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I'd like to be able to power essential circuits with a portable generator. If local code allows, I could use either a manual generator transfer switch (I'm looking at the Reliant Controls ProTran), or a generator interlock and backfeed breaker. It appears that the interlock and backfeed breaker may be the best choice because:

  • it provides breaker for incoming power
  • it makes power available to all circuits in house
  • it's less expensive

Downsides of the interlock:

  • finding an interlock and breaker-fastener that fit my specific panel
  • drilling the panel cover
  • no watt meters

What else should I consider is choosing between the two options?

Other questions:

  • Neither the transfer switch nor interlock disconnect the neutral between utility and generator. Is this not a concern?
  • Some transfer switch panels don't have a door. Does NEC not require a door over breaker switches?
  • When using transfer switch, since there is no main breaker, is there no overall overload protection? (For instance, the switch I mentioned above is rated for 30 amps, but could theoretically pull 170 amps without tripping a breaker.)

I'm in the USA.

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  • If there is no interlock for your panel, there is no question here. Until you determine that, it's shopping. I suggest you remove that bullet from the question. Get help choosing between two actual things.
    – jay613
    Jan 17 at 11:29
  • What make/model is your panel, and do you already have a generator or are you still shopping for that? Jan 17 at 12:44
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    Meters are becoming more common as a built-in feature on portable generators, and in any case, a clamp-on ammeter can be had inexpensively. Also, if there's no interlock kit available for your panel, you might still come out ahead by replacing the panel with one for which an interlock is available.
    – Greg Hill
    Jan 17 at 15:02
  • Not an answer because there are already 2 good answers: I replaced my panel using generator interlock as an excuse, but it was due for replacement (2 fuse boxes + 1 small breaker subpanel) anyway. When all done, I added notes to the breaker list showing which breakers always ON (e.g., internet, refrigerator) with generator, which always OFF (e.g., oven, dryer) with all others able to be used on a "watch what you're doing so you don't overload" basis. And I hope I never have to use it all. Jan 17 at 15:07
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    Get a multi-channel energy monitor like the Emporia Vue to act as the meter. The generator will use up two channels and normally do nothing but when in use you can see instantaneous load on your phone. So long as your Vue has internet. If the outage is caused by EG a tree that also cut the fiber, the Vue won't work.
    – jay613
    Jan 17 at 16:32

2 Answers 2

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Interlock.

I installed a 10 circuit transfer switch because I thought it would be easier, demand fewer skills (I am not a professional) and I liked the meters.

I was wrong on all counts. I switched.

There's cost. I sold the MTS at 50% of new, which easily paid for the breaker and interlock.

The meters are not as useful as they look. You have to plan, predict and manage load actively (*note 1). You can't rely on the meters. The transfer switch is relatively expensive. It's a lot of work to install (*note 2) and fills your panel with wires. You can only run ten circuits.

You don't have to disconnect the neutral from the utility. There are some issues with neutral-ground bonding resolved by neither solution (*note 3)

The main breaker is in the generator. Just be sure the cable to the inlet is big enough for your generator's breaker. EG don't put in #10 cable if your generator only has a 50A breaker.

Drilling the cover was not as much work as getting 22 wires, already permanently fixed at one end to something weighing 20 lbs, through a 1.75in conduit into the panel!


Note 1 - You know that EG 1 sump pump and 1 fridge will push your gen to 80% so you cannot wait for the meters to tell you that. You have to know, and plan. If you need a meter to tell you total power use without any big motors, IE if all the lights and phone chargers and whatever else you want to use are running at 30% or 50% , you can do that with an energy monitor or clamp meter or various other ways, you don't need it to be part of the installation.

Note 2 - It took me a day and a half to install the transfer switch, and I think the second time would be about 6 hours. It took me 3 hours to install the breaker and interlock, and I think the second time would be less than an hour.

Note 3 - Start here.

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Interlock advantages

  • Cheapest solution
  • Easiest installation (no one who struggles with this is ready to install a transfer switch)
  • Most flexibility in which circuits you can run

Interlock disadvantages

  • Kit may be difficult to find
  • User must throw breakers to put generator in service
  • User must manually throw breakers for circuits you won't be running
  • No feedback on power going through each breaker

Transfer advantages (assuming you buy one with meter)

  • Automatic transfer of power to the generator if you buy one that does this
  • easier breakers to throw since you already decided which loads to put on the switch
  • Easier troubleshooting of where your power is going to balance load (must include meters)

Transfer disadvantages

  • No flexibility on which breakers you power - you hard wire the breakers you will power, if you want to something different you will need to run an extension cord in your house
  • Cost of the switch and effort to wire is much higher
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  • @jay, edited, thanks
    – Tiger Guy
    Jan 17 at 21:04

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