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I want to install the Sense electricity monitor to my breaker box to monitor my home's power usage. The instructions call for installation on a 240v breaker inside my electrical panel. Here is a link to the installation video as well as a direct link to the section regarding connecting to the breakers.

My breaker box:

My panel

Looks like I have a few options:

  1. I have one spot left for a breaker. I'm seeing results online about a 240v tandem breaker that would fit into a single 120V spot in my box. Does anyone have any suggestion as to what kind of breaker I need? Search results for tandem breaker run from $10 to $200 but that could be I'm looking at breakers for industrial uses. Looks like this doesn't work? Sense requires being on two different phases. Here is a video linked directly to the email that someone received from Sense.

  2. Add the legs for the Sense unit to the existing 240V breaker for the dryer. According to Sense, this is fine to do since the device uses less than 5 watts of power.

I've done a bit of wiring around the house but this is my first time working in the breaker box. I want to make sure I'm doing the best thing here.

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  • Seems very strange that it would require a 240v breaker for something that most likely runs internally on 5-12VDC.
    – JPhi1618
    Commented Feb 23, 2018 at 15:23
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    @JPhi1618 The reason it needs to be attached to all conductors should be readily apparent due to the fact of it being an energy monitor.
    – Harper - Reinstate Monica
    Commented Feb 23, 2018 at 15:47
  • @Harper, it monitors the energy with two CTs (current transformers) that go around the incoming mains. I assume the breaker tie-in is only to power the device from inside the breaker box because I've seen similar products that only use CTs and get power from an external AC-DC power supply.
    – JPhi1618
    Commented Feb 23, 2018 at 15:50
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    Found the answer... "while the voltage is measured through the breaker wires that supply the monitor with power." From here. So it's really just so it can measure voltage and get power rather than assuming an average voltage.
    – JPhi1618
    Commented Feb 23, 2018 at 15:54
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    Depending on location the breaker box / fuse box can be the domain of a licenced electrician only. For me I can install anything in my own home like cabling and sockets etc, but I am not permitted to open the back of a distribution board.
    – Criggie
    Commented Feb 23, 2018 at 23:20

4 Answers 4

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Attach it to the dryer's breaker. This is fine because Sense is entirely contained inside a steel panel, so even if it entered the worst case scenario of the device drawing more current than its wires can handle, yet less than 30A, the panel enclosure would contain the damage.

Look at your dryer's breaker and see whether its labeling or instructions authorize use of two wires of dissimilar sizes. If not, you will need to get some #10 wire and pigtail it. When using wirenuts on #10 wire, tighten it with great fervor especially if it is solid wire. This would also be a great place to use mini-lugs, i.e. alumiconns.

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  • This is what I'll do then. Looks like this is the quickest way to install it without having to move a bunch of breakers around. Alumiconns like these correct?
    – jmricker
    Commented Feb 23, 2018 at 22:09
  • Yes, those. They rely on the old trick that Al lugs work fine with Al or Cu, but Cu lugs do not play well with Al.
    – Harper - Reinstate Monica
    Commented Feb 24, 2018 at 3:15
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You can get tandem breakers with a double pole breaker in the middle. Take out any two adjacent breakers (utility room receptacles and central vacuum are good choices) and install the tandem breakers. Hook up the existing circuits to the outside breakers, and the Sense to the inside breakers.

enter image description here

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Since you have 1 position open you could get a single tandem breaker, remove 2 breakers wire the wires from the original 2 breakers and snap the tandem breaker in now you have room for the proper sized double pole breaker a bit cheaper also safer than taping the 30 amp dryer doing it this way.

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Just someone who isn’t a certified electrician but certifiable... NEC standards require breakers be tightened per spec. I.e. 45in/lb may be your dryer connection and would crush the mess out of the sense feed wires. Additional this is called double tapping and will not pass electrical inspections per NEC. Buy some double 15 breakers and give the sense it’s own feeds and tighten per spec.

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  • Harper isn't suggesting you double tap the breaker if it's not permissible by the breaker's listing -- if the breaker itself can't handle 2 wires on the lug, then what he suggests is to use a splice and pigtail within the panel to create a tap conductor that way.
    – ThreePhaseEel
    Commented Jun 15, 2018 at 8:04

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