My first 400 amp service. Need help!

[jraymond]

Hey guys, I have a question about a 400 amp service. I’m a master electrician, pretty much only do residential, nothing yet over 200 amps. This is my first 400 amp service. 3500 sq ft house. Customer wants me to setup for a generac and automatic transfer switch. Trying to figure out the service part. Do I just get a 400 amp meter to a 400 amp transfer switch and then to 2-200 amp panels? Can the 400 amp transfer switch count as a disconnect for both panels or do I need 2-200 amp disconnects as well? Does the 400 amp transfer switch have enough lugs for 2 different subpanels? Thanks in advance for any help!

 

[LarryFine]

I recommend a single 200a ATS for only one 200a panel. Not everything can or should be on generator.

 

[jraymond]

I recommend a single 200a ATS for only one 200a panel. Not everything can or should be on generator.

Thank you, I had that thought but wanted a back up option in case the customer wanted the whole house on it. But honestly I’ll just tell them that this is their best option!

 

[Little Bill]

I have done them. I used two 200A ATS, one for each panel. The ATS was the service disconnects. My area does not yet require emergency disconnects.

 

[jraymond]

I have done them. I used two 200A ATS, one for each panel. The ATS was the service disconnects. My area does not yet require emergency disconnects.

I have done them. I used two 200A ATS, one for each panel. The ATS was the service disconnects. My area does not yet require emergency disconnects.

Nice, our jurisdiction requires disconnects, so I’d need to see if each ATS would count as the disconnect, cus that would be cool!

 

[jraymond]

Nice, our jurisdiction requires disconnects, so I’d need to see if each ATS would count as the disconnect, cus that would be cool!

Wait, with 2 different ATS, what would your generator be?

 

[Little Bill]

Wait, with 2 different ATS, what would your generator be?

Don't understand your question.

 

[jraymond]

Don't understand your question.

Would I have to go up to liquid cooled generator or is there an air cooler that supports 400 amps? Or 2 separate generators?

 

[LarryFine]

Wait, with 2 different ATS, what would your generator be?

One generator can supply two ATSs if properly wired and connected.

Remember that you don't have unlimited power.

You and the customer should make 3 lists:
1. Loads that must always be available while on the genny.
2. Loads that will never need to be run while on the genny.
3. Loads that are optional, after seeing how 1 and 2 stack up.

 

[LarryFine]

Thank you, I had that thought but wanted a back up option in case the customer wanted the whole house on it. But honestly I’ll just tell them that this is their best option!

That gets to be real expensive real fast. A 100Kw genny isn't cheap.

 

[LarryFine]

I have done them. I used two 200A ATS, one for each panel. The ATS was the service disconnects. My area does not yet require emergency disconnects.

As have I, except that there were outside discos and I mounted the ATSs directly above the panels.

 

[jraymond]

One generator can supply two ATSs if properly wired and connected.

Remember that you don't have unlimited power.

You and the customer should make 3 lists:
1. Loads that must always be available while on the genny.
2. Loads that will never need to be run while on the genny.
3. Loads that are optional, after seeing how 1 and 2 stack up.

I don’t get it. If the generator is only going to power up the panel that is meant to be the generator panel, what’s the point of two ATS if one panel won’t come on during an outage?

 

[LarryFine]

Would I have to go up to liquid cooled generator or is there an air cooler that supports 400 amps? Or 2 separate generators?

You need to stop and take a breath. You are not going to provide the service's full capacity.

Again, start with the three lists idea. Then turn that list into a load calculation for one panel.

That's the load you need to attempt to supply, but not everything will be on simultaneously.

 

[LarryFine]

I don’t get it. If the generator is only going to power up the panel that is meant to be the generator panel, what’s the point of two ATS if one panel won’t come on during an outage?

EXACTAMUNDO! Your goal is to only need one ATS.

You can present a much more palatable price for a job that is easier to install.

The only double lugs you'll need are the load terminals of the 400a meter base.

 

[Seven-Delta-FortyOne]

That gets to be real expensive real fast. A 100Kw genny isn't cheap.

Unlikely any residence would ever need a 100kW, even with a 400A service.

I did a load calculation on a large restaurant with multiple coolers, multiple rooms, prep equipment, off grid water and septic system, and I came in around 38kW to run the entire place with everything running at once.

They were on a 200A service.

Even a residence with a 400A service, all electric, hot tub, EV charger, etc., they could more than likely get away with a 25-26kW air-cooled.

 

[jraymond]

EXACTAMUNDO! Your goal is to only need one ATS.

You can present a much more palatable price for a job that is easier to install.

The only double lugs you'll need are the load terminals of the 400a meter base.

Thank you. This was helpful

 

[LarryFine]

Unlikely any residence would ever need a 100kW, even with a 400A service.

I know; I was pointing out that it's not necessary to try to supply even the actual load, let alone the full capacity of the service.

 

[hillbilly1]

Unlikely any residence would ever need a 100kW, even with a 400A service.

I did a load calculation on a large restaurant with multiple coolers, multiple rooms, prep equipment, off grid water and septic system, and I came in around 38kW to run the entire place with everything running at once.

They were on a 200A service.

Even a residence with a 400A service, all electric, hot tub, EV charger, etc., they could more than likely get away with a 25-26kW air-cooled.

I put in a 48 kw on my boss’s house, 600 amp service, 600 amp transferswitch, no load shedding. Easily runs it.

 

[Master Nater]

just make sure you get the "service entrance rated" ATS's, and you should be good to use them as your service disconnects.

feed a set of 200a service conductors to each ATS, the 200a inside the ATS will be your service disconnects, and run a separate 200a feed to each separate panels. the controls on the ATS's can be paralleled, so they both operate from a single generator controlling them.

 

[kwired]

Trying to figure out the service part. Do I just get a 400 amp meter to a 400 amp transfer switch and then to 2-200 amp panels? Can the 400 amp transfer switch count as a disconnect for both panels or do I need 2-200 amp disconnects as well? Does the 400 amp transfer switch have enough lugs for 2 different subpanels?

Using service rated 400 amp ATS as the service disconnect. Feed two 200 amp main breaker panels from that and keep the feeders to them in compliance with feeder tap rules, which should be easy unless you have to run way across the house to get to the panels.

400 amp switch likely will have lugs designed for single or paralleled conductors, so you would be installing two 200 amp conductors in them whether it was a paralleled 400 amp circuit or if it were two 200 amp feeder taps.