Two Generators Feeding One Trailer

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alcornjr

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I have a project with the border patrol that they have these little office trailers on their checkpoint sites. These sites are where you get checked by the Border Patrol when coming to and from Mexico.

There is not any conventional electrcity near the site and they want to feed one trailer with two generators. Each generator will produce about 83 amps and has a 50A breaker and a 20A breaker to use on them. One generator does not satisfy the trailer load - so two is needed. There is one panel on the outside of the trailer w/ a 125A main breaker. The trailor load is about 95amps.

My question is - Can this be done? Article 230 of the NEC states that there should only be one source per building. There are some exceptions within ART 230 but I don't think none of them apply. The only one of the possible exceptions within 230 that might apply is "parallel power feeds", but I don't think that even applies.

Other artices - 550 to 552 - have some provisions to mobile homes, but it doesn't give specifics about the use of multiple generators as the primary source for electrical power to a building.

Splitting up the load and adding some to a new panelboard for the trailer will do the trick. One generator for one panel. Another one for another panel. But I don't think this is NEC compliant.

They ordered these trailers and generators already where they want to use these generators that they have an abundance of.

I told them the simple way to do this is give back the 20KW generator and get a 30KW generator for the trailer. But they still want to use these generators.

Any help would be appreciated.

Thank You
 
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i doubt you can parallel those generators, so you would have to split up the loads in the trailer, ex: one generator for HVAC and the other for everything else (i dont know if this is kosher code wise)
 
I do most of my work on the edge of nowhere - and yes sometimes things get designed/installed differently than in downtown America - still safely and reliable, just different.

This customer may well be exempt from local AHJ requirements.

I'd call the mfg and see if there is paralleling gear available. as was said, not likely, but I'd still call. Even if available, this isn't a good solution - it adds a lot of complexity for the operator - which likely be one of the border patrol agents.

Check with the customer and see what code/AHJ they are under - you may be the AHJ.

I think you are dead on about them getting a single larger gen. Hit them with a safety bullet. This will not be a normal installation and that usually spells safety concerns for anybody coming in later to do service work.

You are the engineer - it's your name and stamp, your responsibility - be safe.


Pierre -
I didn't see anything in 225 that would specifically prohibit two feeders. In fact, (2002) 225.30.E would appear to allow two feeders.

What am I missing?

cf
 
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I don?t think 225 comes into play here. If you have a service to one building, and that building has a feeder that supplies a second building, then you are into 225. I think having a generator as the only power source to a building makes that generator a ?service.? Nothing requires a utility company to be involved in the provision of a service.

Can you use two generators? The only way I see is by invoking 230.2(C)(3), the catch-all ?special permission? rule. It seems that getting special permission from someone who claims to have the authority will not be an issue here, since nobody really seems to have authority.

Can you safely use two generators? Yes, if they are not in parallel, if they supply different loads. Also yes, if the manufacturer can provide paralleling equipment, and if the facility?s distribution system can handle the extra fault current that comes from parallel sources. Otherwise, no.
 
charlie b said:
(cut) and if the facility?s distribution system can handle the extra fault current that comes from parallel sources. Otherwise, no.
Click to expand...


Extra fault current from paralleled 20kw gens?? I'm thinking it's less than a 1000A total. Did you have another number in mind? Admittedly, I rarely work with single phase gens.

cf
 
charlie b said:
(cut) I think having a generator as the only power source to a building makes that generator a ?service.? Nothing requires a utility company to be involved in the provision of a service. (cut)
Click to expand...
I have not run into this interpretation before. Anytime I have had self generation, the AHJ has considered our generators as seperately derived systems - not a utility.

cf
 
charlie b said:
I don’t think 225 comes into play here. (cut)
Click to expand...
How about if one considers the pad the generator(s) are on as one structure and the office trailer as the second structure? Then the feeder(s) between them would appear to be under art. 225. I had figured that was Pierre's thinking.

cf
 
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charlie b said:
I think having a generator as the only power source to a building makes that generator a ?service.? Nothing requires a utility company to be involved in the provision of a service.
Click to expand...

Actually the NEC does say that only a utility can provide a 'service'.

See 'Service' in Article 100.



Pierre C Belarge said:
Take a look at 225, this is not an acceptable type of installation, as you describe in the OP.
Click to expand...

I agree it is a feeder and 225 applies.

That being said, the NEC may not even apply here being Govt work.
 
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