I'm doing my own electrical for a home I'm building, and am interested in having a whole house generator at some point in the future, but it isn't in the budget right now.

If I understand correctly, you need a transfer switch to go before the main panel, so if we wanted to add one later, we would need the power company to disconnect the service and redo the whole service entrance.

Is there anything I can do that doesn't cost too much right now, to make it easier to install a generator or transfer switch later?

The house will have a 200 AMP service.


When I hear "minimum" I think "trying to save money".

Do you really, seriously, plan to buy a large 50 KVA generator with an aim toward powering the whole house so you can have life as normal (except for the insufferable roar 24x7 of the machine?) Will this run on natural gas or many trips to the gas station for this thirsty beast? Reason I ask is if you only plan to use a smaller generator to power important loads, this all gets a lot easier.

In this case, you install a main panel in the normal way. Then you run a large, say 100A**, circuit to a generator interlock, then to a subpanel, then you punch down all your generator-desired loads into the subpanel. It can be quite a large subpanel, in fact we recommend that. (Don't be the guy who counts circuits to figure the smallest panel to get, that saves very little money and adds a lot of cost later.)

A lot of subpanels can be their own generator interlocks. That makes things cheaper still.

For instance you could even have two interlocked subpanels 100A** each, at sane cost, and simply put every load them with none on the main panel (except loads that would be completely insane to put on generator, such as a Chevy Volt charger.) If you had a 50KVA generator, you could power both!

So it really is a matter of pricing the different options.

** speaking of pricing, you might also consider 70A. 70A breakers are much cheaper than 100s, and remember, you need 3 of them per subpanel. By the way, the subpanel can be larger than the breaker, so for instance a 70A breaker can feed a 225A subpanel. You'd do that to get more spaces. Spaces are very good, and cheaping out on spaces is a bad idea.

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    Also you cannot install an transfer switch ahead of a main disconnect unless it is service rated. – Retired Master Electrician Oct 2 '17 at 20:29
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    @RetiredMasterElectrician yup, mains service to 200A panel which contains only two 100A breakers going to 2 subpanels. The subpanels have the cheap and simple interlocks or options for same. Or hey, it's a subpanel, you can always switch to an automatic changeover later, because it's easy to de-energize the power feed to a subpanel. – Harper - Reinstate Monica Oct 3 '17 at 3:38
  • I was primarily thinking of keeping my options open while avoiding having to rework the mains at any point down the road. Where I live (very rural) it would be propane or bio diesel. I've also thought about adding solar at some point in the future to subsidize power company power, which would eliminate the need for a generator too if it could run what I needed. The most important thing for me is to keep the well pump running, but if we could have a refrigerator, heat/ac, and a few lights, that would be great. – Nick Oct 3 '17 at 20:37

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