Electrical Load calculaton for large 'guard-shack' with HVAC, Xfmr, Ltg, Recepts etc

[Isaiah]

Hello All;
I've got a set of drawings issued by a subcontractor that calls for lighting load to be increased by 125%. He's referencing NEC 215.2(A)(1), however this is for feeders - not lighting - so I don't see where this is coming from.
Also for his total load calculation, he's adding another 20%. The largest motor load is correctly sized up to 125% of FLA per 430.24, but I don't see the justification for the 125% on lighting or the additional 20% applied to the overall load in volt-amps, which includes Receptacles, HVAC, Kitchen appliances and 'other loads'.
Am I missing something?

Thanks in advance.

 

[david luchini]

He's referencing NEC 215.2(A)(1), however this is for feeders - not lighting - so I don't see where this is coming from.

Lighting is generally considered to be continuous load...215.2(A)(1) is the correct reference for feeders, or 230.42(A)(1) for services.

 

[MasterTheNEC]

Hello All;
I've got a set of drawings issued by a subcontractor that calls for lighting load to be increased by 125%. He's referencing NEC 215.2(A)(1), however this is for feeders - not lighting - so I don't see where this is coming from.
Also for his total load calculation, he's adding another 20%. The largest motor load is correctly sized up to 125% of FLA per 430.24, but I don't see the justification for the 125% on lighting or the additional 20% applied to the overall load in volt-amps, which includes Receptacles, HVAC, Kitchen appliances and 'other loads'.
Am I missing something?

Thanks in advance.

Greetings,

I will assume these are not engineered drawings because you did not state as such. The use of 125% for the lighting is due to them being considered a continuous load as I believe someone already mentioned. The additional 20% may simply be a "corrective" precaution due to poor information supplied to the designer or drafter of the document and they are compensating for that by adding an additional 20%. However, the additional value figured in will not harm anything but could result in larger conductors and so on which as a contractor just results in charging more money (to me anyway). They also could be figuring in the additional 20%, which maybe should be 25% for the largest motor but again that would be only speculation on my part. I would ask whoever did the calculations why they added the 20% and get the answer from the source. Otherwise, install it as drawn and subsequently approved.

 

[Isaiah]

Greetings,

I will assume these are not engineered drawings because you did not state as such. The use of 125% for the lighting is due to them being considered a continuous load as I believe someone already mentioned. The additional 20% may simply be a "corrective" precaution due to poor information supplied to the designer or drafter of the document and they are compensating for that by adding an additional 20%. However, the additional value figured in will not harm anything but could result in larger conductors and so on which as a contractor just results in charging more money (to me anyway). They also could be figuring in the additional 20%, which maybe should be 25% for the largest motor but again that would be only speculation on my part. I would ask whoever did the calculations why they added the 20% and get the answer from the source. Otherwise, install it as drawn and subsequently approved.

Agreed. 125% for continuous load is ok since it applies only to lighting load in this case.
I should have mentioned, these drawings have been engineered and supplied by an independent subcontractor, however it is up to us to review and approve their dwg packages. They've already added 125% for the largest motor, which is correct. But it seems the added 20% for the Total VA is unnecessary. They in turn, sized the MCB's based on 125% of total VA (including the 20%). This increases transformer size, cable etc and of course cost unnecessarily.

 

[MasterTheNEC]

Agreed. 125% for continuous load is ok since it applies only to lighting load in this case.
I should have mentioned, these drawings have been engineered and supplied by an independent subcontractor, however it is up to us to review and approve their dwg packages. They've already added 125% for the largest motor, which is correct. But it seems the added 20% for the Total VA is unnecessary. They in turn, sized the MCB's based on 125% of total VA (including the 20%). This increases transformer size, cable etc and of course cost unnecessarily.

Understood. However, usually, the ones who actually design it actually know their reasons, or lack thereof, of why they did what they did. I would reach out to them. From a contractors perspective, if it is an engineered drawing and "stamped" then I may question it, grumble about it, but I would install it as they designed it. Now, I have my share of "push-backs" but then again I would tend to go to the source and determine why someone did something rather than speculate on it and essentially guess as to why they do what they do.

So my advice, should you choose to take it, is to reach out to them with your concerns by presenting them in a logical format and ask for an explanation for each issue that concerns you. Why, because if you choose to ignore it and something happens they will point to you as not following their design and attempt to resolve themselves of any blame. Even if it was over-engineered they may try to divert blame so I would prefer to go right to the source and ask why someone did what they did and get my answers that way.

 

[Gary11734]

Assuming guard shack is never closed, 125% for lighting.

It would not be unreasonable to have 20% spare capacity. I have seen them apply as much as 40% capacity. 20% expansion looks like a good design.