Wiring a Home Generator Transfer Switch

[techman]

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

Just be aware that these transformers do not have much of a "surge" capability. This means that will generally not be able to start an induction motor device, such as a well pump, air conditioner, etc. The starting inrush current is typically 3-4 times the running current, and unless the transformer is sized to the inrush current, it will saturate and not start the device.

paul

 

[RonMar]

Just be aware that these transformers do not have much of a "surge" capability. This means that will generally not be able to start an induction motor device, such as a well pump, air conditioner, etc. The starting inrush current is typically 3-4 times the running current, and unless the transformer is sized to the inrush current, it will saturate and not start the device.

paul

Yep, you are exactly right, which is a good thing that most well pumps and larger A/C units are 240 already If you were trying to spool up a large 120V window A/c with one of these, you would need to account for the surge load.

In my case, the sizeing of my 3KW is about 30% larger than the combined load of the two devices I am intending to power with it and neither has a very large startup load... The only reason I need it is because I am working with very little power to begin with so balance is very important. That 1200W microwave lighting up on one leg has a noticeable impact on that legs voltage. Moving the reefers typical 600W load across both legs will allow me to refine the balance for my typical loads quite nicely.

 

[Highbeam]

Thanks Ron. I don't think I can really splice that in with my whole house transfer setup and since I am trying to eliminate extension cords I'll just have to try it the old fashioned way.

My genset is a little odd in that it regulates one of the 110 volt legs only. There is a voltage selector switch that sends full power to a single 110 volt plug or sends the full power to a 240 volt plug. Good deal really since the entire genset's power can run through a single 110 volt plug vs. the more typical half power.

I'll have to spend some major time with a killawatt meter to balance my loads reasonably well. Might even be looking at UPS systems to conition the power supply to my more sensitive devices.

 

[JB4310]

Thanks Ron. I don't think I can really splice that in with my whole house transfer setup and since I am trying to eliminate extension cords I'll just have to try it the old fashioned way.

My genset is a little odd in that it regulates one of the 110 volt legs only. There is a voltage selector switch that sends full power to a single 110 volt plug or sends the full power to a 240 volt plug. Good deal really since the entire genset's power can run through a single 110 volt plug vs. the more typical half power.

I'll have to spend some major time with a killawatt meter to balance my loads reasonably well. Might even be looking at UPS systems to conition the power supply to my more sensitive devices.

I just found this thread from a link in another generator discussion, there really are generator discussions all over the place on this site, there should be one category for generator talk as was suggested in yet another thread.

Any way, Highbeam I think I know what your talking about, I have a 3600 watt Multiquip jobsite genny, very stout machine with a japanese 4 stroke engine, mine has the 120 and 240 outlets, but the 240 outlet is only 240, it can't be split into 2 separate 120 circuits, found this out the hard way experimenting in my shop a few years back, made a jumper wire to back feed a welder outlet and fired it up, things were erratic so I checked the voltage on the 2 legs, one would be 80 and the other would be 160 and it was floating around not staying the same.

Well the only thing I fried was the power door controller, learned that that outlet is only for 240 applications and no good for splitting up a house load, so I don't think you will be balancing any thing as you will only have one 120 volt leg if yours is like mine, I just moved a few breakers around in the box to make sure my critical loads were all on the same hot leg of the box as was the outlet I would back feed into. This way I could use the fridge or the micro or the boiler or what ever else was on that hot leg of the main panel, selectively, not all at the same time of course.

I even brought my gen to an electric motor repair shop and they told me it could not be easily converted. the trick is to look at what the outlet says, if it says 120/240 volts then you can get two 120 volt circuits, if it only says 240 volts, then you can't, like mine.

 

[RobS]

Thought I'd post a quick follow up to this thread. I did my final test today and all was well. I hooked up the genny to the house, fired it up then flipped the switches over. This is a pretty stout generator as it was able to power the well while the water heater (gas) was running, an electric heater, some lights and the sump pump kicked in during the well's run. I'm sure if everything turned on at the same time, it would trip a breaker, but I'm reasonably confident that I can leave all circuits on at the same time during outages.

And now that it's run a while, I'll change it over to Mobil 1 and hope I never have to use it!

Thanks to everyone who gave me input for this project.

 

[JB4310]

And now that it's run a while, I'll change it over to Mobil 1 and hope I never have to use it!

Thanks to everyone who gave me input for this project.

That's what I'm thinking, it's like insurance, you pay alot for it but hope you never need it. Now that you have it ready, there's piece of mind that money can't buy, at the time of need sometimes, if that makes any sense.
Glad to hear you have a set up ready to go when needed,

 

[RonMar]

Thought I'd post a quick follow up to this thread. I did my final test today and all was well. I hooked up the genny to the house, fired it up then flipped the switches over. This is a pretty stout generator as it was able to power the well while the water heater (gas) was running, an electric heater, some lights and the sump pump kicked in during the well's run. I'm sure if everything turned on at the same time, it would trip a breaker, but I'm reasonably confident that I can leave all circuits on at the same time during outages.

And now that it's run a while, I'll change it over to Mobil 1 and hope I never have to use it!

Thanks to everyone who gave me input for this project.

Now don't just let it set, or when you need it, it will fail. Probably the biggest killer of small engines is lack of use. The oil leaves the internals for the sump and the case breathes in moisture with each temp change, then when you do need it some dark and stormy night, it chews a while on corroded bearings then throws a rod... Lawnmowers run a good long time because they get run regularly. You should run that generator every few months under load, to keep the lube spread out inside it and drive off any built up moisture. When you do this run all the fuel out of it by removeing the electrical load and turn off fuel so it burns it all out of he carbs...

 

[BobRip]

Now don't just let it set, or when you need it, it will fail. Probably the biggest killer of small engines is lack of use. The oil leaves the internals for the sump and the case breathes in moisture with each temp change, then when you do need it some dark and stormy night, it chews a while on corroded bearings then throws a rod... Lawnmowers run a good long time because they get run regularly. You should run that generator every few months under load, to keep the lube spread out inside it and drive off any built up moisture. When you do this run all the fuel out of it by removeing the electrical load and turn off fuel so it burns it all out of he carbs...

One of my generators manual says run it every two weeks, the other every three weeks. I keep two electric heaters in the generator shed and run them both every two weeks for about 15 minutes with loads. as RonMar said this is very important.

 

[RobS]

Yeah, thanks for the reminders guys. I do plan on running periodically. I like the monthly idea, or thereabouts. It may see some use in remote power and with our camper as well. Reminds me, I need to pick up an adapter to plug the camper into it.