Making a generator interlock kit

I am considering making a generator interlock kit. What it is is a mechanical device that engages both the main breaker in the electrical
panel, as well as one of the individual circuit breakers near the main breaker. Its purpose is to prevent both breakers from being on at the same time.
It is not difficult to imagine one, there would be a flat piece cutout enclosed in some rails that would move and permit the circuit breaker to be engaged only if the main breaker is in the down position.
I would write up exact drawings on paper and make it from 1mm thick galvanized steel sheets that I scrounged somewhere. One challenge is to make sure that the flat piece slides in something very smoothly without getting stuck. It would be hels from the sides by some "channels". I would like some ideas on how to make very smooth sliding combination of the piece and the holder.
Any thoughts will be appreciated. I can write up and post drawings if my explanations are poor.
For an example of an interlock kit see
http://www.interlockkit.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=GIT&Product_CodeP10&Category_Code=SD
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"Ignoramus32538" wrote: (clip) to prevent both breakers from being on at the same time. (clip) ^^^^^^^^^^^ It's neat, conceptually, but a lot of work to do what can be done more simply with a double throw switch.
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wrote:

A suitably rated double throw, double pole switch costs $329 at least, and would involve serious effort to install due to heavy cables, need to secure a permit, utility disconnecting and reconnecting the meter, etc.
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| I am considering making a generator interlock kit. What it is is a | mechanical device that engages both the main breaker in the electrical | panel, as well as one of the individual circuit breakers near the main | breaker. Its purpose is to prevent both breakers from being on at the | same time. | | It is not difficult to imagine one, there would be a flat piece cutout | enclosed in some rails that would move and permit the circuit breaker | to be engaged only if the main breaker is in the down position. | | I would write up exact drawings on paper and make it from 1mm thick | galvanized steel sheets that I scrounged somewhere. One challenge is | to make sure that the flat piece slides in something very smoothly | without getting stuck. It would be hels from the sides by some | "channels". I would like some ideas on how to make very smooth | sliding combination of the piece and the holder. | | Any thoughts will be appreciated. I can write up and post drawings if | my explanations are poor. | | For an example of an interlock kit see | | http://www.interlockkit.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=GI T&Product_CodeP10&Category_Code=SD
I've always wondered what it would take to take a slightly rewired reversing motor starter and connect it as an interlock. Don't know how big the rating would have to be (five?) as I forgot all that stuff when I got out of the trade awhile back. One simple switch, wherever you want to put it to make it switch over from the mains to the generator. You don't even have to get out in the cold.
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Ignoramus32538 wrote:

http://www.interlockkit.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=GIT&Product_CodeP10&Category_Code=SD
What you are after (I think) is a transfer switch. This is deigned to utterly eliminate the possibility of backfeeding the genset output into the grid. Switching 'breakers' does not meet this requirement! With certainty your local power company will *not* approve any home brew solution. Installing such a non-approved switch may guarantee your being in the dark should they find out about it and will also put service personal at risk. Go with an approved (and admittedly expensive) transfer switch.
Regards. Ken.
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snip---

Yep, that's what they are.

Yes, it does, so long as the two breakers, which are mounted opposite one another in the panel, has a permanently affixed bar between the two handles so when one is on, the other must be off. There's a commercial panel sold that works like that, for the very purpose of transferring power to a panel from a generator, and disconnecting the panel from the service. I have one mounted in my shop. It's a modified Square D panel, sold by Eylander Electric, in Everett, Washington (no affiliation, just a satisfied customer). The panel is unlimited within reason in that the appropriate breakers can be installed to match the output of the generator at hand.
Harold
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Yep. An interlock kit, supposedly, does meet the requirements.
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On Wed, 26 Jan 2005 19:03:42 -0800, "Harold & Susan Vordos"

http://www.msen.com/~pwmeek /
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Remember that the generator neutral is connected, permanently, inside the main electcical panel, to the ground/neutral buss bar. The connection is very solid and the ground wire from the panel is connected to the copper water pipes. I have seen it.

Thanks, I am looking at that thread right now.
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On 27 Jan 2005 14:10:12 GMT, Ignoramus8735

You obviously did NOT read the thread I requested you read before replying. The Neutral-Ground bond in the (widely varying by state and jurisdiction) system is NOT reliable. It usually depends on a single screw through the neutral buss into a paint-filled hole in the main panel, as well as bonds of unknown quality through unsupported wires to a ground clamp stuck to a possibly rusty water pipe, through insulating gaskets (which may or may not have been properly bypassed) on the water meter.
And you think this is a good bet to protect the life of a soaking wet lineman who is up a pole doing his best to restore YOUR power. How good is that neutral-ground connection? Say 999/1000? You think that a couple of hundred bucks for a real transfer switch is a bargain in return for a 1/1000 chance to kill the lineman? Think a little before you jury rig something that the life of another person depends on. Risk your own if you think a couple hundred bucks is too much, but you have no right to make that decision for someone else.
-- --Pete
http://www.msen.com/~pwmeek /
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But even a three pole transfer switch at each branch circuit won't fill your bill. The bond at the panelboard means that even once the neutral is interrupted you could still see a fault to *ground* at a piece of equipment. That makes the messenger wire to the pole hot by your reconning.
So it would seem you would advocate some way to open the ground wire out to the pole as well.
Jim
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Apparently peter did not see my question, so I am posting the exchange again, as I am truly interested in his take on this issue. According to him, one would need to completely isolate a residence from teh pole to make it safe for linemen - meaning a three pole interrupt at the service entrance, or a four pole interrupt at each branch circuit, which isolates every conductor including the grounding conductor.
Jim
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wrote:

My understanding is that there are only three wires between the service entrance and the transformer: two hots (L1 and L2) and a ground/support cable from the center tap. The first place where the ground and neutral are separate is at the main service disconnect, right after the meter. This is also supposed to be the only place where they are bonded or connected together. The ground should be hooked to a good earth ground (two 16' copper rods, a few feet apart with thermite-welded connections to the braided ground wire, at my house); it should also be connected to the house side of the plumbing and to any structural steel in the building. BTW, the plumbing is grounded **BY** the electrical ground here; it doesn't provide the ground. I have a buried plastic pipe out to the well with a 12 ga. tracer following it. No trustworthy ground there.
My transfer switch is maybe a little more elaborate than most. It is a Zenith in its own 7'h, 3.5'w, 1.5' deep box. On loss of power, it waits a second or two, fires up an 80kW Koehler natural gas gen set, lets it stabilize, tells the house computer to shut down large loads like air-conditioners, transfers to the Koehler, and then restarts the heavy loads one-by-one. If the heavy loads are more than the generator can handle, the house computer runs them in rotation. When power returns, it monitors for about ten minutes to be sure the power is back for good, and then transfers back to line power. It also test runs the genset once a week and phones the service company if it finds a problem.
BTW, it transfers the neutral as well as the two hots. All grounds stay connected, so the generator frame is grounded to ground, but the coils are connected to the house neutral and the two hot leads. Power flows through hots and neutral but the neutral voltage is held to ground potential via the neutral- ground bond in the main disconnect.
-- --Pete
http://www.msen.com/~pwmeek /
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I am curious, are your large loads like A/C so incredibly energy consuming tat an 80 kilowatt generator cannot handle them? I have hard times believing that. How big is your house? We have a almost 5,000 sq ft house (including a finished basement), and a 28 amp A/C, which works out to about 7kW.
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On 29 Jan 2005 15:54:49 GMT, Ignoramus2396

There are 7 condenser units of various sizes, as well as a lot of other motor loads. I think I can run most likely combinations, but starting them all at once might be a problem.
The main house disconnect/breakers are 800 Amp. Not so much for the load capacity, as to meet code-allowed numbers of sub-circuits. The 800 Amp main panel has 12 (or 13?) 200 Amp sub-panels connected to it with 40-odd breakers in each. Then there are 2 or 3 Lutron panels associated with each 200 amp panel which control (via relay or dimmer) up to 32 circuits each.
I joke that I can send Morse Code to the power company by having the smart-house simultaneously connect/disconnect all the loads at once.
How big the place is is a good question. The architect calculated all floor areas that have a roof over them. It came to over 18,000 sqft. I think a more realistic assessment is in the 10-12,000 sq ft range. You don't count attics, non-living basement areas, porches, or attached garages.
The website below is way out of date, but you can get an idea what we are doing. -- --Pete
http://mywebpages.comcast.net/ford-rd/house /
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Peter W. Meek wrote: ... The ground ... should also

Why would you want to ground the plumbing, if it's not grounded by plumbing connections? It seems to me that by doing so you're just providing lots of places for ground faults to occur. Possibly through humans.
Why not just let the plumbing be independent of the wiring?
Just asking, Bob
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On Sat, 29 Jan 2005 10:23:37 -0500, Peter W. Meek

This is the way it's wired at my house (Alberta Canada) i.e. no ground wire goes to the pole although the neutral is bare and wound around the two hots and is in effect grounded as it is direct burial to the pole. In my case, the in-house ground wire is connected to the metal well casing.
In regards to lineman hazard, do they not typically isolate an under repair line fault from the upstream source *and* short the hot(s) to ground or neutral whilst they are working on it (to avoid said shock hazard)?
I'd also be interested in comments on my gen hookup method. My gen only puts out 120VAC so, to supply both halves of the breaker box, I plug the gen (in parallel) into both sides of a split receptacle located in the garage, this providing 120V to all 120V circuits in the house (the 240V circuits are not functional as the voltage is the same on both sides). Be gentle please............:)

Laurie Forbes
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On Sun, 30 Jan 2005 02:02:43 GMT, snipped-for-privacy@nospam.nospam wrote:

Commercial transfer switches only switch the two hot lines - the Neutral and Ground are all bonded and stay connected. They stay bonded to ground rod(s) and cold water grounds at the house, and they stay bonded through the ground riser and butt plate ground on the pole. (Or a ground rod system at the manhole for an underground feed.)

I'm not a power lineman, but that's how I see them doing it all the time - it's either dead and grounded for safety, or hot and they've got line hose and blankets over everything. And they're wearing rubber gloves and/or working with hot sticks either way.
And "A Lineman's Pencil Has No Eraser" Their first big screw-up is likely to be their last, so they are really careful... That's a job I don't really want, bad enough I work with 120V hot.

You have to be /really/ careful about your phasing if you feed your house from a 120V source like that, Laurie! If you have two circuits in one conduit sharing a neutral (3-wire circuit) and you feed them both with 120V from the same phase, you can overload the neutral wire easily. Load down both circuits and run 40 amps through that 12-gauge white wire back to the panel for very long, and you'll have both a power outage /and/ a house fire to worry about.
In your case, I'd install a separate transfer switch & sub-panel for the emergency-fed loads. And from there out to the loads, rewire those 3-wire circuits that share a neutral with separate ones for each line, to eliminate that hazard. If your house is wired in Romex you won't be repulling anything like you could in flex, you will be better off to run separate new lines to those critical receptacles.

Where did you get this beastie? Sounds like it'd be perfect for people like me so I don't have to way over-buy the generator plant (100KW for a residence when I have a 10KW available) just to be sure it can take up the whole load at once without stalling.

I'd want to see the wiring diagrams on this one - the NEC might not take kindly to switching the Neutral, and I'd want to research the codebook before hooking it up. Seems rather counter-intuitive to me - the LAST thing you want to risk is an open neutral on a 120/240 or 120/208 system.
Open that neutral and make an unbalanced load, and all sorts of really nasty things can happen... ("Snap!" "Crackle!" "Pop!")
--<< Bruce >>--
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Electrician for Westend Electric - CA726700
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On Sun, 30 Jan 2005 07:46:28 GMT, Bruce L Bergman

NEC calls systems with their own separate neutral a "separately derived system". Separately derived systems must have their own ground (ground rod), and they must bond their neutral to their ground.
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On Sun, 30 Jan 2005 07:46:28 GMT, Bruce L. Bergman

Thanks Bruce - I appreciate your comments about overloading the neutral. I should have however included in my first post some additional info. In my case, I have #10 wire running from the garage to the breaker panel (which should be good for 30A). The breaker is also 30 A. My gen is a 3500W unit which limits its output (under normal conditions at least) to about 30A. So, I think I'm OK in that regard although the split receptacle in the garage and the short run of #14 going to the junction box would be overloaded under max load. I've examined it when the gen is working hard however and have not noticed anything getting particularly warm - I probably should however at least upgrade both receptacle and wire to 30A capacity.

You're correct of course - that would certainly be a better way of doing it.
One other thing I've been wondering about if you could comment. It seems to me that the powering both sides of the breaker box with in-phase voltage might result in voltage cancellation at the pole transformer such that a feedback shock hazard might not then exist (not that I would consider dispensing with a disconnect in any case).
Laurie Forbes
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