CT and meter question

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hardworkingstiff

Senior Member
Location
Wilmington, NC
PoCo installed 400A CTs in the pad mount transformer for an 800-amp panel (single-phase, 120/240V). They feed a meter that you need to take the meter reading and multiply it by 80 to get the true KWH usage.

If the panel is drawing 600-amps for a while, what happens to the CT and meter? The CT will be overdriven by 50%, and the meter reads more/less/same (accuracy) as it would at 300-amps.

Basically I'm asking if the 600-amp (or 800-amp) loads will be accurately recorded.
 
Yes they will, the poco cts will have a duty rating of 2 or 3 and they should handle that load just fine. Do it all the time where I work.
 
If anything is gonna work, the cash register will. Honestly, I don't even see a cause for concern here. Unless they have one of those new government Insta-Tax chips in it. No I'm not kidding.
 
hardworkingstiff said:
. . . Basically I'm asking if the 600-amp (or 800-amp) loads will be accurately recorded.
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It is pretty standard to use ? the rating of the current transformer compared to the service size. Also, the accuracy is tested that way. For an 800 ampere service, we would issue 400-5 current transformers. :)
 
charlie said:
It is pretty standard to use ? the rating of the current transformer compared to the service size. Also, the accuracy is tested that way. For an 800 ampere service, we would issue 400-5 current transformers. :)
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Why would you only use half the service size? Why not use a CT equal to the service size?

Do you have to use special CT's in order to do this. We have a case where we look at current on a motor but the CT is to small and caps out before we see total current.
 
philly said:
Why would you only use half the service size? Why not use a CT equal to the service size?

Do you have to use special CT's in order to do this. We have a case where we look at current on a motor but the CT is to small and caps out before we see total current.
Click to expand...

Because the Cycle of service is mostly running way lower than a High point as asked by the OP!

If your have a high ratio of wire mass that measureable per volume of a "CT"
wouldn't metering electrical service not read better?

If the Ratio of the CT is 200: 5 wouldn't that be better that 1 : 10 ?
 
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