Hi All,
I had a few questions about an install I have coming up (and it would also be nice to know for future reference as some of this has always confused me a bit.)
We're installing a 3 phase 208 v condenser unit on the roof of one of our buildings. The name plate calls for a minimum circuit ampacity of 34 amps and a max fuse or HACR breaker rating of 50 amps. It will be about 8 ft from where my circuit emerges from inside to the disconnect I am mounting on the unit.
My questions are as follows:
1. Is it acceptable to size my wire according to the nameplate's minimum circuit ampacity and not the max ocpd used? I understand that in this case it is a mute point because it will be a #8 AWG regardless, but generally speaking is it? (ie: a 24 amp minimum ampacity (So a #10 AWG) protected by a max breaker size of 40 amps (per the nameplate.) Is this what the code is referring to in 440.6 (B) exception 1 and 430.52 (A-C)?
2. Since my wire run is just about 80' total and I'm right on the edge of the allowance permitted by 310.15 (A)(2), I've decided to derate my wire per table 310.15 (B)(3)(c) to ensure a quality install. I figured that the average high in the summers in New England is 96-104 and I'm using foam/strut pyramid roof racks that are about 3.5" high. This put's me at 104+40=144 degrees, a correction factor of .65 (I'm using THHN). Now I'm confused as to whether I apply this number based on the 34 amp minimum circuit ampacity I have or, if I apply it to the 50 amp rating of ocpd. If I apply it to the 34 amp minimum circuit ampacity, I'll have to run a # 6 from inside to the disconnect. If I apply it to the 50 amp circuit as just that, a 50 amp circuit, I have to run a #4AWG.
3. My final install is planned like this. A 50 Amp HACR bolt on breaker at the panel. A #8-3 MC from the panel to a metal splice box inside. 1 1/4" PVC Schedule 80 (lot of falling debris on this roof) from the inside splice box to right before unit (with an expansion fitting of course). Change over to liquitight to make tight sweep to disconnect. (3) #4 AWG THHN ungrounded (hot) conductors and one #8 AWG EGC. Unfused disconnect at unit because namplate specifies fuse or HACR breaker and I already have the HACR breaker at the panel (most breakers are HACR these day). Does this sound correct?
I just recently left construction and went to work for a property management company. I am the only electrician there, so they like to blame me for lots of things (lol). Its difficult not having anyone around to bounce ideas off of any longer and a bit overwhelming.
I sincerely appreciate you taking the time to read this thread. Hopefully you guys will have some insight for me.
Thank You.
I had a few questions about an install I have coming up (and it would also be nice to know for future reference as some of this has always confused me a bit.)
We're installing a 3 phase 208 v condenser unit on the roof of one of our buildings. The name plate calls for a minimum circuit ampacity of 34 amps and a max fuse or HACR breaker rating of 50 amps. It will be about 8 ft from where my circuit emerges from inside to the disconnect I am mounting on the unit.
My questions are as follows:
1. Is it acceptable to size my wire according to the nameplate's minimum circuit ampacity and not the max ocpd used? I understand that in this case it is a mute point because it will be a #8 AWG regardless, but generally speaking is it? (ie: a 24 amp minimum ampacity (So a #10 AWG) protected by a max breaker size of 40 amps (per the nameplate.) Is this what the code is referring to in 440.6 (B) exception 1 and 430.52 (A-C)?
2. Since my wire run is just about 80' total and I'm right on the edge of the allowance permitted by 310.15 (A)(2), I've decided to derate my wire per table 310.15 (B)(3)(c) to ensure a quality install. I figured that the average high in the summers in New England is 96-104 and I'm using foam/strut pyramid roof racks that are about 3.5" high. This put's me at 104+40=144 degrees, a correction factor of .65 (I'm using THHN). Now I'm confused as to whether I apply this number based on the 34 amp minimum circuit ampacity I have or, if I apply it to the 50 amp rating of ocpd. If I apply it to the 34 amp minimum circuit ampacity, I'll have to run a # 6 from inside to the disconnect. If I apply it to the 50 amp circuit as just that, a 50 amp circuit, I have to run a #4AWG.
3. My final install is planned like this. A 50 Amp HACR bolt on breaker at the panel. A #8-3 MC from the panel to a metal splice box inside. 1 1/4" PVC Schedule 80 (lot of falling debris on this roof) from the inside splice box to right before unit (with an expansion fitting of course). Change over to liquitight to make tight sweep to disconnect. (3) #4 AWG THHN ungrounded (hot) conductors and one #8 AWG EGC. Unfused disconnect at unit because namplate specifies fuse or HACR breaker and I already have the HACR breaker at the panel (most breakers are HACR these day). Does this sound correct?
I just recently left construction and went to work for a property management company. I am the only electrician there, so they like to blame me for lots of things (lol). Its difficult not having anyone around to bounce ideas off of any longer and a bit overwhelming.
I sincerely appreciate you taking the time to read this thread. Hopefully you guys will have some insight for me.
Thank You.
