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Generator Back-up/Transfer switch question #171140 11/20/07 02:41 PM
Joined: Sep 2003
Posts: 114
B
bwise121 Offline OP
Member
I haven't seen this done in quite awhile so I thought I'd pick some of your brains. I'm on a large remodel and we are doing a 400Amp panel upgrade with a 200Amp sub-panel directly behind it in the garage. The owner just notified me (change order) that he would like to have a generator to back up the power if it goes out. He isn't interested in powering the entire house , just some lights here and there. I figured we would just back up power to the sub-panel (200A).

I'm curious how the connections would work from the transfer switch to the sub-panel. If someone wouldn't mind giving the a general feel for how this needs to be wired up that would be great.

Thanks,
Byron

Work Gear for Electricians and the Trades
Re: Generator Back-up/Transfer switch question [Re: bwise121] #171141 11/20/07 03:42 PM
Joined: May 2005
Posts: 984
G
ghost307 Offline
Member
From the 400A panel to the 'NORMAL' side of the ATS.
From the 'LOAD' side of the ATS to the 200A panel.
The "EMERG" side of the ATS is fed from the generator.

Watch for proper grounding. The system neutral only gets tied to ground in 1 place.


Ghost307
Re: Generator Back-up/Transfer switch question [Re: ghost307] #171149 11/20/07 10:10 PM
Joined: Sep 2004
Posts: 91
S
sparky 134 Offline
Member
If you are only looking to provide power to certain circuits then you will need to add another panel. This EM panel would receive power from the transfer switch. The transfer switch would receive Normal power from either the 400a or the 200a panel and EM power from the generator.

If you power the 200a panel from the tranfer switch then the entire panel would be 'hot'. If the combined load of the 200a panel exceeds the capacity of the genset then the C/B in the genset will trip.

Re: Generator Back-up/Transfer switch question [Re: sparky 134] #171150 11/20/07 10:18 PM
Joined: Sep 2003
Posts: 114
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bwise121 Offline OP
Member
Okay, I think the best way to go about this would be a seperate EM panel. I'm assuming the circuits that go into this panel will be fed normally through normal AC power that goes through the Transfer Switch. Then if power goes out, the generators are cranked up and the EM panel is then fed and those circuits.

Normally is there some type of switch in the transfer switch that you manually switch when you go to generator and then back again?

Thanks

Re: Generator Back-up/Transfer switch question [Re: bwise121] #171165 11/21/07 08:23 AM
Joined: May 2004
Posts: 55
A
AZSam Offline
Member
As I live in a rural area, I installed a back-up 13 years ago when I built. From one of the 200A main panels a 40/2 feeds the normal side of the xfer. The diesel gen set feeds the emer side. The load side of the xfer feeds a 125A 12 circuit EM panel. The EM panel has various lighting, security system, freezer, refrigerators, kitchen counter outlets, sump pump, etc. Works well. Last outage I ran temp to neighbors home as they had just filled freezer and frig. 16 hours without a hitch.

Re: Generator Back-up/Transfer switch question [Re: AZSam] #171177 11/21/07 11:15 AM
Joined: Oct 2006
Posts: 745
E
EV607797 Offline
Member
You can do it either way. A manual transfer switch is cheaper, but you'll have to be there to activate it. Not so good if you aren't home when the power fails. A true standby generator with an automatic transfer switch does this all by itself with no human intervention, to include starting the generator. Of course, an automatic transfer switch is much more expensive.


---Ed---

"But the guy at Home Depot said it would work."
Re: Generator Back-up/Transfer switch question [Re: EV607797] #171395 11/27/07 07:07 AM
Joined: Mar 2005
Posts: 1,213
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SteveFehr Offline
Member
You only need to segregate the emergency load from non-emergency for an ATS/automatic-start generator. It's acceptable for an MTS/manual-start that the homeowner manually load-shed and open certain breakers.

In fact, you don't necessarily even need a physical MTS- you can often get metal interlocks (just a sliding piece of sheet metal) that fit over your panel and prevent the generator breaker from being closed until the main breaker is opened.

Re: Generator Back-up/Transfer switch question [Re: SteveFehr] #171408 11/27/07 12:09 PM
Joined: Jun 2007
Posts: 301
J
JValdes Offline
Member
I would not use a automatic transfer switch for several circuits, unless I had a seperate emergency panel.
Steve's suggestion is what I would propose. Automatic switches require a seperate emergency panel. I would connect the genset to either the main or the sub, using an interlock kit (www.interlockkit.com)at the panel being fed. You can find other interlocks that are less money. I think the link I gave you runs about $150 and UL approved. You only need one.

Re: Generator Back-up/Transfer switch question [Re: JValdes] #171449 11/28/07 11:56 AM
Joined: Oct 2006
Posts: 745
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EV607797 Offline
Member
I know what you mean. My emergency panel is a GE panel that has the generator and commercial mains across from each other. There is a red plastic interlock so that only one main can be turned on at a time. MUCH cheaper than a transfer switch.


---Ed---

"But the guy at Home Depot said it would work."
Re: Generator Back-up/Transfer switch question [Re: EV607797] #171493 11/29/07 11:11 AM
Joined: Jun 2007
Posts: 301
J
JValdes Offline
Member
Ed,
Yes, for a few lights, TV, HW and fridge auto switches are a bit overboard in my opinion.
Now, people that leave their winter homes and go south it might be a good idea. But only if you have a steady source of fuel like natural gas. And gensets that are not maintained, there is the likelyhood it will not start.
As a contractor you can make good money on the auto switch installation.
I know one contractor here in my area that does this primarily. He has a contract with a generator supplier, so he can also sell the generator and mark it up.


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