We've been getting a lot of requests for suggestions on CT setups. Below is a short guide to selecting CTs.

We have the following CTs:

Solid (Wire has to be removed, and CT needs to be slid over, relatively inexpensive)
- Micro 40 (Up to 40 Amps)
- Micro 80
- Micro 100

Split (CT can split apart and be clamped around the wire, but expensive)
- Split 60 (Up to 60 Amps)
- Split 100
- Split 200
- Split 400

Special Application:
- Split 170 (Bus bar)

All you have to do is look at each breaker and find its rating (usually labelled on the breaker switch), then choose a CT that is rated greater than or equal to the breakers rating.

If it's a 240V load, you need 2 CTs instead of 1.

Special consideration:
- for 240V loads with no neutral – you can get away with monitoring 1 side of the breaker and doubling the rating, if there’s a neutral, you must monitor both sides.

There are some circumstances where if you know a breaker isn't going to exceed a certain amperage, you can use a lower CT than it's rating.

The most common setup is a pair of Split 200s, or 100s, a small amount of Micro-80s, and a large amount of Micro-40s.

Excellent timing I'm talking with my electrician about moving my panel...

I'm in northern europe, (sweden) where we have 3 phase 240. My house has 3x25 amps incoming, in this case, I can go only for the Micro 40, right?

I'm waiting for the GEM, but will probably have to wire the panel before it arrives.

Micael

If it's anything like it is here (can't remove the mains once they're installed without intervention from the Power Company), you'll want to go with Split 60s on your mains.

99% of the time, you'll be using splits on your mains.

I can access the incoming after the meter, so I figured that I'd put them there. Before the meter, we (well, atleast in my old house) it is very little space to reach the wires anyway, so no place for a CT there.

But maybe it is wise to put split 60 there anyway, just to be sure.

Thanks!
Micael


Edit: One thing came to mind, being 'micro', are the micro 40 classified for 400V isolation?

The Micro-40 leads are only rated at 300V, the Split 60 leads are up to 600V.

Ben

Aha!

Are all the 'Micro-xx' sharing the same leads? I'll have to check, but I think all CT needs 400 rating when installed in a 3-phase panel over here..

Thanks
Micael

Yeah, none of our Micros will work, you could put tubing over top of the leads.

Ben

How long can the CT leads be for the various devices? I have an application where I can place the GEM very near a large sub-panel where 95% of the circuits are located, but I want to also monitor three circuits that are 35 feet away. All power originates from one master panel.

thanks, -john-

We've had people successfully extend CT leads up to 100FT with CAT5.