A/C wire size.
- Thread starter Daja7
- Start date
- Location
- New Jersey
- Occupation
- Journeyman Electrician
#10 AWG minimum conductor size, 40 amp OCPD.
yes that is minimum but can you use #8? someone said you cannot.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
You can, but it's wasteful.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Wrong. The MCA defines the smallest wire you can use, not the largest.
That was my point. but they said if used larger than the minimum you have to size the ground larger than the #10 that is proper for for 8. Is there something I am missing?
Technically true, but I would hope an inspector wouldn't pull that. The next AC unit may have an MCA of 31 and now you'd be ripping out that #10 and installing #8. And you'd still have a #10 EGC in the latter case.
I must be in real trouble because the AC tech who installed mine put in #6 NM cable because he only looked at the 50A breaker and not the MCA. Now I have a smaller AC unit on that same wire with an MCA in the high 20's and a 40A breaker.
I must be in real trouble because the AC tech who installed mine put in #6 NM cable because he only looked at the 50A breaker and not the MCA. Now I have a smaller AC unit on that same wire with an MCA in the high 20's and a 40A breaker.
yes, actually they said you can but if you use more than minimum then the #10 ground for 8 must be upsized. I may be missing something.
Last edited:
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
I'm a proponent of the idea that the exception to 250.122(B) added in the 2020 NEC provides an escape clause for all the situations in which "if the load was larger, the smaller EGC would obviously be compliant." As that statement demonstrates that the smaller EGC is still sized "to provide an effective ground fault current path."
Cheers, Wayne
kwired
Electron manager
- Location
- NE Nebraska
Part of the problem is it is kind of written as a one size fits all rule.
Could also have a situation with 6 AWG conductor on 60 amp OCPD and use a 10 AWG EGC.
Thanks. I read the exception that a qualified person can do something about an adequet grounding pat? did not quote that properly but do not have it ifron of me. Could someone explain that for me? Thanks
The exception references 250.4 which discusses an effective ground fault current path.
The effectiveness of that path is a long discussed topic (See Soares Book on Grounding as an example).
IMO, the reference to a "qualified person" in the exception would be someone like a P.E. with expertise in grounding,
The effectiveness of that path is a long discussed topic (See Soares Book on Grounding as an example).
IMO, the reference to a "qualified person" in the exception would be someone like a P.E. with expertise in grounding,
250.122 clearly permits a equipment grounding conductor to be #10 AWG CU for a 40A feeder with #8 CU.
There is no need to upsize your equipment ground in that case.
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
#10 ground is good for up to 60 a breaker or fuses. it has been that way for decades.
Many electricians don't understand that the wire does not have to match the breaker or fuse size because it is a motor circuit. The motors in the unit are thermally protected to prevent conductor overload.
The MCA is the "minimum" circuit amps of the wire, you can always use larger wire if you want but are not obligated to do that.
The MOCP is the 'maximum" size breaker or fuses that the "minimum MCA wire size" is allowed to be used with.
You can always use a smaller MOCP but are not obligated to do that either. But the MOCP must be large enough for the equipment to start.
Many electricians don't understand that the wire does not have to match the breaker or fuse size because it is a motor circuit. The motors in the unit are thermally protected to prevent conductor overload.
The MCA is the "minimum" circuit amps of the wire, you can always use larger wire if you want but are not obligated to do that.
The MOCP is the 'maximum" size breaker or fuses that the "minimum MCA wire size" is allowed to be used with.
You can always use a smaller MOCP but are not obligated to do that either. But the MOCP must be large enough for the equipment to start.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
The main text does not. The main text says that if that same circuit would be compliant with #10 Cu ungrounded conductors, then you've upsized the ungrounded conductors by using #8, so you must upsize the EGC.
However, as this is unreasonable, the exception gives us an out.
Cheers, Wayne
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
You don't need to be a PE to recognize that the whether a ground fault path is effective is independent of what the load is. So changing the load from one type to another type, when the breaker stays the same or is downsized, and the conductors remain the same, does not change the effectiveness of the ground fault path.
Cheers, Wayne
The OP is proposing to use a 40A OCPD with a #10 equipment ground this is done and passes inspections every day.
You can go up to and including a 60A OCPD and use a #10. Only at 65A OCPD (wire) would you need a #8
Last edited:
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The inspector is saying that, because the conductors are larger than required, they therefore must have been "increased in size," which means the EGC must likewise be increased proportionately.
Last edited: