250.122 (b) Increased in size
- Thread starter MichaelJ
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- Logan, Utah
IMHO No.
The EGC must be increased in size proportional to the increase in size of the ungrounded conductors. So for a 30 amp breaker the EGC must be the same size as the ungrounded conductors.
Chris
The EGC must be increased in size proportional to the increase in size of the ungrounded conductors. So for a 30 amp breaker the EGC must be the same size as the ungrounded conductors.
Chris
bfrosty
Member
- Location
- Western North Carolina
My interpretation of this is referring to table 250.122 first, so #10 is good all the way to 60 amps.
- Location
- Massachusetts
You must apply all code sections, not just the ones you like. :grin:
250.122(B) requires an 8 AWG EGC for the installation the OP describes.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
I agree with Chris. It does not matter how far down the table a #10 EGC can still be used. What matters is the conductor size that could have been used for the load conditions (in this case, a #10 conductor for a 30 amp breaker), and what size conductor is actually installed (in this case, a #8 conductor). You have increased the size of the ungrounded conductor from #10 to #8, and you must therefore increase the size of the EGC in a proportional amount. That means you need a #8 EGC in this situation.
- Location
- Logan, Utah
250.122(B) requires that when ungrounded conductors are increased in size (Say for voltage drop) then the EGC's run with them must also be increased in size proportional to the up size of the ungrounded conductors.
So for example #10 copper conductors connected to a 30 amp breaker are up sized for voltage drop to a #8. Therefore the EGC run with the ungrounded conductors must also be up size the same proportion. So a 30 amp overcurrent device requires a #10 EGC with #10 ungrounded conductors in accordance with Table 250.122 and if the ungrounded conductor are increased to a #8 then the EGC must also be increased to a #8.
Chris
if the ungrounded conductors were increased to reduce voltage drop do you still need to increase the EGC also?
Yes you would increase the EGC
chris kennedy
Senior Member
- Location
- Miami Fla.
- Occupation
- 60 yr old tool twisting electrician
If you increase the size of the ungrounded conductor for a reason as simple as 'its all I had on the truck' you would still have to comply.
- Location
- Logan, Utah
Agreed. The term "voltage drop" was dropped from 250.122(B) so no matter what the reason for the increase in the size of the ungrounded conductors you must also increase the EGC.
Chris
bfrosty
Member
- Location
- Western North Carolina
OK
OK
After further review, I stand corrected! Belay my last. But this would require rewiring the entire circuit then. So we would need to get rid of the NM.
OK
After further review, I stand corrected! Belay my last. But this would require rewiring the entire circuit then. So we would need to get rid of the NM.
- Location
- Logan, Utah
It very well might.
This can be a problem when using NM cable.
Chris
bfrosty
Member
- Location
- Western North Carolina
Now that I have fallen on my sword. What if I have this scenario and put the 30 amp breaker in to protect temporary equipment, and the final piece will be a need a 40 amp breaker and 8-2? Let's say it a Dryer change out. and the new dryer isn't here yet? Would this not satisfy 250.122(b)
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
You just hit upon the weirdest aspect of this rule. If you use a 30 amp breaker with #8 wire, then the EGC must be #8. If you use a 40 amp breaker with #8 wire, you can use a #10 EGC. Go figure. 
- Location
- Massachusetts
Code wise you can not have a 30 amp circuit with 8 AWG circuit conductors and a 10 AWG EGC even for temporary installations.
Install a 40 amp breaker and your all set, yes I know it does not make sense but it is what the words in the NEC require.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Yes, until you decide to use a conductor size for the ungrounded conductor that is larger than is shown in the ampacity tables.
Say for the sake we're considering this an old installation, wouldn't you be violating the condition to have either SE cable or an insulated grounded conductor anyway?
Since you're essentially running a new circuit, and having a new installation for the dryer, wouldn't you need to have a 4 wire installation?
- Location
- Massachusetts
Normally yes, but as soon as you increase the circuit conductor size you must increase the EGC size as well. This info is in 250.122(B).
ok, i understand. Is there a code reference for that
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