Questions from email

Received these questions via email because user was unable to use forum. Prefer to answer here so others can benefit from the effort I put into answering these questions. Response in next post.

  1. What are the wire lengths of the CT’s? If less than 24”, is there any problem with splicing in additional cable and if not, can you identify the cable used? I expect the cable lengths I will need for some of the circuits in the panelboard to be as long as 7 feet or so. Perhaps, I should consider a different CT than those packaged with your North American kit?

  2. Will I be able to plug 2 VT transformers into a standard duplex receptacle (which I will split between 2 phases)? If not, I could use a shorty extension cord. I intend to utilize direct reference voltage from each phase and this would use 2 of the available 14 monitoring spaces from the iotawatt.

  3. My project involves submetering several circuits from a main, 3 phase, 600 amp, 120-208V panelboard. The panel board is feed by parallel conductors (2) for each phase. I want to monitor each phase. In reading through the docs.iotawatt, I believe I can place a 100 amp ct on each parallel conductor and combine the 2 CT’s from each phase with a phono jack coupler for insertion into one of the monitoring inputs. Is this correct? Would I need to double the values from the 2 combined CT’s? This mains monitoring would use 3 of the 12 available iotawatt monitoring spaces.

  4. The other circuits I need to aggregate for submetering are:

  • 1- 3 phase, 100 amp circuit for a lift (balanced load) which I intend to use 1- 100 amp CT for monitoring that would use 1 of the 9 available iotawatt monitoring spaces.
  • 1 - split, (2 phase) 100 amp, 208 volt circuit for a car charging sub panel – all loads at 208 v – balanced which I intend to use 1- 100 amp CT for monitoring would use 1 of the 8 available iotawatt monitoring spaces.
  • 1- split phase, 100 amp, 120-208 volt circuit for a sub panel for various loads which are unbalanced. I intend to use 2- 100 amp CT’s for monitoring would use 2 of the 7 available iotawatt monitoring spaces.
  • 1- spare sub panel circuit that would be a duplicate of c above. Do not expect to purchase or install the CT’s for this future panel at this time, but I am allocating 2 CT’s for monitoring that would use 2 of the 5 available iotawatt monitoring spaces.

1 meter.

Not a problem, however the 120V kit does require you select at least two mains CTs. You can use the Generic kit if providing alternate CTs.

Yes, they are sideways so two will fit.

Not really. Conventionally, when you say “3 phase, 600 amp”, that would mean that each phase has a 600A capacity. That is also supported by your description of parallel cables for each phase. So, using 100A CTs is definitely not appropriate, and I doubt the 16mm 100A CTs would fit around the cables anyway.

In this situation, for each phase, you could use

  • 2x400A into 2 IoTaWatt inputs.
  • 2x600A combined with a splitter into 1 IoTaWatt input.
  • 2x400A combined with a splitter into 1 IoTaWatt input changing IoTaWatt burden resistor to 10 Ohm.
  • 1x600A with both cables running through it into one IoTaWatt input. The CT is 36mm opening so your incoming cable would need to be 18mm or less.
  • 1x600A Echun ECS55600 (special order 3-4 weeks) into one IoTaWatt input.


Two ways to do that:

  • 2x100A CTs into two inputs with direct reference on each.
  • 1x100A CT into one input with derived reference. (You can still use direct reference for 120V circuits)

This is technically not a split-phase subpanel. It uses the same physical panel, but the phase of the 208V is not the same as the 120V phases. You have three different phases at play. That said, what you describe will monitor the sub-panel correctly.