# Temporary Job Trailers



## william1978

Do you know the total connected load on each trailer? Beause you might be able to get by with a 400 amp service.


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## Seattlepro

No not really, the vendor said that there is a 17000 watts of demand, which would be 70.8 amps. Not sure why the vendor gives demand in watts though.


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## Bob Badger

Seattlepro said:


> No not really, the vendor said that there is a 17000 watts of demand, which would be 70.8 amps. Not sure why the vendor gives demand in watts though.


Because watts are how loads are calculated.

17,000*6=102,000

102,000/240=425 amp service if you go single phase, I would provide a 600 amp service.

Or ask for a 3 phase service

102,000/208/1.73=283 amps so a 400 amp 208 volt 3 phase service would be fine.

Don't cut yourself to close, they will add loads.


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## Bob Badger

To add a bit more.

In my experience (and I have done a lot of these trailer parks) if the trailer has a 100 amp panel the electric heating unit likely draws close to 60 amps, the air conditioning load is usually less.

Due to the fact the trailers are poorly constructed and insulated the heat runs a lot, often continuously for hours at a time if they go in and out a lot and the weather is cold.

Now you _might_ be able to squeeze these 6 trailers onto a 400 amp single phase service but your going to look like an ass if it trips the main and then you will have to correct the issue somehow.

Then there are the adds, sometimes we end up having to add heat trace on the plumbing if the trailers have water. Often once the job really starts more trailers are desired.

You say 'moneys not an object' so do it right from the start and come out ahead when they want more.


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## Bob Badger

Other random thoughts. Keep in mind you must use Table 310.16 for conductor sizing, you can not use Table 310.15(B)(6) for any of this. You will need grounding electrodes at the trailers per 250.32(A).


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## drsparky

Constrution trailer parks grow like weeds. Bob is correct plan ahead.


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## Seattlepro

*More confusion*

So these trailers fall in the Article 550 on the NEC. Article 550.31 says it is permissible to calculate the feeder or service load in accordance with Table 550.31! Which would look like something like this:

17000 x 6 (trailers) x 29% (Demand Factor)= 29580 sevice load

Does this make sense? 

I was on the same thought process as Bob, (which by the way you rock and thank you very much for the input) you total demand load for your service was 17000 va x 6 = 102,000 va which is 102,000/240= 425 amps. Which would be a 600 amp serive since a residential panel/meter set up can only be at 320 amps, what it is rated for. Need a CT meter setup and cabniet and 600 amp msd setup. But this demand factor has me confused, am I missing something here?


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## JohnJ0906

Seattlepro said:


> So these trailers fall in the Article 550 on the NEC. Article 550.31 says it is permissible to calculate the feeder or service load in accordance with Table 550.31! Which would look like something like this:
> 
> 17000 x 6 (trailers) x 29% (Demand Factor)= 29580 sevice load
> 
> Does this make sense?
> 
> I was on the same thought process as Bob, (which by the way you rock and thank you very much for the input) you total demand load for your service was 17000 va x 6 = 102,000 va which is 102,000/240= 425 amps. Which would be a 600 amp serive since a residential panel/meter set up can only be at 320 amps, what it is rated for. Need a CT meter setup and cabniet and 600 amp msd setup. But this demand factor has me confused, am I missing something here?


I would be a little leery about using that demand factor, I think it is meant more for residential trailers (although that is only an opinion), and job trailers might pull more than the demand factor allows for.
For instance, all the heat might be on full bore during the day, as well as all the lights, etc., if all 6 are in use at the same time.

Also, if you want to go with a 3-phase 208/120 service instead of the 120/240, check to make sure all the heat, A/C, etc, are rated for 208 as well as 240.


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## Bob Badger

JohnJ0906 said:


> I would be a little leery about using that demand factor, I think it is meant more for residential trailers (although that is only an opinion), and job trailers might pull more than the demand factor allows for.
> For instance, all the heat might be on full bore during the day, as well as all the lights, etc., if all 6 are in use at the same time.
> 
> Also, if you want to go with a 3-phase 208/120 service instead of the 120/240, check to make sure all the heat, A/C, etc, are rated for 208 as well as 240.


I agree with John, do not try to apply residential type demand factors to what is much more like a poorly constructed office building with electric heat.


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## JohnJ0906

Bob Badger said:


> To add a bit more.
> 
> In my experience (and I have done a lot of these trailer parks)


Bob, do you normally see 208/240 rated equipment, or is it 240 only?


I ask because the NEC handbook has a bit of commentary under 550.30 saying that a 120/208 supply is unsuitable due to the equipment normally installed in the trailer during manufacturing being rated 240v.

All of the job trailers I have done have had individual 120/240 services, so it has never been an issue for me.


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## Bob Badger

We almost always supply them 208.


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## william1978

Bob Badger said:


> We almost always supply them 208.


 The same here. The last one I did had 5 of those construction trailers hooked together and each got a 100a.


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## nitro71

Some of the trailers I've seen have a transformer jumper that you have to set inside the air conditioning equipment depending on whether you are using 208 or 240. Good idea to check that before energizing the AC. Can't recall if they were also heat units.


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## BEAMEUP

Seattlepro said:


> I need to install a Temporary service and panel that will feed 6 job trailers that have 100 amp 120/240V panels in them. The demand load is nothing out of the ordinary, (heating, lighting, outlets, AC although I don't think it will be in use this time of year,lol). Does anyone know of a service equipment, meter, disbution panel (that can handle this load) that is 3R NEMA rated for a temporary service? Plan posting a pole for the service mast and putting the meter and panel on approved backing and setup, but don't know if I can cover it. This is all happening on a empty gravel parking lot, commercially zoned in a resdential neighborhood. I am sure there are setups out there that are for sale for just this kind of thing. Like you see in the big construction jobs that need several job trailers energized for the duration of the project. Money is not object, doing this for the government under FEMA, and yes I am a electrician. But this the toughest district with the worst AHJ inspector in the northwest, if not the entire counrty, he has over 22 inspector licences in his pocket! :blink: Want to have all my details in line.


 
Seattle, piece of cake, which inspector?I worked in Seattle before moving to Maine a few months ago. Build a "sled" service and set it next to the pole and you can use it on your next job. I wouldn't do anything perminate that will have to be destroyed in order to be taken down. As far as the size of the service 6 full sized trailers, I would set a 600 amp and call it good, as long as it doesn;t serve any temp power elsewhere.

Also you better get your plans into Tim @ DPD for review,he is a little backed up right now, and have SCL get the owners to put in a applacation for power,& service requirements started, they can drag out the process for months to get perminate power to the site. Another also will this building have afire pump or two? get started on that to, that will take some time with Tim & then off to the fire marshal..


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## te12co2w

As already stated, the heating load will end up being continuous and more times than not, at least 50amps. I don't think the lower demand factor would serve you well in this case.


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