Interlock or Transfer Switch?
Recent power outage here after tornados in the area. Total time out was about 10 hours starting around 5pm. Used candles and flashlights for the evening. (There was much grumbling from the females, that there was no tv/internet. The grumbling got much louder when the water pressure went to zero.)
1. House is all electric, forced air heat, stove, 80 gal water heater etc. No sump pump since it is a slab foundation.
2. Main panels are in garage right next to the two car garage door. Two 200A Square D panels.
3. Location is central Oklahoma. Talking with the neighbors, it seems that power being down for more than a day is a relatively rare occurrance.
So, with that being said it would be nice to have power to:
1. some general lighting up (8cf bulbs - 144w total)
2. the side by side fridge/freezer(800w)
3. the well pump(1500w)
4. kitchen vent hood and an portable electric kitchen grill(2000w)
5. microwave oven(1200w)
6. tv and cable box(300w) (Though I don't know if the cable tv service goes down with the electric. I assume it does, since I think they have to use repeaters to get the signal out farther distances. In that case, tv/internet access will not be possible)
7. 2 home office computers(assuming internet access is still up)(700w)
8. In winter, a 1500w 120v plug in radiator type heater for the bedroom.
Obviously the water heater and central a/c can't be run on a portable generator.
There would be enough residual heat in the water heater to take a quick shower if need be, provided the well pressure tank was at full pressure. Turn the shower off while you lathered up and then back on for a quick rinse off. Even if you have a portable generator powering the well pump, that electric water heater (which typically cannot be connected to portable sized genset) is going to be filling with cold well water. So the residual heat in the water heater will drop rapidly unless you shut off the incoming cold water supply to it. If you remember to do that, then multiple people could get showered using the above quick method.
That's a big issue for those on well water, when the electric is out, your well pump is out. That means that you only have water pressure as long as the well pressure storage tank still has working pressure. Once it drops below 40psi, the pressure switch is supposed to trigger the well pump to come on and refill the pressure tank back to 60psi. That won't happen if the electric is out. Which means, soon, there will be no water pressure at all in the entire house after flushing toilets, washing hands, etc. And if you were approaching the 40 psi cut in mark just when the power outage hit, you have even less useable water pressure now.
Also if you have battery powered timers on some portable outdoor sprinklers, better shut them off quick or your pressure tank psi will drop to zero FAST. Not a good thing.
So back to the interlock/transfer switch question.
Since not all the circuits desired during a power outage are on one panel here, not sure an interlock would be the best route to go. How would that have to be hooked up across two 200A panels?
I am thinking a transfer switch would be better. I could probably get away with a 20 ft cord from the generator to the transfer switch and just run the cord under the garage door. Bit less of a hassle than punching through brick to mount a plug box. Though I still have my core bit from the shed electric project.
I know the prewired Reliance transfer switches you can get a Depot and Lowes probably won't have long enough wires to reach across the two panels and hook into the circuits on the panel nearest the garage door. I would have to add wire to get that to work.
Thoughts or suggestions as to brand/model of transfer switch?
The generator size I was thinking of would be around 7k-8k watts, gasoline powered. Bigger is probably better for more flexibility. Assuming also that ALL generator powered stuff is not going to be on at the same time.