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Network Meter in a 240/120 V Meter Socket

Network Meter in a 240/120 V Meter Socket

Network Meter in a 240/120 V Meter Socket


I would like to know if there is any sub-registration of energy if a network meter (12S/25S)is installed
in a bank of meters or meter socket that is being fed from a single phase transformer, 240/120 V.

The normal meter form for a 240/120 V service is a 2S meter, but for some reason someone installed a network meter.

The socket has the 5th jaw/pin, so the network meter is getting the neutral reference, but instead of receiving 208/120 V from a
3 phase transformer bank, it's receiving 240/120 V from a single phase transformer.


RE: Network Meter in a 240/120 V Meter Socket

It should work OK if the 5th jaw is connected correctly.
In the case where there is uneven loading to the point that there is less voltage on one nominal 120 Volt side than the other nominal 120 Volt side it will meter more accurately than the standard meter.

"Why not the best?"
Jimmy Carter

RE: Network Meter in a 240/120 V Meter Socket

Hi Waross,

In this case the 5th jaw is connected to the neutral of the 240/120 V service cable.

Does the fact that there is a phase angle of 180° for the 240/120 V service and a phase angle of 120° for the 208/120 V service, won't affect the a accuracy of the
energy calculation in an electronic meter?

Thank you for your answer.


RE: Network Meter in a 240/120 V Meter Socket

One meter is measuring/metering 240 Volts. The meter is assuming that the two lines are equal voltage.
eg: 120 Volts and 120 Volts. If used on 120/208 Volts the meter will meter 208 Volt loads correctly but will erroneously assume that the 120 Volt loads are at 104 Volts.
The single phase meter uses one channel.
The network meter uses two channels.

Meter operation: The original single phase electro-mechanical meters used one 240 Volt potential coil and two current coils to develop torque to turn the disk. The meter had to make the assumption that the line to neutral voltages on L1 and L2 were equal and 1/2 of the voltage applied to the 240 volt coil.

The 120/208 Volt meters had two separate coil sets developing torque. Each set was independent of the other. The only common ground was that each added torque to the same disk.

The algorithms used in electronic meters are proprietary and not available to us*. However logic and field experience indicate that network meters use independent sections for each 120 Volt leg.

From field experience I have seen (and still have in the memory of an old laptop) memory dumps from an electronic three phase meter. I had the good fortune to be working in an area where the power utility would send a service man out to a meter and do a data dump for the last 30 days or 60 days. They would provide this to me on a floppy disk.
The electronic meter would record and report at 15 minute intervals the following values;
Maximum and minimum voltages.
Maximum current.
Maximum kW demand.
Maximum KVAR demand.
These values were recorded for each phase independently.

*We had an interesting thread a few years ago;
Gunnar was able to determine that an electronic meter was using an algorithm that over reported some types of loads.
We were able to determine that the algorithm was faulty by the observation of the reaction to known loads and comparison to other meters but never did see the actual algorithm.

Energy meter with fast cycling load
thread238-266145: Energy meter with fast cycling load

"Why not the best?"
Jimmy Carter

RE: Network Meter in a 240/120 V Meter Socket

Thank you for this comprehensive answer.


RE: Network Meter in a 240/120 V Meter Socket

I like it. The proposed connection is Blondel compliant.

RE: Network Meter in a 240/120 V Meter Socket

A seafood processing plant supplied shore power to fishing boats along-side.
Their system was 120/208 Volts.
The plant handy-man ran the shore power feeds as two phases and a neutral through a 4 jaw meter.
I pointed out that they would be under-metering the 120 Volt loads by about (1 - (120/104)) = .15 or 15%.
No problem. They just jacked their rate up about 20%.

"Why not the best?"
Jimmy Carter

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