Sense Solar - CT placed incorrectly by electrician? Pics attached

[xdriv3]

Hey all! Excited to be part of this community! I recently had solar installed at my home. At the same time, I had them install Sense w/ Solar for me. My solar system is currently pending inspection and is not active yet. As such, the solar feature hasn’t been calibrated yet. Despite that, I think the CT was placed incorrectly.

As I look at my app, I notice the solar production mimics consumption (yes, even during the night when no sun is out). In fact, the solar system is off. There should be zero production noted. With that said, I think the electrician placed the solar monitoring CT incorrectly.

I have included a few pictures for your review. I have also added some hand drawn labels to make it easier to follow the wires. IF you need the original, unedited photos – do let me know!

Current set up:
A1/A2 = Consumption CT
B1/B2 = Solar CT

My plan:
Turn breakers off → Unclamp A1/A2 → Unclamp B1/B2 → Flip connectors at the Sense box (in other words, A1/A2 will now become my solar CT and B1/B2 will be my consumption CT) → Clamp A1/A2 to the solar line (labeled green) → Reclamp B1/B2 at the original position on the line labeled orange (see picture 3) → Flip breakers on.

Rationale:
There is very limited space in the first breaker box, having 2 sets of CTs will be tricky. Furthermore, that would involve me having to fish the CT through that small conduit entering the main breaker box. My plan would allow me to keep it easy and simple.

Follow up question:
(1) Will my plan work? Does it matter where the consumption CT is clamped? Does it matter if it’s at the blue or orange labeled lines (i.e. upstream/downtream of that very first breaker)? I just want to do this safely. Disclaimer: I am not an electrician – hoping someone can clarify.

(2) I was told the general convention w/ CT is — when attaching CT: one first has to attach connection to Sense and then clamp to the wire. When removing CT: one has to unclamp first, and then disconnect the connection. The reason for this is to avoid voltage spike. This forum mentions the CT provided have “integrated burden resistor.” Does that mean the general convention does not apply in this case and that there will be no voltage spike?

(3) What kind of connection do I have – is this a load side tap connection?

Thank you in advance for reading this! Any advice/suggestion would be appreciated!

[ccook]

Welcome to the forum. This is a load side solar tap on 100amp service. You are correct, the solar CT’s are in the wrong location. Those should be on clamped around the 2 wires you drew the green arrows on. The main CTs and solar CT’s are different, so you can’t just move the connectors on the sense meter then move you current A1/A2 onto your solar only wires. You’ll have to feed the solar CT’s wires thru the conduit like the mains currently are….
If you don’t want both sets of CTs in the smaller box, I would pull the mains out and place them where the solar CTs currently are. Sense can be calibrated for either way meaning
A1/A2 is service mains only (above tabs)
B1/B2 is solar only
Or
A1/A2 is service mains+solar (below tabs)
B1/B2 is solar only.

It’s currently
A1/A2 is service mains only
B1/B2 is solar + mains

Also on your solar AC disconnect down is off and up is on, so in the photos your solar is active unless your DC disconnect is off. Then in your main service disconnect box, the top of that breaker (where you have blue arrows) is hot no matter which way your main breaker is. So be very carefully around those.

[xdriv3]

Thanks for the thorough response.

When you say tabs, do you mean the black rectangular object that bridges the solar feed and utility feed (green and blue)?

When the main disconnect box breaker is off, the orange side is then cold correct?

Would you also advise flipping the switch to OFF for the solar box?

[dannyterhaar]

You correctly suggested it is wrongly installed and I 100% agree with ccook’s remarks.

Other question: Why does the label on the PV AC disconnect say “nominal operating AC voltage 208 V”
Are you getting only 2 phases from a 3 phase setup ?

[xdriv3]

I am in NYC. I was told that’s it common to have the voltage at 208V. They call it “split phase”?

[ixu]

208V is common, the default, in NYC.

Interesting things I guess happen in the city when feeding solar back to the grid. With enough solar panels and generation I suppose you can feed back the juice to the 3 phases but only need to be “on the grid” for 2.

Are you in a location where you had to consider building shadows? That’s always fascinated me and is rapidly evolving “tech”

Shadowmap

[dannyterhaar]

Interesting, didn’t know.
His system seems to be 208V * 36.14amp = 7517 watts.
Will be interesting how this will influence the 3rd phase.
I assume some transformers have to work harder

[ixu]

Well if it’s any indication of transformer size (which it is) most of the buildings I’ve worked in in the city (even the smaller ones) have feeds of gauge that would exclude the Sense CTs from monitoring … not that you’d be sensible doing that.

Typically the scale of supply balances things out between phases but there are no-doubt situations with the more suburban single family or small multi-family buildings where things could go astray. EVs in Queens!

[dannyterhaar]

It would limit the watts an EV can charge
eg: my Bolt charges 32 Amps @ 240 Volt = 7680 Watts
In his setup it would be 32 Amps @ 208 Volt = 6656 Watts or 86% of charging at 240 Volt.
So add 14% more time before charging is completed. Probably not an issue but still.
I just wasn’t aware except condo’s where they were using 2 out of 3 phases.

[kevin1]

From my memories from power “Super Lab” in the 80s:

• A three-phase transformer is a single unit, but there are many flavors - permutations of star and delta topologies.
• In industrial settings the electricians are careful to balance loads and much of the heavy usage equipment is already balanced three phase.
• In residential settings, usually big condo or apartment buildings and even mixed use, the electricians evenly distribute phase pairs to all the subpanels in the building and rely on statistics to do the balancing.

[dannyterhaar]

When you are talking about loading phases is one thing, but if now certain phases will start providing energy, the phase mismatch might become more of an issue. TIL

[ixu]

Thought you guys would enjoy this (from Con Edison) … I’m not in that electrical realm so the first time I see “watts/sqft”. The math gets fun.

[ccook]

I meant “taps” not tabs. The black things that your solar feeds are tapping into your main lines.

240v in most US homes are Single phase also known as split phase, Its changed at the transformer and has a center tap (we all call neutral) it has 2 legs that have 120 each in opposite phase (180deg from each other)… so takes 3 wires to make 240v. Guessing everyone understands the one leg an N is 120v… Then 120+120 since they are 180 degrees of each other makes 240.

208v is actually comes from 3 phase power its “208y/120v” . The “Y” means WYE… So he is getting 2 of the 3 power wires and those aren’t 180 of each other. He has 2 of the 3 phases. So you cant just added them together because 3 phase is 120 degrees from each other. So you never have 2 legs ever hitting the peak of its phase at the same time. So any 2 power wires make 208v. Its 120 * square root of 3… 120 x 1.732=207.84v Not sure how they get by with it buy the power company there say all the 240v items will still work at 208v and run at 25% capacity. I think the electric company there is Con Edison.

[ccook]

Learn more: Three-phase installation

Here is a sense article about the 208Y… It mentions that you would make note of the phase type in the “sense pro app.” He would put 3 phase… I cant find this anywhere in the app.

[xdriv3]

@ccook

Here is a sense article about the 208Y… It mentions that you would make note of the phase type in the “sense pro app.” He would put 3 phase… I cant find this anywhere in the app.

You are correct, my utility provider is Con Edison. My home is also a small single family home (not coop/large building).

Interesting article… does that really apply to me? Even though I’m at 208, I only have 2 of the 3 phases coming into my phone. I was told by Sense support (prior to purchasing) that the device will automatically calibrate and adjust for this.

Hopefully they are correct…

Just waiting for PTO now.

[kevin1]

I think you’re right. Sense will see the 208V and auto-adjust to 2 of 3 phase operation. For 120V devices, there’s not difference. But 240V devices (across 2 phases with no neutral), they’ll see only 208V. Since Sense looks at power and voltage, it doesn’t need to do any scaling, but I’m betting that Sense might to do scaling or normalizing for detection at 208V.

[dannyterhaar]

This is the difference between
2x120 = 240 volt “split phase”
and
2 x 120 = 208 bolt “split phase”

Explanation of 120v single phase, 240v Split Phase, and 208v 3-phase

In your setup you only have 2 out 3 phases connected to your premises.
Let’s say you have L1 & L2, and your neighbor has L2 & L3 and your next neighbor has L3 & L1
The transformer needs to balance that.

Btw: in my street we have 18 kV at the overhead lines, not 11kV
As a squirrel found out trying to hide some acorns in an automated switch device. Didn’t survive that and took the grid down when it arced and the lightning arrestors went up in smoke.
That was an expensive squirrel.

[xdriv3]

Alright, I’ve adjusted the CTs. I believe it went ok. I also went ahead and did a device reset.

Unlike last time — the signal check never went through. I also never heard the “chime” indicating a successful install for the unit. However, I was able to get it to reconnect to wifi.

On the main screen of app, I now see 0W for consumption. Is this normal - even with appliances on and such? The last time, I had near instantaneous monitoring after install.

Solar on the other hand, is showing 5W.

Here’s some pics; do the numbers look right?

[ixu]

It looks like some of the CTs are now flipped in the “wrong” direction but LEAVE THEM ALONE and let them auto-magically self correct via Sense calibration. If you move them now you could interfere with that process and screw things up or slow down the setup. So sit tight for now.

When things calibrate properly you should see non-negative numbers (i.e just watts and not negative watts).

If you continue to see negative numbers you could manually flip the CTs but it’s probably better to contact support and have them do a manual calibration.

[kevin1]

My 2c,
If you didn’t go through a full Signal Check and Solar Calibration this time, or you didn’t pass, you need to do it again. As @ixu notes, the power polarities on 3 of the 4 CTs are negative indicating that Sense doesn’t have the configuration correct. As he suggests, you should contact support@sense.com