Equipment Recommendations for US Residential - 200A

I’m looking for advice on the most practical way to setup an IoTaWatt in my home, with the basic issue coming down to if I should purchase one IoTaWatt or two, based my reading strongly leaning towards one with a fair # of CT’s for the circuits. I’ve read the advice on large number of breakers here and I think that I’m good with one but wanted to run the configuration by the community. In summary, I have:

  • Circuit Box: Siemens I-T-E Indoor Load Center - 200A
    • 120/240 Volts AC 1 Phase 3 Wire
    • Model: G4040MB1200 CU
  • 40 Circuits Total
    • 10 2 Circuit switches of various AMPs
    • 30 1 Circuit switches that are either 15A or 20A

I have some specific questions and then the sample layout and equipment images below.

  1. 240V Circuits - can all of them be measured using a single CT?
    a. Which is easier to wire up? Multiple CT’s or multiple circuits in one CT? Any rules of thumb? on how many you can cover with a single CT?
    b. Any way I can tell if they are two or three wire without opening the circuit box?
  2. Do I have anything in my loads below that I should break out to monitor individually?
  3. I have one breaker marked “Ground Fault Circuit” - is there any good reason to look @ this? Can’t imagine one but …

All advice greatly appreciated, I’m looking to order early next week

First, here’s my box:

Load I want to Monitor (specific circuits in sub bullet):

  1. Water Heater
    a. Water Heater (2x30AMP)
  2. Heat Pump
    a. Heat Pump Main (2x50AMP)
    b. Heat Pump Other (1x20AMP)
  3. Dehumidifier
    a. Basement: Unfinished Bathroom + Hall Outlet with Dehumidifier (1x30AMP, split 15/15)
  4. Air Handlers
    a. Air Handling w/ Heat Strips #1 (2x30AMP)
    b. Air Handling w/ Heat Strips #2 (2x60AMP)
  5. Washer & Dryer
    a. Dryer (2x30AMP)
    b. Washer (1x20AMP)
  6. Kitchen
    a. Range (2x30AMP)
    b. Kitchen: Outlet for Microwave (1x15AMP)
    c. Oven (2x30AMP)
    d. Refrigerator (1x20AMP)
  7. Well Pump
    a. Well Pump (2x20AMP)
  8. Upstairs Misc/Plugs
    a. Upstairs Bath (1x15AMP)
    b. Upstairs Bed Room #3 (1x15AMP)
    c. Upstairs Bedrooms #1 & #2 (1x15AMP)
    d. Upstairs Stairwell (1x15AMP)
  9. Basement Misc/Plugs
    a. Basement Light (1x15AMP)
    b. Basement Heat - we don’t use (2x30AMP)
  10. Main Floor Misc/Plugs
    a. Mudroom and Front Bathroom (1x15AMP)
    b. Master Bedroom & Closet (1x15AMP)
    c. Mudroom North Side (1x15AMP)
    d. Kitchen Above Island & On Outdoor Wall (1x15AMP)
    e. Living Room + Squigly Lights in Kitchen (1x15AMP)
    f. Kitchen reciept (1x20AMP)
    g. Master Tub Jacuzzi - Indoor (1x20AMP)
    h. Master Bath + Office Valence in Dining Room (1x15AMP)
    i. Dining Room Lights & Outlets (1x15AMP)

Circuits I’m not sure about

  1. Unknown: (2x30AMP) - might drop this, not sure if there’s anything on the circuit
  2. Ground Fault Circuit (1x20AMP) - see question above

Notes on Circuit Box

My advice is always to start with one IoTaWatt. You can always add another later, although I don’t think it’s likely you will find a need. You’ve detailed 10 circuit groupings, so after the mains, there are two inputs left, and then the remaining unmonitored can be computed in an output.

Regarding the 240V circuits, there is no substitute for removing the cover and looking at the wires. If the circuit is two wire (usually a black and white wire), you can use one CT and “double”. If it is three-wire (usually black and red on the breaker with a white neutral, you need to use one of the three-wire strategies:

  • Two CTs into two inputs
  • Two CTs combined with a headphone splitter (one reversed)
  • One CT around both wires with one wire in the opposite direction

The last two require CTs rated for the total amps of both breakers.

You can comfortably fit 6 #12 conductors or 4 #10 in a 50A x 10mm CT.
You can comfortable fit 16 #12 or 8+ #10 in a 100A x 16mm CT.

You can combine the 240V and 120V conductors into one CT provided you observe the proper direction for each phase.

When combining 120V circuits, sometimes it’s not easy or possible to reverse the conductor through the CT. If the neutral for that circuit runs by the combining CT, you can capture that instead without reversing.

My guess on the two vs three wire appliances are:

Water Heater - two-wire
Heat Pump - two-wire
Air Handling w/Heat Strips - two-wire
Dryer - three-wire
Range - three-wire
Oven - three-wire
Well Pump - two-wire
Basement Heat - two-wire

Hope that helps. Again - a high res picture of the guts usually reveals more.

Thank you & I will see about taking a better picture. Have never opened up a circuit box before.

In that case I have to strongly suggest you consider an electrician or someone that is familiar with working inside a load center. You could be seriously injured.

I’m going to have an electrician install it. Is there danger in switching the whole thing off and opening up the front panel? Appreciate the safety tips.

Yes, there will still be live conductors even after the main circuit breaker is off.

Bob (@overeasy) - in the post referenced above you stated “One input on an IoTaWatt can be used to monitor multiple circuits. You can run multiple circuits through one CT, and you can combine multiple CTs into one input.” For multiple circuits through one CT, I imagine that you just put multiple wires within the single CT. For the latter, how do you combine multiple CTs into one input? Any pictures of this? Just about to make my order.

From the docs (admittedly not easy to find)

Two individual CTs can also be combined with a common headphone splitter and fed into a single IotaWatt input. When combining this way, both CTs must be the same model with an individual capacity sufficient to measure the combined capacity of the two circuit breakers.

The important points are:

  • Must be same model CTs
  • Individual CT capacity sufficient to measure combined load of all CTs

Virtually any headphone splitter can be used to combine them.

I’ll say this now in case I don’t get an opportunity later. When you start combining, it’s best to put the CT around each of the conductors individually first, insuring each read positive in the intended orientation. Then you can put them all in. Any that would read negative would subtract rather than add to the combined power.

TY for the debugging tip. Should multi-way splitters like this or this work?

Second, if I’m reading you right and I was doing a 2-1 split/combine and each child CT was around 3-15AMP circuits, then:

  • Each child CT would have 45AMP total circuits
  • The combined AMPs would be 90
  • So all 3 CT’s (child and parent) would need to be the 100AMP CTs?

Please let me know if that’s right or I could get away with 1 100AMP CT and 2 50AMP CT’s.

Whatever combinations we end up using, I’ll be sure to take some good pictures that you can use as examples.

+/Edit - Depending on your answer, I’m going to add a few 100-AMP or 50AMP CT’s to my order.

TY --Mike

Should work but combining 5 CTs isn’t necessarily the best way to combine. Better to focus on getting multiple conductors into one CT and then combining maybe two or three (say one for the conductors on one phase and another for conductors on another phase). In the first link there is a three way that looks good.

I’m not following you here. You describe two CTs, each with 45A worth of circuits. You could combine those into one input. Both CTs need to be the same, so lets say you use two 50A CTs. You would configure the input as that model 50A CT.

Regarding capacity, I think 50A would work OK. Here’s why:

Add up all the breakers in your panel. Do they exceed the capacity of the mains? That’s the usual case. Most electrical codes say that a circuit should have a normal draw no more than 80% of the capacity of the breaker. So there is a 25% safety margin. When you see a 30A breaker for, say a water-heater, the nameplate should not exceed 24A. Same goes for all those 15A circuits. Usually a 15A is a lighting circuit, and isn’t expected to draw more than 12A, more like a couple of Amps these days with LED lighting. Plug circuits are 20A and not expected to regularly draw more than 16A. A 1,500W hair dryer draws about 12.5A.

So unless you’re Clark Griswold at Christmas, most of those circuits will never see anything close to 15A, and even less likely at the same time.

So in your example, if there is a major appliance in the mix, discount that at it’s nameplate rating, and then use your judgement for the rest. Once you get everything working, you can look at the actual amps and if there’s a high-roller, it can be segregated.

Got it! Thank you.

My motivation in asking is that I’m trying to get it right on the first setup since I’ll have to pay for each electrician visit - can buy a few extra CT’s and splitters for well under the price of another visit.

Just bought - TY for all the support!

Receipt: 51D0113867372764N

Equipment arrived and have done the basic setup. Looks great and TY. Have a setup question that I’ll post in a separate thread.

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