Generators and Back-up power

Ryan · 2004-01-07T15:10:15+00:00

We have an rural machine shed (100 amp single phase) mostly used to storefarm vehicles and also is our workshop where we have the mill, lathe,welder, etc. It is prone to power outages more and more these days and at weseem to be working in there everyday so it obviously becomes veryinconvenient when the power is out. As it turns out, we are one of threeproperties in a rural area that has "easily tripped" power. We are alwaysthe first to lose power, and the last to get it back up. I'm not sure whatthey call it, but the part they always have to fix is on a power pole a fewmiles up the road from us, and it looks kind of like a paper clip. Anyways,usually the power flickers for a bit, then poof, it is off until they send aservice truck out to repair it.So last month we bought a 7500 watt generator to make life smoother and atleast keep the heat and lights on Here is where my question comes in. Someof the people around here say you can go to the breaker panel and turn offthe main breaker (from the grid) and make a "cheater plug" to back-feed thebreaker panel thru a 240volt outlet (of which we have several "welder" plugsthat would be ideal for this). What are the thoughts of the group to dosomething like this? I understand it is a shortcut, but if one was sensibleabout it is this a viable temporary option over the "transfer switch" thelocal electrician wants 1000 bucks to install?Thanks in advance to all helpful posters, Ryan

Jan 07, 2004 24 Replies

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Gary Coffman 22 years ago

I use the same box in my house. It is Square D part number QO4-8M6DS-GP. Home Depot carries it. I have one 30 A

240 volt load breaker for the furnace/air conditioning (takes up 2 of the available positions), and the other two are duplex 120 volt 15 A breakers feeding four "critical" circuits in the house.

The interlocked main breakers in the transfer panel eliminate the possibility of backfeeding the utility or damaging your generator.

Installing this is simple. Just mount it next to your main panel, feed its mains side breaker from a 60 amp breaker in the service panel, feed the generator breaker from the generator, and move the load wires from their breakers in the main panel to the new load breakers in the new panel. It took me less than half an hour to mount and wire it. It is just like any other simple residential wiring project. You do not have to pull the meter to install it.

Now there *is* another sort of transfer panel. This type goes between your utility meter and your service entrance panel. That one would cost lots more, and you'd have to pull the meter to install it safely (requiring a permit for a reconnect in this jurisdiction). That's probably the $1000 solution the electrician was quoting.

But a 7500 watt generator isn't going to be able to carry a 200 amp service panel anyway, so you don't want that sort of transfer switch. The little 60 A Square D transfer panel is perfect for this sort of job.

Gary

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Bob Engelhardt 22 years ago

Several replies have voiced this sentiment and it is the official position of the power company and every other authority that you could think of.

BUT, it seems to me that as a _load_ the power-less mains coming into your house look like a dead short! I.e., the combined loads of all your neighbors as well as the load back through your local pole pig. In which case your generator breaker would blow in about a millisecond. The chance of a lineman touching the line AND being grounded during that ms would be very small. And even if he were, the momentary shock is unlikely to be fatal or traumatic.

The exception, of course, is is the power outage is in your drop. I.e., isolated from your neighbors.

Strictly my opinion of course. I'm sure there are those who will disagree :-)

Bob

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Carla Fong 22 years ago

When we rewired our house we put in two panels side by side in the basement - the main one fed from the meter and a second (smaller) panel that carries just the 'emergency' circuits.

We put a two pole breaker in the main panel and fed it to a dryer outlet adjacent to the main panel and just under the emergency panel.

We connected a dryer pigtail to the feeder lugs in the emergency panel and plugged it into the dryer outlet from the main panel.

The generator feed comes from the external generator location to another dryer receptacle near the first one. We also connected a single ceiling light fixture directly to this feeder.

When the power fails, we crank up the generator, unplug the dryer pigtail from the main panel and plug it into the generator receptacle. Seems like this always happens in the dead of night, so putting the light fixture on the generator feeder allows easier access to the arrangement... The voice of experience..

Cost about 20 bucks for the pigtail and two receptacles. Idiot proof. (I think)

Carla

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