Sub metering for condo units, need to confirm parts

I’m in need of splitting each of our 2 buildings electrical bills between 10 units . Each building has a main panel with a 50amp line that runs off to each of 5 units. The other breakers in the main panel feed communal items (ie. water pump) where costs would be shared evenly between the 10 units. Correct me if I’m wrong, but I don’t think I need to measure every breaker. My thought is to install an IoTaWatt in each building, measure the incoming power and each of the 50amp lines that feed the condo units. If I subtract out all the power that went to each unit I’ll be able to split the remainder between all 10 units as the communal power usage. That being said I need to confirm the correct parts to order.

Lower Building: Has 450amp of breakers, so an IoTaWatt Generic Kit, power supply, 9v reference transformer, 1x 600amp CT for mains?, 5x 50amp CTs for measuring condo usage.

Upper Buidling: Has 420amp of breakers so an IoTaWatt Generic Kit, power supply, 9v reference transformer, 1x 600amp CT for mains?, 5x 50amp + 1x 30amp CTs (Unit E has additional 30 amp breaker).

In case it matters, the main panels can be switched over to generator in case of power outage, it’s very rare, will that mess anything up?

I wouldn’t mind any insights or recommendations you may have.

Thank you kindly,

It looks as though you have split-phase power. Is it 120V/240V?

I can’t see details of the mains cables coming in. 600A would be unusual. The panels should have a nameplate that states the maximum capacity of the panel. I would guess it’s not more than 400A and maybe less. There should be another panel someplace feeds these panels. You should find that and see the capacity of the breakers feeding these panels. That would determine the size of the mains CTs. You will need 2 in each panel.

You will also need two 50A CTs for each of the condo units. So total of 12 CTs for each including the mains.

Final word. My personal feeling is that IoTaWatt is accurate enough to do sub-metering, but it’s not an electric meter and is certified only to safety standards, not accuracy standards. It’s up to you and your condo-association whether to accept it for billing purposes.

We are in USVI and power is 120V. You must be right about split-phase since we have a/c units that run at 240V.

The panel at the electric meter has 100amp breaker. So I should order the starter kit with 100a mains CTs?

So the order should be 2 starter kits, 10x50A CTs for condos + 2x50A CTs for the E+ breaker.

Thank you for your assisstance.

Are you saying that each of the sub-panels is fed from a 100A breaker in the main panel? Are there separate breakers for each sub-panel?

Perhaps a picture of the main panel would eliminate any guesswork.

Sorry, for some reason I didn’t see the picture.

Seems like a 100A breaker feeding 10 50A condos would be overloaded. That breaker feeds both sub-panels? Is it close to one of the sub-panels?

I’ll try and post pic again, but the electrical meter only has a 100 amp breaker that feeds main panel in basement which in turn feeds sub panels for 5 condos at 50amps each.

Main panel

You are looking at getting two IoTaWatt units to be installed at each of the sub-panels. So the question was whether the main panel or the meter box is next to one of those sub-panels such that a set of mains CTs could connect to the IoTaWatt. If you can do that, you can get by with one set (2j of 100A mains CTs. If not, you will need to add 2 x 100A mains CT to each of the sub-panels, in addition to the 10 x 50A.