Stand by Generator

[transferguy]

posted by: diyguy

Thinking of adding a stand by power generator to my home, live in a rural area of new York state.

Now I know you need a transfer switch of some kind to prevent any possibility of power being fed back to the grid. What I want to just to be able to power the essentials such as the furnace, some lighting, the fridge, freezer, and perhaps a microwave so we have some basics if the utility power goes off.

Now is the best way to have a sub panel that has only the circuits that run these essentials that way the transfer switch can be placed between the main service panel and the sub panel?

If I could get some advice on this and the best way to do that that would be great

[transferguy]

posted by: chrisb

There are transfer switch that have 6 or 8 circuits in them. You don't need a separate sub panel and then a transfer switch.
This one has eight circuits including one double pole

[transferguy]

posted by: suemarkp

The problem with the above type transfer switches is they don't allow regular breakers. Some inspectors will want AFCI breakers on circuits required to be AFCI whether on generator power or POCO power. Another problem with the above type is they are "solid neutral" meaning the switch doesn't transfer the neutral only the hots. Generators with a bonded neutral or a main GFCI output can't use a solid neutral transfer switch.

So first you need to pick your generator and decide if you want it cord-and-plug connected to your house or hard wired. Most of the cord-and-plug ones will be coming with GFCI and bonded neutrals now because of UL and OSHA requirements. Hard wired can come either way. But you have to know this or else just assume worst case and get a transfer switch that switches the neutral.

Then, pick the transfer switch. If you want an auto transfer switch (ATS), the generator must be large enough to power anything connected to it. For a whole main panel, you'd need a huge generator. You could then either install load shedding equipment or power a subpanel with only enough calculated load that the ATS will work. If you choose a manual transfer switch, you are permitted to manually load shad (i.e. turn breakers on/off as required so you don't overload the generator).

Finally, installing a transfer switch that can do the entire main panel is a more difficult task (meter must be pulled or your service turned off so you can put it in). Then, you have to separate all the ground and neutrals in the main panel and wire it like a subpanel. If that is too much work, then go with the subpanel approach.

To future proof, I'd install a 3-pole manual transfer switch (so the neutral is switched), and feed a subpanel having all the loads you could possibly want to be generator powered. Especially if you're thinking of a cord-and-plug connected connection between the house and generator. There are subpanels made by Reliance that have a dual tied main (one side is a feeder from your main panel, other side is breaker for generator feed). They take normal breakers. and they have one with 10 or even 20+ breaker slots. And the have a new line of 3-pole ones.

So this is kind of a circular process (amount of load to power, generator size & type, auto -vs- manual transfer switch, and all the little details that one component puts on the other).

Mark
Kent, WA

[transferguy]

posted by: diyguy

Although it would be nice to be able to run everything in the home, something that generates that much power would be costly compared to something that runs what you can survive on until the utility is back on.

I think I would prefer a hard wired system, a auto transfer and auto start on the generator helps if we are not at home at the time of the utility blackout. My understanding is that somewhere in the system neutrals and grounds become one, and if so does the neutral have to be transferred switched to prevent feedback to the grid?

[transferguy]

posted by: suemarkp

A recent code change mandates that the generator be able to supply everything connected if you use an auto transfer switch. If you can't afford or don't want one large enough to run your whole panel, you either need a manual transfer switch or automated load shedding equipment to turn off things the generator can't supply.

Yes, neutrals and grounds must become one at one place, and this is at the Main Bonding Jumper. Switching the neutral -vs- a solid neutral has nothing to do with backfeeding the grid (just worry about isolating the hots for that). The NEC worries about parallel paths in the grounding system. With a solid neutral system, the neutral and ground in a 4-wire generator cable will be paralleled if the generator neutral is internally bonded. If you can buy a generator that has a floating neutral, then you can use a solid neutral transfer switch. But look to see what is available to you. If the neutral is bonded to the generator frame and you can't remove that bonding, you must install a transfer switch that also switches the neutral in order to be code legal. This type also requires a ground electrode system at the generator.

I prefer a floating neutral generator and would rather use the house neutral-ground bond in the main disconnect for the main bonding jumper. But UL and OSHA have screwed that up in encouraging most generator to now have bonded neutral outputs and by putting GFCI's on the entire output instead of just a few branch circuits (a neutral and ground paralleled both at the house and generator will trip a GFCI). So go see what choices you have for generators and whether they have full GFCI protection or bonded neutrals (you will have better luck looking at pad mount generators instead of wheeled types). Try avoiding both issues or else just install a 3-pole transfer switch.

Mark
Kent, WA