Installing a separate watthour meter and confused by bonding neutral and ground

[paul.peavyhouse]

I am installing a separate watthour meter in my home to monitor the power usage of a high load appliance in my garage. The meter is 2 phase 3 wire and is designed w/ the neutral (center pole) bonded to the housing; there is no way around this, nor have I seen any meters that make this an option.

I plan to run THHN 4446 wire from my main panel through metal conduit to the meter housing; the conduit and the meter housing would both be ground.

Thus, when I tie down the neutral to the meter I would have no choice but to bond it to ground (as the housing is designed).

From my understanding, neutral and ground are only supposed to be

bonded together in one location: the main service entrance breaker box. If I am bonding neutral to ground at this second location (my meter housing), isn't that bad?

What am I supposed to do w/ the ground in a meter housing? Am I not supposed to bring ground in to the meter housing? Is it OK to bond ground and neutral in a meter housing? If not, do I not connect the conduit/housing to the main service ground, and then just run a separate ground for my garage conduit/housing?

Thanks!

Pv

[professorpaul]

I have seen a meter for just this -- you plug in the appliance and it gives you the wattage drawn (I assume it is calculating real power, not VA's)

[RBM]

It's single phase three wire, not two phase. Typical watt hour meters used by utility companies bond their neutral to the fifth jaw of the meter, which is grounded by the utility companies neutral and you don't run a separate ground to the meter box. If you are trying to sub meter, you may be better off using something like an "emon demon" designed for that purpose

[volts500]

You should be able to purchase a "neutral isolation kit" from the manufacturer, just for that purpose.

[Eric9822]

Yes bonding the neutral and ground at a second location is bad and it violates NEC. If you do bond them here you will split the neutral current across the neutral conductor and the ground conductor. The ground conductor should not have current on it during normal operation. You must find a way to isolate them. What exactly are you trying to meter?

[paul.peavyhouse]

An electric vehicle charger. A MagneCharger to be precise. It will draw ~33amps @ 240V.

[paul.peavyhouse]

Sorry, I meant 2 pole (single phase), not 2 phase.

At first I considered getting an emon, but it seemed that a watthour meter and housing was more professional looking.

I am using an Itron Centron meter.

Do I need a "neutral isolation kit" in order to properly set up a submeter?

Thanks!

Pv

[RBM]

I'm not familiar with that meter, that's why I suggested an Emon, to avoid the problem

[Don Young]

I am not sure but I seem to recall that at least some 240V meters do not use a neutral connection. If not, you could just run the neutral thru the socket and tie the grounds to the meter base.

Don Young

[Eric9822]

Thats a pretty good load. Hopefully you can find a meter base that allows an unbonded nuetral and ground. Good Luck.

[volts500]

A neutral isolation kit should be available from the place where you purchased the meter socket enclosure. If the enclosure is any common brand name, such as Milbank or Siemens, etc., any electric supply house should have one.

There is an exception in NEC (2002) Section 250.142(B), Exception #2, that does permit one to ground meter enclosures on the load side of the service disconnecting means by connection to the neutral IF all the meter enclosures are located near the service disconnecting means, plus some other requirements that don't apply to you.

In other words, you can install the new meter enclosure next to your existing electric service and feed it off a breaker in the main panel, then mount a disconnect next to or below the new meter, then run a conduit to where you need to go from that disconnect. That's how I would do it anyway.

I must tell you, however, that even though this is permitted by NEC, some electrical inspectors will not accept it, and will make you install the neutral isolation kit. You should call your local electric inspector to see if they will allow it.

[gfretwell]

It doesn't sound like you need a neutral at all. I doubt the meter uses it. The meters I see only have 4 stabs on them, 2 in, 2 out and only connect to the phase conductors. If your load is 240v only there doesn't need to be a neutral.