Posted by EHWollmann on November 27, 2009, 6:43 am
Posted by Jim Wilkins on November 27, 2009, 8:04 pm
Several cycles could pass through before a large contactor (>10A power
relay) opens and it will need to break a very substantial arc current.
IIRC the short circuit current rating of a utility pole transformer is
around 5000 Amps.
Posted by EHWollmann on November 27, 2009, 5:26 pm
Posted by Ron Rosenfeld on November 27, 2009, 8:45 pm
needed. All done.
It seems my news server missed a few messages, and this appears as a reply
to mine, which I'm sure you didn't mean.
I've had two different setups,in different homes, to avoid the problem
alluded to by the OP.
1. A 200A DPDT manual transfer switch connects the house to either the
grid, or the generator.
2. An automatic transfer switch, also 200A, that when it senses an absence
of grid power for some length of time (maybe 15-30 seconds) will start up
the generator and then, if grid power continues off for a while (can't
recall how long), throws the switch connecting the house to the generator.
When grid power is restored, after some time delay, the house is switched
back to the grid and the generator stopped.
Both of the above required a certified electrician to do the wiring between
the meter and the main circuit breaker box in the house. And, in neither
case, is it physically possible for the generator to be connected to the
There are also "boxes" that merely switch designated house circuits. I'm
not familiar with them but again, the switching precludes ever having the
generator physically connected to the grid.
Posted by Jim Wilkins on November 27, 2009, 4:36 pm
On Nov 26, 11:21pm, Ignoramus17202 <ignoramus17...@NOSPAM.
The real hazard is applying generator power back out to the grid when
it's down, and repairmen might be working on it. Around here the
linemen short the high-voltage lines to ground before starting repairs
and the fire department checks out any generators they hear running.
The idea passed around to shut off the main breaker and connect a
generator to the wiring through a home made male to male adapter cord
in a clothes dryer outlet. We lab techs call those "death cords" when
we are ordered by inexperienced engineers to use them in test setups.
I hope that isn't the potential grid connection you mean.
I first ran extension cords from the generator to power the few things
I really need, then decided they were a tripping hazard in a dark
house and bought a few second-hand UPSs to have power right where it's
used, no cords on the floor. I run the generator only a few hours a
day to watch TV news and especially weather and to recharge the
batteries. The Tripplite recharges much faster than the APCs.
This site and its local links are better than weather reports to show
if I can work on storm damage to the house or should cover it up: