Called a transfer switch right?

Yes. Or an inlet plug with an interlock, such as this one:

AggieGunslinger said:

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I have what Todd02 has, it cost $300 to have a licensed electrician install it. I ran my gas furnace for 18 straight hours on about 3 gallons of gas and kept the house at 68 degrees. Jury rigging electrics in your house to save $300 seems foolish.

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Yeah but if I put an interlock on my welding circuit how do I weld?

So once a generator is hooked up properly to your breaker box, do you choose which breakers revive power by flipping them? What happens if a generator gets over drawn ? Does it just shut off or does a breaker trip ?

Yes. You identify which circuits are critical to you and plan to power those when the generator is online.

You could end up with a "brown out" condition, where the generator isn't providing enough watts, so to compensate for the voltage drop and the amperage rises. If the amperage rises high enough to trip the breaker, it will. If it doesn't, lower voltage could damage whatever it is you're trying to operate. If it's just lights, for example, they'll get dim (thus why it's called a "brown out").

I also spent some extra money and bought a monitoring system where I can watch, in real time, the power consumption of my sixteen most critical circuits.

Here's a post I made on another thread about how to go about hooking a portable generator to your house:

Quote:

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Here's my $0.02 for anybody that wants to read it...

First of all, you need to map out the circuits in your house. Determine which circuit runs what light, plug, appliance, etc.

Second, determine what lights, plugs, appliances, etc are critical if you lost shore power. Consider both summer and winter power needs. Probably want HVAC, water heater, fridges, freezers, some lights, and some plugs. Probably don't need to run the washer, dryer, dishwasher, etc. You'll probably learn during this step that your house wasn't wired with much consideration for running on generator power.

Third, determine the power consumption for each of those circuits. The easiest way to do that is multiply the amperage rating of the breaker on the circuit by the voltage. A single pole breaker with a 15 amp rating is generally capable of 1,800 watts (15 amps x 120 volts = 1,800 watts). A double pole breaker with a 50 amp rating is general capable of 12,000 watts (50 amps x 240 volts = 12,000 watts).

Fourth, add up all the watts you calculated in step 3. That's the size of generator you'll need to be able to run ALL of those circuits completely loaded ALL at the same time.

***You probably don't NEED to run all of the circuits all at the same time on your generator.

Once you figure out your needs, you'll need to decide how you want to hook it up. Some permanent gensets are capable of sensing a power outage and starting up on their own. Some must be started manually. Some, such as portable generators, must be positioned and plugged in through a power inlet. Some have a transfer switch that only feeds a fixed number of circuits. Some can be hooked up with a mousetrap style interlock that backfeeds the panel.

No matter what you do, you ABSOLUTELY MUST make sure you don't backfeed power onto the grid. You run the risk of injuring someone who might be working on a down line. If you're powering your house from a generator, you must disconnect the house from shore power.

My personal setup at my house is a portable generator with a power inlet. I have an interlock that keeps the generator from feeding power to the panel unless the main disconnect is off. I mapped my whole house and determined which circuits are critical. It takes some knowledge of how the system works, but I can run basically everything in my house EXCEPT the emergency heat strips for my heat pump, the oven, and the dryer. My whole setup was $850.

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For those of you looking at automatic transfer switches, some of them, maybe all, require you to pick a head of time what circuits you want to power, the I terlock let's you pick and choose. It was nice to have a the TV, modem and router runnings during the day along with the heater, then shut those off and have lights on in certain rooms at night.

archangelus2 said:

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I was able to successfully power my gas furnace off my Dad's Harbor Freight Predator 3500 generator. It took me 1/2 the day to figure out how to do it but was worth it. The trick was apparently some generators do not have bonded neutrals and newer furnaces (high efficiency?) will sense this and throw error status on the control boards. Easy workaround was to force a bonded-neutral on the generator by plugging in an extension cord that I sacrificed with the neutral and common connected. Voila!

Apparently the RV community is well aware of this as they have all kinds of discussion forum conversations on it. Not as well documented for connecting to a gas furnace. If anyone needs more details let me know.

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I would like more details. This sounds like exactly what I need to do but am not clear on all.
Thanks.

garyt73 said:

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archangelus2 said:

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I was able to successfully power my gas furnace off my Dad's Harbor Freight Predator 3500 generator. It took me 1/2 the day to figure out how to do it but was worth it. The trick was apparently some generators do not have bonded neutrals and newer furnaces (high efficiency?) will sense this and throw error status on the control boards. Easy workaround was to force a bonded-neutral on the generator by plugging in an extension cord that I sacrificed with the neutral and common connected. Voila!

Apparently the RV community is well aware of this as they have all kinds of discussion forum conversations on it. Not as well documented for connecting to a gas furnace. If anyone needs more details let me know.

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I would like more details. This sounds like exactly what I need to do but am not clear on all.
Thanks.

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If you want to get something hooked up quickly you can shoot me an email at my username and we'll exchange phone numbers. Will be much quicker to thoroughly explain over the phone. Now that I know how to do it I can have it hooked up in under an hour starting from scratch.

1. Determine if your generator is suitable for powering a furnace. Mine drew 9amps on a 3500 watt generator that was rated for 25 amps max to give you an idea. I have a 5 ton HVAC system. Also, apparently some generators can give off dirty power that doesn't play nice with sensitive electronics. I am told "inverter" type generators produce nice clean sine waves that don't cause any issues. The Harbor Freight Predator 3500 that I used was an inverter type and didn't cause any issues with my brand new goodman high efficiency furnace.
2. If you have a high efficiency furnace with fancy electronics/control board it may require a bonded neutral which many generators don't have. This is very easy to fix. You can test for this with a multimeter and your generator turned off.
Video of how to test:

3. If you determine you need a bonded neutral you can make one easily by cutting off the end of a power cord and connecting the ground and neutral together. After this plug it in to one of the other outlets on your generator. See this video to give you an idea what to do:

4. Turn power off at your panel
5. Find where power is going into your furnace, I believe most can be traced to an switch. This switch is where you will disconnect grid power and replace it with generator power.
Below is a video that shows you an overview of how to splice into the Furnace:

6. You will need to sacrifice an extension cord with a 3 prong male by cutting it several feet from the male end.
7. Disconnect grid power from the switch, I capped the wires off and used electrical tape to keep them safe.
8. Connect sacrificed extension cord wires where grid wires were previously.
9. Plug in sacrificed extension cord to generator.
10. Start generator and check thermostat and furnace to see if it works

Thanks for your response. Pardon my ignorance but I do not know how to send an email to your username.

I was reading the instructions on my duromax, and instructs to always ground the generator. Using a copper wire, attached to a copper piece that has been put into the ground. I'd never heard that before. I don't recall ever seeing a generator that is grounded like that. Any thoughts on that?