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#8604 - 03/29/02 03:27 PM Monitoring KWH usage
Chris Paul Offline
Junior Member
Registered: 03/05/02
Posts: 6
Loc: Owenton
Hello everyone,
I was wondering if anyone had any idea on where I can get a CT for a 3000 amp service. I'm trying to monitor the KWH consumption for my facility and the largest CT I can find is a 2000 amp. Maybe if no one knows of any CTs that big they can give me some info on how I might accomplish my goal. These pulse inputs are going back to a monitoring device called a gateway which can be accessed anywhere through a modem. Thanks for any help.
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#8605 - 03/29/02 06:04 PM Re: Monitoring KWH usage
Redsy Offline
Registered: 03/28/01
Posts: 2056
Loc: Bucks County PA
Could you monitor one of a parallel group and have your software multiply the results by the number of conductors?
(Forgive my ignorance)
#8606 - 04/01/02 06:39 AM Re: Monitoring KWH usage
JBD Offline
Registered: 07/12/01
Posts: 599
Loc: WI, USA
Check out a company called Flex-Core at They make all sorts of different CTs, including split core styles for mounting on existing cables.

Square D also lists window style units up to 6000:5 ratios and split cores to 5000:5
#8607 - 04/02/02 07:15 AM Re: Monitoring KWH usage
bgautreau Offline
Junior Member
Registered: 04/02/02
Posts: 3
Loc: Milford, MA, USA

Most CT's will have a "rating factor" (RF). For instance, if the CT was a 2000 amp unit with an RF of 2, then the thermal capability would be 4000 amps.

Because of this, it is not always necessary to "match" the CT size to the service size.

Feel free to email me if you have more questions.

#8608 - 04/03/02 07:37 AM Re: Monitoring KWH usage
JBD Offline
Registered: 07/12/01
Posts: 599
Loc: WI, USA
While bgautreau is technically correct concerning "rating factor", you must still take into account your transformer ratio.

In your case a 2000:5 CT is a 400 to 1 ratio, so when it is used on a 4000A service it will provide an output of 10A. Your measuring equipment may not be able to deal with this large of a value.

The rating factor should only be used to allow for momentary overcurrents (i.e. motor start-up)which do not need to be be measured accurately
#8609 - 04/03/02 05:26 PM Re: Monitoring KWH usage
HotLine1 Offline

Registered: 04/03/02
Posts: 6775
Loc: Brick, NJ USA
Try National Meter Industries
or 1-800-325-6674
They have any ct's and are very helpful

#8610 - 04/03/02 05:42 PM Re: Monitoring KWH usage
Bill Addiss Offline
Registered: 10/07/00
Posts: 3875
Loc: NY, USA

You can ask the "Meter Guy"

#8611 - 04/14/02 09:09 PM Re: Monitoring KWH usage
Bjarney Offline
Registered: 04/10/02
Posts: 2527
Loc: West-Southern Inner-Northeast ...
They're around but the freight might be stiff.

Assuming window CTs with big enough windows, how about a pair of 1500:5 units in series?

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