Dear james, Excellent thank you. basically what you are saying if i am correct unless the SWA with 90C capacity is run on its own or with other cable with the same rating theen we should use the tables for SWA with a rating of 70C. being retired i didnt know they stopped making 70C rated cables but it makes sence.
Hi Angelo, Thank you for your message. Yes, if a cable with an operating temperature of 90 degrees, is to be grouped with other cables that are not rated at 90 degrees, also if the equipment being supplied is not rated at 90 degrees, then it's necessary to select the size of cable from the table for 70 degree cables. This means that the cable will work at a lower temperature. Kind regards James
@@JamesCurnowElectricalEngineer Hi James, just a further thought in regards to 90c rated cables running with 70C cables, if the 90C cable was separated by 2 x D away from the 70C cables on the same existing tray then this would allow for the cable to be installed. Am i right?
So if the 90c cable is taking the max amount of amps it says in the book, then it will be a temperature of 90c? I don’t get the correlation between the temperature rating and the current been used?
Hi, Thank you for your comment. The current has a heating effect on the cable. If you look at the tables for current carrying capacity, you will notice that the 90 degree cables can carry more current than the 70 degree cables. This is because the 90 degree cables are able to operate at the higher temperature. One thing to bear in mind is that if we select the 90 degree cable, we need to be sure that the switchgear and any equipment connected is also rated at 90 degrees. If we can't be sure of this, we would select the cable from the table for 70 degree cable, so that the cable operates at 70 degrees. I hope this helps. Regards James
Hi, Thank you for your question. k is a factor of the resistivity, temperature coefficient and heat capacity of a conductor. Common values for k can be found in table 43.1 in BS7671. Regards James
Dear james, Excellent thank you. basically what you are saying if i am correct unless the SWA with 90C capacity is run on its own or with other cable with the same rating theen we should use the tables for SWA with a rating of 70C. being retired i didnt know they stopped making 70C rated cables but it makes sence.
Hi Angelo,
Thank you for your message. Yes, if a cable with an operating temperature of 90 degrees, is to be grouped with other cables that are not rated at 90 degrees, also if the equipment being supplied is not rated at 90 degrees, then it's necessary to select the size of cable from the table for 70 degree cables. This means that the cable will work at a lower temperature.
Kind regards
James
@@JamesCurnowElectricalEngineer Hi James, just a further thought in regards to 90c rated cables running with 70C cables, if the 90C cable was separated by 2 x D away from the 70C cables on the same existing tray then this would allow for the cable to be installed. Am i right?
So if the 90c cable is taking the max amount of amps it says in the book, then it will be a temperature of 90c? I don’t get the correlation between the temperature rating and the current been used?
Hi,
Thank you for your comment. The current has a heating effect on the cable. If you look at the tables for current carrying capacity, you will notice that the 90 degree cables can carry more current than the 70 degree cables. This is because the 90 degree cables are able to operate at the higher temperature.
One thing to bear in mind is that if we select the 90 degree cable, we need to be sure that the switchgear and any equipment connected is also rated at 90 degrees. If we can't be sure of this, we would select the cable from the table for 70 degree cable, so that the cable operates at 70 degrees.
I hope this helps.
Regards
James
What is "K"? Please
Hi,
Thank you for your question. k is a factor of the resistivity, temperature coefficient and heat capacity of a conductor. Common values for k can be found in table 43.1 in BS7671.
Regards
James