I have a 400A service and took the he other alternative - connected the Sense CTs to the pre-meter 400A mains. I have Solar as well so that was an additional motivation to keep things within one Sense unit.
So far we have never even come close to 200A, even with 3-4 EVs and AC. The closest moments came when we had a Model S (80A) and a Model X (72A) charging concurrently. We have since swapped the X for a Model 3 (32A), so we’re less likely to get close.
how big were your 400A mains? did the clamps fit? were they copper or aluminum?
@kevin1 has a picture somewhere on the forum of his setup.
I’ll link if I can find it
Ok now I’m inspired. I just sent a request to my electric company asking if they would allow opening the panel to put the clamps on.
Here’s the photo from another (long) 400A thread. I think mains are aluminum. Even with insulation, Sense clamps fit neatly around them. But CTs did not fit around the bus bars running between the two panels. BTW, the big red and black wires at the bottom on the breaker side run to one of my car chargers.
https://community.sense.com/t/multiple-monitor-and-400a-support/566/127
I’m surprised that yours is aluminum @kevin1
It appears you have 4/0 aluminum rated about 230 amps. Here they use 2/0 copper for 200 and 4/0 copper for 400. Or they use dual 2/0 copper which would be my personal choice.
I’m just guessing based on color. BTW, I say I have a 400A service based on my meter ratings plus the 200A main breakers on both my subpanels.
I don’t know. I would think if you had 200 amp meter and had two 200 amp panels, there would have to be a single 200 amp breaker between the meter and the panels.
It would probably be easier to tell if we could see or knew how each panel was fed from the meter. I only see single wire from each lug. Where does a split happen where the two panels are fed?
The split happens in a buss bar just inside the meter. This is in my side of house service closet where all my utilities enter. You can kind of see the buss bar on the upper right side. One branch feeds the breaker sub panel to the right. That panel has a lot of the 240 utilities on it - both EV chargers, both AC compressors, the dryer outlet plus the solar backfeed. The other buss bar branch runs to big wires that run to my other sub panel in the garage. Both subs have a 200A breaker
I think I’m following now. The wires going down are feeding one panel and, out of sight, a duplicate set of wires leaves elsewhere feeding the other.
I was afraid there were two 200a panels fed of those wires. Although it’s incredibly difficult to use 200a at one time, it’s does occasionally happen.
How can you tell how many amps you’re using?
Watt divided by volts equals amps.
With Sense you don’t really need a clamp meter but I found the Sperry DSA-500 a handy device to have around. Here is a link to a video on same. Sperry Instruments DSA Series Clamp Multimeters - YouTube
And as samwoly1 says you can do the math (watts / volts (120 or 240 depending on the circuit)
One thing @brbeaird will need to keep in mind is the Timeline of Sense does not differentiate between 120 and 240.
So amperage would be somewhat difficult to get an exact calculation on as 240 would run exactly half the amps as 120.
If you know all the devices that are on then it would be okay, it’s when things are in Other that it gets tough.
Unless your panel is fairly unbalanced, you can probably safely assume that your current is simply power/240.
Let’s say Sense says you are using 12kW on the Mains (as viewed in the Power Meter).
Consider three cases:
All the load is from 240V devices … you calculate your current as 12kW/240V = 50A on both legs, i.e. 50A on each leg.
All the load is 120V on one leg … you would calculate your current is 12kW/120V = 100A on one leg. i.e. 100A on one leg and 0A on the other.
All load is 120V and oscillates between the legs: the “average” load per leg over time tends toward 100A/2 = 50A.
So unless you have case #2 (unlikely) power/240 should give you your current.
BTW: I have a 208V panel (2 legs of a 3-phase supply like many urban panels) … the 2 phases are at 120deg. My calculation would be power/208.
Electricians feel free to correct me.
My answer is a little different than the others. I’m know I’m only close to my max when so have my cars charging and I know the current limits for both of those. I only have at most another 7000W going on top of those, mostly 240V.
Thanks for the info everyone. Some good news - I actually just got off the phone with my electric company, and they’re coming out next week to see about letting me move the clamps into the main meter box! They were super cool about it, but it may help I live out in the county, and it’s actually a membership co-op electric company. If it all works out, I’ll take some pictures.
That’s what I’m in, a CO-OP. Ours is great about stuff like this and doesn’t charge.
Hope yours gets worked out
Well, the electric company guys came over to take a look today. At the moment, I’m a bit confused. My meter box has more things happening in there than some of other pictures because the split happens right under the meter, and you’ve got multiple wires going to both panels to the left and right side.
However, it does of course have the two main leg wires coming from below. The electric guys said putting the clamps on those wires wouldn’t do any good because they wouldn’t be able to read the actual load. However, if I’m correctly reading some of the other pictures people have posted, it seems like that’s exactly what they’re doing. Is that possible? Even if it is, I’m not sure they’ll allow me to have something on the wires before the meter, but I could at least ask.
The guys said they thought if the clamps were big enough, they could put each one over two wires post-meter and achieve the same thing, but it seemed like they were referring to basically having one clamp over both legs going to the left panel and the other clamp going over both legs going to the right panel, which does not seem quite right to me.
Unfortunately, they only had the panel open for a couple minutes, and I didn’t grab my phone out quick enough for a picture. At the time it seemed pretty clear cut that it wouldn’t work, but now I’m kicking myself for not taking a picture anyway. Here’s the basic gist I drew on a whiteboard from what I remember seeing:
The electric company is t used to using clamps. They would disconnect and use an inline meter for readings to take measurements.
In other words, they are incorrect.
What you’ve seen pictures of here, absolutely works.
It appears you are only using Sense for the left panel. By clamping the bus bar in the center panel, upstream of division to each panel would provide you with measurements of both.
