Long Island, NY USA
Adding CT’s to my shop, completely confused but only started yesterday.

I discovered my 8ga. (240 volt 1 ph) wires insulation was kinda krinkled up.
I suspect possible pulling to much current.

I had bought some SCT013 CT’s a couple of years ago but had not installed or done anything with them.
Because of the possible problem with my wiring I thought I had better see what was going on.

My shop started out four years ago as a woodworking shop but then my neighbor decided he was too
old to safely use and maintain his metal working tools. So I bought his vertical mill, 12x36 lathe and
a 7x12 mini lathe, now I will have a wood shop and a metal shop.

My air compressor (2hp 240 volt 15 amps) is the heaviest load.
I might run the compressor the shop lights (fluorescent lighting) and my mill (3/4 hp 120v) or Lathe 1/2 hp 120v).

So I do not see where a 8ga (40 amps) wire would get overloaded so maybe the krinkled insulation was from
bending the wire when I installed it.

Yesterday I bought an Arduino emonTx, I have spent a couple of hours reading through things but at the moment I am more confused so I will be looking for a lot of help!!

Be prepared for lots of dumb questions.

First is will these SCT013 CT’s work with 8ga wire?
Then since I will not be pulling more than 50 amps can I/should I loop the wire through a couple of times.

I will have questions about the emonTx promise.

Hi Ralph,

Welcome aboard!

I wish I had wood and metal working tools like those. :wink:

I’m in the US too. (Oklahoma) so I’ll try to answer your US specific wiring questions.

Do you know what type of wire you have. e.g is it THHN or THHW? The type should be printed on the jacket. It sounds like it’s just the outer moisture jacket that’s been affected. If that’s the case, and the inner jacket is OK, then you’re in good shape provided your wiring is installed in a dry location.

The SCT013s will fit on AWG 8 wire, with room to spare. (the CT’s wire window is 13mm x 13mm)

You don’t need to, but if you do, the CT will be operating closer to the optimum part of its rated range. That’ll help with measurements at the low end of your expected load range.

8 gauge is some fairly stiff stuff, so if you can get 2 turns (one complete loop, as opposed to just a single wire) through the CT without stressing the CT (the core is brittle and cracks fairly easily, rendering the CT unusable) and ensure there isn’t a gap between the mating surfaces of the jaws when the CT is clipped shut, you’ll be OK.

Did you buy an emonTx - with the processor on-board and in an extruded ali box, or was it the emonTx Shield and you’re plugging it into an Arduino board? Because the two are very different beasts although they serve the same purpose, you’ll totally confuse us if you use the wrong name.

Thanks for the replies!!

I thought I said an Arduino Shield.

I am new to this so bear with me, till I get up to speed.

Really looking forward to seeing this work.


Oh the 8ga wire is THHN.

I would like to double loop through the CT but do not know if I have the slack as it is installed and working already.


Sounds like it’s just the exterior moisture jacket that’s wrinkled. Check the affected area to see if the underlying insulation has any nicks or cuts in it. If the inside jacket integrity is good, you’ll be OK.

Can you post a picture of it? That would give us a better idea of what shape its in.

Quite common, actually.
Wiring slack inside a load center (breaker box) is usually at a minimum if it exists at all.