Sense on an Interlock transfer switch?

I am thinking of buying a transfer switch to run a portable generator, specifically the Interlock switch since it allows for all circuits to potentially be used. The problem as I see it is, the Sense monitor connects to the mains which will get bypassed during an outage. Is there a way to utilize Sense on a transfer panel as well? In fact, it’s even MORE important that I am able to monitor the output of the generator than utility power!

As long as you loop the transfer breaker wires through the Sense CTs along with the Mains, assuming you can get both wires through the clamps, things should function fine.

When the transfer feed is inactive it will have no effect on the signal to Sense; likewise when the Mains are inactive it will have no effect on the transfer wire signal to Sense.

OK, that is a brilliant answer. I will put that breaker at the top near my mains and make it happen. Thank you!

BTW: Obviously you’ll need to make sure that the Sense monitor is wired to one of the breakers that remains switched on after a transfer (assuming you do that thing where you might keep certain breakers off when running from a generator).

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Since the main breaker is after the incoming main wires, wouldn’t it still monitor incoming utility electricity, assuming it was live?

Not sure I’m following your question in regard to install of a transfer switch (breaker) + Sense:

A manual transfer switch action AFAIK involves switching off the main breaker and switching on the transfer breaker = “transferred”. You’ll only be transferring when your mains go out = no current passing through the mains feeds.

I meant when the main feeds come back on, would that be a problem with both the mains and the live transfer circuit being on the same time.

Manual mains/generator switching, via a transfer switch, is mutually exclusive. Meaning you won’t have both feeding your panel (and Sense) at the same time. An automatic transfer switch would toggle the feed automatically.

In theory if you aren’t using the solar CTs, btw, you could clamp those on the generator input (no device detection but you can check your power).

Ultimately it depends where you can put the clamps and what the nature of the transfer switch is.

If your clamps are after the main breaker ahead of panel bus and your transfer breaker is similarly upstream of the clamps, then you would need to do any rewiring beyond the install of the transfer breaker install … Sense will “just work” in that configuration.

FYI: I believe, given the difference between Utility (grid) and generator power you likely won’t get the same Sense-detected devices propagating when you do a transfer.

My main breaker is right before all the circuits, so the clamps are “above” that on utility power. If I shut off the main breaker, Sense stops working. (I realize it stops working without power too, but even with generator power on that dedicated circuit breaker, it won’t have anything to ‘watch’.)

If the Solar CT’s can be plugged into my same unit and and least give me basic wattage info during an outage, that would be wonderful. It’s all I need. I’ll order them.

The only real caveat with using the solar CTs is that in order to calibrate you’ll need to get 500+watts on the generator inputs.

I would be inclined to just run the transfer switch feed (from the generator) through the Sense main CTs anyway. As I said, you won’t have issues of “double” power … you just need to make sure to run the wires in the right direction through the clamps. That way any load (the panel circuit breakers that are left on when you are in transfer mode) will be clocked by Sense in the same way it’s clocking the Mains.

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Personally, I’d probably go the solar CT route. With a small gasoline generator, device startup signatures will be quite different due to the less “stiff” source. This could very well start mucking with your detections if you run long enough that way.

Also, if you run the generator and mains feed in parallel thru the main CTs, be aware that if you’re running the generator when the utility power is on (for a periodic test) you’ll get some wacky results due to the two sources being out of phase with each other.

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Good points, I tend to agree … I’m back to the solar as well.

Actually makes me think though it would be nice to be able to “fork” the detection without having to reset things. Go into “transfer” mode or whatever. Version 3.0

One other question, although this is a different topic…

My generator outputs 120v only and doesn’t do 240. So my plan would be to turn off all the 220/240 breakers before using it, except Sense. Would that still work? Would Sense work since its plugged into both legs?

There would be less-than-trivial ways of getting things to work but you are poking at the edges of:

  • A dangerous panel setup

  • Costing more (especially in “complication”) than getting a 240V generator … which is what I would suggest.

The panel + 120V generator + Sense + necessary fudge is beyond what I’d be comfortable suggesting solutions for.

I don’t think a it’s dangerous. In fact I would be doing the opposite (moving to something LESS dangerous).

I did get a confirmation from Sense Support that using the Solars will work on a separate transfer panel (or input) just fine. I won’t get any appliance detection features, but that is fine. Want I need to know is if the Sense device itself will run on a single 120V leg, or will that throw the whole thing off.

Assuming a get a traditional separate transfer panel, I could make the Sense 220V circuit be one of the ones that get transferred over, but if that panel supported ONLY 120V circuits, I would also need to transfer Sense’s power to a 120V circuit breaker. The question is, would that work? Would it still power up? Would it still detect?

I don’t need 220V sensing capabilities since in a backup scenario, there is only a single 120V leg anyway. What I need to know is if the Sense box itself will power up and function?

I suppose I could grab a spare 15-amp circuit breaker and try it myself on my main panel, but I thought I’d ask here first.

I will note that the sense monitor internal power supply is indeed only connected to one leg of service, and will happily power up if you supply it with 120VAC on that leg only.

I will also note, importantly, that this installation is rapidly falling out of NEC compliance. If you do get this working safely, you will still run the risk of feeding all sorts of bad data into your monitor and risk causing very much unwanted “adjustments” to your device models when running on generator.

Honestly if I were you I’d pick up a cheap combination digital volt/amp/watt meter from eBay and install it in your transfer panel. Then you can use that to keep an eye on generator loading during the time you’re using it, leaving Sense for utility monitoring only.

Sense is really only practical to use with a 240v generator, ideally with a transfer switch upstream of the monitored panel.

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