400 Amp Panel

ramsfield

I am a realitively new contractor, and as such, trying to save a few bucks. I am building a new house which will have a single 400 amp panel. The house is 170 feet from the transformer / meter base. Power will be supplied underground. I have been told by the utility that a CT meter base will be required and I will have to use atleast 350MCM from the transformer to the meter base, but they will not tell me the size to use to the house. This is located in Washington State.

Can I use 350MCM from the meter to the house?

Also, I want to bury the wire in coduit. What size conduit, at minimum, do I need to use?

Since this is the first time dealing with current transforming meter bases, I am a little lost. Any help would be appreciated.

Celtic

What year NEC is Washington using?
Will the service be 1Ø or 3Ø ?

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cmec

Copper or aluiminum?

mickeyco

Black or brown?

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Some people climb mountains. I take out the trash. But we both do it for the same reason.

Speedy Petey

Sorry, but these two quotes are mutually exclusive.

If you want to save money WHY are you going with a 400A panel and CTs????
Why not go with two 200A panels?

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Celtic

Will the POCO allow dual meters for the same dwelling unit?


BTW....I smell poopies

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Speedy Petey

Who said anything about dual meters???

I mean two 200A laterals and panels fed from a 320A meter can. All you need is double lugs on the load side of the meter.

This is completely typical these days.

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Celtic

I did


Typically....I don't get to see the mega McMansion

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Speedy Petey

Mansion nothing. Everyone's doing it these days.

Seriously, it is getting very common to see these in even modest homes.

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Celtic

I'm still using a 50A FPE main ....who needs all that up sized wire and conduit.

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ramsfield

The wire will be aluminum.

2005 NEC

I am using a 400 amp panel because that it what the sub said he was going to install. My original plan was to install two runs of 250mcm, essentially 1 to each of two 200 amp panels coming from a 320 meter base.

My only involvement in this stage is to dig a trench, put in some conduit and pull the wire from the meter base to the house.

No, the PUD will not allow dual meters.

220/221

This says 400 amps = 500 mcm in the 90 degree column

http://www.cerrowire.com/default.aspx?id=46


The wire BEFORE the meter is probably sized down because.....because they let you do that. There is a seperate chart for the service conductors.

This says 3" for 3, 500's and a #1 ground.

http://www.cerrowire.com/default.aspx?id=49

I say ask someone who is going to inspect/approve it. You don't want to do it twice.

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Just because it's within code doesn't make it safe.

Just because it's against code doesn't make it unsafe.

cmec

Did it on my house 17 years ago ,1 lateral to the house ,1 lateral to the garage.

Be careful when I did it the utility co didnt require a disconnect

Be sure to check the utility co rules Apco wants a disconnect at the meter now

I would look into alcan stabaloy compact conductors its really nice to work with

Speedy Petey

220, I know you will probably take this as an attack, but is that what you really use to size a residential service??? The Cerowire web site?

Most of us use NEC T310.15(B)(6).
This tells us we must use 600MCM AL for a 400A service. If this will be a 320A service the lateral can be 500AL.
How can you use the 90 deg C column for anything but derating? The 90 deg column is meaningless for circuit/feeder ampacity.

Also, why are you running a ground between a meter and main panel???

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Speedy Petey

The 400A route is more expensive, harder to do, and limits you to 42 spaces in the main panel, making a sub-panel mandatory.

Also, why would you have run 250's to the house from the pad for only 170'??? Did someone suggest that?
170' is NOT that far to have to upsize to 250's. 4/0AL is fine.

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220/221

I don't see that as an attack Petey. It's all in the presentation.

1. The only wire sizing I do here for service conductors is down the mast if it's overhead. The POCO here always brings the service right to the structure. I think they run 4/0 AL for 400 amp feeders. If I remember correctly I had to do parallel copper 4/0's or a single copper 350 the last time I did a 400 amp overhead service.

Somebody linked me the ampacity chart so I linked him.


When a job comes up that require me to size the wires I consult the EE that we work with instead of asking some internet clown .


2. re: the ground, I assumed that he would have a disco right after the meter which would make that the service.. Again, that crazy regional thing.




The thing is....I don't really understand what you're saying. I look at a chart and see that X wire is good for x amperage. I thought the wire was rated 90 degrees as opposed to NM for example that is 60 degrees?

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Just because it's within code doesn't make it safe.

Just because it's against code doesn't make it unsafe.

Speedy Petey

Fair enough. You are lucky to have someone to go to with this stuff. Most of us need to do it ourselves.


Not a very rational assumption IMO. Very few places do actually require an outside disconnect.
That is mainly a west coast thing.






NM is rated for 90 deg C as well. We are limited to 60 deg C by 334.80.
I am saying just like NM is limited to the 60 deg C column, we are limited to the lowest rated item in the chain. There is pretty much nothing out there rated for 90 deg C except for wire. Most circuit breakers and terminations are rated for 75 deg C, so this is the column we use for pretty much everything but NM cable when figuring circuit ampacity.
Derating however does go from the actual conductor temp rating.

Again, this is just us poor folks needing to know this for ourselves.

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cmec

LOOK AT 310.15(B)(6) and read the article with the (6) before you apply the chart this aint rocket science