Load study for new, permanently connected cord and plug equipment.

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MrBP

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Long time reader - first time poster. I was wondering if anyone has any citations for some common sense reasoning that can be founded in a formal statement from either the IEEE or the NEC. I have not found any such details to date.

I have a situation where existing 'as-built' electrical plans and equipment schedules are not readily available for some facilities. It is desired to add new cord-and-plug connected load that will draw up to about 4A on a non-continuous basis, and perhaps 1A on a continuous basis.

The impact of such loading is akin to that of plugging in various consumer electronic devices to general outlet receptacles. However, it seems difficult to formally qualify that a full and complete load-study, from the point of connection all the way back to the service entrance, is unnecessary.

A further point is that for any load addition, the existing load has to be determined in accordance with NEC 220.87 so that adequate headroom can be verified. If this is to be done via 30 day metering (per the 220.87 exception), then the load-metering study surely has to be applied on every feeder and panel affected by the increased burden - all the way to the service entrance (right?). Just because one panel is not overloaded makes no guarantees about upstream supply panels and feeders. For such a small load, this seems incredibly and unnecessarily complex, especially on services that are as large as 1600A @ 480V, for instance.

Has anyone run into such a situation before? Common sense intuition needs to be substantiated with some codified or detailed engineering guideline or requirement from a recognized body such as the IEEE or NFPA.

Thanks,

Brendan.
 
One more point is that I believe that as this is a low-burden connected device, this may not really qualify as a "load-addition", but rather as a device that is utilizing the loading headroom given to the branch circuit. This reasoning assumes the electrical installation was code compliant to begin with.

For example, saying that plugging in a wall-wart transformer would be a "load addition" would be scoffed at. It is merely using the electrical headroom granted to it through the 180VA allowance per strap connected to that branch.

Thanks,

Brendan.
 
I have never seen a load calculation or study needed when you add one load like that. I guess it is withing the EI's rights but most services are generally not filled to capacity. I do mostly resi work so perhaps others can chime in.
 
MrBP said:
to add new cord-and-plug connected load that will draw up to about 4A on a non-continuous basis, and perhaps 1A on a continuous basis.

A further point is that for any load addition, the existing load has to be determined in accordance with NEC 220.87 so that adequate headroom can be verified.
For such a small load, this seems incredibly and unnecessarily complex, especially on services that are as large as 1600A @ 480V, for instance.

Thanks,

Brendan.
Click to expand...

Let's say a load study shows a draw of Y amps and is accurate within +/- X%.
If the added load is less than X/5 it should be negligible.
At the lower limit of this benchmark, X/5 = 4A so X is +/- 20A. If X is 5% of the Y, then Y is 400A.

If load calcs are less accurate, then X/5 is larger.
 
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Kind of get interesting with cord and plug equipment.

If calcs were done originally then each receptacle was calced at 180VA of load x10 gives you about 20A availible. If you are pluging in one piece of equipment that only pulls 4 amps and none of the other receptacles are being used, you have 16 amps to spare. In theroy of couse.

Now on the same hand you could plug two pieces of equipment in that both pull 15 amps and have all kinds of problems.
 
MrBP said:
... It is desired to add new cord-and-plug connected load that will draw up to about 4A on a non-continuous basis, and perhaps 1A on a continuous basis.

...
Click to expand...
IMO, if you are plugging into a general use receptacle, no additional load calculation or determination is necessary. That's what general use receptacles are for.
 
Smart $ said:
IMO, if you are plugging into a general use receptacle, no additional load calculation or determination is necessary. That's what general use receptacles are for.
Click to expand...

I do not disagree, my point was along the lines that you have no idea whats going to be plugged into them.
 
Smart $ said:
Point noted... but what's that got to do with performing (or not) an updated load calculation or determination.
Click to expand...

You don't or can't. I think his question was something that we've all had to deal with at one time or another and the simple answer is usually...."you'll just have to unplug something."

That's why sometimes as inspectors we ask so many questions about what your putting in a building. Had one that the guy said that he was using it for storage so we let him build it. When we asked what he was storing in there we were told that it was none of our business and when pressed he took it to the BO and the BO told us to back off. Come to find out he was storing and working on his automobile collection and we had not wire the building to be a service garage.

Long way to a point, but it's important to know whats going in an office area. I bet everytime you ask, the answer is almost always just a computer on the desk. Then you show up for some service call and there are three printers and a copier and a couple of little heaters plugged into that circuit also. I know, you can't stop them, but you could have helped them. Might also have made a difference as to whether you installed a 100 amp sub panel or a 150 amp sub panel.
 
Thank you for your replies. Good points with which I concur. I see this as a situation where the multiplicity of 180VA allowances should make sense to utilize as the necessary headroom required.

Regarding:

ptonsparky said:
Curious. How can a cord & plug connected piece of equipment be permanently connected?
Click to expand...

Probably not the best choice of language when I said "permanent" - obviously it could become unhooked at anytime. What I meant is that it would essentially be equipment "fastened in-place" (per NEC parlance) and intended for permanent operation in that setup.

Thanks, all.
 
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