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Old 01-29-2012, 02:00 PM   #1
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Homebrew Generator Interlock


I have a 5500 watt generator I use mostly to power the water pump (we're on our own water system) during outages. It would be nice to be able to install this so that I can backfeed the full house panel. Finding an interlock that will do what I need for a reasonable price has left me frustrated, so here is what I am thinking:

My main panel is a 30-year old GE load center. Two 60A breakers feed power to two subsections. I'd like to be able to power both subsections, but I don't care about the stuff on the 'main' (unbroken) section.

For each section, I can by a small 4-space load center for less than $20. In the small load center I would install a pair of breakers - one 60A, coming from the 60A breaker in the main panel, and a second, probably smaller (30A) breaker coming from the generator. The main bus from the small panel would go back to the subsection of the main panel. The two breakers in the small panel would be mechanically interlocked and retained.

So, for the price of a small panel, two breakers, and an interlock I have a generator interlock. I'd need to double this to be able to feed both subsections in my main panel. (Or, maybe find a load center with 8+ slots and two separate sections/busses?) How does this sound?

Thanks,

Kelly

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Old 01-29-2012, 03:19 PM   #2
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Homebrew Generator Interlock


I think I understand what your wanting to do. But I can't think of a way to do a split bus panel (like yours) and be code compliant with a home made interlock. The interlock cannot just tie two breakers together. It has to prevent the main breaker from being turned on while the generator is in use. Maybe yours is doing that but I can't tell from your description. You also need to be protected from any powering up of the circuits when the power comes back on.

Just so you know how this works. You almost always have to get approval from your power company for the interlock you are going to install. This is so they know that a lineman will not be subjected to a dangerous backfeed if your interlock isn't an approved one. Then you need to have the installation inspected by local building codes to sign off on the installation as being code compliant with the NEC and local codes.

Not having that done could expose you to some huge liabilities in the event of injury or fire. Your insurance may be voided in that event.


This is just FYI but I'm reasonably sure none of what you are wanting to do is going to be acceptable to the people that matter.

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Old 01-29-2012, 05:00 PM   #3
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Stubby,

Thanks for the feedback.

For more information, my panel does not have a 'main breaker'. The power is always on, on the upper portion of the panel. Only the two subsections can ever be disconnected. The setup and interlock I describe will ensure that anytime the generator is being fed to the two subsections of the panel, that those subsections are disconnected from the upper section/mains. Only one (the generator or mains) can be connected to the subsection at a time.

So, I know that what I've described will 'work' and prevent any possibility of backfeeding onto the line. I was looking more for info about code compliance etc. And it sounds like your feedback on that aspect is "it doesn't look likely".

Thanks,

Kelly
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Old 01-29-2012, 06:19 PM   #4
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Homebrew Generator Interlock


In my opinion you should just purchase a generator transfer switch with the necessary breakers. It's going to be a bit more costly (just a bit) but it will be UL listed and safe for anyone to operate. They are foolproof and won't allow any backfeeding no matter how you switch it. And the utility company won't frown on that installation.....Just my opinion.
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Old 01-29-2012, 06:23 PM   #5
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Originally Posted by Missouri Bound View Post
In my opinion you should just purchase a generator transfer switch with the necessary breakers. It's going to be a bit more costly (just a bit) but it will be UL listed and safe for anyone to operate. They are foolproof and won't allow any backfeeding no matter how you switch it. And the utility company won't frown on that installation.....Just my opinion.
I agree.
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Old 01-29-2012, 06:50 PM   #6
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Homebrew Generator Interlock


That small a gen. is only going to be able to power a small amout of power anyway. Correct me if I'm wrong but it's onyl got one 20 amp twist lock connection.
I bought a 6 breaker tranfure switch from Northern tool and a 20 amp male flush mounted outlet box.
My 5500 watt gen. will power all my lights and outlets, the ref. and water pump but that's about it.
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Old 01-30-2012, 12:01 AM   #7
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Quote:
Originally Posted by Kelly62 View Post
Stubby,

Thanks for the feedback.

For more information, my panel does not have a 'main breaker'. The power is always on, on the upper portion of the panel. Only the two subsections can ever be disconnected. The setup and interlock I describe will ensure that anytime the generator is being fed to the two subsections of the panel, that those subsections are disconnected from the upper section/mains. Only one (the generator or mains) can be connected to the subsection at a time.

So, I know that what I've described will 'work' and prevent any possibility of backfeeding onto the line. I was looking more for info about code compliance etc. And it sounds like your feedback on that aspect is "it doesn't look likely".

Thanks,

Kelly
Yes that's my opinion. As I said earlier you have what is called a split bus panel. The top section of the panel conforms to NEC 230.71 where six or less disconnects/breakers remove all power from the panel. There isn't a single main as such .. all the breakers in the top section are considered the 'main' means of disconnect and can't be more than six single movements of the hand to remove power from the dwelling. A simple gen tran transfer switch would be much better and along the lines that Missouri bound is speaking.
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Old 01-30-2012, 08:56 AM   #8
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Quote:
Originally Posted by Kelly62 View Post
Stubby,

So, I know that what I've described will 'work' and prevent any possibility of backfeeding onto the line. I was looking more for info about code compliance etc. And it sounds like your feedback on that aspect is "it doesn't look likely".

The mechanical linkage needed might not be as simple as you think. The switch has to work in a break before make fashion. That is the branch you are leaving has to be open contact before you close the other side. I don't think you could guarantee that with a mechanical linkage. Tolerances could stack up such that for a brief instant both sides are energized and even for a cycle or two that could be ugly.

This probably isn't something to skimp on. Buy no name beer for 2 months to offset the cost.
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Old 01-30-2012, 12:19 PM   #9
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Thanks guys! Again, I appreciate the feedback.

curiousB: I understand your point. The interlock I am considering would require one breaker to be in the fully 'off' position before the other could be engaged at all.

The problem with a 'transfer switch' is that, if I understand correctly, these allow you to select some small subset of circuits to power with the genny. sometimes the power is out here for as long as 4-5 days. In that time I will need to power the water pump, the garage freezer/refrigerator, and the kitchen refrigerator. I may need to occasionally power the shop panel, barn lights, and a few areas in the home for lighting and outlets. I don't think I can handle all of that without getting into big bucks for a transfer panel.
(Of course, I don't expect to power all of that at once, but I'm comfortable using the main panel to send power where it's required for the task at hand).

So, it seems an interlock is what I need. If I can put the interlock in between the main and the subsections, then it seems that the cost and installation effort is reasonable. If I need to put something in between the meter and the main panel, then we're talking orders of magnitude more cost (I'd need something that could handle the 200 amps or so that the main panel is rated for) plus I'd have to hire out the installation, again at orders of magnitude more cost.

I'm not disputing anything you guys are saying - I appreciate all the seasoned advice and I'm soaking it up - I just wanted to explain my rationale for proposing this plan. I'm not trying to save the cost of a few beers, I'm trying to save up to a thousand bucks.

Thanks,

Kelly
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Old 01-30-2012, 01:13 PM   #10
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How about just a manual transfer switch capable of switching your entire panel load, after the meter and before the main panel.

Something like this:

http://www.northerntool.com/shop/too...ories-_-100021
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Old 01-30-2012, 01:44 PM   #11
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Yep, that's probably what I need. Except I may need to go to 200 amp (of course I'd never drive that with my genny, but I'm not positive that I wouldn't trip a 100A breaker when I was running on mains), and the prices for those - at Northerntool - start at $650. And add several hundred (?) for installation, because the mains coming in are about 1/2 diameter (not counting insulation) and I'm not sure if I want to DIY that.

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Old 01-30-2012, 01:54 PM   #12
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No, it wouldn't be DIY but neither would swapping out a panel.

Along the lines of your idea with the smaller panels, Square D has these panels. They're not $20 but they do what you want.

http://www.homedepot.com/h_d1/N-5yc1...1&ddkey=Search
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Old 01-30-2012, 02:25 PM   #13
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Thanks AandPDan! Hadn't seen those.

But, now I need clarification: If I were to get two of these, and install each one between the breaker on the main panel and the subsection which it controls, would this be code compliant? If not, why not? I'm still meeting NEC 230.7, as far as I can tell.
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Old 01-30-2012, 02:54 PM   #14
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Do you mean 230.71? If you put them after the existing 60 amp breakers that you have then it should not change anything.

One more idea, what about just putting in a sub panel off the existing panel. Get a new panel" and an OEM interlock breaker for it (you're making a bigger version of the Square D panel). Move everything off of the lower portion of your split bus panel into something new, with an approved interlock.

One thing to consider, adding these panels and the associated wiring will likely cost more than buying a new panel board. While not DIY, it may be a better plan in the long run. Siemens, Murray, and others make panel boards that will take an interlock device (OEM not interlockkit). I know you may want to DIY but you'll probably have issues with your AHJ if you try to be "creative" here. Updating the panel will likely be the better option for you in the long run.
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Old 01-30-2012, 11:22 PM   #15
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Quote:
Originally Posted by AandPDan View Post
One thing to consider, adding these panels and the associated wiring will likely cost more than buying a new panel board. While not DIY, it may be a better plan in the long run. Siemens, Murray, and others make panel boards that will take an interlock device (OEM not interlockkit). I know you may want to DIY but you'll probably have issues with your AHJ if you try to be "creative" here. Updating the panel will likely be the better option for you in the long run.
+1

I really feel this is your best option if you want access to all circuits.

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