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I bought a device called Sense to monitor home electrical usage that is installed in your electrical panel.

The device needs to be connected to a 240v breaker like this: enter image description here

The problem is that I only have one 240v breaker and it is already in use and the whole electrical panel is full. I don't want to spend a lot of money on this and I am looking for cheaper solutions (e.g., not installing a subpanel!).

Could I pigtail this device with the existing 240v breaker? The electrical usage of the device is minimal. I don't know what is already on this breaker (it is unlabeled). I have gas for stove, dryer, hot water, and heat. Maybe the fridge or washing machine is the biggest electrical device.

Could I replace the breaker with a double tap breaker? I don't know if that exists for 240v. Here is a photo of the current breaker:

enter image description here

Are there other options?

I will be calling an electrician to come in and do the work, but I'd like to be sure there is a relatively easy way to do this before he gets here.

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You can install tandem breakers which will free up some additional space in your panel. You mentioned being concerned about cost and these are relatively inexpensive ($10 range) and available at your local home store. For each tandem you use, it will free up a 1 pole space. You would need two tandems to create enough space for a 2 Pole breaker.

  • The panel is completely full. Are there 240v tandem breakers? Or would I replace some 120v breakers with tandems to make space for the 240v? – gaefan Jan 12 '16 at 18:54
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    For every tandem you install (120V), you will free up a single pole space. If you install two tandems, you will have enough space for a 2 pole breaker. A tandem is generally used to create more space for other breakers. There are a variety of different tandems. Some will combine two 15 or 20 amp single pole breakers into the space of a single breaker. They do have quad breakers that will take up the space of a two pole breaker and allow you to have a 240V breaker and two 120V breakers. Take a clear picture of your panel to the home store and see what they have. – J G Jan 12 '16 at 19:04
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    Please replace the irrelevant information in your answer with the more useful information in your comment to make the answer more valuable. – isherwood Jan 12 '16 at 19:19
  • @JG, you were the first to provide this suggestion so you get the correct answer. I'm surprised you got two downvotes. Tough place here. – gaefan Jan 13 '16 at 4:03
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Since it's low amperage, my guess would be that it's feeding a multi-wire branch circuit - two 120V circuits fed off of a three wire two pole breaker. They share a neutral just to save on running more wire, but have to be disconnected together - which is the cause of the two pole breaker.

I'd suggest flipping the breaker and see what it cuts, first guess would be in the kitchen. Since the meter doesn't use much power, as you said, you'd probably be good to share the breaker if it really is only feeding receptacles. I don't know of what the code requirements might be for installing something like this inside of a panel, but it definitely would work this way.

And of course, like the last poster said, breakers don't really cost that much if they need to be moved around a bit.

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One of the easiest things to do would be install a double-tandem (aka triplex) breaker, in place of two existing single-pole breakers. The big advantage is it keeps rewiring to a minimum.

enter image description here

This keeps the two single pole breakers, but essentially adds a 2-pole circuit in between. Quick search finds that Murray has 15 and 20-amp outer (single pole) circuits with combination of 20 and 30-amp inner (double-pole) circuits.

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    I'm not sure if this exists in the Siemens/Murray line, but I know Eaton BRs have common trip quadruplex breakers (BQC part numbers), so it's something to look for at least -- with a common trip quadruplex, he could replace his existing 2-pole 20A and not have to touch any other breaker slots. – ThreePhaseEel Jan 13 '16 at 3:21
  • @ThreePhaseEel, thanks for the suggestion, Murray does have these as well: amazon.com/Murray-MP220220CT2-20-Amp-Circuit-Breaker/dp/… – gaefan Jan 31 '16 at 21:07
  • The photo I posted is a Murray triplex breaker, available at (at least) one of the huge box chain home improvement stores. The one @kekito linked replaces an existing double pole (so you get two double poles), the one I posted replaces two single poles with two single plus a double pole. Just depends on existing panel layout what makes the most sense. – gregmac Feb 1 '16 at 1:49
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The only 2-pole breaker? If you have whole-house A/C, that is what that breaker is for.

Otherwise it may be an MWBC for the garbage disposal/dishwasher (one on each pole, shared neutral) as this is common practice. Or it may be pre-wired for future A/C service (too small for dryer or range at 20A). I'd want to know what that breaker is for sure, but yeah, I'd consider pigtailing it. Make sure to use at least 12ga wire for the pigtail (match the wire size run to it, may be 10ga.)

The Sense needs both poles so it can listen to voltage and line noise induced by appliances, listening for certain signatures. It certainly does not need a high-current or double-pole breaker. Most likely it draws its own tiny operating power (10 watts at most?) from only one pole, and has the other pole only to sense activity on that pole. But this can come off any two breakers which are on opposite poles, as long as they are not GFCI breakers.

  • No A/C in the house and I'm pretty sure it hasn't been prewired. There is a labeled breaker for the garbage disposal so it isn't that either. Thanks for the comments. I'll let the electrician decide whether to pigtail or use a triplex breaker. – gaefan Jan 14 '16 at 15:11
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If your panel accepts them, you could install some tandem breakers in place of a few single pole breakers. This would create open space in the panel.

Depending on what the double pole breaker supplies, you might be able to wire the device on that circuit.

I'd contact the manufacturer, and determine the exact installation requirements.

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