Temp service

[Billyh]

I was looking not for the answer but the calculation to size a temp service. Others are multiple office trailers 240/120 100 amp a 480/277 v crane at 300 amps two buck hoists at 40 a each 480/277 35 hp. Incoming voltage available is 480/277. There are also 2 buildings 12 stories each but no sq footage given. If someone could explain how to figure this out it would be awesome. Thanks in advance!!!

 

[Billyh]

Any direction would be great!!

 

[ActionDave]

Wire it all up to a 600A main and you should be fine.

What exactly is it you are trying to figure out?

 

[JFletcher]

Welcome to the forum.

Any direction would be great!!

Lemme see here... 480V service, a 300A crane, two 12 story buildings of completely unknown usage type or sq ft, bosses trailers... multiply by root 3, add the 'some other stuff' fudge factor, and I get 600.0000A, exactly as Dave predicted. Unfortunately it's not that easy.


I would direct you toward finding out a lot more about your scope of work. The 2 12 story buildings, are you providing just site lighting and receptacles, or do you have to keep the existing buildings and all their equipment powered up while they are being renovated?

 

[Smart $]

.... Unfortunately it's not that easy. ....

No practical experience on no-so-high and high-rises, but I agree. Site lighting and receptacle power plus unnumbered office trailers plus 300A crane and several hoists easily justify a 600A. I was thinking 800 off the top of my head but for some reason, I was only thinking one building, not two. I didn't see any mention of existing... or just thought this was a break-ground type of project.

 

[Billyh]

Let me more clear 480/277 service available at street. 14office trailers to power up 100amps each at 240 single phase. So how to size the service for the trailers as well as the transformer to get the voltage where it needs to be. I understand about the lights and power for building. I do not have any information on that.

 

[Smart $]

Let me more clear 480/277 service available at street. 14office trailers to power up 100amps each at 240 single phase. So how to size the service for the trailers as well as the transformer to get the voltage where it needs to be. I understand about the lights and power for building. I do not have any information on that.

While the office trailers may have 100A main breaker panels, most do not have anywhere near that as a calculated load. Just take your time and do a load calculation... or take a best guess... or perhaps someone with firsthand experience on sizing for office trailers will join the discussion.

You'll obviously need one or more step-down transformers. With your service being three phase, you have the option for them to be 480V–208/120V 3Ø 4W or 480V–120/240V 1Ø 3W preferably in sets of three so as to balance the load on the three-phase source or use offset transformer kVA's to achieve load balance.

 

[zbang]

While the office trailers may have 100A main breaker panels, most do not have anywhere near that as a calculated load. Just take your time and do a load calculation... or take a best guess... or perhaps someone with firsthand experience on sizing for office trailers will join the discussion.

Certainly not an authority here, but most of the office trailers I've done were quite happy with being fed from a 50a 2-pole breaker (often at 208/120V from a spider box distro). That won't cover intense heating needs, but for basic heat/AC, lights, and receptacles, it was fine.

That said, there's no substitute for a load calc, which means getting real info from the trailer's HVAC system, but it's probably around 3-4 tons cooling and 5-10kw heating (MCA 35-45A). It's usually the heating that'll drive up the feeder size.

 

[JFletcher]

Certainly not an authority here, but most of the office trailers I've done were quite happy with being fed from a 50a 2-pole breaker (often at 208/120V from a spider box distro). That won't cover intense heating needs, but for basic heat/AC, lights, and receptacles, it was fine.

That said, there's no substitute for a load calc, which means getting real info from the trailer's HVAC system, but it's probably around 3-4 tons cooling and 5-10kw heating (MCA 35-45A). It's usually the heating that'll drive up the feeder size.

Windsor, CT, where the OP is, has a winter where the avg daily high is 40 and low is 21. I'd think w/e electric heat they have per trailer is gonna be on x 14 units x >3hrs each, i.e., full demand.

 

[zbang]

Agreed, but even with a 10kw heater, the whole trailer isn't going to top maybe 70A with everything going, then figure in diversity for all of them.

This is really all guessing. Billyh (the OP) needs to forget about the "temp" part and treat this as he would for any new service, which points back to real info about the trailers & buildings, then to doing load calcs.

 

[Smart $]

... Billyh (the OP) needs to forget about the "temp" part and treat this as he would for any new service, which points back to real info about the trailers & buildings, then to doing load calcs.

Agreed. It is actually required by 590.2(A) and the lack of any modification mentioned therein upon a service. In fact, 590.4(A) requires services be installed per Article 230.