400 amp service calcs?

[DunhamElectric]

looking for some idea's or alternatives. My customer has already made up his mind and whants a 400amp service on a pedastal about 300' up the hill from his house. The ground pad transformer is about 50' from where he whants his pannel. He says that his "buddy" told him he could pull 3/0 from the 400amp, down the hill to the house in a 3" conduit. Now I told him that I believe 750 kcmil would be required. Any body got any any ideas or recomendations for this.

Thanks

 

[LarryFine]

Load calcs?

 

[DunhamElectric]

Thats the thing There are no plans available yet. Right now we are only setting up a temp pole, and running conduit in a 285' garden wall for L/V lighting. They whant a 125amp temp put up for when they build the house. The only hint of what is to be in the house that I have heard is that there will be a 200amp in the garage, and a 100amp at the other end of the house for bedrooms and a media room. there is also a well for the property at the top of the hill, about 100' from where they whant the 400amp. This is supposed to be a 5000 sq foot house, but like I said, I have seen no plans for a house yet. The problem I am running in to is that the owner is telling the general one thing, PGnE is telling him another, and I am caught in the middle.

 

[bob]

VD calculations per 100 amps:

3/0 - 2.6%
500 kcm - 1.2 %
750 kcm - 1.0 %
This does not include an flicker problems from starting large motors.
If you are installing a 400 amp service don't you think 3/0 would not be an option.

 

[Dickieboy]

90 degree-500 MCM would be minimum if you wanted the full 400 amps or parallel 90 degree-2/0 as an alternative which would be 390 amp(borderline) and thats not adding the 125% factor in

Whats the voltage and VD allowable for a better look see.

dick

 

[bob]

90 degree-500 MCM would be minimum if you wanted the full 400 amps or parallel 90 degree-2/0 as an alternative which would be 390 amp(borderline) and thats not adding the 125% factor in
Whats the voltage and VD allowable for a better look see.
dick

You are not allowed to use the 90C rating of conductors except when adjusting ampacity per 310.15(B)(a) and temperature correction factors for the conductors. Max rating for 500 kcm is 380 amps. 2-2/0 would be rated at 2 x 175 amps = 350 amps max. See 110.14.C

Dickieboy,
you are listed as an electrical designer. Have you been using the 90C rating in you designs?

 

[nakulak]

If you are going to size a service, its kind of important to know the load. I suppose if the utility will go for it you could just go for 400, but around here you need to do a load letter, which means you have to have some idea of the loads.

jmsho

 

[DunhamElectric]

The only load info i can get is that they need 14kva and the transformer in question is a 25kva supplying another property at 14kva, i just got this info today, and I polietly told the owner "well 14 + 14 is 28 in my world) so I explained that what I told him in the first place as far as setting our own ground pad and transformer is about his only option. I got some accuratre measurments today and the run is 175.8 feet from the proposed pull box, wich is 56' from the vault. 28.09 is the only other number listed as energy use. Thanks guys for all your help.

 

[iwire]

You really should not be doing a service without some load calcs and in many areas your would not get a permit without them.

You absolutely should not be trying to figure voltage drop without having a good idea of the connected load.

The size of the power company transformer does not enter into any of it.

 

[wbalsam1]

..........You absolutely should not be trying to figure voltage drop without having a good idea of the connected load...........

I couldn't agree more. Around here it is amazing how many home owners, yes, and even contractors, arbitrarily decide they need a 200 amp service, or a 400 amp service without so much as any load calculations at all. None. I just scratch my head when they tell me about what they "need" and what they estimate the VD to be. :smile:

 

[dicklaxt]

Bob,We design by 75 and buy 90,,,,,,,,,this post was in the buying phase it looked like to me so thats where I came in.


dick

 

[DunhamElectric]

You really should not be doing a service without some load calcs and in many areas your would not get a permit without them.

You absolutely should not be trying to figure voltage drop without having a good idea of the connected load.

The size of the power company transformer does not enter into any of it.

In most case I would agree with you but in this one I am only trying to get them temp power for the construction of the retaining walls. The load calcs for the house will be available when the final plans are complete. the only thing that is a definate is that a 400amp service will be required. The problem I am having is that the county is telling us that we have to set the 400amp to supply the 125amp temp and the 50amp well before they will inspect anything. I know it all seems backwards but trust me, here in Monterey California this is the norm. Now I have come up with some numbers of my own, and I figure 14kva is what we are looking at in the future, but for a temp I tried to get a 125amp meter set 86' from the transformer with a 4" conduit and 1/0 wire. The inspector was OK with that but the owner did not whant the pannel in the front. I know this may not be a normal situation for most of you, and it is not exactly typical for myself. But I am looking for suggestions at this point to present to the owner, the general contractor, and the power company. Any help or ideas are greatly appreciated.

 

[tallgirl]

looking for some idea's or alternatives. My customer has already made up his mind and whants a 400amp service on a pedastal about 300' up the hill from his house. The ground pad transformer is about 50' from where he whants his pannel. He says that his "buddy" told him he could pull 3/0 from the 400amp, down the hill to the house in a 3" conduit. Now I told him that I believe 750 kcmil would be required. Any body got any any ideas or recomendations for this.

Thanks

Tell the clown he's responsible for Global Warming and will be one of the first people up against the wall when the revolution comes?

Just a hunch, but he's playing "keeping up with the Joneses" and his "buddy" doesn't actually have a 400A service, which would explain the 3/0. You can probably make extra money figuring out ways to hide however much of whatever it is you have to install, and he'll be more than happy to pay. Including making sure it looks like, and he thinks he has, a 400A service even if the load calculations say he doesn't need it.

 

[sc57ford]

Looking at tbl 310.16, the 3/0 is good for 200 amps. Maybe his buddy has paralell 3/0, but just doesn't know it. In the case we are talking about, 3/0 would not account for any voltage drop, so my guess would be to opt for the parallell 4/0 unless and until I had enough info to do a VD calculation to assure myself the 3/0 would be sufficient. And then again, if you had enough info, you could properly size the Service.