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monsoon 09-30-2007 04:42 PM

Feeding multiple subpanels with a single generator
In my home I have two 200 amp main panels being fed from a single 400 amp metering transformer. Mounted below each main panel is a 60 amp subpanel with an interlocking breaker for a generator, and each subpanel's main breaker is fed from the main panel above. I have a 40 amp generator feed coming in from outside the house that comes into a single 40 amp breaker so that I can disconnect the generator from inside the house. My question is how to feed the two subpanels from that 40 amp outside generator feed. Can I feed two subpanels from a single generator feed? If so, how do I accomplish this? Should I run separate hots, grounds, neutrals from the generator breaker to each subpanel? Or can I daisy-chain the hots, grounds, and neutrals from one subpanel to the other if I use breakers rated for multiple conductors? What makes me most uncomfortable with this setup is that if I connect the grounds and neutrals through from one subpanel to another (either by daisy-chaining or going back to my generator breaker) that I'll set up a loop with the neutral. I'm not talking about a bonding issue, but rather an actual loop where the neutral splits at the metering transformer (for each of the two main panels) and recombines back at the subpanel or generator breaker. My thought is that I'd tie the ground and neutral into just one of the two subpanels (allowing the ground/neutral to flow to the other subpanel through the main panels) and then daisy-chain the hots between the subpanels, but I'm not sure that this is the best way to do this. One final note, the subpanels are not bonded ground to neutral, but I believe that the main panels are.

J. V. 10-01-2007 11:17 AM

If the sub panels are fed from the main service panel then you need to do nothing except, mechanically or with a transfer switch, protect from back feeding the main incoming service and generator.

You see electricty does not know any certain direction. You could use one of the sub panels to back feed all the panels as an example.
Then you can pick and choose existing breakers to use when the power goes out.

The 40 amp breaker you mention will distribute power to all of panels.

However, You must provide protection for the generator and the incoming power grid. They make some lockout devises that will not let you turn on the (main service breaker) if the (generator breaker) is on. And visa versa. Transfer switchs while very expensive are the best choice, but are not always needed.

Take the time to mark your panels breakers as to what they serve. Saves alot of time during a black out.

If you have any doubt about this. Please call a qualified electrician, to at least verify what I have told you.
I can read your description but I cannot actually look at the situation.

Mike Swearingen 10-01-2007 11:49 AM

Here is an alternative to expensive transfer switches called a Connection Hub. I have one on my home (this is from our power company).
It goes on the meter base, can be moved to a new location, and it uses your existing breaker panel.
I only have a portable 5500 watt generator, so I turn off the 240v breakers and run all of my 120v circuits. When I want hot water, I turn off all of the 120v breakers and turn on the water heater breaker for about an hour.
Works for me.

J. V. 10-01-2007 02:32 PM

looks like a nice set up. But looks expensive.
Take a look at this inexpensive one.

Stubbie 10-01-2007 03:48 PM

There are many methods for transfer to back-up power. All have there appeals. And for many cost is a big factor. The interlock kit is cheap however it is removable (safety disadvantage) and it requires a Back fed breaker (need space in your load center for it). It will often times not be allowed by local power companies. Who in general must approve your transfer device before installation.... assuming whether you care to tell them.
I've had a couple over the years and for ease of use and convenience I like the meter panel hubs of which there are several to choose from. Their disadvantage is they are, as J.V. mentions, on the high end of manual transfer devices as to cost. Many power companies install them for you and you purchase them or they charge a monthly fee of around 5.00 a month last I checked.


frenchelectrican 10-01-2007 05:24 PM

Mike that is nice set up but only one catch that metering device you provided the link that is rated for 200 amp meter socket only if have 320/400 meter that will really change the picture really fast because some area do used the CT's for metering and some used the bolted on type and some used the 400 amp verison of common 200 amp socket.

Merci, Marc

monsoon 10-01-2007 11:36 PM

Maybe I wasn't clear (which wouldn't be unusual :yes: ), but the subpanels with interlocking breakers are already in place and all the circuits that I want to power have been moved. The issue is connecting the single generator source to the two subpanels via the generator breakers in a way that would comply with the code. It's unclear to me if I can daisy-chain the hots from the generator to the generator feeds on each subpanel, and if I should feed the neutral and ground from the genset to both panels, thereby creating a loop in the neutral and a separate loop in the ground.

Mike Swearingen 10-02-2007 02:14 AM

Thank you for that inexpensive Interlock Kit link. I know local area people who have hot-wired illegal generator hookups due to the cost of transfer switches and connection hubs, so I will pass that one along to those who will listen, assuming our power company approves them. I would think that something is better than nothing.
There are so many illegal hookups around here after hurricanes, that I now see some kind of electrical hoops put around lines (to detect backfeed I assume). We had two out-of-state power company linemen (from Mississippi I believe) killed after Isabel in 2003 here from an illegal generator hookup.
It is so dangerous, I don't know why they don't patrol and inspect every generator hookup and confiscate those that are illegal. The jerk that caused those two linemen to get killed was only fined $10,000 each, without any criminal penalty.

Andy in ATL 10-02-2007 04:25 PM

I here you mike and agree... That being said, lineman should and are trained to be aware of the possibillity of backfeed in this situation and should only work on lines that have been grounded for this very reason. I'm not wanting to upset anybody and everyone--DIY's and pro's should do everything in there power for compliant hookups but still.....

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