I'm interested in buying a home-energy monitoring product, the type with current sensors that clamp onto one or more main electrical feed wires. In order to determine what products would work, and how many sensors are needed, I'm wondering what sort of electrical supply arrangement I have. It looks to me like there are two hot lines, one neutral, and one ground line.
Specifically, I'm wondering if based on this arrangement, is all of the current flowing through the neutral line (i.e. I'd need only one current sensor), or would it fit into another category as shown in the chart below?
Here's an image of the panel (I believe it is a subpanel, it is in a condo building):
Here are the sort of categories mentioned in the product literature:
Best Answer
You'll need two CTs
The relevant thing is you have a 2-phase panel.
Look at how the fingers on the buses reach out to the bus stab locations. It's obvious they are alternating A-B-A-B-A-B, and not A-B-C-A-B-C. That's the bog-standard North American 2-phase design, commonly used for 2-pole 120/240V (the second line) or 2-out-of-3-phase 120/208V as found in New York City or city apartment buildings (the third line).
2 phases = 2 CTs. End of discussion.
It really doesn't matter which one you have, as far as the Sense monitor is concerned.
However you will need to tell the Sense whether you have 208V or 240V, because it needs it to calculate KWH correctly.
There's no need to monitor neutral since it can be calculated from the other two and knowledge of 208 vs 240V... assuming nothing is broken.
The chart is wrong
The first line describes plain 120V service, which is 2 wires from the service. It is NOT standard North American service - it's extremely rare (though I happen to have it). You definitely use one CT.
The second line describes normal common North American service. 2 CTs.
Beware dangerous, unlisted power monitors
While there are excellent power monitor products like Sense that are fully UL-Listed for their purpose... we have also seen some "hobby-tier" power monitors knocked together by amateurs working in their garage, that take very alarming design shortcuts. UL is telling them "Oh hell no"... but they have been using tricks to slink around the safety standards. Like get component approval from a third party testing lab, then selling the components direct mail as pieces to sidestep the system certification. So the typical installation is a hatchet job, with CT cords and wall-wart cord running in and out of a service panel, Ethernet (God save you!) running in/out of the panel, etc.
They market toward "smart geek" types who think the products are oh, so clever.... if they can't even follow the UL White Book like everyone else, how clever can they be?