Shorting CT outputs indefinitely

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bandtank
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Joined: Fri Mar 08, 2019 8:43 am

Shorting CT outputs indefinitely

Post by bandtank » Mon May 27, 2019 3:22 pm

I may not need to measure the current in a handful of wires, but I would like to install CTs just in case because pulling the leads through the wall will not be feasible in the future. I read in the CT's instructions that the outputs can be shorted if the load needs to be energized while the CTs are not connected to a meter. Is there any reason the short circuit condition can't be indefinite? Would putting a small resistor in series do anything of value or is a literal short okay in perpetuity?

Jameson
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Re: Shorting CT outputs indefinitely

Post by Jameson » Tue May 28, 2019 11:49 am

Yes, you are correct, whenever you have your CTs installed on a primary wire with a significant amount of current in the primary, it is always best to short the two secondary wires from the CT together. You can leave them shorted together indefinitely.

If you do not short them together, the CT will buzz, and if there is enough current in the primary wire, you could damage the CT.
Jameson
EKM METERING
http://www.ekmmetering.com
831.425.7371

bandtank
Posts: 6
Joined: Fri Mar 08, 2019 8:43 am

Re: Shorting CT outputs indefinitely

Post by bandtank » Mon Jun 03, 2019 6:35 am

Thanks for the response. How can you tell if the CTs have become damaged? Is there a test that can be performed? I have a lot of test equipment and the background to do it, but I'm not sure how to accurately assess the condition of a CT. For reference. I heard a buzz for approximately 3 seconds before killing power to the panel. Nothing was on that would have been drawing a large amount of current as far as I know. The CTs in question are a pair of BCT-025-200.

Jameson
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Re: Shorting CT outputs indefinitely

Post by Jameson » Thu Jun 06, 2019 9:49 am

We dont have a good way to test your CTs using something like a handheld multimeter. But a good test that you can run yourself with an Omnimeter is to put 2 CTs on the same primary wire, put them on the primary wire facing in opposite directions. Then put the black wire from both CTs into port 1 on the Omnimeter, and put the white wire from both CTs into port 2 on the Omnimeter. In this scenario, they should cancel each other out, if one of the CTs is damaged, they will not cancel each other out and your Omnimeter will register a current, or watts on line 1.

I would imagine you are fine with the 3 second buzz, it should take longer than that in most cases.

Let us know how it goes.
Jameson
EKM METERING
http://www.ekmmetering.com
831.425.7371

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