How to test a Delta 120/240 (Wild Leg) 3 phase electrical system , explained!!
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- Опубліковано 28 сер 2024
- 3 phase Delta 120/240 volt system.
I’m new to UA-cam. Everyday I watch videos of how to, or how do you?....etc. I am a hands on type of guy and every day I am working on something different. So I figured that maybe if I start posting some of what I run into in may help someone else with what they are doing as the videos I have watch helped me throughout the years.
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NEC 110.15 requires the high leg be marked orange, or other effective means, so in theory it could be red, I've heard old timers referring to this as red leg delta. NEC 408.3 (E) (1) requires the high leg to be on the B phase, in Panelboards. NEC 408.3 (F) (1) requires such a panelboard be field marked with CAUTION: ___ PHASE HAS ___ VOLTS TO GROUND. in most cases that will be 208. In very rare installations you will see a 240/480 volt 3ø 4 wire system, in this case the high leg is 415 volts to ground.
Installations before 1975, typically have the high leg on phase C. And a common (and very expensive) mistake is to accidentally connect a single pole breaker to the high leg and destroy everything on that circuit. Having said all this, it's crucial to verify the voltages with a suitable meter, never rely on colors.
Came across this today at an older building. Delta 120/240 with the high leg 208 on C phase to ground/neutral. Cool for me to see as I'm new to that and just getting exposed to commercial work. Makes sense as far as the time period when the work was done.
I worked on a 120/208 Delta panel before. They're rare these days. 120/208 wye is more the normal nowadays.
Love the knowledge
The wild leg should measure at 208
Correct. If you took line to neutral in this case 120V and multiplied that by 1.732 you'd get 208V, similarly if you had a 240/480V 4 wire delta to find the high leg voltage you'd do 240*1.732 and you'd have between 415 to 416V.
@@Sparky-ww5re I'm just curious to know why it measures at 208 while all the others measure at 240
@@yiannitrakas5582 since this is a delta system, the transformer winding are connected end to end in the shape of a triangle, with one winding cut in half. For the high leg we need to find the hypotenuse, so we use Pythagorean theorem. 240² - 120² =43,200. Square root of 43,200 = 207.8461, in the field we simply say 208V. With a 240/480 delta we would use 480² - 240² = 172,800. Square root of 172,800 = 415.6922, or 416V basically. The line to line voltage is the same from A-B, A-C, & B-C, line to neutral is half the line to line because we split the number of windings in half.
@@yiannitrakas5582 if you look at the delta transformer diagram and how the phase B is tapped, it will quickly make sense.
@@Sparky-ww5rethe 208 being the phase voltage correct? We’re learning this in school but only on paper. This video is nice because it show an actual field application
High leg is B
Systems installed prior to 1975 typically were required to land the high leg on phase C. If a 4 wire delta is supplied by a service the utility company requires the high leg to land on phase C at the metering equipment because some meters require a 120V connection on phase B, so the utility must choose phase A or C to avoid destroying the meter.
Quick and to the point. Love it!
I subscribed.
Simplify show in a circuit drawing form it is easier to understand
Why when you do either a or b leg to the high leg c you don't get 120 plus 240 equals 360?
Shouldn’t high leg be b
With all due respect bud…. High leg or wild leg to neutral/ ground should be 208v, not 220v or 240v.
Dude your not right with everything you said
It's called a 208 system cause it's got a 208 leg. Lol
120 x sq rt 3= 208. Basic electricity.