A friend asked me to install a small 4 circuit transfer switch little combo panel next to his sub-panel in his laundry room. The goal is to provide some lighting, a few outlets and keep the refrigerator going during a power outage. He has a typical 5000 watt portable generator with twist-lock and u-ground receptacles. How much circuit tracing and load calculating is typical in the planning of a small system like this. The homeowner knows he has limited power to only run the refer and a few lights.
5000W will power everything in his house but the heat and hot water heater. I only have a 3500W, and I have to run around turning on lights to load mine down enough to drop it from 126 to 125V so my UPS stops beeping about the "high" line voltage. He could probably even run his stove or a modest (2-3 ton) heat pump on it, but not both at the same time.
If he's using an MTS, there are no load calculations required per NEC, he just has to be aware he has to open a few breakers on his panel before transferring to generator.
He may not even need a physical MTS; something as simple as shuffling breakers in his panel and installing a sliding piece of sheet metal that forces you to open the main breaker before closing the generator breaker is acceptable.
You can get a surprising amount of backup power from a typical 5KW generator. As always, you just have to be careful with load management. Mine covers my stove, water pump, ejector pump, sump pump, frezer, two refrigerators and just about all lighting/small appliance circuits. Granted, we can't fix Thanksgiving dinner and have all of the lights on at once, but it has never let me down. We also can't run the heat, water heater, washer/dryer or A/C at all, but beggars can't be choosers.
During one particularly long and frigid outage, we used a 1,500 watt portable heater in one room and spent most of our time in there. We did just fine.
I'm using a MTS on mine that is rated at 60 amps which feeds a 100 amp sub panel. If the load use gets carried away, I'll just turn off some of the branch breakers to prioritize the available power. In your situation with only four circuits, you should be just fine with even a 3.5KW generator. I'd be inclined to pick up a couple more circuits while I'm at it if I were you.
One thing that I've found to be valuable is to include the lighting circuit that serves the area of the panel(s) so that you can see what you are doing. I've also found that an emergency light set in this area helps to get things going without fumbling for flashlights.
If I'm getting this right, no load calculations are necessary for the feeder,xfer and mini-panel. Is this related to 702.5? system capacity and rating to supply all of the equipment "intended" to be operated at one time. The "intended" part gets you off the hook if the owner overloads the system? It just seems strange for the NEC to not require a formally designed system. This residential temp gen. stuff is a first for me and I'm trying to save a little digging time. Thanks for the input!
I came up with an idea for my ex, who doesn't want any kind of "fancy" (read:expensive) transfer equipment. I told her to put a 3 way switch in place of the regular snap switch that functions as the disconnect for her furnace blower and flange mount plug out other side of the switch. Then in a power out situation she can just run an orange cord from the genny over to the furnace, flip the switch and she is good to go. A couple more cords for the fridge, the TV and a couple of lights gets her going.
Other than the 110.3(B) I am not sure where the problem is.
If the genset has an internal bond and the trailer is plugged into the main power source and running the genset can cause havoc with the power. A double bond can create CEMF in the wiring and have seen especially extension cords that were properly sized and used burn up without tripping the breaker. Odds are failure will not be that bad plus being you ex, then it is a sound way to go....JUST KIDDING!
Yea, that's the kicker. I made a very easy-to-make mistake on a UPS system, and everything tested OK .... until there was an actual power failure, and some 120 circuits got 240 instead. There goes another tuition payment ....
Yet another reason to 'buy it' rather than 'build it.'