Wiring a Home Generator Transfer Switch

[RonMar]

In our area, if the main panel is more than 12 feet from the meter, there has to be a service disconnect near the meter. If it is 12 feet or less from the meter, the main breakers in the panel can serve ase the service disonnect. Several years back, I replaced our main panel, so I had an electrician add a service disconnect under the meter as described before. That makes it so much safer for me to do my own work.

Makes good sense, and is probably the same here, but I don't recall comming across any where the panel wasn't located in close proximity to the meter.

 

[RobS]

In our area, if the main panel is more than 12 feet from the meter, there has to be a service disconnect near the meter. If it is 12 feet or less from the meter, the main breakers in the panel can serve ase the service disonnect. Several years back, I replaced our main panel, so I had an electrician add a service disconnect under the meter as described before. That makes it so much safer for me to do my own work.

In Rob's case, which panel is considered the main panel? Is there a service disconnect anywhere? It would seem that you would still have power in half the house if you turned off one of the main breakers in one of the panels.

We cannot get 400 amp residential service here. We can get 100, 200, and something in the 300s out in some parts of the county.

Dave, your post reminded me of a conversation we had at build time. I don't recall the details but the layout of the propane inlet, AC units and electic meter almost caused us to need a disconnect. And I think you are right, it was about 12 feet which we just snuck under. With my dual panel, neither is a main, or both are. They are equivalent, each having it's own 200A main breaker that has no affect on the adjacent panel.

Ron, logic tells me I shouldn't have a problem bringing the two panel neutrals together, but it's one of those electician questions I'm not qualified to answer.

 

[MossRoad]

The interlock method described above would still work. You would just need to make sure all of the circuits that you want the generator to run are on the same panel. In a power outage, you would just flip the interlock to lock out the power company and flip your one generator breaker. Then turn off all breakers. Then fire up the generator. Then trun on any breakers you want the generator to run once the genny has come up to speed and settled.

You did mention you want it to be used by your family when you are not at home. You could easily color code the breakers with stickers and put directions inside the panel.

If you are going to go with the generator transfer switch and dedicated circuits, you are still most likely going to have to manage breakers in that box since your generator is only 5K, so you'll still have to have a procedure if you are not home.

Anyhow, sounds like a very good project. The first time I used mine, the wife came home to a dark neighborhood, except for our house. My daughter and her neighbor friend were watching a movie on the VCR in the living room and I was drinking a cold pop. She was happy.

Any thoughts as to where you will mount the generator or are you going to have a receptacle outside for it to plug in? Also, if it is a 3600 RPM gas engine, it may be very loud, so consider running it somewhere away from the area of the house where you will be hunkered down.

 

[RonMar]

If everything you wanted to power was in one panel, the interlock is the cheapest way to do this IMO. If the loads are split between the two panels, it could still be done but you would need two of them, one in each panel. You would also need a split hardwired power pigtail going to a single power cord or receptical. Or a generator power input receptical for each panels and a "Y" power cord to connect the gen to both. That is $300 for two kits plus the additional cords/recepticals. That is getting into the price range of a 10-15 circuit transfer switchpanel that could be wired into both panels, most likley already has the generator power inlet receptical installed in it and could use a large off the shelf twistlock extension cord between generator and panel.

The interlock plates would be Overall probably simpler to install, but a little more complex to operate. They would be more flexible as you can send power anywhere your current wiring goes, and not just down the circuits that are available in the add-on transfer panel. And if you ever decided to upgrade your generator, running more stuff is just a circuit breaker flip away...

 

[Pilot]

Ron,

I have a transfer switch & a 6500 watt generator. Works well. If I had to do it over, however, I would not put my freezer on it. I would use that circuit for more lights. Then, a couple times a day, I would shut down a circuit & run an extension cord to the freezer. In our area, it is usually cold when the power goes out and the freezer isn't going to warm up much, especially if you don't open the door often. And the more stuff you keep in the freezer, the colder it will stay.

We have our well, some lights, the microwave, refrigerator, furnace fan and freezer on the transfer switch. When dinner is over with, we unplug the microwave and plug in an extension cord to run the TV. I would make sure bathroom lights are on it so you can shower in the light & meditate in the light. As much as I dislike compact fluorescents, when the power goes off & you are on your generator, it is nice to have the light while using less power.

Our generator has electric start. I keep the battery charged with a float charger from Harbor Freight, usually on sale for around $8. I keep a checklist beside the generator so my wife can fire it up if I am not home when the lights go out. When you switch over to the generator, switch your heaviest loads first so the generator can handle the load better. If you have a desktop computer and no uninterruptable power supply, don't try to use it while on the generator as the power is too erratic. The well comes on, or the refrigerator, etc and it lugs down a little for a second or so while it adjusts to the load.

Put the generator outside when running it, not in the garage. We tried it in the garage one windy, rainy night (instructions say to keep it out of the rain) & it wasn't long before we had fumes in the house. Next project is to make a cover for the thing.

Lastly, when you have been on the generator for days and run out of gas & run to town for more, the rule is as soon as you get it fueled and running again, the power will come back on.

 

[ultrarunner]

My uncle built a small concrete block enclosure for the generator at his cabin... the roof was also concrete. It was very quiet even with the outside air intake. The enclosre was only about 4 x 4 x 5 high.

 

[RonMar]

Compact Florescents lights make a huge difference in electrical load. I have 99% CFL's and I can turn on every light in the house and not really see much effect on the generator load. They also cut down on flicker present in the simpler single cylinder generators. If you have many automated loads, such as reefer, freezer and wellpump, a UPS is a real good idea on computers and expensive electronics to deal with fluctuations in power output as these loads switch on and off.

Pilot
Your description dosn't sound like all that much load, but if you are seeing the effects of loading, then that is an indication of reaching the generator limits. This can sometimes happen prematurely if more 120V load is placed on one leg than the other, so it takes carefull balance to get full rated capacity out of a small generator. Another problem sometimes is with the generator rateing itself. Some are a little generous with the numbers on that sticker they place on the side. Sure it is 6500W, for a short time it can hold that. That is where the HP rateing of the generator helps. If you have a 6500W generator with only a 10HP engine, you might look on that 6500W rateing with a little doubt(probably closer to 5KW continous)...

I have an honest 3KW plant. It will run that 3KW load indefinitely. The generator head is actually rated at 5KW continous so I have a generous surge capacity, but I only have HP for a sustained 3KW. I have the following on mine:
2/3 HP wellpump. 1-1.2KW
13 CU/FT freezer. 400W
16 CU/FT Reefer/freezer. 600W
These first 3 are automated and run whenever they have need.
Pellet stove 400W
all house and garage lighting circuits and outlets. I typically only run the lights where I am at and the TV/entertainment system or computer(400+W?).

As long as reefer/freezer are caught up(fully cool), I can run 2 small stove burners. The microwave is problematic as it is my largest 120V load. It currently is on the same 120V leg as the entertainment system and the UPS there goes into backup when the microwave runs. I bought a 3KW 240-120V transformer to spread this 1.3KW load across both legs. I will probably configure it to power the reefer as well. If I am not cooking, I typically have enough reserve to run a 1KW electric heater in bathroom or bedroom as needed. It is all about balance and energy managment...

 

[RobS]

I got the switch and wired it in today. Piece of cake, it even came with a video though it wasn't very useful. The only twist for me due to the two panels was running a conduit between them and tying the neutrals together. After some consultation with an electrician neighbor, we concluded that would be no issue as they are together at the meter base anyway.

Two panels did provide one point of convenience: I could run my work light off a circuit in the other panel so I always had good light to work in.

I still have to run the generator input cord through the rim joist and mount the outside plug-in box for it. No biggie, but it's only 7 degrees or so right now. I'm thinking it can wait for a nicer day.

Ironically, I am going to the Lake Michigan shore tomorrow morning to photograph the wind/waves/ice. Maybe I'll finish this project after that while I'm still bundled up.

Thanks everyone for the bits of advice.

 

[Highbeam]

"I bought a 3KW 240-120V transformer"

Tell us more about this and how you applied it. I am a little bit worried that my generator will only regulate voltage across one leg of the 240 volt output which is fine for a 240 volt load but if I unevenly load the legs then I could end up with a voltage fluctuation problem on the unregulated leg.

Is uneven loading of the 240 volt output an issue with the typical generator? Does the typical generator have two voltage regulators to address this?

 

[RonMar]

"I bought a 3KW 240-120V transformer"

Tell us more about this and how you applied it.

These transformers are actually quite common and are used for people who wish to operate US domestic appliances(120V) abroad on the 220-240V commercial power. If you search "220V appliance step down transformer" or some such, you will come up with quite a few hits from vendors selling them. Shop around as prices vary greatly. I got mine thru these folks Region Free DVD Players, PAL/NTSC LCD TV, 110/220 Volt Appliances & Electronics , but have seen prices over $150 for 3KW versions.

My application plan will be to wire it with a dryer plug and plug it in in place of my 240V dryer. The output will split to two 120V outlets, one for fridge and one for microwave. I will unplug the dryer and plug in the transformer and the two appliances to these additional outlets when I am on generator power.

I am a little bit worried that my generator will only regulate voltage across one leg of the 240 volt output which is fine for a 240 volt load but if I unevenly load the legs then I could end up with a voltage fluctuation problem on the unregulated leg. Is uneven loading of the 240 volt output an issue with the typical generator? Does the typical generator have two voltage regulators to address this?

Differences in generator types notwithstanding, a typical domestic use generator, you should only have a single 240V output from your generator. The stator winding that creates this output is tapped in the center, just like the transformer out on your local commercial electrical pole that feeds your house. The voltage from end to end is 240V. The voltage from either end to center is your 120V so you have two separate 120V legs. Also like the commercial power entering your panel, the center tap wire is the neutral. In general, The voltage output of the generator is controlled by the rotor's magnetic field. This field is built from DC current fed back to the rotor windings. The more intense the field, the greater the output voltage. The frequency is dependent on the RPM of the rotor.

The regulator measures the output voltage and decides how much current to feed the field to maintain a stable output. As you increase the load, more field current is sent to maintain the output, and this larger field requires more mechanical energy to maintain RPM. Most generators measure the 240 for regulation(as that is where the heavy 240V loads are drawing their power from) and can have different 120V outputs if one leg is loaded more heavily than the other. A typical generator can't regulate those two legs separately as they are the sum of the single magnetic field from the rotor. That is why it is common practice in installation to balance the 120V loads applied to a power panel regardless of the source. As mentioned before, this is very important on a small generator as you don't have a lot to work with initially.

A box store generator will typically have 3 recepticals. A single 240 and two 120V outlets. If you plug a single 120V extension cord into one outlet and run it into your house, to distribute the power there, you are only ever going to get 1/2 the rated generator output and the voltage regulation(looking at 240) will only ever compensate for 1/2 the voltage drop on that one 120V leg as the voltage reg will keep the sum of both 120V legs totalling 240V.