CONDUCTOR SIZING

[RLMJR]

i have two ea condensing unit ACCU that needs to be connected to power supply. An existing single 2" pvc conduit will be use as raceway for the feeders of each ACCU. as per catalog the MOP max overcurrent for the unit is 45 Amps and the minimum circuit ampacity is 34 amps typical for two accu. I decided to use the max ocpd and put a two 45 AT MCCB on the panel board and put a non fuse disconnect (2 ea) switch near the unit for servicing . Question is, what size of THWN wire is code compliance for this project, with respect to all necessary considerations. is it 8awg or 6awg? (note: terminal ratings of equipment and breaker are not known)


Thanks in advance for the answers.

 

[Greentagger]

#10 would’ve worked with individual conduit . 4 or more CCC will have to derate. #8 will work long as ampacity isn’t further reduced because of roof temp, etc. BTW the circuits are not feeders but are branch circuits.

 

[augie47]

Agree with Post #2... #8 due to derating.

 

[RLMJR]

Therefore short answer is to use #6 right? I cannot use individual cond for budget reason. Using new conduit means new excavation and concrete breaking.

 

[RLMJR]

I dont understand why #10 would work when the minimum circuit ampacity is 34 amps. And you have to use the 60 degree column ampacity when sizing 100 amps circuits and below per ufc 110.14 (c) (1) (a). Even you choose higher temp cable rating like thwn you have to use the 60 degree C ampacity. Since temperature rating of terminals are not marked for 75 degree C

 

[petersonra]

I dont understand why #10 would work when the minimum circuit ampacity is 34 amps. And you have to use the 60 degree column ampacity when sizing 100 amps circuits and below per ufc 110.14 (c) (1) (a). Even you choose higher temp cable rating like thwn you have to use the 60 degree C ampacity. Since temperature rating of terminals are not marked for 75 degree C

I tend to agree that #10 will not meet code.

Just because the terminals are not physically marked does not mean they are not marked with the temperature rating. That rating can be in the instructions or marked on the packaging.

If necessary, you could conceivably run a smaller wire in the conduit and put a larger tail on it at the termination point.

I don't understand your statement about #6 though.

 

[augie47]

I dont understand why #10 would work when the minimum circuit ampacity is 34 amps. And you have to use the 60 degree column ampacity when sizing 100 amps circuits and below per ufc 110.14 (c) (1) (a). Even you choose higher temp cable rating like thwn you have to use the 60 degree C ampacity. Since temperature rating of terminals are not marked for 75 degree C

The conclusion of using the #10 is based on the probability that your terminations are rated 75°. Modern day circuit breakers and your NF disconnects are likely rated 75° thus the allowance per 110.14(C)(1)(2). In the event a termination temperature is rated 60° then the #10 could not be used.
Of course, do to the 80% derating factor, as noted the #8 would be required in the conduit containing 4 or more conductors.

 

[RLMJR]

I tend to agree that #10 will not meet code.

Just because the terminals are not physically marked does not mean they are not marked with the temperature rating. That rating can be in the instructions or marked on the packaging.

If necessary, you could conceivably run a smaller wire in the conduit and put a larger tail on it at the termination point.

I don't understand your statement about #6 though.

Yes but per NEC 110.14(C) (1) (a) if it is not mark you have to use the 60 degree column. If the project is still in design phase you do not have the materials yet of course or packaging. Or instruction manual. You have to assume the terminals are 60 deg C right? Correct me if im wrong. Thanks in advance.

 

[infinity]

Yes but per NEC 110.14(C) (1) (a) if it is not mark you have to use the 60 degree column. If the project is still in design phase you do not have the materials yet of course or packaging. Or instruction manual. You have to assume the terminals are 60 deg C right? Correct me if im wrong. Thanks in advance.

I would not assume that any modern equipment terminal is limited to 60° C.

 

[petersonra]

Yes but per NEC 110.14(C) (1) (a) if it is not mark you have to use the 60 degree column. If the project is still in design phase you do not have the materials yet of course or packaging. Or instruction manual. You have to assume the terminals are 60 deg C right? Correct me if im wrong. Thanks in advance.

how do you know they are even listed if you have no information on them?

 

[wwhitney]

Therefore short answer is to use #6 right?

No, if there is no temperature correction required, #8 with a 75C or 90C rating suffices (which excludes conductors in LFNC in a wet location). As even if the termination rating is 60C, #8's 60C rating of 40A suffices. And with 75C ampacity of 50A, along with 4-6 CCCs in the conduit, you still get 50A*0.8 = 40A for the conductor ampacity (or higher if the insulation is rated 90C).

Cheers, Wayne

 

[Dennis Alwon]

Yes but per NEC 110.14(C) (1) (a) if it is not mark you have to use the 60 degree column. If the project is still in design phase you do not have the materials yet of course or packaging. Or instruction manual. You have to assume the terminals are 60 deg C right? Correct me if im wrong. Thanks in advance.

All new equipment is rated 75C that I am aware of except some rare situations of 90C. 60C would be a very old piece of equipment

 

[tom baker]

The only equipment I have seen in 44 years as an electrician was a dryer plug in a house I bought in 1979. The dryer plug was probably from the 50s