What is the maximum distance a meter can be located from CT blocks?

[tortuga]

What is the maximum distance a meter can be located from its CT blocks?
Say for a 800A 240/120 4W 3PH service if an example is needed.
Does the NEC come in to play here? of just the manufacturers specs?
Thanks is advance.

 

[GoldDigger]

What is the maximum distance a meter can be located from its CT blocks?
Say for a 800A 240/120 4W 3PH service if an example is needed.
Does the NEC come in to play here? of just the manufacturers specs?
Thanks is advance.

The NEC does not come into play.
The CT specifications will list the maximum burden (series resistance of wiring and internal resistance of meter itself) which is allowed and still deliver the rated accuracy. As long as the wiring impedance does not go too high, there is no limit to the length.

 

[tortuga]

The NEC does not come into play.
The CT specifications will list the maximum burden (series resistance of wiring and internal resistance of meter itself) which is allowed and still deliver the rated accuracy. As long as the wiring impedance does not go too high, there is no limit to the length.

Thanks GoldDigger!

Is there any (new?) way to CT a service with a clamp on type CT and not have to re terminate the service? Say a 800 ~ 1000A 240/120 4W 3PH ?

 

[GoldDigger]

Thanks GoldDigger!

Is there any (new?) way to CT a service with a clamp on type CT and not have to re terminate the service? Say a 800 ~ 1000A 240/120 4W 3PH ?

There are split core CTs, but I do not know whether POCO would accept them for billing purposes. Incorrect installation, not necessarily easily seen, would result in a systematically low output current.
Any answers from utility folks?

 

[meternerd]

There are split core CTs, but I do not know whether POCO would accept them for billing purposes. Incorrect installation, not necessarily easily seen, would result in a systematically low output current.
Any answers from utility folks?

Our utility supplies their own CT's, which are tested and certified by the manufacturer for accuracy. We do field testing to insure continued accuracy. No, we would not allow flex CT's, split core CT's, etc. It's our cash register, so we are understandably picky. If a customer wants to add his own CT's outside of the sealed compartment, it's none of our business.

 

[meternerd]

The NEC does not come into play.
The CT specifications will list the maximum burden (series resistance of wiring and internal resistance of meter itself) which is allowed and still deliver the rated accuracy. As long as the wiring impedance does not go too high, there is no limit to the length.

In case anyone cares....when we test CT services, we test the CT's at 4 ohms burden and they must test within 0.2% accuracy. That's a lot of wire, since CT secondary wire size is typically #10 and voltage wire is #12. Primary injection current is 100A.

 

[goldstar]

I don't believe there is an NEC issue. However, from what I remember POCO's in my area require not more than 1 (10') length of 1 1/4" rigid gal between the meter and the CT. Not sure what their reasoning is.

 

[chevyx92]

What is the maximum distance a meter can be located from its CT blocks?
Say for a 800A 240/120 4W 3PH service if an example is needed.
Does the NEC come in to play here? of just the manufacturers specs?
Thanks is advance.

Here in Virginia you're allowed a maximum of 150 FT from CT using 1 1/4" conduit with no more than 180 degrees of bends. Excessive runs can utilize pull boxes. This is governed by the POCO.

 

[kwired]

I don't believe there is an NEC issue. However, from what I remember POCO's in my area require not more than 1 (10') length of 1 1/4" rigid gal between the meter and the CT. Not sure what their reasoning is.

Many padmount transformers here have CT's in the padmount and the meter mounted on a separate post - ten feet would be mostly used up just entering the ground and coming back up in the padmount with that conduit run

 

[tortuga]

Thanks all for your replies.