Combining CT's - want to make sure I get it right before ordering

So the main question - when does it make sense to double up and combine CT’s using a headphone splitter, instead of using two inputs? Based on my readings seems to be an # of inputs thing, and needing a slightly larger CT, any other downsides?

The other Q, is for those combined stove & dryer - the breaker rating is likely optimistic on what it will actually pull (gas stove, electric oven), so would 50’s be ok, or should they be 100’s?

My setup:

Standard north american 120/240 panel 100a. Mains wires are just under 11mm in diameter. Panel is a max of 125a, and 30 circuits so it will be a little tight I’m expecting with a full complement of CT’s in there.

The main things I would like to measure:
Breaker size / #CT needed / CT size / desc
100a / 2 / 100 / mains, two inputs?
2x50a / 2 / 100 / 3 wire, hot tub, combined to one input
2x40a / 2 / 50? / 3 wire, stove, combined to one input
2x40a / 2 / 50? / 3 wire, dryer, combined to one input
2x30a / 1 / 50 / 2 wire, a/c
15a / 1 / 50 / 6 other standard 120/15a circuits - thinking that they’ll be fridge, dw, office (with pc’s), furnace, washing machine, pc server

Which will put me at 12 inputs being used (with 4x100, 11x50 CT’s, does that make sense?


Combining with splitter
Pro: Use fewer inputs, Don’t need to define output to see total.
Con: Need more and maybe larger$ CTs, need splitters

Combined into one CT
Pro: Only need one CT, Don’t need to define output to see total. No need for splitter.
Con: Can be difficult to route wires together.

Breakers are supposed to be 25% oversized by code. For example if you have a 4,500 Watt water heater, the draw would be 18.75 Amps so code requires about 23.5 Amps protection. The closest available is 25A, but they are not always available and #10 wire is needed anyway which is commonly protected with a 30A breaker.

The maximum you should expect in a 30A breaker is 24Amps, so a double 30A should be fine passing both through a 50A CT or using two 50A with a splitter.

Pretty clean panel, should be no problem.

Check the double breaker circuits for a neutral wire. Those without a neutral can use one CT in either of the hot conductors.

Those double circuits with a neutral will either need to be doubled through a single CT or use two CTs. If you use two CTs, you can combine or use two inputs. If you use two CTs with two inputs, the CTs need only be sized for the capacity of one the breakers. If you pass both wires through a single CT or use two CTs with a splitter, the CT(s) need to be rated for the sum of the two conductors. I know, complicated.

Note this simple technique for reversing to use one CT on a 240V circuit.

With respect to getting it all into your panel, you have a lot of room at the bottom, and your neutrals are all down there. If you can identify and label the neutrals from the 120V circuits, you can put the CTs there. In labelling them, try to color code them for which leg they are on You can combine several from the same leg, or even combine them from different legs if you pass one leg through the opposite way.

Thanks for the reply, I didn’t think about putting the CT’s on the neutral side, (or combining) the general circuits with one CT - that will give a bit more granularity to for the rest (and I guess I can always move them around too - if it turns out there is something interesting to look at.)

I’ll verify the Watt rating’s on the stove & dryer, and then put in the order.

Thanks again.

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Figured I should close the loop on this, in case anyone searches and finds it useful - looked at the manuals for both the stove & dryer, no meaningful info on them. The rating plates on both had the info I needed to find their actual draws.

Jenn-air gas/electric stove:5.8KW 120/240V, so a quick touch of math = 24.2A
LG dryer: 115/230V 24A

So the 50A CT’s should just have enough headroom when doubled up, if the appliances pull the full load they are rated for.

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The dryer rating is for 230V, so it will draw 25A at 240V. Still OK, but you might consider 100A for that.

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