Q: My residence has a Crouse Hinds 400A power panel. It is split with a 200A
panel at the meter, and another 200A breaker that feeds a sub-panel inside the house,
about 40 feet away. Both 200A breakers are in the same outside panel functioning as dual
main breakers. I am hooking up a 6500W generator that has 120 or
240+neutral (4 wire) wiring capability. With this panel there is really no way to safely
just flip the mains and back feed for emergency use. Don't really want to back feed
anyway. Therefore a Transfer Switch is needed.
The most of the important stuff like refrigerators (of course) are located on
the sub-panel inside the house. This raises some questions for me.
In all cases the generator will be protected by it's own breaker. An yes I do
understand you can't turn on everything anyway. My limitation is that I have an all
electric house, water heater, heat pumps and water pump.
Therefore should I wire the system by ??
a) Placing a 400 amp transfer switch outside (where the generator will be) at
the main panel and bypass everything. This requires me to call Edison and have an
electrician shut down the power to rewire the meter section into the xfer switch, routing
the output of the meter to the xfer switch then back. I cannot replace the meter section
because it is a part of the outside panel and would definitely be too much work.
b) Wire two separate Gen/Tran type panels at each panel location, connecting
some of the circuits, then connect both panels back to the generator.
Your comments???
One thing that I have noticed is the limitation of the reliance
and Gen/Tran panels with 20
amp circuits. My water heater is breakered at 30A/220 and pulls 20A/220 when on. Should I
configure a switch to feed it with 110V across the leads in a generator situation?
The only other important factor is the water pump, fused at 20A/220 and pulls
10A/220 after startup. The water pump and the refrigerator are at the top of the food
chain and the water heater is last
This generator at 220v, 6500 watts, derated to 6,000 watts, will produce 27 amps
at full load. Needless to say, the water heater at 4,400 watts running will not allow the
water pump to start. The water heater is on the inside panel and the well pump is on the
outside making manual selection of these circuits confusing and a hassle.
Do you know of any type of current sensing device that will relay drop out the
water heater (or inversely let the water pump turn on) when the generator output has
enough margin?
An my last question is how to safely protect the Generator. Do I simply connect
30A dual breakers? Am I correct in assuming the generator (Onan 6500,1800RPM) has some
short term overload/surge capability?
What components do you carry that would provide a solution here? Thanking
you in advance for your assistance.
A: It is obvious you have put a lot of thought into your options. Here are some ideas for
you to consider:
1) Is the utility meter in the same panel as the two 200 amp breakers? If it is
and the meter is bussed (rather than cabled) to the breakers, it might not be practical to
wire a 400 amp transfer switch between the meter and the two breakers.
2) It would be fairly easy to install two Reliance or Gen/Tran switches, one at each 200 amp
panel. But this would be rather cumbersome to use during an outage. You would have to read
two sets of watt meters in two different locations (4 meters total) to manage your load
total within the generator rating. And, like you noted, this will not address the large
water heater load.
3) It appears that you should try to move the well pump and any other important
circuits to the inside panel (assuming you can make space). Then you can just supply that
one panel with generator backup in one of three ways: (a) with a 30 amp switch,
or (b) replace this panel with a transfer panel, or (c) subfeed to a
transfer panel.
Here, (a) won't allow you to power the water heater but (b) & (c) will.
For option (b) the only difficulty with the transfer panel is its total capacity. It
comes with interlocked utility and generator breakers. The largest utility breaker
on some models is
100 amp. You will have to look at the number and size of the loads on your indoor 200 amp
panel to see if a 100 amp panel is sufficient. Or, you might be able to move a couple
non-essential circuits to the outside panel.
Option (a) is the most economical and easiest way to go if you can live without
the hot water heater. I have the same issue in my home that is total electric. I have
decided for now to go without the hot water heater on my backup generator. If a little hot
water is required I can always heat some in the microwave or in a kettle on a Coleman
stove. Not too convenient, but it uses about 2/3 less fuel than a gasoline generator would
to heat the same amount of water. And, if you are preparing for a prolonged or widespread
outage, conserving fuel may become a big concern. The other option
would be to install a single-circuit 30 amp transfer switch dedicated only
to the water heater. See the Reliance CSR series. Whenever you
needed to heat water, just plug the generator cord into this switch until
the tank is hot. Then move the cord back to your other switch.
As for your other questions:
... a current sensing device? yes, Gen/Tran just announced that they are
introducing an automatic transfer switch with microprocessor control that WILL load shed
less important circuits to keep the total within a generator's rating. But this device is
presently at UL for testing and won't be available for sale until at least December 1999.
... short term overload capability? You mention two ratings for your generator:
6000 watt and 6500 watt. The higher number sounds like the short-time rating. To be sure,
you might call Onan's technical support line with your particular model number and ask.
Hope these ideas are helpful. Of course, the more money you can invest, the
better backup system you can get. I have tried to minimize costs in the above options. But
if you have a lot of power outages, you would presumably want to invest more.
