Romex and SER ampacities.

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Thomas R

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I know this has likely been beaten to death, but I'm happy to bring it up again. Correct me if I'm wrong; romex(nm) wiring is limited to the 60 degree column in table 310.16. So a 60 amp hot tub's disconnect could not be fed with 6/3 romex, but the load side to the tub could be #6 THWN. It's my understanding that the insulation on romex is rated higher than 60 degrees, but because it's part of a cable assembly it is limited. The same way that SER is comprised of individual XHHW conductors, but because it's part of a cable assembly it too is limited to 60 degrees.

Hoping we can put this to rest (yeah right). I see a lot of electricians with many more years in the field than me purchasing 8/3 for a 50 amp circuit and 6/3 for a 60. I'm pretty certain I'm correct on the romex issue, but I'm a bit unsure on the SER issue.

Thanks in advance all!
 
You are correct, even though NM cable is made with 90° C conductors it must be used at the 60° C ampacity in T310.15(B)(16). 8/3 NM cable is only good for 40 amps. SER can be used at 75° C under certain conditions and depending on the code cycle.

Welcome to the Forum. :)
 
Cable assemblies are not generally limited to 60 degrees. NM specifically is limited to 60 degrees, and I am not sure of the reasoning for that. The temp rating of SER has changed quite a few times. it used to just be 75 and then the NFPA did a bunch of hand-wringing over multiple code cycles, and I believe its back to where it was at 75 now, but it would depend on what code cycle you are on.
 
Thomas R said:
I know this has likely been beaten to death, but I'm happy to bring it up again. Correct me if I'm wrong; romex(nm) wiring is limited to the 60 degree column in table 310.16. So a 60 amp hot tub's disconnect could not be fed with 6/3 romex, but the load side to the tub could be #6 THWN. It's my understanding that the insulation on romex is rated higher than 60 degrees, but because it's part of a cable assembly it is limited. The same way that SER is comprised of individual XHHW conductors, but because it's part of a cable assembly it too is limited to 60 degrees.

Hoping we can put this to rest (yeah right). I see a lot of electricians with many more years in the field than me purchasing 8/3 for a 50 amp circuit and 6/3 for a 60. I'm pretty certain I'm correct on the romex issue, but I'm a bit unsure on the SER issue.

Thanks in advance all!
Click to expand...
Read 334.80

Roger
 
As far as SER it seems that #4 is the best choice for a 60 amp feeder cable, (if we can use 75 degrees) since it is usually readily available, and #4 romex would be severe overkill. Talking hot tubs specifically, it seems 60 amps is becoming the new standard which leads to this line of thought on ampacities, provided your AHJ is okay with aluminum to the line side of a hot tub disconnect.
 
Correct me if I am wrong...
The conductors from the OCP in the main panel to the disconnect are feeders, and as such, they may be sized for 100% of the continuous load + 125% of the non-continuous load. So, by my understanding of 215, 240, & 334, if the nameplate rating of the hot tub does not exceed 55A, then #6/3 NM may be used to the disconnect.
 
Thomas R said:
As far as SER it seems that #4 is the best choice for a 60 amp feeder cable, (if we can use 75 degrees) since it is usually readily available, and #4 romex would be severe overkill. Talking hot tubs specifically, it seems 60 amps is becoming the new standard which leads to this line of thought on ampacities, provided your AHJ is okay with aluminum to the line side of a hot tub disconnect.
Click to expand...
I believe using aluminum ser would be problematic for hot tubs because you need a copper EGC. there might be an exception for existing feeders that you come off of, I don't remember I would have to brush up on my 680.
 
electrofelon said:
I believe using aluminum ser would be problematic for hot tubs because you need a copper EGC. there might be an exception for existing feeders that you come off of, I don't remember I would have to brush up on my 680.
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I am curious, why does code not allow AL?
 
Rock86 said:
Correct me if I am wrong...
The conductors from the OCP in the main panel to the disconnect are feeders, and as such, they may be sized for 100% of the continuous load + 125% of the non-continuous load. So, by my understanding of 215, 240, & 334, if the nameplate rating of the hot tub does not exceed 55A, then #6/3 NM may be used to the disconnect.
Click to expand...
Is that flip flopped?
 
Dennis Alwon said:
Most of the tubs I have done are 50 amp not 60. I know there are 60 amp tubs but are you sure all are 60 amps?
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Not all tubs are 60A, some are 50A. The ones I've wired that were 60A had the option of pumps and heaters all running at the same time when wired for 60A. If they were wired for 50A, you couldn't run, say, all the pumps and heater at the same time. You could run heater and low speed at the same time, but not both pumps and heater. I never choose the 50A as I know I would get call backs when they couldn't run everything.
 
oldsparky52 said:
Thanks, I used a lot of SQ D and like you said, theirs was not rated for 120/240 back then.
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I looked within the past year and couldn't find one. I had to use a standard QO 260 in an existing pool panel, and add a separate GFCI breaker in its own enclosure on the opposite side of the post.
 
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