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Back-feeding a panel from a portable generator

Bill Lantry

Bill Lantry

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Ok, so, here's the scoop:

I've got a main panel, with a 100 amp main breaker. I've got something like 16 or 20 breakers in there. I'd prefer to leave this panel alone. I've already replaced every breaker in there (except, of course, the main one). I've got a double breaker on there, rated for 50 amps, which goes to a subpanel right next to the main panel.

I've got 8 slots in that subpanel. Its circuits go to various places: the shop, the upstairs. I still have two open slots, enough for another 50 amp breaker.

The generator is sitting outside the house, a few feet from the wall where the main panel is, in it's own building.

Here's the plan: Drill a hole through the brick/cinderblock wall. Run a 6/3 w/g cable through the hole. Put a 220 dryer plug on one end, so it'll plug into the generator.

Inside the house, I've got a couple options.

Option one: Put another plug on the "inside the house" end of the cable, which will plug into an outlet permanantly wired to the subpanel, into a new 50 amp breaker.

Option two: permanently and directly wire the cable into the new breaker on the subpanel. (don't have a whole lot of room on that wall, so can't really move the subpanel around).

Option three: get a transfer switch. (don't really have the funds for this, and even if I did, I've got too many circuits to run).

The main advantage to option two: it seems safer, or at least more doofus proof. To get power, I'd need to 1.) turn off the main breaker. 2). engage the 50 amp breaker in the subpanel. 3.) plug in the cable. 4.) start the generator.

I did think of simply getting a bigger subpanel, but even if I had room, it would be a bear to rewire the heater circuit, etc. onto the new bigger subpanel.

I hope this is clear. Please let me know your thoughts: any and all advice is appreciated...

Thanks,

Bill
 
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Bill Mine Gen is a bit smaller then your but I back feed my panel through the breaker that would normally feed the 220 to my table saw. I Open the main and the heat pumps and air handlers and the breaker for the table saw, then I plug the generator in start the generator then close the breaker that would normally feed the TS.
 
Bill Lantry said:
Ok, so, here's the scoop:

I've got a main panel, with a 100 amp main breaker. I've got something like 16 or 20 breakers in there. I'd prefer to leave this panel alone. I've already replaced every breaker in there (except, of course, the main one). I've got a double breaker on there, rated for 50 amps, which goes to a subpanel right next to the main panel.

I've got 8 slots in that subpanel. Its circuits go to various places: the shop, the upstairs. I still have two open slots, enough for another 50 amp breaker.

The generator is sitting outside the house, a few feet from the wall where the main panel is, in it's own building.

Here's the plan: Drill a hole through the brick/cinderblock wall. Run a 6/3 w/g cable through the hole. Put a 220 dryer plug on one end, so it'll plug into the generator.

Inside the house, I've got a couple options.

Option one: Put another plug on the "inside the house" end of the cable, which will plug into an outlet permanantly wired to the subpanel, into a new 50 amp breaker.

Option two: permanently and directly wire the cable into the new breaker on the subpanel. (don't have a whole lot of room on that wall, so can't really move the subpanel around).

Option three: get a transfer switch. (don't really have the funds for this, and even if I did, I've got too many circuits to run).

The main advantage to option two: it seems safer, or at least more doofus proof. To get power, I'd need to 1.) turn off the main breaker. 2). engage the 50 amp breaker in the subpanel. 3.) plug in the cable. 4.) start the generator.

I did think of simply getting a bigger subpanel, but even if I had room, it would be a bear to rewire the heater circuit, etc. onto the new bigger subpanel.

I hope this is clear. Please let me know your thoughts: any and all advice is appreciated...

Thanks,

Bill
Click to expand...

I think a transfer switch is the only way to go. Even if you rigged up a manual one. If a system is set up where it can back feed someone will.

May not be you but you may get injured ands someone comes over to help out your family and doesn't understand...

Garry
 
I'd probably recommend a transfer switch as well. You can usually get a smaller amperage transfer switch cheaper, so if you can single out a few circuits to move over to a backup panel that would be on the generator, it may be more cost effective.
 
Bill, I have a few questions to ask regarding your setup.

What size is your generator?

What duty cycle is it capable of?

Is this something you see being needed frequently?


Depending on the above, besides the concerns raised already which i fully agree with, i would also be concerned about the potential to either kill the gen by running it too long or overloading it given you are hooking it up to the whole house.

So were you going to go ahead with the gen feed to the whole house via another breaker i would make that breaker closer to the limits of overload rating for the generator. That way should someone accidently turn on that additional item that pushes things over the top, instead of the gen trying to meet your needs and suffering in the process the breaker would trip and alert you to it.

I think you also have to consider the voltdrops in this equation. The more wire you have to run through from the generator the more loss you have. The generator will be using as feedback to its regulator circuit, the output at the generator itself. It has no way of knowing what the voltage is way up on your second story bedside clock unit for example.

So you might want to consider the effect of what a low voltage will have on whatever you plan on operating. If its is just lighting and an odd cell phone charger etc, then one thing. If it has to do with the kind of current drain prevalent with heating well thats entirely different.

In heating its not going to affect the device as much as its output but that kind of load with increase the voltdrop due to current drawn and other items could be affected.

Personally i dont see a portable type gen being a sustainable and viable change over between supplied power and home gen power for more than an hour or two of provision of lighting and perhaps keeping the fridge freezer going maybe the television. But all that will quickly add up.

I hear you on the finances side but i would look to make do with however you have it at present and are using it and look into the correct kind of beast and connectivity when finances permit.

This is more like the kind of unit i would think one should be considering if the power supply from the local authorities is suspect and unreliable.

Here is a transfer switch set up

I would strong advise you dont do it the way you thinking and consider your insurance if by accident (and these things happen to the best of us) something went wrong and you have some kind of issue. The setup you thinking of aint gonna be approved.
 
Just to clear up my previous post. If I need to use this very often I would install a transfer switch, where I'm at it one every couple years for a few hours. Just a note. when I used it last I used my clamp on amp meter to check the load, I had normal lighting, couple of TV some celling fans 2 fridges and 1 stand alone freezer on. On leg measured 11 amps and the other leg measured 9 amps.
 
When we moved in to this house one of the first things we did was have a transfer switch installed. I called an electrician. All I knew about this thing was what the electric company advertised they wanted you to do to prevent frying their line workers. It was an expense we considered a priority.
I haven't a clue what you are talking about in most of the post.
Except your sequence at the end. The instructions that came with my generator (and my previous small one also) said to start then plug in the cords.
So, when/if, severe weather is threatening I take the wires out under the garage type door of my shop, put the plugs in a plastic bag and leave there. When/if I need the generator I'll go to shop, throw the transfer switch, go outside and start generator then plug in the cords, all the time praying I don't get fried doing this in the rain. :eek:
 
Bill:

Check around with the mfg. of your panel.

I believe Square D has an interlock kit for some of their panels that mechanically link the MAIN breaker to a 2 pole breaker in one of the upper positions.

With the MAIN "ON" (Connected to Electric Co - or Hydro for you Canadians) the "SPECIAL" breaker is OPEN.

With the MAIN "OFF" the "SPECIAL" breaker is CLOSED allowing the back feed.

I have a 5000W Master Generator with a Honda engine. It's loud but will run the stuff I need in case of an extended outage. It ran the house one spring for 3 days after a T-3 Microburst decimated the main power feed into my neighborhood 5 or 6 years ago.

Cheers

Jim
 
ok, I'm trying to understand this one.

My generator is something like this:

http://www.costco.com/Browse/Produc...=0&Ntx=mode+matchallpartial&Nty=1&topnav=&s=1

mine was actually more expensive, for a slightly lower output (5,500 watts). I'm hoping it's better quality, but who knows? I did get it at costco.

The reason I link to that one is because there's a link to a transfer switch on the same page. Here's the direct link: http://www.costco.com/Browse/Produc...=1&whse=BC&topnav=&prodid=11596000&lang=en-US

If I'm understanding this right, it's just a subpanel, wired in exactly the same way, but it's got two power inputs: one from the line, and one from the generator. You flip the switch one way, and it pulls from the line, flip it the other way, and it pulls from the generator. See this picture:

544099LL_v1.jpg


So I'm just paying for that one switch, essentially. How can that possibly cost three hundred bucks???? :dunno:

Here's the cost of a subpanel. That's actually got a main breaker on it, so it's more expensive. So why is a transfer switch so much more expensive???

Anyway, forget I mentioned that, that's just me complaining. Essentially, what I should do is simply replace my subpanel with the transfer switch, and make sure that any circuits I want to run when the blizzard hits next week are wired into the transfer switch panel, instead of the main panel. Is that about it???

I'd like to do this right, even if it's a little more expensive. I just want to understand...

Thanks,

Bill
 
Jim Mattheiss said:
I believe Square D has an interlock kit for some of their panels that mechanically link the MAIN breaker to a 2 pole breaker in one of the upper positions.
Click to expand...

Jim,

Thanks for your note. I'm actually standardized on cutler-hamer, and found this, thanks to your link: http://www.interlockkit.com/cutlerhamer01.html

The only problem: it looks like I'd have to pull the main to install. Based on my setup and local codes, I can't do that, I'd have to pay someone to come in and shut off power at the meter. It was a good idea, though. Don't forget, even though I've replaced all the breakers, my panel is 48 years old! :(

Last winter, we lost power for five straight days. That's about the limit I'm thinking of for running on generator power. But five days of freezing in the dark is more than the family can take... ;)

Thanks,

Bill
 
Bill the switch you have a link for switches from line power to the generator power. It contains 6 to 10 circuits that run independent from your house panel. That's where the cost comes from. The one in your link is also for a bigger generator than you have. That generator wont even come close to powering your whole house.
Jim is spot on with the gen switch in your main panel. The one I had put in for my mother was 50 bucks installed. But with a 5000 wat gen you still have to turn off a bunch of breakers. And plan when the well pump is going to run or when the furnace is going to have it's turn on the power.
 
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Well, that was my next question. The 20 amp switches I'm finding are rated for generators up to 3,750 watts. Looks like I need one *at least* this big:

http://www.homedepot.com/webapp/wcs...-_-202019403-_-202019408-_-N&locStoreNum=2583

It'd be a hassle, but I could rewire the main panel so I'm only moving 30 amps off to the subpanel/transfer switch. I don't actually need to feed the shop off that: if the power's out, I won't be using the shop.

That leaves me with a few necessary circuits:

Heater (the heater is gas, but the blower's electric)
freezer
refrigerator
lights (downstairs and up)
TV, computers, router.

That's pretty much it. Seems to me that would be way under 30 amps. In fact, I've been powering all those off extension cords from the generator already (with the exception of the heater).

Given the circumstances, hiring an electrician can't happen... It's transfer switch or extension cords. Transfer switch seems like much the safer option...

Thanks,

Bill
 
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Chuck Thoits said:
plan when the well pump is going to run or when the furnace is going to have it's turn on the power.
Click to expand...

Chuck,

Thanks for your note. Luckily, I don't need to worry about a well pump. Freezing in the dark is one thing, freezing in the dark with no plumbing is quite another! ;)

If I'm understanding right, I need double capacity coming off the main panel to the transfer switch. In other words, if the switch is rated for 30 amps, I need a 60 amp breaker coming off the main panel.

Unless I'm missing something, which is always possible, it's better to have too much capacity rather than too little. I'd rather have a switch rated up to a 7500 watt generator than one for a 3,750 watt generator. That doesn't mean I'd try to jam in all the circuits I could, I'd still just be running the limited list I gave above. Doorlink couldn't turn on her oven, I couldn't turn on a saw, and nobody gets to run a space heater... ;)

Thanks,

Bill
 
Bill,

I'm going to agree with the others. Get a transfer switch! I've been in our house for eleven years. One of the first things I did when we moved in here was buy a generator and transfer switch. We've got a LOT of trees here with the utility poles and wires in very close proximity to the trees. I knew that there was a better than average chance we'd be without power for extended periods of time. I bought a 5500 watt generator and it's never let me down. No, I can't run my stove or A/C but I've never overloaded it. I bought a six circuit transfer switch and I wired it to the six most important circuits in the house. The furnace was the first one and then the circuit with the fridge. Then four other general lighting circuits. I've used the generator MANY times in the last eleven years and it's a great thing to have! This is an updated version but basically the same switch made by the same manufacturer.

http://www.homedepot.com/h_d1/N-5yc1v/R-100045357/h_d2/ProductDisplay?langId=-1&storeId=10051&catalogId=10053

I installed it myself and it was very easy. The first time I fired it up and put it to use, my neighbor came over saw it. He went out a couple weeks later and bought a generator and switch for his place. I installed that system for him too. It's WELL worth the investment in a transfer switch. It's MUCH safer for everybody!

Good luck!

John
 
My transfer box originally cost about $400.00. That was box and the labor. During the 2009 ice storm we used our 3500 w to run some things. But we could not operate our furnace or well. Wifey didn't like pouring water from jugs to flush the toilets. (I kept about two dozen empty 3 gal. jugs on hand just for that purpose).
So, I shopped and shopped and shopped and finally settled on a 10KW from Sam's.
Called electrician again to add a circuit to the garage for our freezer and the well. That was another $100.00 or so, not bad.
I doubt there is one generator in a thousand around here that has a transfer switch set up. When I called the electric company to inspect to see if mine met their requirements (not a legal requirement, just what they want to keep their linemen from cooking) they said I was the first person ever to call and ask that.
BTW, my tenner cost less than $900.00 and I sold the old thirty-five for $300.00. Came out well on the deal. I feel ready for most emergencies with our set-up.

Edit: Forgot to mention, again, about the sequence. You elektrikal types.....is it important to plug in the cords after the generator is started, or does it not matter?
 
Frank,

for ten years I've been taking the generator out to the other end of the house where my meter and outdoor plug is located. I plug the generator into the outlet and start the generator. Then I go down into the basement and turn all six circuits on the transfer switch from Line to Off. Then I plug the cord into the switch. My switches are labeled A through F. One by one I turn the switches from Off to Generator. I generally do it in the order A,D,B,E,C, & F. This balances the load as I turn things on. I've never had a problem doing it this way.

This spring I plan on upgrading my system a little bit. I'd LOVE to have a 12KW automatic generator that runs on natural gas but they're about $3K and I haven't got that kind of money. About a week ago, I was doing some searching online and found that for about $700 I can get a 5500W electric start generator. I plan on putting it around back and building a weather shelter for it. Then I'll change the location of the outlet box so that I can leave the generator there full time. If the power goes out, just go down and plug the cord in and turn the key. In the summer it's generally not a big deal, but if the power goes out in the middle of a snowstorm in January, it's a pain in the butt to drag the generator out and hook it up. When it's really cold, the thing is a real pain to start. It starts well, it's just hard to pull. With me having broken both shoulders now, electric start will make my life a lot easier!

John
 
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