Is there a "rule of thumb" for going to a 480V service instead of a 208V?

[bbaumer]

Is there a "rule of thumb" for say building size for commercial or educational type occupancies where it probably makes sense to go to a 480/277V service instead of a 208/120V service?

Not looking for a detailed analysis just looking for a guideline that says "air conditioned office buildings greater than X square feet are worth it to go to 480/277V".

The thinking is the savings on copper, # breakers, number of lighting circuits, I2R losses, bus sizes etc. more than offset the cost of the dry transformer and higher voltage rating of equipment.

eg You probably would not feed a small 2,500 SF office building with 480V but you probably would a 50,000 SF building.

Anyone consider this before?

thanks,
bbaumer

 

[drbond24]

I have designed both (480 and 208) in the past, but I never really gave your specific question much thought. I would say it had more to do with the equipment being fed and not the square footage of the space. Even with a small building, if there are a couple of heat pumps, air handling units, exhaust fans, blah blah blah then you'd probably better go with the higher voltage. It's a judgement call really.

 

[realolman]

If you had mostly 120v loads it wouldn't make much sense to go with 480.... other wise I think I'd prefer it.

I think you'd probably just have to decide on an individual basis.

 

[480sparky]

Large lighting loads and a lot of mechanicals can make choosing 480 easy.

 

[mdshunk]

An air conditioning load greater than 10 tons for a single unit seems to be one of the main things that triggers the need for a 480 service. That, and larger locations with primarily lighting loads.

 

[iwire]

It really depends on the needs of the customers building.

We have done a few large hotels, 4000 amp 208Y/120 services. Not much use for 277 or 480 there and transformers take up space they want to rent.

OTH I have done 200 amp 480Y/277 services for small industrial occupancies.

All machines, some lighting that can be 277 and the 120 loads can be served by a 30 kVA transformer.

 

[bbaumer]

Thanks for the replies. Trying to convince a client it makes sense to go to 480V on a particular project without having to do a bunch of analyses and estimates.

 

[mdshunk]

Some people simply don't want to own transformers. I have one customer who's building has three 5000 amp services, all at 208. They get all their manufacturing equipment made for 208, and order their A/C for 208.

 

[peter d]

We have done a few large hotels, 4000 amp 208Y/120 services. Not much use for 277 or 480 there and transformers take up space they want to rent.

The hotel that we've both worked at (Rt 1, Norwood) actually has two separate poco transfomers outside, one 208 and one 480, and obviously a separate set of indoor distribution for both systems. I thought that was a clever way around having multiple transformers inside the building , and not something I've seen anywhere else.

 

[iwire]

The hotel that we've both worked at

That was not one of the ones I was thinking of.

That one is kind of of weird, I think the next door neighbor owns the 13.8 distribution supplying the Hotel. So I think the Hotel has two feeders not two services.

 

[peter d]

That was not one of the ones I was thinking of.

I figured that. Plus, the hotel doesn't have a 4000 amp service to my knowledge.

That one is kind of of weird, I think the next door neighbor owns the 13.8 distribution supplying the Hotel. So I think the Hotel has two feeders not two services.

Interesting, I didn't know that. I remember the job foremen talking about NP&L being involved with a shutdown there so I wasn't sure if the transformers were services or owned by FMG.

 

[iwire]

Interesting, I didn't know that. I remember the job foremen talking about NP&L being involved with a shutdown there so I wasn't sure if the transformers were services or owned by FMG.

I am not 100% sure but that ugly building at the back of the property has 13.8 distribution as I recall.