I'm trying to wire a transfer circuit for a generator.
The generator will be located in the barn. The electrical service is at the house. Two 120vac wires and a ground go to the barn. There is *one* unused wire from the house to the barn I can use for a signal circuit.
When the power goes off at the house, I need to disconnect the service to prevent backfeed and activate for generator power to both the house and the barn. When the service power goes on I need to disconnect the generator to avoid damaging it and restore normal service to the house and the barn.
First, hire an electrician! There are safety issues involved with stuff like this that leave you open to liability questions otherwise.
If you insist on doing this yourself, the 240AC relay is used to isolate from the mains. It should be fail-safe i.e. no power means that it is connected and the others are not. Your system needs to do the switching of load to the rest of the circuits.
Your personal liability varies by the culture of your state -- the two examples I know if are Kansas and Oregon. In Oregon, if a neighbor gets drunk, breaks into your yard, and drowns himself in your kid's wading pool, then you'll get sued and it might succeed. In Kansas (unless it's changed since my sister lived there), if a neighbor kid goes swimming in your backyard pool without permission and drowns himself the jury will shake their heads and tell the kids parents they should have kept a closer eye.
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Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
2: Do an enormous science project, and plan on buying more relays.
One way I can think of to do this is to have the generator in the barn set up to disconnect the _barn_ on power loss, then start itself up. Power the one wire (against the 120V neutral reference) with what the generator produces. Then up in the house, use the absence of street power and the presence of generator power to switch off the street and onto the generator.
You could complicate this further to automatically switch the generator off, but you're already looking at a mad scientists dream; were I to do this (I'd dig the @$%# trench) I'd just plan on _walking_ out to the barn after the street lights come on and shutting things down manually.
If you're smart you'll check your local codes very carefully before proceeding -- home generator setups that inadvertently apply power back to the street can create very hazardous situations for line maintenance folks, and power companies generally take a dim view of people winging this sort of design. At the very least you'll need to use some power-company-approved switchover device that locks out the generator when you're on street power.
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Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
In Arizona, self closing/latching gates with releases only on the inside serve as the tort prevention. If the kid gets inside, he committed "break-and-enter".
For my own comfort in dealing with eight grandchildren I added double latches on the house outside doors, requiring at least 5' height and arm-stretch to match to open them (standing on a stool to reach the upper puts you out of range to reach the lower at the same time :-) ...Jim Thompson
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| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
There are MG sets that have automatic switch-over built-in. Back when I lived in total boonie land I was considering purchasing one. Then APS upgraded everything.
Now I'm on SRP with relatively modern infrastructure. Only one short outage in 16 years... a lightning strike on the distribution yard. ...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
1st question- Is the existing wiring out to the barn up to the job? i.e. how many amps is your genset capable of suplying- 60 amps through #10 ain't gonna cut it.
2nd- how many amps is your service rated for & how many can the genset supply? A 60 A feed into a 200A service means you're gonna be manually flipping brakers off anyhow...
3rd- Is there a seperate main service dissconnect from your breker panel? If not you'll have to add noe between the meter & panel if you want the xfer swittch to feed th whole house
4th- how understanding is the carrier for your fire insurance? Jerry-rigged transfer switches using non-approved parts aside if there's any problems at all with *any* of your wiring (whether you were the last one to touch that particular part or not) that causes a fire you can probably kiss your coverage goodbye :(
Personally I'd go with a type approved manual transfer switch, with a seperate feed coming to it from the generator, feeding a "essential services" sub panel .
Remember- The Life You Save May Be Someone Else's.
Answer: Ask your insurance company if they will buy you a new house (and barn) if (for any or no reason) the thing catches fire.
You need a listed mechanical switch, not a relay. You can buy automatic transfer switches, of course - which are a form of motorized mechanical switches.
As for control wiring to an automatic transfer switch, these are typically low-voltage, but not always. Although, most ATS I've seen will sample the utiliity and switch by themselves, and the control wiring is mostly for cycle-timers and testing, stuff like that.
If I understand where you're going.... NO. You can not use an extra (unused) wire in the bundle that already carries the two 120 VAC. The control wiring is separate. Can't even be in the same conduit.
Of course, check your local codes -- one obvious exception is that the local Inspector probably has the ability to "approve" anything, but I wouldn't hold my breath. Way too much liability.
Go get yourself a real switch, designed for this purpose. Manual or Automatic. They cost much less than your house, or yours or someone else's life!
Also, I hope your "extra" wire is not the neutral. If so, ask yourself what happens if the neutral to your house lifts. Also, (totally different issue), remember that the Utility and your generator will not be synchronized. So, if you attempt an instaneous switchover, at some point, you'll be high on the AC cycle from the utility, and low on the genertor -- or vice versa. This causes maximum current to flow for a split second, and will probably nuisance-trip the breakers. You can by phase monitors, but for residential use, a simple time delay between switch activations should do the trick. Generator - disconnect (wait) - then switch back to utility. Easy.
Also, come to think of it, you probably want a safequard to your generator is not connected until it reaches the proper output and waveform.
120vac service lines 120vac | | | | | | signal line *------(coil A)------*--------------* | | | | | | --- --- | --- --- | | A | A | | | | | | | o--- house/barn -----o | | | | | | | --- --- | -/- -/- (coil B) | B | B | | | | | | | o-----generator------o --- - gnd
coil A 240vac contacts 200 amps N.O. coil B 120vac contacts 100 amps N.C.
I don't need to turn the generator on right away. I just want to take the guesswork out of turning the main breaker on and off every time the electric goes out. Then I don't want to have to test if the power goes back on and I can't tell. With this arrangement I can save trips back and forth to the house and barn. If this works when the power goes off all we need to do is go to the barn and fire up the generator.
I guess I could also add a generator kill switch off of coil B.
It's a no-go from the start. The electrical code requires you to use a listed transfer switch. It *may* also prohibit you from doing it yourself, even if you use listed equipment, and require that the work be preformed by a licensed electrician. Next, you need some large gauge wire from the generator to the existing service if you will supply > 20 amps from the generator. You need to do a voltage drop calculation based on how much current you will allow to be drawn and the distance the wire must run, to verify that you are using large enough wire. Next, the code won't allow you to use the same wires, regardless of transfer switches, for both branch circuit wiring and feeder wiring.
What can you do yourself? Dig the trench, plan the system, check the codes, make sure the licensed electrician (if you use one) agrees with all that is to be done and who is to do it, lay the wire between the buildings. Start by making a *complete* list of *every* electrical device, receptacle, appliance etc that is permanantly connected to your wiring and identify which fuse/breaker controls which circuit. Then figure out the absolute minimum that you intend to run from the generator, and "layers" beyond that. The "layers" could be something like: "minimum", "convenient", "nice to have" and "full service". The more you want, the more it'll cost.
If money is no object, the simplest is to hire a pro and specify complete backup, automatic transfer and let him/her specify the equipment. Unless you have a huge wallet, that's probably a non-starter, too.
Howard Eisenhauer wibbled on Wednesday 24 February 2010 22:37
I second that. Not sure about the paranoia re: insurance, but what *is* very important, is that the OP does not under any circumstances back feed into the utility supply. Otherwise, in a power outage, some poor linesman up a pole gets a live line he thought was dead.
The IEE Wiring regs in the UK have something to say about local sources (be it generator, UPS) - does the USA NEC code have regulations on this too? IIRC, the NEC is available for free online (we have to pay for a copy of the IEE Regs) so there's no excuse for not reading them.
I personally would go for a "proper" transfer switch. It's not just about switching over - it's about maintaining required levels of mutual isolation (eg contact separation distances etc) too.
Don't forget issues of earthing too - in the UK, we cannot count on the utility earth (ground) in such a case, we must provision a local earth rod for local generation with all that entails (eg correct use of RCD/GFCI).
Cheers
Tim
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Tim Watts
Managers, politicians and environmentalists: Nature's carbon buffer.
The grid is home brew. Otherwise we wouldn't need a generator for power outages. The question is if I'm going to let their incompetence ruin my own grid... and they're not getting any of my electricity, either.
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