NM, UF and 60 degree column

[jar546]

Is it just me or are there any other areas where electricians are somehow convinced that NM and UF cable is actually THHN and allowable ampacity is out of the 75 degree column?

I should not have to spend any more time trying to educate both electricians and supply houses that a 50A Range or a 50A Hot Tub needs to be supplied by 6/3 NM cable and not 8/3. If they want to use 8awg copper then run conduit and pull THHN. This has been happening all year long.

334.80 Ampacity.The ampacity of Types NM, NMC, and NMS cable shall be determined in accordance with 310.15. The ampacity shall be in accordance with the 60°C (140°F) conductor temperature rating. The 90°C (194°F) rating shall be permitted to be used for ampacity derating purposes, provided the final derated ampacity does not exceed that for a 60°C (140°F) rated conductor. The ampacity of Types NM, NMC, and NMS cable installed in cable tray shall be determined in accordance with 392.11.

 

[RJJ]

Re: NM, UF and 60 degree column

Jeff: I have always felt it was 6/3. Fail the install.

 

[Bryan Holland]

Re: NM, UF and 60 degree column

I find the selection of ampacities to be one of the most frequently misunderstood and misapplied sections of the NEC. The specific issue you describe is very common. And now that SE cable must follow the same 60 degree limitation under the 2008 NEC when used as a branch-circuit or feeder, even more compliance problems are showing up on plans in in the field.

I too understand your frustration...

 

[jar546]

Re: NM, UF and 60 degree column

Yesterday I did a hot tub inspection. The owner was present but not the electrician so I left the paperwork with her and explained the problem. She said she would contact the electrician. I knew they were hacks just because of the undersized wire but also the fact that they DID run 3/4" pvc conduit from the disco to the hot tub and pulled UF cable through it. Of course I got the phone call from the electrician a few hours later arguing with me that he has the Table right in front of him and the 75 degree column says it is OK. Another 10 minutes of trying to explain to him he needs to reed Article 334 but he still did not get it.

Unfortunately some other multi-disciplined inspectors with no electrical background don't catch this in the areas he works in therefore I am a dick in his eyes.

 

[raider1]

Re: NM, UF and 60 degree column

Is the hot tub installed outdoors?

UF cable, even if it is sized properly, can't be used for the outdoor portion of the hot tub supply. 680.42© only permits UF or NM cable to be used on the interior of a dwelling. The outdoor portion of the supply must comply with 680.21(A)(1) and contain an insulated EGC.

Chris

 

[jar546]

Re: NM, UF and 60 degree column

Is the hot tub installed outdoors?UF cable, even if it is sized properly, can't be used for the outdoor portion of the hot tub supply. 680.42© only permits UF or NM cable to be used on the interior of a dwelling. The outdoor portion of the supply must comply with 680.21(A)(1) and contain an insulated EGC.

Chris

UF is not limited to interior wiring.

 

[raider1]

Re: NM, UF and 60 degree column

Is the hot tub installed outdoors?UF cable, even if it is sized properly, can't be used for the outdoor portion of the hot tub supply. 680.42© only permits UF or NM cable to be used on the interior of a dwelling. The outdoor portion of the supply must comply with 680.21(A)(1) and contain an insulated EGC.

Chris

UF is not limited to interior wiring.

Did you read the sections I quoted?

I understand UF cable is not limited to interior wiring, but in a pool application the wiring method used to supply a motor to an outdoor hot tub must have an insulated copper equipment grounding conductor. UF cable does not meet this requirement.

Chris

 

[jar546]

Re: NM, UF and 60 degree column

Yes, I see your point. Insulated grounding conductor. I missed that.

 

[raider1]

Re: NM, UF and 60 degree column

Yes, I see your point. Insulated grounding conductor. I missed that.

Not a problem, you would be surprised by how many electricians are not aware of this requirement.

I have had to argue this quite a bit with pool and hot tub installers.

Chris

 

[jar546]

Re: NM, UF and 60 degree column

Update for ya raider1. Reinspection today. They replaced the NM inside the house to the disco outside with 6/3 and instead of pulling THWN from the disco to the hot tub like I recommended, they pulled #6 UF inside the conduit.

Not getting too far with this one. Wonder how many inspections before they figure out what to do.

 

[raider1]

Re: NM, UF and 60 degree column

Update for ya raider1. Reinspection today. They replaced the NM inside the house to the disco outside with 6/3 and instead of pulling THWN from the disco to the hot tub like I recommended, they pulled #6 UF inside the conduit.Not getting too far with this one. Wonder how many inspections before they figure out what to do.

I had a pool that took 5 re-inspections before they finally got everything right.

Chris