Meter madness

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rojay

Senior Member
Location
Chicago,IL USA
I have a feeder that originates in a tenant metering switchboard. Switchboard is 800 amp 3 phase 4 wire 277/480 wye.
My feeder is a single phase 480 volt circuit (2 hots w/ground) that runs to a single phase transformer (480 volt primary w/120/240 volt secondary) to power a panelboard. Only the two phase wires of this feeder were connected to the load side of my meter. Will the meter read properly? POCO says no and states that I have to run three phase 4 wire circuit to the line side of my xfmr disco switch. :?
 

iwire

Moderator
Staff member
Location
Massachusetts
I have a feeder that originates in a tenant metering switchboard. Switchboard is 800 amp 3 phase 4 wire 277/480 wye.
My feeder is a single phase 480 volt circuit (2 hots w/ground) that runs to a single phase transformer (480 volt primary w/120/240 volt secondary) to power a panelboard. Only the two phase wires of this feeder were connected to the load side of my meter. Will the meter read properly? POCO says no and states that I have to run three phase 4 wire circuit to the line side of my xfmr disco switch. :?

It will read as correctly with or without the additional wire not connected to anything.

I would just run the wire and move on.
 

kwired

Electron manager
Location
NE Nebraska
If you connected 3 phase 4 wire to your disconnect and leave disconnect with 2 phase conductors and one ground conductor you still have same amount of current on the unused phase conductor which is none.

Line side of meter will need voltage - to work correctly in many instances - if you are using a three phase meter. If you are using a single phase meter in a three phase socket - you need to use the proper poles that line up with the meter tabs.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
A single phase 120/240 meter with neutral loads will not read correctly on a two out of three phase connection since it will assume that the line-neutral voltage is 104V. POCO will not like that!
And the phase angle will seem odd too, shortchanging POCO even more.
 

kwired

Electron manager
Location
NE Nebraska
A single phase 120/240 meter with neutral loads will not read correctly on a two out of three phase connection since it will assume that the line-neutral voltage is 104V. POCO will not like that!
And the phase angle will seem odd too, shortchanging POCO even more.
Sounds like POCO's problem to me if they supply the wrong meter.

Though OP has 480/277 supply and will have similar problem if they have single phase meter that assumes 240 volts to neutral but only if there are 277 volt loads being supplied, his 480 volt transformer primary being only load should be fine though.
 

iwire

Moderator
Staff member
Location
Massachusetts
A single phase 120/240 meter with neutral loads will not read correctly on a two out of three phase connection since it will assume that the line-neutral voltage is 104V. POCO will not like that!
And the phase angle will seem odd too, shortchanging POCO even more.

No kidding, but adding the conductor the POCO is requesting will not change that.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
No kidding, but adding the conductor the POCO is requesting will not change that.
Agreed, but the OPs situation seems to involve a three phase meter, not the hypothetical single phase meter which came into the discussion later. In the case of that single phase meter the neutral is not even electrically connected to the meter regardless of whether or not it goes from there to a disconnect.
 

iwire

Moderator
Staff member
Location
Massachusetts
Agreed, but the OPs situation seems to involve a three phase meter, not the hypothetical single phase meter which came into the discussion later. In the case of that single phase meter the neutral is not even electrically connected to the meter.

:?:?:?:?:?

Single phase, three phase, seventeen phase. The extra wire being requested is not changing anything.
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
I have a feeder that originates in a tenant metering switchboard. Switchboard is 800 amp 3 phase 4 wire 277/480 wye.
My feeder is a single phase 480 volt circuit (2 hots w/ground) that runs to a single phase transformer (480 volt primary w/120/240 volt secondary) to power a panelboard. Only the two phase wires of this feeder were connected to the load side of my meter. Will the meter read properly? POCO says no and states that I have to run three phase 4 wire circuit to the line side of my xfmr disco switch. :?
Ask to talk to someone higher up on the chain of command.
 

kwired

Electron manager
Location
NE Nebraska
Agreed, but the OPs situation seems to involve a three phase meter, not the hypothetical single phase meter which came into the discussion later. In the case of that single phase meter the neutral is not even electrically connected to the meter regardless of whether or not it goes from there to a disconnect.
Unless I read it wrong, it likely is a three phase meter socket with three phase meter installed. What POCO is requesting is a conductor be attached to all three load terminals - even though one of them will not be landing on any potential loads. It is understandable the meter may need all three supply conductors to get proper voltage references for metering, but load side connections shouldn't matter. It will meter whatever current passes through it, or "not meter" non existing current.

Proper single phase meter for 120/208 would work in this socket in this situation - but center phase would have to be the one with no connected load as the single phase meter would not have plug tabs in that position.
 

meternerd

Senior Member
Location
Athol, ID
Occupation
retired water & electric utility electrician, meter/relay tech
Depends on the meter. Older solid state meters used A phase to neutral as the source for meter power. Newer Form 9S meters will power up on any phase. A true 4 quadrant 3 Ph 4 Wire meter will meter correctly for any load on any phase, but they do need a neutral reference even if loads are phase to phase only. Any downstream transformer loads would not change that. To meter a single phase circuit with only two phases and a neutral fed from a 3P 4W source you would need a Form 12S rated for 277V. Pretty rare. The 3P 4W meter would work fine but you'd have to disable the "loss of phase" alarms. To meter the secondary of you transformer, you'd just use a standard Form 2S 240 meter.
 
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iwire

Moderator
Staff member
Location
Massachusetts
Here is what I believe the OP has

SERVICE CONDUCTORS > THREE PHASE METERING SWITCHBOARD > NEW SINGLE PHASE FEEDER


There is almost nothing the electrician can do with the new feeder that will change how the metering works. The power company either has the correct metering in place or they do not.
 
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