Transfer Switch Question

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bill j

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Montana
Very simple question. Please don't ask why, it's existing situations.
Is there a problem with a generator ( optional standby, home ) feeding a automatic transfer switch and a manual transfer switch?
Let me explane.
320 Amp service, 2 - 200 amp panels.

Generator sized properly to handle 1 automatic transfer switch of 1 200 Amp panel according to NEC.

Generator also feeding a Cutler Hammer mechanical interlock panel. The 2nd 200 Amp panel.

Upon power outage and transfer the auto switch activates the first 200 amp panel.
The 2nd is manual and requires the owner to physically move the mechanical interlock to power up the 2nd 200 amp panel.

The question.
Does the load of the 2nd panel need to be calculated in any way in the sizing of the generator.
My thinking is that it is the same as load shedding and the homeowner controls the load shedding. The manual loads are not automatic and therefore are excluded from any calculations.
Any ideas?
 
ericsherman37

ericsherman37

Senior Member
Location
Oregon Coast
bill j said:
My thinking is that it is the same as load shedding and the homeowner controls the load shedding. The manual loads are not automatic and therefore are excluded from any calculations.
Any ideas?
Click to expand...

I'll defer to the experts on this, but I do have one question. If the 2nd panel isn't going to be used at all on generator power, then why even have it on a transfer switch?
 
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bill j

Member
Location
Montana
The 2nd panel is going to be used on generator power but now the gen isn't required to be sized to carry the entire load, a cost saving. The home owner now has the option of selectively powering up individual items on it, keeping an eye on load.

Follow up idea.
Same criteria, optional standby - home situation.

If a panel backed up by generator power has a circuit breaker feeding a gentran or similar style manual transfer switch http://www.gen-tran.com/eshop/10Browse.asp?Category=VPTS that would seem like the same thing. Don't count the load. The only problem I see is the backup power feed conductors to the manual transfer switch are always either hot with utility power or generator power. ( unless a contactor on the feed conductors to the gentran is installed, controlled by optional contacts on the primary automatic transfer mechanism. The contactor would be open on utility and close on generator power.)
 
ceb58

ceb58

Senior Member
Location
Raeford, NC
bill j said:
Very simple question. Please don't ask why, it's existing situations.
Is there a problem with a generator ( optional standby, home ) feeding a automatic transfer switch and a manual transfer switch?
Let me explane.
320 Amp service, 2 - 200 amp panels.

Generator sized properly to handle 1 automatic transfer switch of 1 200 Amp panel according to NEC.

Generator also feeding a Cutler Hammer mechanical interlock panel. The 2nd 200 Amp panel.

Upon power outage and transfer the auto switch activates the first 200 amp panel.
The 2nd is manual and requires the owner to physically move the mechanical interlock to power up the 2nd 200 amp panel.

The question.
Does the load of the 2nd panel need to be calculated in any way in the sizing of the generator.
My thinking is that it is the same as load shedding and the homeowner controls the load shedding. The manual loads are not automatic and therefore are excluded from any calculations.
Any ideas?
Click to expand...

How is the ATS feeding power to the second panel?
 
B

bill j

Member
Location
Montana
The power is split in a gutter above both panels. It drops to each panel. And that was the question. Since one panel has a manual transfer switch it should not count on the load calc.
 
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