DIY Message Boards
generator wiring

This topic can be found at:

Dec 08, 2013, 11:18 AM
generator wiring
so ya, i'm a bit of an amateur electrician... i know what i can do and i know what i can't do...

i've got a cottage that has regular power failures that can last from minutes to days...
i want to get a generator to support basic functionality...

i know that the 'right' way is to get a transfer switch installed, etc, etc...
but, since it is just a cottage, i don't want to invest too much into it...

my understanding is this:
-city power goes down
-i open main breaker to disconnect house from grid
-power up generator
-plug generator in to 120v house plug (this will light up one side of the electrical panel)
-or, plug generator in to 240v house plug (which will light up the whole electrical panel)

obviously, load and capacity is an issue, but right now i am just trying to confirm that my logic is correct or incorrect...
any electricians out there that can comment?

thanks in advance
Dec 08, 2013, 11:44 AM
Your logic is correct until you get to the point of having the gen power up by back feeding through either a 120 or 240 circuit. While you may get voltage your power will be limited by size of the individual circuit.

IF you have disconnected from the main power then the place to connect the generator is at the bottom end of the cut-off point. This will provide 240v power to all circuits in the house. The big thing is that you must not have both the gen and the land power able to be connected at the same time. Hard-wired automatic generator systems use a switch system to isolate the two - by far the best way to go.

Again, in the rawest form, you can turn your main breaker off and then clamp the gen to the main feeds below the main breaker - but if you mess it up it will cost you.

Since you know your electrical limits, and since you are asking about this it means that you are obviously past those limits - get an electrician to wire in a contact point for the generator that includes a switch for either generator power or land power.

Dec 08, 2013, 11:59 AM
OK, that actually makes a lot of sense.
The best response I have gotten so far (and I have posted this to a few places).

I'm guessing that a simple transfer shouldn't be too much of a deal for any competent electrician, or too expensive?
Dec 08, 2013, 01:18 PM
because of a smallish market, full-break transfer switches are somewhat expensive.

reverse-energizing the line and blowing a lineman off a pole is going to cost you everything by the time the courts are through with you.

now, let's see, which is the better investment? hmmm, let me do the math......

sig: if this is a new economy, how come they still want my old-fashioned money?
Dec 08, 2013, 01:20 PM
I'm having trouble dividing infinity by near-zero, I'll get back to you....

sig: if this is a new economy, how come they still want my old-fashioned money?
Dec 08, 2013, 04:35 PM
swschrad took one of my points and made it into the most important point - as it should be.

A licensed electrician will not be able to jury-rig a set-up. Whatever he does will have to be done in such a way that you cannot feed land power into your generator or feed generator power back down the power company lines.

If you are planning on doing this, it should be a simple thing to call a local electrician to get a quote.

Dec 08, 2013, 06:35 PM
Wiring a jury rigged set up like you described is a recipe for death. Call an electrician and get quotes on a proper set up. Besides possibly killing someone you could possible lose you power supplier.
Do as others onboard and correctly have said. Get a pro. Wink

This message has been edited. Last edited by: CommonwealthSparky,

Popeye only reached for the Spinach can as a last resort...
Dec 08, 2013, 08:30 PM
the only acceptable jury-rig is to unplug the essential items when the power goes off, run a full-bore SO rubber cord from the generator through a window (or back to back twist-loc connectors through the wall) and to a splitter box of outlets, and plug the essential items into that splitter.

I did that when we had a 2-day outage, and it works.

it is a wise move to know how long the fuel tank is good for, disconnect everything an hour before, turn off the generator, let it cool, and refuel. once it's running and stable (my little toy job says 5 minutes) then plug the essentials back in.

two reasons... stuff does not like dirty power on starts and stops... and you won't be able to crank the generator into a load, the Hulk can't pull hard enough.

fortunately, it was not cold enough for me to have to dewire the furnace line, build an extention cord for it, and hook that to the genset. with below-zero temps lately, it would be a necessity. just for the record, you can't leave dangling hot wires out and about, so it's not a 10 minute job, they have to be correctly terminated in a solid junction box with a plate on the front.

if furnaces are an essential to you, again, you need that done to code. so we circle back around to calling the man.

This message has been edited. Last edited by: swschrad,

sig: if this is a new economy, how come they still want my old-fashioned money?
Dec 09, 2013, 07:07 AM
That temp power set up during an outage is far and away the smartest plan going. Simple, quick, easy and safe, what more can a homeowner need?
We always add sta-bil and run equipment off season as well. And unplugging the setup before a start up when in use is wise as well. Even though most units have circuitry that should prevent problems that arise this is not always the case.
And yes while temporary wiring may fall into a special NEC slot, making those set ups properly is paramount.

Popeye only reached for the Spinach can as a last resort...
Dec 09, 2013, 10:46 PM
For what it's worth, I just had a manual transfer switch installed by a licensed electrician.
I'm relieved to have it.
The setup I have makes it impossible to run off the grid and the generator at the same time. It's one or the other.
I've needed to use the generator several times in the past and, I'll tell you, it's no fun running around passing cables through a window and plugging up a partially opened window when it's cold and blustery out.
Plus, my HVAC guy scolded me for jury rigging my furnace (I don't want to get on his bad side). He claimed I could blow the circuitry in the furnace.
The transfer switch had been on my wife's and my wish list for several years, but finally shelled out the money to get one when we upgraded our service to 200 amp (our panel was dangerously overloaded).
Dec 10, 2013, 08:06 AM
Thanks for the reply to the post Sturdynail, and congrats on wisely adding a transfer switch while having the service upgrade. Look at it this way, by combining the two instillations into one a money savings was possible.
While HVAC guys are generally shape pencils, as having to understand a few trades I wonder about his comments about possible circuit damage.
As mentioned generator start ups tend to provide unclean power [spikes or surges] for a nano second or so. Generators usually have circuitry to prevent startup problems, but never say never. [This may be what he is speaking about]. And if you add into the equation by bypassing breakers and or fuses problems occur. Either one may have problems catching a spike as they not designed for that action and hence the possible problems. But by disconnecting your power supply during startup this action will skirt that issue. Overloading a generator can result in problems as well. More of a load on the setup can result in a slight voltage drop and an increase in amperage, thanks to our buddy Ohm's Law.
Any of these issues can result in fried electronics, but lighting issues can result in damage TVs. electronics, microwaves, etc. And most often more likely.
Just my 2ยข. Have a great day all...

This message has been edited. Last edited by: CommonwealthSparky,

Popeye only reached for the Spinach can as a last resort...