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Discussion Starter · #1 ·
Does anyone understand how the POCO CT metering works? We have a customer that the POCO is coming back to and stating that their CT's failed and they owe a ton of money for the past 3 years of under billing. I was able to see this before the POCO did anything with the CT and meter and everything seemed fine, but now everything is switched out. On a CT service if the wire was removed from the CT to the meter what would this cause and wouldn't the POCO know about this? The CT's are 200:5
 

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Discussion Starter · #5 ·
Or a ct was put in back words or the multiplier they used was wrong if it is just ct the multiplier is 40 if they didn't have one hooked up on the secondary side it would blow the F up.
What would blow up? I know the CT's can act like transformers but I've personally never seen anything happen. I know the CT's need to be installed the correct way, but have you seen what happens if they are installed backwards?
 

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What would blow up? I know the CT's can act like transformers but I've personally never seen anything happen. I know the CT's need to be installed the correct way, but have you seen what happens if they are installed backwards?
Backwards would just throw off the readings, he is refering to opening the secondary, do that to a CT and it will usually blow up.

A CT is going to try and maintain the correct current through the secondary (Based on load and ratio) and it will change voltage on the secondary to maintain that current, so if you open the secondary voltage will increase until something fails, that's why you short the secondary of a CT before disconnecting anything.
 

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Backwards would just throw off the readings, he is refering to opening the secondary, do that to a CT and it will usually blow up.

A CT is going to try and maintain the correct current through the secondary (Based on load and ratio) and it will change voltage on the secondary to maintain that current, so if you open the secondary voltage will increase until something fails, that's why you short the secondary of a CT before disconnecting anything.

When a CT is opened under load, doesn't the voltage sky rocket to thousands of volts?
 

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A current-transformer is just a special type of step-up transformer with a fixed primary (the conductor being measured).

As long as the CT secondary is closed through a load or short-circuited, you're fine. The CT isn't destroyed because it can't force the primary wire to source enough current to damage itself; the influence of the CT is only a tiny part of the primary circuit impedance.

If you open the secondary, suddenly it's gonna take the voltage induced by that single primary turn and multiply it by the ratio of the CT, so it will be doing it's job as a step-up transformer, and on a 800:5 CT for example, you'd be bucking up your primary voltage by 160 times, which can produce many thousands of volts, and can definitely destroy the CT.
 

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Cts, like every other part of an electrical system, can fail. It's pretty rare, but they do fail.

If one CT didn't transmit its current signal to the meter, the meter would read low. If it's anything other than one of those new-fangled 'smart meters', there isn't any indication that a CT has failed. Usually, there is an indication if one of the voltage inputs fails, but not current.

I don't see how they could bill a customer for their equipment failing, it seems to me that would be a basic business expense. But, it the failure was because one of the CTs was disconnected, then they certainly should bill the customer.
 

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I have seen CT's with an opened secondary, with pin holes in the case, others fried. Was on a job were the utility employee left the shorting block open and when they energized the service there was a loud whistle sound, smoke shooting out of the CT cabinet and everyone running like hell.

We had just spent 4 days rebuilding the service after a blow up and no one was sure for about 10 seconds what was going on.
 

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Remember its all fun till you have to scrape what's left of a CT off the bus with a gasket scrapper :laughing:

We've had to teach that lesson to a lot of contractors and EE's

I don't see how they could bill a customer for their equipment failing, it seems to me that would be a basic business expense.
I've seen them try it.
 

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Remember its all fun till you have to scrape what's left of a CT off the bus with a gasket scrapper :laughing:

We've had to teach that lesson to a lot of contractors and EE's



I've seen them try it.
What I have seen is the old "You Never Know Until You Try" The ask for 6 years and if they get 4 they are happy, Particularly if the law only allows them to ask for one year.
 

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What I have seen is the old "You Never Know Until You Try" The ask for 6 years and if they get 4 they are happy, Particularly if the law only allows them to ask for one year.
Yep, big POCO's are the worst at following commission rules, they'll beat smaller utilities to death for not following them but you know....:whistling2:
 
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