Unusual metering

[Bert_]

Thought I'd throw this in here. I know there are a few guys here that will understand.

Working with a local REC. Normally they just put their CT's in the transformer right over the lugs. When I was talking to the meter tech he asked to put them in my disconnect. I was a bit surprised, the REC's don't have a lot of ridiculous rules and are pretty easy to work with but putting metering equipment in an accessible box was a first for me.

 

[wyliesdiesels]

yeah that IS odd. Wouoldnt fly around here.

MID and PG&E require CT cabinets with meter seal studs

Does your PoCo's install book list a requirement for a CT cabinet?

I wonder if he will get in trouble.

 

[MattT]

Yeah that's "unusual" alright. Maybe those smartmeters are smart enough to tell if somebody did something....................

 

[wyliesdiesels]

Yeah that's "unusual" alright. Maybe those smartmeters are smart enough to tell if somebody did something....................

naw.

no way to know that someone added a conductor on the line side of the service

 

[MattT]

naw.

no way to know that someone added a conductor on the line side of the service

If the bypassed load is large enough it could cause detectable voltage changes as it cycles. The meter could report those to the light company if it's smart enough.

 

[Bert_]

yeah that IS odd. Wouoldnt fly around here.

MID and PG&E require CT cabinets with meter seal studs

Does your PoCo's install book list a requirement for a CT cabinet?

I wonder if he will get in trouble.

The guy won't get in trouble This is a rural electric company. Working with the REC's is a totally different experience then with most other POCO's.

I'm doing a service soon with a little REC that has like 90 miles of line. Supposedly the oldest in Iowa. They gave me a hand drawn picture of what they wanted for the transformer pad and verbally told me that they wanted something like a 36x36 CT cabinet.

Honestly I was surprised they required either one. The other are REC's just set it on a fiberglass basement and do the metering right in the transformer.

 

[wyliesdiesels]

If the bypassed load is large enough it could cause detectable voltage changes as it cycles. The meter could report those to the light company if it's smart enough.

But how would they know its a bypassed load vs a primary line voltage drop caused by another load down the line?

 

[MattT]

But how would they know its a bypassed load vs a primary line voltage drop caused by another load down the line?

A drop on the primary will show on other meters too. I had to put a data logger on another service one time to convince the light company a problem was on the primary.

 

[Norcal]

Back in 2000-2001 in Houston saw a few services with CT’s on the drops below the weatherhead they certainly were not a clean looking installation.

 

[manwithtools]

Exposed CT's just below the weather head is very common in the southeast, I remember seeing them a fair amount in the Midwest too.

 

[wyliesdiesels]

There’s a couple really old services out here with CTs on the crossbar up on the top of pole with the meter socket and meter in a can at the base of the pole

Next time I’m in the area I will snap a picture and post it here

 

[foolishpride]

What a **** install. He put the potential wires for the Watt Hour Meter through the primary (Hole) of the C.T.'s. This won't fly.

 

[wyliesdiesels]

What a **** install. He put the potential wires for the Watt Hour Meter through the primary (Hole) of the C.T.'s. This won't fly.

oh good catch!

 

[Bert_]

What a **** install. He put the potential wires for the Watt Hour Meter through the primary (Hole) of the C.T.'s. This won't fly.

Now I'm not a meter tech but I'm pretty sure it's correct. The potential wires connect on the load side of the CT. That would be wrong. Passing the potential wires back through the CT corrects the issue.

 

[Bert_]

I pulled another picture of the more common CT metering with several of the REC's.



In this scenario the potential wires are after the CT. Maybe somebody with some experience can chime in here. What is correct? Or does it really not matter?

I don't imagine it makes a lot of difference but these are both 400A single phase services.

 

[foolishpride]

Now I'm not a meter tech but I'm pretty sure it's correct. The potential wires connect on the load side of the CT. That would be wrong. Passing the potential wires back through the CT corrects the issue.

The only thing that should be passing through the Primary (Hole) of the C.T. is the main conductors. The secondary C.T. wires are fine, they are going to the Watt Hour meter without going through the C.T. I've tested a few in my time.

 

[Bert_]

The only thing that should be passing through the Primary (Hole) of the C.T. is the main conductors. The secondary C.T. wires are fine, they are going to the Watt Hour meter without going through the C.T. I've tested a few in my time.

Should the potential wires connect before or after the CT? I'm under the impression that they should connect before the CT.

 

[MattT]

The only thing that should be passing through the Primary (Hole) of the C.T. is the main conductors. The secondary C.T. wires are fine, they are going to the Watt Hour meter without going through the C.T. I've tested a few in my time.

What problem does running the potential wires back through the CT cause?

Should the potential wires connect before or after the CT? I'm under the impression that they should connect before the CT.

I'm thinking ideally before the CTs so the meter power consumption isn't metered. In the setup you posted, where there isn't an easy way to do that, running the potential wires back thru' the CTs looks like a good "fix" for that on face

 

[foolishpride]

Should the potential wires connect before or after the CT? I'm under the impression that they should connect before the CT.

It really doesn't matter. The Watt Hour meter just needs a set of potential wires fed to it, along with the wires from the secondary side of the C.T.'s. They just shouldn't be run through the C.T.'s, because they measure the current of the main feeder cables only. They don't need to measure the current on the potential wires feeding the Watt Hour meter.

 

[Bert_]

They just shouldn't be run through the C.T.'s, because they measure the current of the main feeder cables only. They don't need to measure the current on the potential wires feeding the Watt Hour meter.

That's what I'm getting at. By running the wires back through the CT it is no longer measuring the current on the potential wires, it cancels it.

 

[foolishpride]

That's what I'm getting at. By running the wires back through the CT it is no longer measuring the current on the potential wires, it cancels it.

Yeah, I get what you're saying. But the 500/5 Ratio C.T.'s won't hardly see any secondary current from the load on the potential wires. I've just never seen it done.

 

[Bert_]

Yeah, I get what you're saying. But the 500/5 Ratio C.T.'s won't hardly see any secondary current from the load on the potential wires. I've just never seen it done.

So why is it a "**** install"? I am genuinely trying to understand.

 

[mm08822]

First off, the pt wires have minimal load thru them. How much could it really add to the bill? How much load does a dvm add to a power circuit to alter the real reading?

Another way to look at is - I'm the POCO. You want power. You pay to power my meter to read your usage. If you weren't consuming, I wouldn't have to power it. Kind of like a trip charge to a job.

Agree - running the pt leads back thru the ct cancels the pt meter load.

The only odd thing I see in the first posted pics is the ct's and pt connections aren't sealed. That's the POCO's risk.

 

[MattT]

First off, the pt wires have minimal load thru them. How much could it really add to the bill? How much load does a dvm add to a power circuit to alter the real reading?

It's not just a DVM it's a smart meter. The ones they put in here are radio based so probably use a few watts.