BIG HOUSE

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alfonso1900

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We are working on the design of a house that is going to be feed with 480V 3 phase service. The question is how do you size the low voltage transformers for the 120/208V distribution panels? Do you use the dweling unit calculations (which apply more to the service size and has derating) or do you prepare a panel scheduele that includes the loads (like in comercial work)? If i go one way the transformer could be undersized, if i go the other way it could be oversized. Sugestions?
 
alfonso1900 said:
We are working on the design of a house that is going to be feed with 480V 3 phase service. The question is how do you size the low voltage transformers for the 120/208V distribution panels? Do you use the dweling unit calculations (which apply more to the service size and has derating) or do you prepare a panel scheduele that includes the loads (like in comercial work)? If i go one way the transformer could be undersized, if i go the other way it could be oversized. Sugestions?
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LOL, wait until the homeowner learns about "Peak Demand Charges" that will come along with that 3 phase service!
Oh well, probably too rich to care...

I'd do it like a commercial service.
 
I would probably size the load both ways and perhaps go somewhere in the middle. However, I do not see why the residential demand shouldn't work.
 
We did one like that about 15 years ago, the load will probably be much higher than your run of the mill mansion. The chandeliers were so big that they were hung with log chain, had a full commercial kitchen in the basement, 600 kw backup generator, etc.etc.This was his private hunting lodge that he stayed at only a couple of months a year.
 
Many of the new homes around here that are very large use lots of LED. It appears this place is burning the juice. What size service is it?
 
The residential calc would work for sizing the service in most cases, although I've had a few residential projects with enough specialty lighting or other unusual loads that I treated them like a full commercial project. If you have multiple panels then each panel would need to be calculated individually like a commercial panel, based on the actual loads in that panel. For general lighting and receptacles I generally calculate a total load (3VA/s.f., plus loads allowed to be included with general L&R, with allowed L&R diversity applied) then distribute that load evenly among the applicable breakers in all panels. Everything else is calc'd on the panel level with no diversity unless the panel by itself qualifies for a specific allowance (like multiple appliances). Since my designs are sealed each panel/feeder has to calc out properly. I figure that clients at this level want everything to work with no breaker trips unless something actually shorts, so I tend to err on the high side.
 
Jraef said:
LOL, wait until the homeowner learns about "Peak Demand Charges" that will come along with that 3 phase service!
Oh well, probably too rich to care...

I'd do it like a commercial service.
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Here they do not charge peek demand on a dwelling, service size or type does not matter, KW wattage usage does, as over 750kwh it goes up to a different rate, but it's rare to find a 3-phase service in a dwelling because its rarely available in residential areas, but we have a few.

But I have installed some 1200 single phase services and even a 1600 amp one once, on a 28ksqft per floor house that had a totally underground full size Olympic size swimming pool, three basement levels, with a tunnel going underground to the pool.
 
alfonso1900 said:
We are working on the design of a house that is going to be feed with 480V 3 phase service.
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Considering that 210.6(A) forbids you from using 277V for lighting, I would be really curious what you're intending to feed with the 480/277Y portion of the service. Seems like it's gotta be more efficient to stick with a high amperage, 120/240V service for a house. I'd love to see your one-line and panel schedules.

In answer to your question, I would use the lower number.
 
George Stolz said:
Considering that 210.6(A) forbids you from using 277V for lighting, I would be really curious what you're intending to feed with the 480/277Y portion of the service. Seems like it's gotta be more efficient to stick with a high amperage, 120/240V service for a house. I'd love to see your one-line and panel schedules.

In answer to your question, I would use the lower number.
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The question becomes - what is the dwelling? Is the entire facility the dwelling?

Things that may be present that may not be considered a part of the "dwelling": swimming pool, gymnasium, outdoor lighting, other recreational areas, parking areas, helipad. The kitchens in some of these places put many small commercial kitchens to shame. There could even be a fire sprinkler system with a fairly large fire pump. The place may be more similar to a resort than what most of us call a home, yet is owned and used by a single owner and his/her family and friends.

I am not familar with large mansions - I don't have the right family or friends. If I did, I probably wouldn't be hanging out here. But they are not a typical single family dwelling either.
 
Dennis Alwon said:
I believe in the 2011 they tried to make it clear that residential included all the associated buildings.
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Not a NEC issue but zoning and other building codes may come into play as to what you are going to call it.

NEC does not use the term "residential" they use the term "dwelling"

Large hotels and resorts most would agree are not dwellings yet can contain units that are defined in NEC as dwelling units. Now complicate it with a large mansion that is like a hotel or resort, yet is somewhat a single family dwelling.

There are manisions in Hollywood that have larger party rooms and larger parties than the community centers and auditoriums here in small town USA. Please tell me that these areas are not single family dwellings for purposes of emergency egress, fire protection, and such.

We have had for years, a local group that sponsers a "haunted house" on halloween - mostly for the kids. They usually do this in a vacant building on a low budget as the group is a community charity type of group. They can no longer do this because the fire marshal wants the building to have sprinkler system, egress lighting, ADA compliance and everything else otherwise required in other buildings. It will cost more to comply with all that then they will ever make from the gate. We are talking about groups of maybe 10 max that go through the place at a time.

I know I am starting to veer off topic... it does have some similarities - what kind of occupancy is it?
 
George Stolz said:
Considering that 210.6(A) forbids you from using 277V for lighting, I would be really curious what you're intending to feed with the 480/277Y portion of the service.
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It'd seem like he'd have to feed transformers all over the place. Not that the customer would care but if the house is that big they are going to have a lot of transformers and a lot of transformer loss. I don't think there's any way I'd put a transformer in a house.

What would you do when they start complaining about the hum? You can't just tear it out....?

Why not a 120/208 or 240/120 service?
 
Cow said:
It'd seem like he'd have to feed transformers all over the place. Not that the customer would care but if the house is that big they are going to have a lot of transformers and a lot of transformer loss. I don't think there's any way I'd put a transformer in a house.

What would you do when they start complaining about the hum? You can't just tear it out....?

Why not a 120/208 or 240/120 service?
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Why do they need to have transformers all over the place? They obviously need at least one to get 120/240 or 208.

Generally it would not be a good idea to supply this with 277/480, but we do not know what the loads all are either, nothing is much of a suprise with some of the wealthy these days.
 
kwired said:
Why do they need to have transformers all over the place? They obviously need at least one to get 120/240 or 208.

Generally it would not be a good idea to supply this with 277/480, but we do not know what the loads all are either, nothing is much of a suprise with some of the wealthy these days.
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I'm making assumptions since the OP hasn't responded. The only reason I'd think to feed a house with 277/480 is because it's HUGE. The 480 is for distributing around the home and installing LV subpanels everywhere. If he doesn't need 480 for distribution, then why wouldn't a guy make his POCO give him 120/208 or 240/120 like every other house?
 
Cow said:
I'm making assumptions since the OP hasn't responded. The only reason I'd think to feed a house with 277/480 is because it's HUGE. The 480 is for distributing around the home and installing LV subpanels everywhere. If he doesn't need 480 for distribution, then why wouldn't a guy make his POCO give him 120/208 or 240/120 like every other house?
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All it takes is one large load, and you possibly consider 277/480 for service. The wealthy people today have big imaginations.
 
kwired said:
All it takes is one large load, and you possibly consider 277/480 for service. The wealthy people today have big imaginations.
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Too true! I had a friend who had an uncle who was a custom home builder. He had an indoor pool and the space was almost bone dry. If any of you have much experience with indoor pools, you'll appreciate how unusual this was. The secret was a humongous industrial-strength dehumidifier sucking the water out of the air as fast as it evaporated. I could easily see the chiller being hooked up to a 480 service.
 
George Stolz said:
Considering that 210.6(A) forbids you from using 277V for lighting, I would be really curious what you're intending to feed with the 480/277Y portion of the service. Seems like it's gotta be more efficient to stick with a high amperage, 120/240V service for a house. I'd love to see your one-line and panel schedules.
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I agree.

We do large hotels and even they have 208 volt services, some as large as 4000 amps.
 
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