How to determine CTs for your panel

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ben
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How to determine CTs for your panel

Post by ben » Wed Jul 25, 2012 10:29 am

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.
Ben
Brultech Research Inc.
E: ben(at)brultech.com
vespaman
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Joined: Sat Oct 08, 2011 2:48 am
Location: Sweden

Re: How to determine CTs for your panel

Post by vespaman » Wed Jul 25, 2012 11:29 am

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
ben
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Re: How to determine CTs for your panel

Post by ben » Wed Jul 25, 2012 12:44 pm

vespaman wrote: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.
Ben
Brultech Research Inc.
E: ben(at)brultech.com
vespaman
Posts: 68
Joined: Sat Oct 08, 2011 2:48 am
Location: Sweden

Re: How to determine CTs for your panel

Post by vespaman » Wed Jul 25, 2012 3:53 pm

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?
ben
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Re: How to determine CTs for your panel

Post by ben » Wed Jul 25, 2012 5:01 pm

vespaman wrote: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
Ben
Brultech Research Inc.
E: ben(at)brultech.com
vespaman
Posts: 68
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Location: Sweden

Re: How to determine CTs for your panel

Post by vespaman » Thu Jul 26, 2012 3:02 am

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
ben
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Re: How to determine CTs for your panel

Post by ben » Thu Jul 26, 2012 3:13 pm

vespaman wrote: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
Ben
Brultech Research Inc.
E: ben(at)brultech.com
jloram
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Re: How to determine CTs for your panel

Post by jloram » Tue Aug 14, 2012 3:22 pm

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-
ben
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Re: How to determine CTs for your panel

Post by ben » Wed Aug 15, 2012 11:48 am

jloram wrote: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.
Ben
Brultech Research Inc.
E: ben(at)brultech.com
jtoutee
Posts: 20
Joined: Thu Mar 05, 2015 11:37 pm

Re: How to determine CTs for your panel

Post by jtoutee » Thu Mar 05, 2015 11:47 pm

Hello Ben,

About this:
===============
Special consideration:
- for 240V loads with no neutral – you can get away with monitoring 1 side of the breaker and doubling the rating,
===============

Do we have to double "manually" the rating, i.e. to remember that the Watts for this channel will need to be doubled, or is there a means in the software to apply automatically this x2 factor for the concerned channels before it is graphed ?

All electric baseboard heaters for example are 240V with no neutral, I intended to install a single CT on each.

I have received my GEM+Dashbox but did not install yet.

Brgds/Jerome
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