After the recent ice storm and 10 days without power in the Northeast, I’m getting rid of my extension cords and setting up a full generator control panel.
My 5 kW generator is only 110 volts – no 220. I’ve seen many generator panels that allow you to remove 8 circuits from the main box and place them on the generator panel. But then you’re limited to items on those 8 circuits when running off generator power. My critical items aren’t very power-intensive, but they’re scattered on a bunch of different circuits. I’d rather have power to the whole house and have everything (110v) available, but simply limit the loads in use at any given time. My house has a lot of small circuits that I’d like to be able to use – a few at a time.
1. Do they make a transfer panel that will transfer my whole panel between utility power and generator power rather than just certain selected circuits?
Assuming there is, then….
2. Because I have only 110 volts on my generator, obviously I’d not be able to use any 220v appliances. But I need circuits from both 110v legs. If, in the generator mode, I connect both legs to the generator, will any harm be done to any 220v appliances that are accidentally turned on? My plan would be to trip all tandem breakers before transferring to generator power, but the best laid plans….
In other words, if I accidentally turn it on, and apply the same 110v to both legs of my 220v dryer or water pump, is any harm done?
Edited 12/30/2008 8:57 am ET by KentMich
Replies
With the dryer, the most likely thing is that it just won't make heat enough.
with the other, you could damage the pump, the wiring and the generator.
The whole idea is a great booby trap for burning up the undersized genrator, IMO
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No problem with the generator - it has electronic load-shedding. It will simply disconnect if overloaded.
The pump shouldn't be damaged since it's a pure 240V load and hence would see zero volts.
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I see now how that would be with that way of tying it.
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Not a transfer panel.
But you can get transfer switches that switch the whole service (200 amps).
And if you connect the two hot legs together the 240 volt loads will see zero volts. They just won't work. Not damage.
Dryers and stoves are 120/240 loads. For the dryer the motor and timer will probably work, but it won't heat. Again no harm.
For the stove the controls and oven light might work, but again no heat. If you have a very old stove with 5 - 7 position switches you will get heat in a couple of postions as it connects some elements across 120.
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What you want to do is a little bit dangerous and may not be legal. In particular, if there are any shared neutrals (sometimes done for kitchen circuits, in particular), those circuits cannot be legally fed from 120V unless the breaker sizes are cut in half. If you have no such shared circuits, though, then what you propose was at least legal under older code (though I don't know about the current one, or about all the exception clauses).
Most 240V appliances would probably just see zero volts if turned on while on a 120V feed, but there is very a slight danger that "modern" computerized appliances could be damaged.
You would need a standard whole-house transfer panel, and those tend to be pretty pricey. When you see the price you may recalibrate your desires.
What you say about shared neutrals makes sense. Each of my 220v appliances have their own tandem breakers powering nothing else. Also each 110v circuit comes out of the box with a single cable - for example, no 12/3 powering two circuits on black and red with a single white neutral (except for the tandems). Does that mean shared neutrals isn't a factor for me?Actually this is more academic, since you've all convinced me that a regular generator panel is the way to go. I hadn't thought about how a whole-house transfer would have to be 100 amps capacity. I'll just have to make do with only 8 circuits.
Edited 12/30/2008 4:41 pm ET by KentMich
You can't be sure, without a closer examination of the panel, that there aren't any, say, kitchen circuits with a shared neutral.
The mark of the immature man is that he wants to die nobly for a cause, while the mark of a mature man is that he wants to live humbly for one. --Wilhelm Stekel
you've all convinced me that a regular generator panel is the way to go. I hadn't thought about how a whole-house transfer would have to be 100 amps capacity. I'll just have to make do with only 8 circuits
You definitely want to use a transfer switch subpanel, but you don't need 100A capacity if you're not transfering heavy loads to those circuits. The transfer panel is basically a subfeed panel with a double-throw, double-pole switch. Only the circuits you move to the subfeed panel will be loading that box. The rest will remain in the main breaker box and be activated only when utility power is available.
You can get transfer panels with a front power socket for a corded generator supply or without for a hardwired generator supply. Some come with dual wattmeters, but you don't need them since you won't have to balance two legs of a 240v generator.
You can get a decent transfer panel for less than $250 (such as the Reliant TRC0603D).
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"You definitely want to use a transfer switch subpanel, but you don't need 100A capacity if you're not transfering heavy loads to those circuits."He wants to transfer a large number of circuits, more than 8. While in emergency mode he might only use a small amount of power. But during more operation he has to be able to supply the full amount of possible power to all of those circuits. That will require a transfer switch that can handle that amount of power.What he really needs to do is to identify what are the REALLY CRITICAL loads and if need rewire some of them to be on common circuits.That way he can get down to a more realistic 4-6 circuit switch..
William the Geezer, the sequel to Billy the Kid - Shoe
Perhaps the easiest and lowest cost is to simply use common 3-way lighting switches as transfer switch.
Common to the outlet or lighting lines, one side to C/B in service panel, the other side to your generator bus. You can put on as many 3-way switches as you have circuit breakers. Like Bill said, dont try to power 240 V motor or some 240 V electronic loads. Item like your dryer or electric oven probably won't heat unless you also add another 3-way switch to ground (neutral) one side of the appliance - need to know what you are doing to attempt that.
UGH! Here we go again ...
It sounds like you are planning to use a manual transfer switch. It's pretty important that the switch be intended for use with your 120v. generator. No, it's not good enough that the panel be rated for 240 volts!
A manual transfer switch is, in many ways, comparable to a bank of 3-way switches. The difference is, the transfer switches are rated for the load ... most 3-way switches are rated for less than 10 amps. That's one of the differences between a $1 switch and a $20 switch.
As such, the generator NEVER supplies power to the panel. Rather, generator power is supplied to the circuit, and the circuit is removed from the panel altogether. That's another difference between a transfer switch and a 3-way switch: the transfer switch has overcurrent protection - breakers or fuses - for each circuit when the generator is supplying the power.
The one thing to watch is the size of the neutral wire ... but with your small generator, you're not likely to run into problems. If you get a larger generator, you might be overloading that neutral.
Since the transfer switch physcally removes a circuit's connection to the panel, it matters not which 'leg' of the panel feeds the circuit. It DOES matter, however, if any of those circuits share a neutral. Again, your generator is small enough that you probably won't have a problem .... but a larger generator would introduce the issue.
Yes, transfer switches are made for transferring your entire panel to a generator. These are sure to cost a lot more than you're planning to spend, and you'll want a larger generator. For such a project, I strongly recommend you hire a real electrical contractor .... there are simply too many design issues for the DIY to address on his own.
One of the reasons for this far greater expense is that the transfer switch will need to be rated to the capacity of the panel ... and a 100 amp switch costs a lot more than a 20 amp switch!
Gen/Tran Makes a subpanel to accommodate a 110 volt generator. I installed one this past summer. You need to install a 60 amp 220 breaker in your main panel. Then feed it to the Gen/Tran subpanel. You can plug the correct sized and plugged extension cord directly into the top of the subpanel, or do as I did and hard wire an outside plug ( gotten from Gen/Tran) on the outside of the building. Then wire the circuits you want to back-up to the subpanel. When the power goes off you manually switch from city power to the generator. You will have to provide a ground for the generator separate from the normal building ground. I have my furnace, water heater, and two plugs that I can run extension cords from to whatever I want to. Used it when Hurricane Ike came up the Ohio Valley this past summer to power freezers and refrigerators.