2x200A ATS vs 1x400A ATS (Auto Transfer Switch)

[avm32]

Hello,

Doing an install for a standby generator for a customer that has a 400A (320A) meter that feeds 2x200A panels via 2 sets of conductors (the split is at the meter base). The Generator is a Generac and both 200A and 400A transfer switches are available. The 200A's can be put in parallel.

I was wondering what are the pro's / con's of installing either:
#1: 2x200A ATS - The 400/2x200 split will remain at the meter base.
#2: 1x400A ATS - The split will be done in the 400A ATS (it comes with double lugs)

What I'm thinking so far:

Pro's of 2x200A:
- Cheaper (2x$750 vs $2900)
- PoCo will not give me any trouble by changing the wire configuration in their meter
- The meter base is guaranteed to be compatible with this setup (it might not support 1x400A output)

Pro's of 1x400A:
- Less points of failure
- Easier install for the customer to understand
- Better safety in case of cross-wiring circuits inside the house
- No tapping of conductors or replacing factory lugs required (if doing 2x200A have to swap out single lugs with double lugs).

What are your recommendations ? Anything else I'm missing ?

Thanks !

 

[augie47]

How large is the generator ??
Reason I ask is that in order to comply with 702.4 if you feed both panels you will need a lot of load sheding unless your genny is good for 400 amps. Normally I see the "necessary" loads in one panel.

 

[avm32]

How large is the generator ??
Reason I ask is that in order to comply with 702.4 if you feed both panels you will need a lot of load sheding unless your genny is good for 400 amps. Normally I see the "necessary" loads in one panel.

24KW. Luckily mostly everything is gas and the service is way oversized. So have to disconnect only a few loads (oven, dryer) to be in compliance.

 

[LarryFine]

24KW. Luckily mostly everything is gas and the service is way oversized. So have to disconnect only a few loads (oven, dryer) to be in compliance.

I'd definitely go with the two-200a ATSs route, as it matches the existing service configuration.

Consider using only one panel on one ATS if you can move loads around to suit this method.

A dryer need not be load-shed, since it won't restart without someone starting it manually.

 

[avm32]

I'd definitely go with the two-200a ATSs route, as it matches the existing service configuration.

Consider using only one panel on one ATS if you can move loads around to suit this method.

A dryer need not be load-shed, since it won't restart without someone starting it manually.

Thanks. Are you sure that it's OK to have manually-started loads not shedded ?

NEC 2020 / 702.4(B)(2) says:

(a) Full Load. The standby source shall be capable of supplying the full load that is transferred by the automatic transfer equipment.
(b) Load Management. Where a system is employed that will automatically manage the connected load, the standby source shall have a capacity sufficient to supply the maximum load that will be connected by the load management system.

It's a bit ambiguous - is this what you are saying that would allow manually-connected loads to be excluded from load calculation or is there another section I'm missing ?

 

[LarryFine]

Thanks. Are you sure that it's OK to have manually-started loads not shedded ?

It's a bit ambiguous - is this what you are saying that would allow manually-connected loads to be excluded from load calculation or is there another section I'm missing ?

I'm saying a load that can not automatically start with power applied does not need to be considered.

 

[avm32]

I'm saying a load that can not automatically start with power applied does not need to be considered.

Yes, this is what I mean also. I guess I'm not using "manually connected" appropriately, but we're on the same page.

Any particular section of the code that makes you think this is the case ?

 

[LarryFine]

Any particular section of the code that makes you think this is the case ?

What you posted above. A dryer will stop faster than an ATS will restore power.