generator

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paul renshaw

paul renshaw

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Cordova, Maryland
This situation was proposed to me. A single family dwelling with a 400A service, two 200A panels fed out of a meter. The owner wants to install a 200 amp xfer switch outside and feed one of the panels through it, with the two sources (util, gen) feeding the xfer sw. Are there any code problems with doing this? What about disconnecting means? The generator is 15 kw, can that be fed into a 200A switch? I had just never heard of this particular installation. I suggested putting in a seperate, smaller panel and xfer sw and moving the loads he wants on the generator there. Thanks
 
Re: generator

To place it as you describe would require a service rated disconnect.

My suggestion is to install an new 200 amp service rated disconect (fusible switch or single breaker enclosure) from that feed a standard transfer switch than the 200 amp panel.
 
Re: generator

(a) unless the transfer switch is "service rated", you will have to have service protection ahead of it (you did not mention service disconnects ahead of your panels, so I assume there are none)
(b) in most jurisdictions, if you install a service disconnect outside for the transfer switch (or if it has one built-in) you would also need to install a disconnect outside for the 2nd panel in order to meet the grouping of disconnect rule.
(c) 15 kw will not normally carry the load in that 200 amp panel. I've seen this done a few times, but it normally requires the homeowner to be selective with the loads and if they aren't the gen breaker trips, etc...
My persoanl opinion from seeing a number of such installations in this area, is that your "critical circuit" sub-panel is best on this size installation
 
Re: generator

The switch would be the service disconnect and not the panel it feeds. If the switch has no integral overcurrent protection, then it must be installed immediately adjacent to the main breaker panel it feeds (230.91). This will call for 4 wires from the transfer switch to the main panel and isolation of the main panel neutral from its chassis.

This will be a rather strange installation, as the transfer will be one service disconnect, and the second panel main breaker will be the other of a "grouped disconect" (so they both need to be next to each other). I think this is legal, and it would be nicer if the transfer switch was 400A and fed both 200A panels. But a 200A simple service rated transfer switch (no breakers) can be had for $300. A 400A one, or ones with integral breakers are going to cost a lot more.
 
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