connect CT to KWH meter

[stodgyguy20]

Hey guys,
I have an existing mini-sub with a Kwh meter that was never wired on its secondary (480V).
But now we have to wire it. Does anybbody know what kind of CT do I need for it?

The mini sub is rated 2240Kva, fla 2695A 13800/480V.
I will really appreciate it.

 

[davidbeach]

Probably a metering CT. Perhaps some more detail could elicit a better, more complete, answer.

 

[stodgyguy20]

thanks DavidBeach,
what other details do you need?

 

[davidbeach]

Oh, basic things like:
What do you intend to meter?
Types of loads to be metered?
How accurate does it need to be?
Where in the world you're located?
Where/how the CTs are to be installed?
What kind of meter is it?
Probably several other things too.

 

[waross]

The form number of the meter will influence the number of CTs needed.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stodgyguy20]

We are trying to see how many kwh this mini-sub is using.
This mini-sub is feeding a small building.
If it can be accurate up to 1%, this will be great.
I'm located in arizona, I work for a plant.
I have never used CT so I don't know how they are to be installed.
I can send you the pic of the mini sub if that may help

 

[davidbeach]

Your best bet is probably to find somebody locally who knows about such things and can look at the installation to help you out. It would be real easy to get the right answer for the wrong system over the Internet. But, what you need is the right answer for the right system.

 

[waross]

A slight mistake with a CT may lead to thousands of volts appearing where normally there is less than 5 Amps and less than one or two Volts. If the high voltage flashes over, it may result in the victim describing his last sight as
"A Big Orange Basket-ball."
Death or blindness (temporary or permanent) may result from inexperience with CTs.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

What Bill says is true. CT circuits are unlike anything else you've ever worked with. With everything else, shorts are bad and opens are safe; with CTs shorts are safe and opens are highly dangerous. Lots of other differences.

 

[stodgyguy20]

Thanks guy for all these ideas. I think I will just go with a contractor for this.
I will let you know how they will do it.

 

[stodgyguy20]

hey guys,
quick one: How do you pick the ratio of a CT?
I am working on a 480V system with 2695A.

 

[waross]

a 3000:5 or 5000:5. If you don't anticipate 100% loading you may use 2500;5 in a pinch. You will probably need three CTs.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rbulsara]

Assuming the meter is rated for 5A...It could be 1A too. Look up the specs for the meter.

No offense but judging from your questions, you should have a good engineer or contractor check the sub to see if there are any existing CTs and they were just not connected! If they do not exist, it will be bear to install CTs on existing bus or cables of a switchgear this size. You can also check its shop drawing, if you could find one. Most manufacturers will have a record.

Rafiq Bulsara

http://www.srengineersct.com

 

[ScottyUK]

Bill,

"Death or blindness (temporary or permanent) may result from inexperience with CTs."

Temporary death?


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[waross]

LOL

Bill
--------------------
"Why not the best?"
Jimmy Carter