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#197187 - 11/14/10 04:07 AM CT question
sparkyinak Offline
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Registered: 07/08/07
Posts: 1295
Loc: Alaska
Providing a CT has the amperage output, can a single CT provide accurate signalling to two or more meters requiring a CT?
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#197202 - 11/14/10 02:45 PM Re: CT question [Re: sparkyinak]
LarryC Offline
Member

Registered: 07/05/04
Posts: 776
Loc: Winchester, NH, US
I will take a wild guess, but if the two meters are physically close AND you connect the two meter's CT inputs in SERIES, I think yes.

Acceptable practice, I do not know.

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#197207 - 11/14/10 05:16 PM Re: CT question [Re: LarryC]
HotLine1 Offline

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Registered: 04/03/02
Posts: 6804
Loc: Brick, NJ USA
Another wild guess of 'yes'. Pondering a little deeper, I would venture a guess that as long as the 'meter' device doesn't exceed the power (correct term?) output of the CT, multiple 'meters' could be attached.
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#197215 - 11/14/10 08:11 PM Re: CT question [Re: HotLine1]
sparkyinak Offline
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Registered: 07/08/07
Posts: 1295
Loc: Alaska
It makes sense to me, but would degrade the accuracy is what I'm concern.
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#197216 - 11/14/10 09:20 PM Re: CT question [Re: sparkyinak]
gfretwell Offline

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Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
My guess is the manufacturer will not guarantee the accuracy if it is not installed exactly the way they say.
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#197225 - 11/15/10 06:07 AM Re: CT question [Re: gfretwell]
resqcapt19 Offline
Member

Registered: 11/10/00
Posts: 2209
Loc: IL
CTs have a rated maximum current output and a maximum circuit resistance. As long as the load of the multiple meters is below the maximum permitted load, there will be no issues with the operation or accuracy.
http://www.nktechnologies.com/pdfs/ct-tutorial.pdf
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#197234 - 11/15/10 10:54 AM Re: CT question [Re: resqcapt19]
JBD Offline
Member

Registered: 07/12/01
Posts: 599
Loc: WI, USA
In the days of electromechanical meters it was standard practice to provide a single set of CT's to feed both the Ammeter and the Wattmeter. Even in today's world of electronic meters it is still common.

However, it is rare that a protective device and a meter will share a single set of CT's (although it seems common in MV starter applications).

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