- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
I like the 2014 change to 250.122(B), in which they defined the starting point for upsizing the ungrounded conductors. But I would like some opinions on the new wording. It says you upsize the EGC if the ungrounded conductors have been upsized ?from the minimum size that has sufficient ampacity for the intended installation.? Here is an example:
QUESTION:
Do I now have to upsize the EGC from the #10 that would otherwise be appropriate for a 50 amp circuit?
- Four identical single phase, 208 volt circuits will be run in the same conduit.
- The calculated load for each circuit is 46 amps (includes any consideration of continuous loads).
- I will use a 50 amp, 2-pole breaker for each circuit.
- The wire will be THHN copper.
- Looking at table 310.15(B)(16), I see that #8 has an ampacity of 50 amps. However, I know I need to derate for having 8 CCCs in the same conduit.
- I can use the 55 amp value from the 90C column, and multiply by 70%. That gives me an ampacity of only 38.5. This is not enough for my installation.
- I next try #6. Derating its 90C value of 75 amps using the 70% factor, I get an ampacity of 52.5. So I decide to use that size wire.
QUESTION:
Do I now have to upsize the EGC from the #10 that would otherwise be appropriate for a 50 amp circuit?