# POCO CT Metering issues



## oliquir (Jan 13, 2011)

if i a ct is removed the meter may record only 2/3 or half the kw/h
i think this is the poco responsability unless other people have opened the metering box


----------



## Whatsmyname789 (Jul 1, 2009)

Can anyone explain how the POCO metering works with CT and the new smart meters?


----------



## Nvsparky (May 2, 2012)

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.


----------



## Whatsmyname789 (Jul 1, 2009)

Nvsparky said:


> 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?


----------



## Zog (Apr 15, 2009)

Whatsmyname789 said:


> 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.


----------



## Meadow (Jan 14, 2011)

Zog said:


> 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?


----------



## 8V71 (Dec 23, 2011)

meadow said:


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


Isn't that exactly what he is saying?


----------



## Zog (Apr 15, 2009)

meadow said:


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


It does, until something arcs over anyways


----------



## Big John (May 23, 2010)

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.


----------



## micromind (Aug 11, 2007)

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.


----------



## Bad Electrician (May 20, 2014)

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.


----------



## Bad Electrician (May 20, 2014)

I have been involved with similar issues with utility metering foul ups and it took some tough negotiating to get anything out of the utility.


----------



## Nvsparky (May 2, 2012)

I work for one and the PUC will only allow us to back charge a year and we have to pay back three years


----------



## eddy current (Feb 28, 2009)

CT cabinets also have a seal on them so they can not be tampered with. Was the seal removed?


----------



## Jlarson (Jun 28, 2009)

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



micromind said:


> 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.


----------



## Bad Electrician (May 20, 2014)

Nvsparky said:


> I work for one and the PUC will only allow us to back charge a year and we have to pay back three years


That's because you are seen as evil by lawmakers.


----------



## Bad Electrician (May 20, 2014)

Jlarson said:


> 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
> 
> ...


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.


----------



## circuitman1 (Mar 14, 2013)

down here there hi up on the pole, not in a cabinet usually. don't belive i would want to tamper with them.:whistling2:


----------



## Jlarson (Jun 28, 2009)

Bad Electrician said:


> 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:


----------



## Meadow (Jan 14, 2011)

Big John said:


> 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.


Ok that makes sense now.  












micromind said:


> 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.


 
Depends who disconnected the ct... at least that could be hard to prove. I wouldn't want to be part of that. If I knew appromiatly when it was disconnected I would jest re-calc the bill by figuring out the average current per leg than assuming the lost ct was under the same current and re-calc it that way. Far from perfect especially if the load is poorly balanced but it gives you a rough idea for most services. 


Out of curiosity, would the above method work for a 4 wire system where the loads were perfectly balanced and no neutral current present? I think it would...


----------



## Meadow (Jan 14, 2011)

Jlarson said:


> 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:


 Never liked that... never.

Smaller utilities imo, especially municipals do a far better job at keeping the lights on than the big guys. The big guys just know how to peddle the blight into the next century. Plus customer service becomes Comcast status being the monopoly law of business protecting any unjust.


----------

