Sub Panel with Two Furnaces and Basement lights…

[Usmcss]

Hey guys,

Sitting here waiting for my monitor to arrive from Amazon. I have a 200A Main Panel and a sub Panel right next to it fed by a double 100amp Breaker for two Furnaces and some lights smoke and detectors in my basement.

Can I just put two 50 amp clamps on each leg that is feeding the Sub Panel? I’m not worried about  differentiating between the two furnaces or lights.

Thanks Guys!

[Usmcss]

https://www.dropbox.com/sh/56cw9tku5ikwfke/AAD53LFFubBhShRFrC557dpma/IMG_2444.HEIC?dl=0

[djwakelee]

Yes.  That is how you’d typically monitor the full draw of the subpanel.

Other option is to not monitor the subpanel main feeds, but put individual circuit clamps within the sub panel (so some circuit clamps in each panel).  If your panels are close and the wires reach (or can be extended) – that’s an option if you need to know the individual draw of the furnaces and lights.  Or of course, a 2nd Vue2 setup for the subpanel.  All are options, depending on how low level you want to monitor, and how many circuits.

[Usmcss]

Thanks a lot DJ! Didn’t even think of connecting directly to the components in the Sub Panel! Thanks again!

[yyzguy]

Not quite.    You can’t use 2 x 50A CTs to measure a 100A circuit.   If more than 50A passes through the clamp, it will “max out” at 50A.   Placing two clamps on the same line, doesn’t make it measure up to 100A.

However, if the current is less than 50A on each leg you could use a single clamp on each leg to measure up to 50A.   Once you exceed the range of a CT the measurement won’t be accurate  (It won’t hurt anything, it will max out).

Looking at the picture, it looks like the 4 breakers in the sub panel are 15A each, so the total is unlikely to be exceed 50A at any given time.

If you have enough CTs and enough available channels, I’d say you’re better off treating each circuit separately.   One of the reasons for using the VUE is to see if any particular circuit is using more than you expect.    (I discovered my hot tub is using much LESS than I thought, so that was nice to learn)

If you’re running low on CTs or channels, I’d still monitor each furnace, and forgo measuring a known lower use circuit.    I have 17 circuits, but since there’s only 16 channels on the Vue, I’m not measuring the lights in a spare bedroom.

[djwakelee]

Yes of course with that setup the total sub panel must not draw 50A total or the reading would clip with a 50A clamps.  But even though the subpanel is on a 100A 240V circuit, it doesn’t sound like there is 100A of loads on either phase from what is described.  And like you also stated, in the photo there are (4) 120V 15A breakers, and (1) 20A breaker.  I don’t see a continuous draw of more the 50A on either phase, so this will work fine.  And yes, can measure the loads separately if he wanted to – with just sharing clamps between panels and circuits, or with a 2nd Vue2 (and circuit clamps) for the subpanel.

• This reply was modified 2 years, 2 months ago by djwakelee.

[yyzguy]

Yup.  His original question was whether he could use two  50A clamps on EACH leg in order to measure a 100A subpanel.   I think we’re all saying the same thing now.

[Usmcss]

You guys are the Best!!! Thank you all very much for all the Amazing Info!!!

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