DIY Home Improvement, Remodeling & Repair Forum > DIY Home Improvement > Electrical and Wiring > generator . my dryer 240 is a 3 wire. do i have to make it a 4 wire?




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Old 11-02-2012, 12:41 PM  
nealtw
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In other words, don't do it.



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Old 11-02-2012, 08:15 PM  
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Originally Posted by Wuzzat? View Post
Or judicious use of overcurrent devices to prevent operator error. With low impedance systems like this the difference between normal current and current due to operator error should be considerable.
What does this mean?


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Old 11-03-2012, 11:58 AM  
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What does this mean?
It means install devices to prevent operator error or inattention from causing bad things to happen.

But, suppose the OP leaves the main breaker on and feeds 240v back into a temporarily dead PoCo line.
The danger is to lineman who are thinking the line is dead, and a warning device for the OP would be rather complicated (but someone probably does make such a device).

Did you want to know about the impedance consideration?
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Old 11-03-2012, 05:27 PM  
speedy petey
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Did you want to know about the impedance consideration?
You're an engineer, aren't you?
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Old 11-03-2012, 05:57 PM  
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You're an engineer, aren't you?
That's the guy down the hall. Should I call him?

It seems to me if you hook a generator into dead PoCo lines you will be trying to power up at least all the houses on your pole transformer, including yours. Since your neighbors are not expecting this, you could cause some harm.

If you hook a generator into live PoCo lines, you'll still get 240V but within a few milliseconds probably 5000A will flow between the gen and PoCo's transformer and your generator's breaker will trip, if it doesn't explode first because its interrupting current rating has been exceeded.

Sounds like a transfer switch is the first order of business.
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Old 11-03-2012, 06:22 PM  
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I think I said that in my first post. Get a proper transfer switch or interlock device for the panel.

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Old 11-04-2012, 07:20 AM  
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Keep sayin it, joe, till the OP acknowledges it. The rest of us are you're reinforcements. 'Course the OP may have done blowed his self up already.

I wasn't even thinkin about the power going out into the grid, but think of the pride you'd feel from sending your electritricity to another state. Who would have thunk that just by plugging a generator into an outlet you'd have to notify the local distribution authorities that you were a producer? I was mostly thinkin about the other outlets he might be powering up without knowing it, screwiness of the various grounding and neutral lines, and the concerns arising from having a male plug on the generator, at least I think that was what he wanted to do. Or perhaps the ever popular male-male jumper. I did use one of those in a Scout Camping eguipment/ chuck wagon trailer once, but we were dealing with 12 volts from battery for lighting.

I've never been involved in permanently installing a large back up generator. One thing I'd worry about with an automatic system is storm damaging some wiring in home, perhaps along with a gas leak. Authorities do warn us when power and gas go out to turn mains for both off so there are no surprizes when they come back on, especially if you are not home when they do.
I have built a few shelters for smaller ones for essential power, refrigerator, freezer, few lights, TV. We ran a short line to switch box near reefer to keep extension cords to minimum. Switched outlets to cut off big drains to run another one. Reefer off a few while well pump, micro wave, or small space heater or window AC is on etc.

I reckon its an individual decision how big a generator to buy, whole house or bare minimum for freezer and a light bulb, . Cost of generator compared to how long you may have to use it. Folks got along without electricity longer than we've come to rely on it. Of course some folks want it all and right now! Like that mayor who damned the Red Cross 'cause they weren't right there and fixed his town good as new within an hour of the storms passing.

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Old 11-04-2012, 08:57 AM  
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I forgot to take into account the resistance of the gen. The 5000A is probably more like 500A, but even with this analysis there is too much uncertainty to suit me. There's too much riding on this if something goes wrong.

I'd do something to absolutely prevent the gen from powering PoCo's lines.

IIRC Grainger wants about $100 for a transfer switch. A DPDT or 3PDT contactor may be cheaper but if you have no power you'd need to use a battery to power the contactor coil.



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