Re: [Hazards vs. code] Re: Backfeeding one subpanel via the main from another subpanel

I really agree with you Ralph and certainly a person who is careful can do the "trip main breaker/suicide cord" thing. The problem is, as soon as people stop warning folks a stupid person will try. Electrical accidents are usually a series of unlucky breaks and flukes. I agree you might not kill a lineman but you might get the guy next door who is doing his own dumb thing.

I still think there are ways to do this without a few hundfred bucks worth of new stuff but you still need a transfer switch of some kind ,,, even if it is just a "3 way" snap switch and a plug socket for your furnace disconnect. (fridge outlet or whatever).

field service of industrial / electric / heavy equipment can be quite hazardous even to trained personal. why add to the problems?

you unload a gun before cleaning it. what happens if someone can load the gun unbeknownst to you while working on it?

if the "lines are down" who is to say what the load if any will be? you cannot assume there will be a load. note: pole transformers work both ways.

220 fed back will step up to high voltage.

or "fuse" into a sold glob of metal and plastic. or maybe just turn the gen into a motor. note: no gen specs have been included.

safety concerns deserve constant repetition.

thats "might"

my friend had been cooking on an electric stove. she began getting electric shocks. the insulation has worn broken down on the heating elements. i replaced a couple with grounded retrofits and explained as best i could that

220 at the current in a stove burner could kill several elephants at the same time.

is it fear mongering to be concerned enough that when you observe a potentially dangerous situation that you emphatically recommend a course of action?

(note: no live elephants were injured in my explanation) :)

to what end? and why ask here? if you need injury / death statistics i doubt that a newsgroup is the place to ask. would you believe the answer?

it appears you are in California. these companies are probably you beast lead to a specific answer about lineman injuries. Pacific Gas & Electric, Southern California Edison and San Diego Gas & Electric

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Generally though Id say there is not enough current available from the average home generator to kill a lineman.. linemen make it a point to be very well insulated...it could of course, just as 110 can kill a person...but its not real common I dont suppose from smaller home gen sets.... the surge amperage is very limited. with line power you have almost unlimited surge capacity available. thats the difference.

over 10 hp, into the 220 volt range it would be more dangerous...a 100 hp commecrical gen set could be very dangerous.

Phil scott

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Thats relevant of course... but still very low amperage from most home gen sets...so the net wattage available to perform and electrocution is way down... possible of course..and a consideration but not what you see in live utility lines.

for instance a 40 amp 110 volt gen set, 460 watts... if it leaks back though a line tranformer to 6000 volts, would translate to less than a third of an amp... high voltage but not much current flow ...electrocution would be possible but stretching the envelope.

Phil Scott

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This topic comes up weekly on alt.home.repair.

A while back someone cited a recent actual instance of a lineman being shocked by a backfed circuit; though I don't think he was killed.

Still, what you say is essentially correct. They only time it would be truly dangerous would be if the lineman was working almost directly on wiring going to your house. But it is also true that backfeeding is a pita and a transfer switch is easier to work with once you have gone to the trouble of installing it. It also avoids the embarressment of running the generator for a few hours after everyone else gets their power back.

It is claimed that people running generators can get checked out for compliance during blackouts, and the penalties are severe. Never heard of that happening either; I would expect they can't spare any personnel for that duty.

I have seen reports of several, but I don't know how many occur.

Many accidents occur to power line workers for various reasons, so obviously these safety procedures are either not always followed or not always effective. This leaves open the potential for a generator backfeed accident.

An electrocution can occur at much lower cuirrent than the trip rating on the generator breaker.

Or, the generator breaker may blow up because it can't interrupt the available fault current from the utility side.

If you use a stinger cord, you could kill linemen, blow up your house, or electrocute yourself.

Ben Miller

in this discussion so few parameters are set forth that it necessitates generalized observations. it may be a typo but i would say that a 40 A 110 V gen would output something like 4,400 VA or watts into a non-reactive load. when i use your assumption of 6,000 V my handy computer calculator comes up with .73 amps. (i'm ignoring the loss in the 7 extension cords in series that are probably being used and all other losses too!)

i still have a feeling that i'm missing some real world factor like how much power will a 5 kW gasoline powered gen output under a near zero ohm load and for how long before a magnetic breaker opens or the engine stalls?

| I would bet that these problems actually hardly ever occur. Why? | Because | (a) Linemen will treat any line as energized, except when they have | grounded and/or disconnected it themselves and can verify that it | is and will remain safe.

If the service drop to a single home has come loose from the pole, the lineman MAY ... when working for 24 hours straight during a major emergency situation ... get sloppy and fail to properly test for voltage on the wires coming from the house.

Mentally, they know their own lines have lethal voltages. But after working with hundreds or thousands of homes, none of which have any voltage on them, they could just fail to test that next one with the generator running. That failure might be because having done so many so fast, they thought they did check this one.

And there is the chance the situation changes while working on it.

| (b) If you try to backfeed the grid (which means backfeeding a lot of | electricity users at once), the breaker on the generator will | simply pop due to overload, so the situation dangerous to a | lineman will correct itself very quickly.

This is only if the line *is* connected to the grid. If the line to the house is down, there is no such backfeed taking place. It MIGHT be sizzling on the ground ... or not.

| (c) If a generator is connected to a de-energized utility line, and | then the utility line comes back on, the breaker on the generator | will simply pop long before the generator is damaged (after all, | that's what the generator is there for).

You assume it is connected. When major storm damage takes place, the lines can be done right there. I've seen home service drops down just due to small thunderstorms. Imagine what 4 hurricanes in a few weeks can do.

| By the way, I am in no way advocating that people connect their | generators in an unsafe, non-approved or illegal fashion. Even if | these problems occur extremely rarely, you really don't want it to | happen to you. But I'm getting quite tired of the constant repetition | of mantras such as "if you use a stinger cord, you will kill linemen | and blow up your house", which I think is just paranoia and | fearmongering.

Certainly the "will" part of it is overblow. It could be worded better. But it is important to realize that you could be energizing a downed line and not know it because there is no load there. You _could_ kill a lineman, or someone else that happens across your wires and does not understand that power can be coming the other way.

| Again, I'm not asking for opinions whether connecting generators the | wrong way is a good or bad idea (I know it is a bad idea). I am | asking for verification that it actually causes harm and continues to | do so.

I do not personally know of a case where it has. But I don't work for an electric company, nor do I know any linemen. I have listened in on the radio traffic following a big ice storm that took out thousands of poles and nearly all the service to the county. While I was lucky and had my power back on in 2 days, some parts of the county waited 2 weeks. Some areas lost _every_ pole as far as you could see (which was quite far given the flat terrain). In that radio traffic, supervisors were very regularly warning the linemen of various safety procedures. They may very well have been tired of hearing it, but they would also be tired from the work, and could get sloppy. I think that was the right thing for the supervisors to do.

Although I don't know of cases, I do know it is very plausible to happen. If someone does connect a generator wrong and a lineman is killed, then I would hope to see them charged with 2nd degree manslaughter.