A Generator Transfer Panel Installation: How to and how not to

| January 8, 2010 | 7 Comments
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In our town, the power goes out on a regular basis, so when a friend of mine moved to town, a generator was one of the first things purchased.

To safely use a generator to run your home, you need a transfer panel. Most of us have generators that are connected manually to the house power – we wheel the generator our into the yard, hook up the power cord to the transfer panel, and flip the transfer switch.

transfer panel

Even with the main breaker off, there is live power in the top of the box, so I cover the top to avoid touching it

A transfer panel allows you to safely connect a generator to your circuit breaker panel AND more important, keeps the generator power from leaving the breaker box, going out of the house, and down the power line from the local electric utility.

If you don’t connect your generator to your home electric system correctly, you can have power from the generator running thru the power line that serves you house, this is dangerous for many reasons, the most important being you can electrocute a line worker who may be working to restore your electric power.

Here is how the Columbia River Utility explains it:

Standby generators make life easier during power outages, but if used improperly, they can be deadly. During an outage, electricity from your generator can backfeed the power lines, killing or seriously injuring our line crews who are working to repair the lines.

A transfer switch stops backfeeding, and also makes using your generator much more convenient, allowing appliances to be operated much like when the power is turned on.

A transfer switch also protects your generator when your local utility restores power, it keeps that local power from feeding back into your generator and damaging it.

Do not fashion an extension cord to plug the generator into one of your electrical outlets. A neighbor had a friend do this for him, only problem was the guy hooked up the generator side of the cord to the 220 volt output of the generator. They plugged in this very unsmart idea and burned out all the TVs, microwave, etc in the house.

There are a number of transfer panels that the a homeowner who is handy can install. ( check with your local building codes, they may require a qualified professional to install transfer panels ) Most stores and websites that sell generator also sell transfer panels.

this transfer panel has a 10-2 line going to an outdoor outlet to connect the generator

this transfer panel has a 10 guage line going to an outdoor outlet to connect the generator

The first thing one must do is figure out how many watts-amps your home will require when running on generator power. When calculating this, figure out what essentials you need: furnace, well pump, lights, fridge, freezer. Don’t plan on running your washer and dryer with an emergency generator. Your power needs determine how large a generator you need, and what size transfer panel you’ll need. Also pay attention to how many 220 volt and 110 volt items you have, some transfer panels only have one 220 volt circuit breaker.

Installing the transfer switch involves working inside your circuit breaker panel. If you don’t feel comfortable doing this, don’t.

Be sure to turn off the main circuit breaker before opening up the panel. You can use your new generator with an extension cord to power a work light when you’re wiring up the transfer panel. Pay attention to the directions that come with the transfer panel, many come with a video. Watch it, you’ll learn.

I think the hardest part of all this is getting the bx cable from the transfer panel to connect with the breaker box. The bx cable ( the silver armored flex cable that contains all the transfer panel wires ) has to be connected to the breaker box by going thru a hole in the breaker box. Most boxes have a number of holes pre-punched, but they can still be hard to punch out. I use a cold chisel, but there are real electrician tools to open up these holes.

You need to balance the generator load; there are two meters on the transfer panel, and you want the load on each side of the transfer panel to be relatively equal. An example is you should put the furnace on one side of the panel, and the fridge on the other side.

Why? The fields in the generator – those coils of wire that generate the electricity – work best when the north and south coils have equal loads.

John De Armond sums it up best:

About balancing the load. Loading one side of a 2 pole (3600 RPM) generator but not the other can set up torsional vibrations in the rotor that have, in a few reported incidents, resulted in broken shafts. This is a rather extreme condition not often encountered. The onset of this vibration is a growling noise from the generator. If you ever hear an un-natural sound coming from the generator (not the engine) then hit the breaker and find out what is wrong. I’ve tried and have never been able to induce one of my generators to vibrate but the reports are in the literature so it’s a good idea to keep that in the back of your mind.

As long as both legs are loaded reasonably the same, no problem. That should be the case with a properly designed residential electrical system where the electrician selected branch breaker locations to balance the legs.

This whole process requires some thought and planning. Before you go out and buy a generator, calculate how much power – amps – you need. All the appliances have a label that says how many amps or watts it requires. I have an 8,000 watt 14 HP generator and I can light up my whole house, and it still has power to spare.

DO NOT run your generator in your home, basement, garage or any enclosed space, you will likely kill yourself.

Again, I’m not the expert here, but wanted to share some of my experiences with generators and transfer panels. Please be careful, and hire a professional if the job requires it.

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Comments (7)

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  1. Thanks for this, really appreciate the input on this subject.

  2. Barry A Clarke says:

    I enjoyed your article regarding the “how’s” and “not’s” when installing a generator transfer panel. I have a rather large generator being delivered tomorrow so I have been doing a little reading on this subject. I am not an electrician, but I do have a question. I just found a 200 amp double pole main breaker on the internet and this brought up an interesting question, at least in my mind. Why install a transfer box when you could install a double main breaker? One side would be for commercial power and the other side would be for generator power. This seems an easy solution but when things seem easy, there is always something lurking in the background that prevents it from being so……………

  3. Eric Gunnar Rochow says:

    The main goal of the transfer switch is to keep power generated from the generator from flowing back out of the house into the utility lines. If someone is working on the utility lines near your house, they could be killed if power from the house generator flows back out to the utility power lines.

    One should always use an approved transfer switch, it just not worth the $ savings if someone is hurt.

  4. Barry A Clarke says:

    Hmmm, I don’t think you understood what I was asking. This is an approved main breaker 200 amp switch from Home Depot Hardware (web listed below) It would replace the single throw 200 amp main breaker that I now have.

    http://www.homedepot.com/p/t/202276726?productId=202276726&storeId=10051&langId=-1&catalogId=10053&ci_sku=202276726&cm_mmc=shopping%2d%5f%2dgoogleads%2d%5f%2dpla%2d%5f%2d202276726&ci_gpa=pla

    When you are on the one side of the breaker, you would be on utility power and when you are on the other side of the two pole breaker, you would be on generator power. When on generator power and from what I understand from a two pole breaker, the workers on the utility lines would be safe from back feeding. Would this be correct and as you said, “the main goal of the transfer switch is to keep power generated from the generator from flowing back out of the house into the utility lines”………………

  5. Eric Gunnar Rochow says:

    i see what you are saying, but the “two pole” term might be confusing.

    the breaker you linked to is for 240 volt, and the two poles refers to the fact that it connects two separate “Hot” power lines to something like a well pump or breaker box. the breaker referenced does not turn one pole off while turning the other on, it turns two separate poles on at the same time.

    i am not a licensed electrician, but this is what i know from experience. thanks for the question, eric.

  6. jonny highline says:

    I understand what you’re saying, first of all although it’s a double throw both sides still are connected to the load side going through the meter to the line side, now your question Was to leave one side off and use it for generator power, I know that this would work but you will not be able to get 220 and also you would have to install an interlocking device, this is to prevent that switch from being turned on while its on generator power. I hope this helps answering your question

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