Article 310.16 derating

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gblakowski

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I ran a feed to a 120/208 volt 75 hp fire pump motor with the wire size based on a running load current of 188 Amps X 125%. I used 250 KCML copper rated in the 75 degree column of 310.16 for 255 Amps. The electrical inspector tells me my wire is undersized due to the fact that I should have based my running amps from the hp table of Article 430. I checked the code, and he is correct. Even though I am using 90 degree C wire, I must use the 75 degree C column due to the terminal ratings of 75 degrees. Could I use a 90 degree C rated barrel / reducing splice to increase my wire size to 350 KCML in the panel and controler in order to be able to use the 90 degree column of 310.16 therefor making my 250 KCML wire legal?
 
Welcome to the forum.

The lugs at the supply and controller contribute in determining the degree column along with the conductor, in other words these lugs will have to be rated 90 degree as well.
 
gblakowski said:
I Could I use a 90 degree C rated barrel / reducing splice to increase my wire size to 350 KCML in the panel and controler in order to be able to use the 90 degree column of 310.16 therefor making my 250 KCML wire legal?
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The 75C limitation is not just for the conductor. It is for every component of the circuit, such as the enclosure(s), conductor and termination points. Most likely, one of or all of the components of your circuit are 75C rated, and changing out just the termination ends of the conductors will not satisfy the requirements.
 
gblakowski said:
Could I use a 90 degree C rated barrel / reducing splice to increase my wire size to 350 KCML in the panel and controler in order to be able to use the 90 degree column of 310.16 therefor making my 250 KCML wire legal?
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In my opinion yes, you can and it will solve your immediate problem.

HOWEVER, have you run the calculations to determine if 250 Kcmil is large enough to keep the voltage drop under 15% during start up as required by 695.7?

480sparky said:
You're wanting to install a piece of 350 on each end of the 250? How does that increase the ampacity of the 250?
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It increases the ampacity of the 250 because now the rating can be based on 90C.

Supply>75C term>350Kcmil>90C term>250 kcmil>90C term>350 kcmil>75C term>Fire pump controller.
 
iwire said:
IMO the code would allow as short as you can make it, but I would try to have some distance.
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I think by splicing on a piece, we may be trying to get around the 'intent' of the code (yes, I know Charlie, the codes says what is says :smile:). Still, if the piece is too short, it won't be able to dissipate enough heat to make a difference.
 
Pierre C Belarge said:
The 75C limitation is not just for the conductor. It is for every component of the circuit, such as the enclosure(s), conductor and termination points.
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In the OPs case not the entire circuit, in the OPs proposed arraignment there are three separate sections. We can chose to run certain sections at different temps.
 
hardworkingstiff said:
I think by splicing on a piece, we may be trying to get around the 'intent' of the code
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I disagree. :smile:

Say I have to run a 50 amp feed to a range in a dwelling unit. Due to the panel location I have to leave the panel with pipe and THHN, but at the other end I change to NM.

What size conductors am I required to use?
 
iwire said:
In the OPs case not the entire circuit, in the OPs proposed arraignment there are three separate sections. We can chose to run certain sections at different temps.
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Yes... but in OPs case, he wants to make the transitions in the panelboard and controller enclosures. This may violate listing restrictions, i.e if the equipment is listed for specific temperature rise or has termination temperature limitations. In such case, the transition(s) will have to be made beyond the confines of said enclosure(s).
 
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Smart $ said:
Yes... but in OPs case, he wants to make the transitions in the panelboard and controller enclosures. This may void listing restrictions, i.e if the equipment is listed for specific temperature rise or has termination temperature limitations.
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I agree it might


Can you point to any such restriction?
 
If one has ever taken the UL classes/seminars, the 75C requirement has been discussed in detail during the classes/seminars.


The termination location is not the sole portion of the circuit to be required to be rated. All the components of the circuit are. As of now, I am not aware of any enclosures rated higher than 75C. Just changing a termination to 90C rating is not sufficient to change the circuit rating. The bus, terminations (both sides), enclosure, conductors, etc... Adding onto the conductor does not satisfy the change necessary to the whole circuit in regards to the 75C requirement.

SQD has a good PDF in their site, that explains this very well.
 
Pierre C Belarge said:
If one has ever taken the UL classes/seminars, the 75C requirement has been discussed in detail during the classes/seminars.


The termination location is not the sole portion of the circuit to be required to be rated. All the components of the circuit are. As of now, I am not aware of any enclosures rated higher than 75C. Just changing a termination to 90C rating is not sufficient to change the circuit rating. The bus, terminations (both sides), enclosure, conductors, etc... Adding onto the conductor does not satisfy the change necessary to the whole circuit in regards to the 75C requirement.

SQD has a good PDF in their site, that explains this very well.
Click to expand...

I think you either misunderstood what they told you or misunderstood the application here.
 
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