alarm circuit question

The relay is relatively slow, 10-15ms response time. Worst case is a total short with the gen, or a one AC cycle short with the gen. What you need is a automatic transfer-switch. And you may need to switch L, N and G if it?s a secondary branch. Spend the extra bucks and do it right.

Cheers

A potential candidate for the 2010 Darwin Awards?

No, you get an electrican who can interrupt the power to do the connection(s).

Neat trick, but that's no the issue. You need to prevent backfeeding the power system even when the power is OFF.

This absolutely, positively won't work the way you think it will. It also will violate both safety and probably legal rules.

Oh, no... Worse, a potential candidate for a manslaughter charge, and

Jon wibbled on Sunday 28 February 2010 03:30

Can you not get the supply made dead by requesting the supplier remove the main fuse to your drop? I assume you have a main fuse (well, fuses)?

OK, I'm in England, but I went one better - I needed my line made dead for a day to install a new breaker panel, so I tool the chance to add one of these:

(Isolator switch, top right). It is actually the one that *some* electricity suppliers fit, but not mine alas. Technically I'm not supposed to put it in that box (belonging to the supplier) but I reached an friendly agreement with the supply fitter.

At least now, I don't have to call them if I need to make my cables dead, and lose power for the whole day (they pull the fuse in the morning, and come back in the afternoon when they feel like). And they charge each time...

Is there a neutral there? I though you lot were 120-0-120 or does that vary? Because you would want to isolate the neutral too. Also the use of the utility earth (ground) is in question in the event of a power failure.

With all due respect, your proposal is *wrong* on many levels and I can't believe I'm seeing this on an engineering forum. I don't know your codes, though I'm fairly up on mine, but the basic tenants of good design are pretty universal.

You need a break before make changeover device which will switch all lives and the neutral at least, mechanically interlinked and with guaranteed isolation (contact separation) of all conductors (probably including ground, check the NEC). Note, other ways of achieving this could be to present key circuits (eg heating supply to oil burner, lights) on a plug which is either plugged into a suitably fused utility side socket, or unplugged and replugged into another totally isolated socket fed by the generator. Indeed this is an approach occasionally used in the UK where someone may which to power the gas/oil heating system and maybe a lighting circuit from a small genny. This would be the recognised poor mans method, though it is sound and not automatic.

Anything else is a disaster waiting to happen. It is also not just about you

- you have obligations not to back feed your generated supply into an otherwise dead utility supply and possibly kill an innocent third party engineer.

Sorry to be harsh, but as you seem to persist in this dangerous, unnecessary and cheapskate approach without any regard for even the most basic levels of good design that would be obvious to a half clued up trainee electrician, you need telling.

Don't be a cheap sod. Either don't do it, pay someone to do it or buy the appropriate equipment and stop trying to use the crap in your garage spares box.

And FFS go and read your bloody regulations man:

Tim

Hook up a harmless shock box to the alarm circuit. Guaranteed efficacy.

--- That circuit isn't fail-safe, it's fail-deadly.

Here:

Assume that mains power has failed, that the contactor's coil is no longer energized, and as a consequence the contactor's contacts have gone to their normally closed state.

Now assume that the generator starts and, once it has come up to speed, is connected to your house wiring.

So far so good, but what happens when the service goes hot?

1. Until the contactor's contacts open, which takes time, the service and the generator will be connected together (shorted) with no regard to phase and there will very likely be some very nasty things happen.
2. And what about when someone's up on a pole fixing whatever it is that caused the service to go down in the first place? Since you've provided no isolation between the mains and your generator, whatever the generator puts out will appear on the lines coming into your house, which means all the other houses connected to the secondary of the transformer you're connected to.

And worse, the service person won't know that the transformer secondary isn't hot and... "Involuntary manslaughter" I think it's called.

1. Your insurance company's going to have a big grin on their face when the fire inspector finds your circuit.

Get yourself a licensed electrician, tell him what you want to do, and pay the big bucks so you can sleep at night without having to worry about burning up the kiddies.

--- That doesn't look like it'll work but, even if it did, what's to keep normal audio on the speaker from turning on the alarm?

JF

After your conviction for manslaughter due to your generator wiring scheme you will have no problem waking up in prison. Art

Ok. Here is your wake up call.

The code requires that the transfer equipment make it physically impossible for the generator to be connected to the utility power lines UNDER ANY CONDITIONS.

Common sense requires that the transfer equipment make it physically impossible for the generator to be connected to the utility power lines UNDER ANY CONDITIONS.

Safety for personnel requires that the transfer equipment make it physically impossible for the generator to be connected to the utility power lines UNDER ANY CONDITIONS.

Safety for equipment requires that the transfer equipment make it physically impossible for the generator to be connected to the utility power lines UNDER ANY CONDITIONS.

USE PROPER TRANSFER EQUIPMENT. HAVE IT PROPERLY INSTALLED BY A LICENSED ELECTRICIAN.

Ed

If you have no contactor on the service feed, what are you doing to prevent back feeding the generator onto the utility lines? Backfeeding is dangerous to lineman working on what they believe to be de-energized lines and is illegal.