CTs in Switch Gear

mannyb

Senior Member
I noticed customers switchgear has 2 CTs at bottom of panel located near 1200a and 800 a breakers. The conductors run outside CTs do the conductors need to be installed thru the CTs? We didnt install the equipment but we are adding to equipment
 

jim dungar

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Wisconsin
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Engineer
It sounds like these might be zero sequence CTs used for ground fault protection.
if nothing is run through the CTs then they will provide no input signal to whatever device they may be wired to. You would need to look at the protection scheme in the relay to see if this signal is needed.
 

mannyb

Senior Member
It sounds like these might be zero sequence CTs used for ground fault protection.
if nothing is run through the CTs then they will provide no input signal to whatever device they may be wired to. You would need to look at the protection scheme in the relay to see if this signal is needed.
Are all the conductors suppose to feed thru the CTs? The Cts dont appear to be large enough. They have 3 paralllels per phase.
 

Jraef

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Electrical Engineer
If there are no conductors going through the CTs, then whatever those CTs were for is not functioning. You can surmise that if someone went to the added expense of adding them, there must have been a reason. Find that reason.

One of the things I like about our trade is that we get to be detectives...
 
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jim dungar

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Wisconsin
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Engineer
Are all the conductors suppose to feed thru the CTs? The Cts dont appear to be large enough. They have 3 paralllels per phase.
If they are for zero sequence GF, then yes they all need to go through the same CT.
It is not unheard of that the provided CT is too small for all of the conductors, In which case the protection scheme might have be changed to a residual GF instead and the CTs were abandoned in place.

You need to look at the protection scheme.
 

mannyb

Senior Member
If they are for zero sequence GF, then yes they all need to go through the same CT.
It is not unheard of that the provided CT is too small for all of the conductors, In which case the protection scheme might have be changed to a residual GF instead and the CTs were abandoned in place.

You need to look at the protection scheme.
I took a little more notes on the subject and I gather that the CTs are WL Air Core Neutral Current Sensors and from diagram I need to install a jumper from Neutral to ground and feed thru CTs. Does this sound like something you are familiar with? The diagram from installation guide shows a single conductor running thru each CT to and from neutral buss. what do you guys think?

Guide for Siemens Ground Fault Application Guide for 3-Pole WL Low Voltage Power Circuit Breakers
 

ATSman

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Location
San Francisco
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Self Employed
I took a little more notes on the subject and I gather that the CTs are WL Air Core Neutral Current Sensors and from diagram I need to install a jumper from Neutral to ground and feed thru CTs. Does this sound like something you are familiar with? The diagram from installation guide shows a single conductor running thru each CT to and from neutral buss. what do you guys think?

Guide for Siemens Ground Fault Application Guide for 3-Pole WL Low Voltage Power Circuit Breakers
Manny
Before you answered I was betting that they are in fact neutral CT's and part of a GF protection scheme called Ground Strap:
https://www.google.com/search?q=grou...g70yiXIucNTzM:

a better link:
https://electrical-engineering-portal.com/scheme-sensing-ground-faults
 
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