Power Meter Wiring

[kipperg]

I need assistance on a good practice for putting in the attached power meter. A wiring diagram is in the back half of the document, but it is not really clear on where the power source comes from (except for implying to splice the feeder for power). I'm still pretty new to this, so any guidance is appreciated!

Thanks!

 

[GoldDigger]

Nothing attached?

 

[kipperg]

Ah, must not have attached. I just tried to upload again and it kept saying it failed. Anyways, the device is a Veris meter that can be found here:
http://veris.com/Item/E23C6.aspx

 

[Jraef]

... but it is not really clear on where the power source comes from (except for implying to splice the feeder for power). ...

Not implied, it specifically shows that. You tap a voltage off of the line you want to measure, using fuses, feed that to the voltage inputs of the meter device. Then you put CTs on the line you want to measure and feed those to the CT inputs. Good practice on the CT inputs is to use "shorting block" type terminal blocks because if you even need to remove the meter, you cannot leave the CTs in the circuit without shorting them out. Their manual mentions this in the verbiage:

To avoid unwanted energy accumulation, short unused CT inputs or, on communicating models, configure the correct system type to disable unused inputs.

But they don't show that in the wiring diagram, shame on them.

 

[greenspark1]

Not implied, it specifically shows that. You tap a voltage off of the line you want to measure, using fuses, feed that to the voltage inputs of the meter device. Then you put CTs on the line you want to measure and feed those to the CT inputs. Good practice on the CT inputs is to use "shorting block" type terminal blocks because if you even need to remove the meter, you cannot leave the CTs in the circuit without shorting them out. Their manual mentions this in the verbiage:

But they don't show that in the wiring diagram, shame on them.

Agreed.

Remember that orientation of the CT matters- get it backwards and your meter will read negative power (producing). Some tricks to it but do it carefully once and you'll be set.

 

[kipperg]

Not implied, it specifically shows that. You tap a voltage off of the line you want to measure, using fuses, feed that to the voltage inputs of the meter device. Then you put CTs on the line you want to measure and feed those to the CT inputs. Good practice on the CT inputs is to use "shorting block" type terminal blocks because if you even need to remove the meter, you cannot leave the CTs in the circuit without shorting them out. Their manual mentions this in the verbiage:

But they don't show that in the wiring diagram, shame on them.

Thank you, that's the way I thought it was showing in the diagram too. But my electrician believes that we can't tap the voltage off the line because it's not up to code. He is telling me he thinks we need to add a breaker to the panel. Is that what you mean or is there a special method for this? Good advice on the shorting block.

 

[greenspark1]

Thank you, that's the way I thought it was showing in the diagram too. But my electrician believes that we can't tap the voltage off the line because it's not up to code. He is telling me he thinks we need to add a breaker to the panel. Is that what you mean or is there a special method for this? Good advice on the shorting block.

NEC tap rule covers taps (240.21(B)). Depends on numerous factors including length of tap and size of wires. If you can keep the tap to 10' long, you are allowed a fair amount of flexibility.

A breaker would work fine too. Often owners/clients don't want someone to be able to or accidentally easily turn off the meter.

 

[kipperg]

NEC tap rule covers taps (240.21(B)). Depends on numerous factors including length of tap and size of wires. If you can keep the tap to 10' long, you are allowed a fair amount of flexibility.

A breaker would work fine too. Often owners/clients don't want someone to be able to or accidentally easily turn off the meter.

Thank you very much, I appreciate the help fellas!

 

[Jraef]

NEC tap rule covers taps (240.21(B)). Depends on numerous factors including length of tap and size of wires. If you can keep the tap to 10' long, you are allowed a fair amount of flexibility.

A breaker would work fine too. Often owners/clients don't want someone to be able to or accidentally easily turn off the meter.

Also notice that they show fuses on those wires, that's the OCPD for the wires feeding the meter, allowing the tap rule implementation. What is often done for that is to use a fuse holder that can act like a switch so that if you need to kill power to the meter for some reason in the future, you don't have to lift wires.

 

[GoldDigger]

Also notice that they show fuses on those wires, that's the OCPD for the wires feeding the meter, allowing the tap rule implementation. What is often done for that is to use a fuse holder that can act like a switch so that if you need to kill power to the meter for some reason in the future, you don't have to lift wires.

Not critical in this case, but note that many of the disconnect type fuseholders are not rated to break load current by opening the fuseholder You would have to make sure the load is turned off first.

 

[Jraef]

Not critical in this case, but note that many of the disconnect type fuseholders are not rated to break load current by opening the fuseholder You would have to make sure the load is turned off first.

Correct and that's an important point in many cases, but I don't think the voltage sensing circuit of a meter is considered a "load". Technically it is because it's the ONLY load, but it's going to be milliamps of current.

PS: 4VA load... so worst case at 120VAC, 33mA.

 

[infinity]

We do sub metering with Veris boards. The potential taps go to the three phase CB on the left;

 

[greenspark1]

We do sub metering with Veris boards. The potential taps go to the three phase CB on the left;

Looks nice. What's that ribbon cable and circuit board for?

 

[infinity]

We do sub metering with Veris boards. The potential taps go to the three phase CB on the left;

It connects to the CT's that are mounted on those board right next to the breakers.

 

[greenspark1]

It connects to the CT's that are mounted on those board right next to the breakers.

Oh, now I see that you have CTs for each circuit. Nice! I've never done this level of metering before, does it work pretty well?

 

[infinity]

Oh, now I see that you have CTs for each circuit. Nice! I've never done this level of metering before, does it work pretty well?

Yes very well, although the CT's mounted adjacent to the CB's are only soldered to a PC board so they're rather fragile.