I read a pretty nasty story about this happening. Yes, it burned out the generator, vigorously enough to ignite the fuel tank. This, in turn, was vigorous enough to ignite the camper that it was sitting near.
It seems this method is the commonest one for which they sell transfer switches. However, it has the disadvantage that you have to plan in advance which items get generator service. In my house, with baseboard electric heat and multiple bedrooms that get occupied and deserted at random unpredictable times due to family members coming and going, I think this disadvantage outweighs the advantage of not needing to remember which breakers to shut off (and besides they’re all clearly labeled).
My hope is to install a transfer switch that powers the whole panel, and conditionally manage which rooms get power, which might include “none” if it’s laundry day. I have a 10 kW generator and think I can fit my requirements into its capacity with a little care – and I believe I’m NOT doing anything dangerous. We’ve lost power for as long as 11 days, including well water and heat, which is a tough thing in a country setting with animals to take care of. But a 200 ampere generator is a pretty pricey proposition. Any problem with this approach, other than the power management choices I’d have to make during an outage?
Slight hijack: when the homeowner is disconnected from the power grid and using a generator, how does he typically find out the utility has come back into service? Is there such a thing as an indicator light on the utility side of the transfer switch? or does he have to keep trying shutting down the generator and all, and then changing the transfer switch position?
When you have a sub-panel, the sub-panel’s main breaker is sized for the capacity of the generator. That way if you overload it you’ll just pop the breaker before you cause any damage.
If you put the transfer switch before the main breaker panel, you can’t rely on the panel’s main breakers to trip before you overload the generator. That means you’ll need a separate breaker installed on the generator feed, sized according to the generator’s capacity, so that if you do overload the generator you’ll just trip the breaker instead of causing harm.
As long as you do that, there’s no danger of back feeding onto the main line and there’s no danger of overloading the generator, so it’s safe. The worst that happens is you pop a breaker.
The utility company can check that the lines are dead at the moment of the check, but they may have a hard time guessing when the homeowner is likely to refill his generator, turn it back on, and plug it in.
My solution is a mechanical interlock on a pair of breakers by the main feed to the house - I can only activate the generator jumper if I’ve turned off the main feed. Once that’s done, I have power for the whole house. Not enough to run everything at once, but I can run just about anything in pieces.
ETA: I’m glad you’re changing your plan. Also, I agree with the layers of redundant safety comment.
They do make transfer switches with an indicator light to tell you that the main power is back on. Some of them also have a yellow warning light to indicate that your generator is getting close to its maximum capacity.
Thumbs Up!
The utility may very well check for backfeed before touching the lines. But what then stops the homeowner from turning on the generator when the workers are already handing the previously dead lines?
A stupid Q:
(I’ve got 60+ years of this kids, don’t try this at home!):
From an electrical standpoint, what is a “Transfer Switch”?
It sounds like a name to use to charge 10x the price of a 3PDT (house is switched to either line or aux).
Think of those blade switches from grade school science - imagine such a switch with 3 blades (US residences have 2 black, 1 white - do not cross) and contacts on each side of their hinge - the house is wired to the blades. The grid goes into one side of contacts, the generator is wired to the other set of contacts. Flip the switch to the right, and you’re on the grid; switch it to the left, you’re on the generator.
The commercial ones I just looked at have such switches on individual circuits, with indicator lamps and C/B’s - a great deal of trouble.
engineer_comp_geek’s suggestion of gathering all circuits you want to be able to run off your generator into a separate sub-panel is, IMHO, optimal. Now, you are simply switching that panel instead of the entire house.
p.s. - how can the lineman protect himself against the idiot who kicks in his generator while the lineman (having already check and found line dead) is working on the transformer?
Short of taking out entire acres of houses (ask PG&E, San Mateo, early 2000’s) by grounding an entire distribution switch’s feed. I doubt they can protect at the transformer-on-the-pole level.
The only way I can imagine a lineman’s life to be assured against all idiots with generators and suicide cables is to have the ability to ground any range of circuits from anywhere.
PG&E had a fellow follow procedure: dis-connect power to switch, ground switch (fail safe against someone energizing switch while it was being worked on).
Work completed.
Somebody neglected to remove the ground cable before energizing switch.
On the plus side, it proved that the switch grounding technique works.
The switch was in San Mateo; houses affected stretched into San Francisco.
Oh, while we are into backup generators - real ones do not run of liquid fuels; they use gas (natural or propane). I saw a note in the news a couple of days ago - to date, 3 in the area dead from carbon monoxide from their “ready for anything” generators.
Yea, that’s how a lot of people do it around here.
It works. I would do it if I were desperate. But I wouldn’t recommend others to do it.
I was wondering this myself. Luke the Lineman tests the fallen lines, sees that they’re dead, gets to work and is the middle of repairs then Harry the Homeowner fires up his generator and Luke gets cooked. I’m not seeing any formulation by which this is anyone’s fault but Harry’s.
a generator subpanel
gives you a number of slots for essential circuits. you flip the handle to feed those circuits from the mains or the generator. when you are using the generator to feed those circuits you are safely and legally (USA) disconnected from the mains.
these are affordable devices.
people run them in their garages and die.
the generator should be outside.
if you want to shelter the generator (good idea) kick the dog out of the dog house and throw that (dog house not the dog) over it.
I’m on day 6 here in mid Michigan of no power. I have a propane genny now, with a proper automatic transfer switch. There are manual switches. I have hillbilly rigged a generator into my panel prior to getting my present genset. I would pop the mains, wire a 110 into each side of the bar, so I would be backfeeding the panel. A manual switch does essentially the same, except it isolates the utility lines. When doing this, you know when the utility is back on when you neighbor’s lights come on…
Auto switches do a couple of neat things:
They come on automatically, so if you aren’t home, it doesn’t freeze up.
They sense the load, and balance it out, so that you don’t overload the genny.
They shut off when the utility comes back on line. I live in a rural area, and once ran a genny about 4 hours more than necessary, using the hillbilly rigging.
Always buy the biggest generator you can. I have a 15kw, and wish I had a 20Kw or 25 kw.
Propane or NG is best.
My Two Cents
We’ve had what I consider to be an unreasonable number of multi-day outages here (NH) in the last few years. During the first one, it was clear to me that I would be out for a week plus, with several days of 0F forecast. I was able to get a relative to drive one to me from an unaffected area. One of the advantages of being an early riser, as he was a couple of hours away and by the time he paid for mine, the store was sold out.
I Rube Goldberg’d the two essentials (heat and well) by disconnecting them from the mains and wiring them directly with Romex, and managed the other items (refrigerator, some lights, coffee maker, etc) with extension cords.
I didn’t regret the $1000, but I never thought I would use it again- after all, even a four or five hour outage can be more or less ignored. Well, after the THIRD time in five years, I consulted an electrician. I was going to go for the transfer switch, but he convinced me to go with an “InterlockIt,” (trade name, there are probably others) and I am glad I listened.
On the generator end, this is the usual- L14-30 outdoor receptacle. I ran 6ga. to the panel, into a 30A breaker, which is located at the top right of the panel. The Interlockit is just a metal switch which makes it impossible to have both the main breaker and the feed breaker in the on position at the same time. So to switch over, I just kill the main and turn on the feed.
The upside: I can energize whatever circuits I want, and that could well be different things at different times. For instance, if the outage goes on long, the young children can make the no laundry a real hassle. If I had limited available slots I don’t know that I could justify one going to laundry.
The downside: It is my responsibility to make sure that I turn all breakers off and then back on one at a time when the generator is back up, lest I hit the generator with a huge sudden load, and I have to take responsibility for spreading the load- this arrangement would make it very easy to become forgetful and try to run everything.