Equipment needed for 200A residential US installation

Hello everyone!

I’m looking for advice on what I need to buy for a new system.

  • This is a residential home in the US
  • On the outside of the house, I have a main breaker for 200A. It’s a “double wide” breaker, it is my understanding that this means I have 240V split phase service with 2x 100A. Is this correct?
  • What is a good way to measure the diameter of the wires to ensure they fit in a 16mm CT? Or is there perhaps someone who’s able to tell “from experience” by looking at the picture? :slightly_smiling_face:

This is what my panel looks like with incoming mains:

In order to monitor overall consumption, I would need

  • 2x 100A CT, one for each phase (black+black with red stripes)
  • 1x Reference Transformer (if I install one of the 100A CT in reverse)

This is my complete panel:

Except for the dryer (30A, top left) and A/C compressor (40A, top right), everything is 20A single phase (this is not completely true as I also have an extra 50A breaker for my induction range that’s coming in directly from the outside box because it was installed after the fact – I understand that I will be completely blind towards it if I only monitor the distribution panel in my garage, but for now, I don’t want to install anything on the outside of the building).

  • It is my understanding that I can simply install 1x 50A CT to monitor any of the 20A single phase circuits
  • What do I need to monitor the 40A two-phase A/C circuit? Can I loop both wires (black+grey) through 1x 50A CT? From the looks of it, it would be difficult to reverse one of the wires if needed. Is it the same for the 30A two-phase dryer circuit (red+black wires)? Or do I need a separate CT for each wire?

Regarding CTs, is there a difference between the ECS and AccuCT models, is one of them preferable for anything or are they essentially identical?

Completely unrelated to IoTaWatt, but maybe someone can educate me:

  • I have two phases @ 120V each (left and right mains coming in; black + black with red stripes)
  • There is one (common?) neutral (middle mains wire coming in; black with white stripes) that doesn’t seem to be connected to anything
  • There is an exposed large-diameter stranded wire coming in (aluminum?) – is this my grounding?
    This is my first house in North America, I grew up with 230/400V three-phase electricity in Europe and it’s confusing :smile:

That’s the first time I have anybody say that split-phase is more confusing than three-phase. I guess it’s what you’re used to.

Although the neutral connection does not appear to go anywhere, It connects to the neutral buss down each side of the panel where the all of the white wires are connected.

Judging by the size of the mains cables, I think you have a 200A service, which is 200A per side (or leg as we sometimes say). The 200A CTs in the North American Bundle will work fine here. Even if it is 100A, I doubt the 16mm CTs would fit. (I measure these things with a plastic vernier caliper)

You may benefit from the split-phase documentation.
Your AC unit appears to be two-wire, so can be monitored with a single 50A CT and click the “Double” box when configuring.

The Dryer is three-wire, so will either need two 50A CTs, or a single 50A CT with both the red and black wires passing through in opposite directions. If you don’t have enough slack in the wires to do that, you might consider moving the breaker to get some slack.

As you say, all of the others are 120V circuits, so need only one 50A each. You can also combine several of the 120V circuits into one CT. The above mentioned documentation explains how to identify the “leg” of each breaker. If you combine circuits associated with different legs into one CT, use the black wire for circuits on one leg, and the white wire for circuits on the other.

1 Like

That’s the first time I have anybody say that split-phase is more confusing than three-phase. I guess it’s what you’re used to.

One thing that makes it easier is that I can get 3.6kW from a standard outlet (without using a lot of copper, but that’s another topic), so there is typically only a single three-phase circuit on the panel going to the cooking range – which is normally not that interesting to monitor (granted, especially older homes may have electric tankless water heaters and air conditioning is slowly becoming more common – apart from storage heaters that still exist in the UK).

Although the neutral connection does not appear to go anywhere, It connects to the neutral buss down each side of the panel where the all of the white wires are connected.

Now it makes sense!

Judging by the size of the mains cables, I think you have a 200A service, which is 200A per side (or leg as we sometimes say).

Would that mean I have 2 x 200A x 120V available in total? The double circuit breaker on the outside is simply labeled “200A”, I assumed that was total and not per wire.

Does that mean the 40A breaker for the A/C is actually 2 x 40A x 120V as well (since it’s twice as wide as the 20A breakers, it made sense to me that it would be 40A in total and not 80A)?

Your AC unit appears to be two-wire, so can be monitored with a single 50A CT and click the “Double” box when configuring.

Perfect, that couldn’t be easier. I’m still confused about the coloring; if white is neutral, how can there be 240V for the A/C if it’s connected via black+white? The “split-phase documentation” describes this as well but without further explanation.

The Dryer is three-wire, so will either need two 50A CTs, or a single 50A CT with both the red and black wires passing through in opposite directions.

To me, this seems much more straightforward, there’s 240V between the black+red wires. Since the drier uses the white neutral wire as well, does that mean it uses 120V in addition to 240V?

Thanks for your help, I greatly appreciate it!

I believe that’s the case, but without seeing the unit can’t say for sure.

Yes, or reducing that formula to two terms you have 400A x 120V or 200A x 240V.

I’d look at it as 40A x 240V = 9,600kW.

They don’t make cable with just a red and black wire. Two conductor cable is black and white, so that’s the convention for two-wire circuits, whether 120V or 240V.

Yes, usually a dryer uses 240V for the heating element and 120V for the drum motor.

1 Like