and have stated that is not under the same requirements for metal as the main CU'. You said on this video it wouldn't comply, so is this based on new information as your comment was made 4 years after this video?
What if you don't connect the case the earth?
Per Mejdal Rasmussen Not connecting it wouldn't comply either, and would still leave the case live if a wire shorted to it.
Of course in the US you would NEVER see a plastic breaker box or dodgy grounding regulations with the utility company, ya know safety and all.
I am not British, TT stands for?
pcuser80 T=Terre (French) or Terra (Latin) meaning earth. TT as there are two connections directly to the earth, one at the supply and one at the installation.
I think using metal conductive units are dumb.