But the two rules are:
1) the wires have to be on the same phase/same hot leg
AND 2) the current has to be flowing the same direction.
I’ve done this for things like:
- Split system air conditioner with a separate air handler/furnace from the outdoor unit, making it the same as measuring a package unit.
- Three pool pumps where I had no interest in seeing their individual consumption (can be mix of 120v and 240v).
- Two 120v clothes washers and two 240v electric clothes dryers – the 4 “Laundry” wires and yes they fit in the sensor!
- Two electric water heaters
- I don’t do this for multiple fridge or freezer circuits, because I want to know that those things are running the proper amount and watch them via Custom Alerts.
So back to the two rules …
Same hot leg
- Else the half a Hertz cycle difference between the two hot legs will cancel out part or all of the reading.
- This is easy to see in the breaker panel and easy to verify with a volt meter.
- For a 2 pole (240v) breaker, the top half is on one leg and the bottom half is on the other, and it alternates all the way down the panel.
- The single pole (120v) breakers are on only one leg.
- So if you want to put a 240v load through the same current sensor along with a 120v wire, you have to pick the same hot leg on the 2 pole as the single pole 120v breaker.
- For multiple 240v loads, you pick the top or bottom of both/all the breakers to run through the sensor.
- With a volt meter on the same hot leg on two different breakers, it reads ZERO volts (but there’s 120v voltage there between you and the ground so don’t be fooled into being careless.)
- If only sensing one leg of multi-pole circuits and also mixing in a single pole 120v load, you’ll need an ammeter to and some math skills to calculate the Multiplier for the entire group. But you can always sense all poles involved and leave the Multiplier at 1.0.
Same direction of current flow
- Else the sensor will measure negative amps on one wire and positive amps on the other and the net will be something far from reality.
- Easy to envision the flow direction as most all the wires are leaving the breaker panel and leading to the load.
- No way to measure this with a volt meter but a decent clamp-on ammeter is directional and displays positive and negative amps.
But if the wires in the panel are mess, it may be difficult to find a accessible spot where you can clamp the sensor on the multiple wires. Beautiful to have 16 sensor channels, isn’t it?
And when Emporia offers “combining” of multiple sensors into one display line in the Home screen, there won’t be as much of a need for this. We’ll be able to create our own “logical” groups of sensors instead of physical grouping of wires, and I’m hoping the combined line will be drop down arrow expandable, so we can easily see each sensor when we want that detail. Until then …
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