Updated Breaker and Wiring - Wire type question

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thoppiepe

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North Carolina
A heat pump replacement caused the need to replace an existing 20A breaker + #12 wire with a 30A breaker +#10 wire. The new #10 wire is NM-B. The original #12 wire was UF-B.

From the circuit breaker the wire is routed thru a conduit to below grade. The wire makes approx. 90 deg bend into the dirt for 12-18" then passes thru a hole drilled into the brick foundation. Under the house (dark dry place where no one wants to go - approx 24" height), the wire is routed approx 24" barely covered with dirt (assumed to pass by the crawl space opening without getting snagged when one crawls in) and then another 36" on top of dirt to a conduit exiting the brick foundation to the outside heat pump unit.

If I've read the NEC correctly on the use of NM type wire, it should be ok. The only concern is the 12-18" in the dirt. Can NM be used in this installation?
 
The idea that the OP is mentioning breakers and conductors that "match" makes me wonder what the MCA and max OCPD for the unit is.
 
He shows himself to be an EE. I'm hesitant to respond beyond No NM in ground or outdoors.

If the OP answers Texie, we may be able to tell him the #12 can stay.
 
texie said:
The idea that the OP is mentioning breakers and conductors that "match" makes me wonder what the MCA and max OCPD for the unit is.
Click to expand...

mfg install manual indicates
Max overcurrent protection = 25A
Minimum circuit ampacity = 18A

heat pump installer indicated a need for 30A breaker and #10 wire.

I"m just looking over their shoulder.
 
LarryFine said:
He shows himself to be an EE. I'm hesitant to respond beyond No NM in ground or outdoors.

If the OP answers Texie, we may be able to tell him the #12 can stay.
Click to expand...

I am an EE but NOT an Electrician. I know my limits. I'm looking over the shoulder for a relative who I don't want ripped off. I've followed Mike Holt for years and knew I could get reliable confirmation/interpretation of NEC here. The #12 was already replaced with #10. My concern was with the wire type.
 
"heat pump installer" is incorrect on 2 counts. Barring voltage drop problems (for extreme length), #12 would be fine for a 18A MCA unit and a 30 Amp breaker would be oversized for a unit with a nameplate showing 25A max but as to your concern, as noted in Post #2 & #$4. NM is not allowed in a damp/wet location.
 
thoppiepe said:
mfg install manual indicates
Max overcurrent protection = 25A
Minimum circuit ampacity = 18A

heat pump installer indicated a need for 30A breaker and #10 wire.

I"m just looking over their shoulder.
Click to expand...

The installer needs some education. #12 is compliant for an MCA of 18 amp. This has no bearing on the breaker size in this application. For the OCPD a 30 amp is not acceptable. A 25 amp breaker is a standard value and is what should be used.
Sounds like they removed perfectly compliant UF of adequate size and replaced it with a non compliant cable type that is oversized.
 
texie said:
The installer needs some education. #12 is compliant for an MCA of 18 amp. This has no bearing on the breaker size in this application. For the OCPD a 30 amp is not acceptable. A 25 amp breaker is a standard value and is what should be used.
Sounds like they removed perfectly compliant UF of adequate size and replaced it with a non compliant cable type that is oversized.
Click to expand...

:thumbsup:

Roger
 
The I’ve seen several times where people interpret MOCP as MINIMUM over current protection instead of MAXIMUM. That seems to fit here because if that was his first mistake, the rest makes sense; 25A “minimum” OCPD is not in stock at Home Depot, but since that would result in #10 wire anyway, he figures it can have a 30A breaker.

That, combined with the mistake in applying NM in the ground, indicates to me that this “installer” was not a licensed electrician and this was not undertaken with a permit, so it was not inspected. None of that would have happened unless that were the case. Your relative likely tried to save money by using a “handyman” or some other untrained and unlicensed person for this. They got what they paid for...

Side note: I’m not denigrating all handymen, some are fine. But this points out the fact that when there are no standards or licensing involved in a trade like that one, you are taking chances with their competency.
 
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