Serving a home with 480/277?

[fastline]

Working on a commercial building design for someone that desires to have a small living area in it. By code, the full roll out is required for the living area, in which I need to make sure we can bring in 480/277 and run a 120/240 1P xmfr to handle the living area.

I simply don't recall anything in NEC that restricts much of this other than certain loads "may not exceed 120V". To be clear, in no way am I wanting to have 480/277 in the living area, but rather ensure there is not some conflict that would disallow the 480/277 entrance due to having a living area.

 

[augie47]

Should be no problem.
It is not unusual to have 480/277 in a commercial structure for such loads as HVAC with 208/120 or 240/120 for residential occupancies

 

[electrofelon]

Here is the AI response, completely wrong

No, you cannot run 480 volts to a dwelling unit; the standard voltage for residential applications in the United States is 120/240 volts, and running 480 volts to a home is extremely dangerous and not permitted by electrical codes due to the high risk of shock and potential damage to appliances and wiring.

 

[fastline]

Should be no problem.
It is not unusual to have 480/277 in a commercial structure for such loads as HVAC with 208/120 or 240/120 for residential occupancies

Would you happen to recall anything in code that may "allow" this verbatim? The reason mainly is that the building is basically commercial level, but being built on a residential lot. I very much expect to get kickback from the county. They are notorious for citing their "opinion", but when I ask for code references, I get crickets from them.

The occupants want 480 to be able to run their industrial toys.

 

[electrofelon]

Would you happen to recall anything in code that may "allow" this verbatim? The reason mainly is that the building is basically commercial level, but being built on a residential lot. I very much expect to get kickback from the county. They are notorious for citing their "opinion", but when I ask for code references, I get crickets from them.

The occupants want 480 to be able to run their industrial toys.

The only restriction is for certain types of branch circuits. See 210.6

 

[WD40]

We looked into this years ago same thing, ask your customer how often they want to use the 480?
It ended up being a 240/120 hi-leg service with a very small step-up to 480/277
480 equipment was not going to be used daily so the transformer losses to step down 24/7 would have added up on the bill.
The 2nd reason was the utility offered the 240 bank at about 1/10 the cost of the 480, they only needed two transformers for the 240.
I also 'rewired' a old lathe for the guy 480 to 240 just by swapping a few motor leads and changing the tap on the control transformer, I probably committed a huge UL violation there.

 

[D. Castor]

Most utilities around here will not provide three-phase power to a residence. And if they did, the customer would have to pay for all costs associated with bringing in three phase primary.

IMO, if the US was starting from scratch today, everything would be 240 V (or 400/230 V), with no 120 V. But that's not where we are.

 

[CoolWill]

Most utilities around here will not provide three-phase power to a residence. And if they did, the customer would have to pay for all costs associated with bringing in three phase primary.

IMO, if the US was starting from scratch today, everything would be 240 V (or 400/230 V), with no 120 V. But that's not where we are.

Yes, because it's simpler.

 

[norcal]

Came across a shop with a bootleg MIL unit, shop had a 480/277V service & was the only residence where I saw 277V lighting, I removed the 277V so they could have ceiling fans in place of the 2X4 troffers, was a wild story.

 

[hillbilly1]

The previous company I worked for wired a southern mansion that was a hunting lodge for the owner. ( not the company owner) 480 three phase with a transformer in a closet on each floor. Full commercial kitchen in the basement. Two big generators in the horse stable. All this for him, his wife and a couple of kids.

 

[Jraef]

Most utilities around here will not provide three-phase power to a residence. And if they did, the customer would have to pay for all costs associated with bringing in three phase primary.

IMO, if the US was starting from scratch today, everything would be 240 V (or 400/230 V), with no 120 V. But that's not where we are.

This is the salient point. I used to have a side gig helping home machinists upgrade their machines to use VFDs, this subject came up a lot. In every case where someone looked into getting 3 phase brought in to a residential neighborhood, the cost was very very prohibitive, because the utility would charge per FOOT for the cost to get a 3rd primary line brought in from the nearest point where it existed. So it generally ranged between $5k and $15k. Then on top of that, the new surprise for those users was a "demand meter", which came along with a commercial service drop, something most of them were unaware of, along with the SHOCK of what it did to their bill on the months when they exceeded their peak demand!

The other aspect, alluded to by WD40 above, is the cost of the LOSSES. When you have a purely residential service, the UTILITY owns the transformer and the losses in that transformer, because your meter is DOWNSTREAM of that transformer. With a 480V service drop, they might own the 480V transformer losses, but the USER will own the 120/240V single phase site service transformer for the residence feed, and that means THEY will own the losses of that transformer. They might be low, but they are 24/7/365, whether you use power or no and it adds up. Let's say it's a 25kVA transformer, the losses will likely average out at about 350W. That's over 3,000kWh per year, so even at 12c/kWh, it will cost them an extra $30/month just sitting there.

If it's a residence, I advise a residential service drop, even if it has to be 400A, then power up phase converters or VFDs for the machines that they RUN, only when running them. The losses are only when in use, and if they separately meter the shop power, it can be assigned as business expenses against whatever they are making.

 

[fastline]

Just to clarify, the primary use is actually commercial, running some automated equipment, totaling about 300HP running at least 80h/week. The residential component is actually the small part.

I am familiar with the idle costs of such transformer and have discussed with the POCO. I am probably recommending a 250kva xfmr and owner is fine with the extra costs.

The costs cited above are spot on and this POCO just just a flat fee to break out of the losses, which is $1/kva/mo. IE, use at least that amount per mo. That amount does not 'add' to the bill, just a minimum at billing. If actual use exceeds that, there is no issue. However, another, and better POCO rarely charges a dime to get 3P with reasonable demand, and does not charge for idle loss.