New 200 amp service

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rojay

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Chicago,IL USA
Our company is being asked to "mirror" an installation that was done by another contractor. It is for a single phase 200amp 120/208 volt service. The feed for the service is coming from some switchgear located in the basement of a 5 story building(three phase 4 wire 120/208). The previous contractor has installed a three phase meter and a fed it three phase to the line side and went single phase out of the meter through the disconnect and to the load. Does anyone have any thoughts as to why I would want to mirror this kind of setup vs. using a single phase meter and disconnect?
 
I agree with don, but might mention, if it is a 208v system, the POCOs I work with have meters that requires the 5th jaw jumped to the neutral. When you talk with POCO you might verify that as all sockets don't have that capability.
 
Do you have OC ahead of this meter ? -- If so, You are saying you have a 3 phase circuit feeder supplying single phase equipment. After going thru the meter in what type of electrical equipment do you terminate? --Is this 1 of 6 disconnects for the building at the service equuipment? If not, I would question how the POCO would have authority if this is past the service point.
 
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mwm1752 said:
Do you have OC ahead of this meter ? -- If so, You are saying you have a 3 phase circuit feeder supplying single phase equipment. After going thru the meter in what type of electrical equipment do you terminate? --Is this 1 of 6 disconnects for the building at the service equuipment? If not, I would question how the POCO would have authority if this is past the service point.
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Yes, the meter is being fed from 120/208 3 phase switchgear. After the meter we would be going into a 200 amp fused disconnect switch and up five floors to feed 200 amp single phase panel. As I indicated before, this installation was to mirror a previous install done by another EC. I was just trying to make sense of their use of a 3 phase meter and disconnect for a single phase application.
Augie47 brings up an interesting point about the 5 terminal meter. Was it just a matter of economics, and the three phase meter was cheaper? Not sure, as I cant recall running into any 120/208 single phase services.
 
I think I have it now- unfused tap from the service equipment to a 3 phase meterbase -- load side of meterbase feeds single phase OC device which in turn sends a feeder to a remote part of the building - does sound as if it is under POCO authority for meter configuration -- Here the POCO will allow you to set up to 200 amps single phase on their 3 phase transformers. Maybe they are being futuristic in case an upgrade to the service is needed.
 
rojay said:
Our company is being asked to "mirror" an installation that was done by another contractor. It is for a single phase 200amp 120/208 volt service. The feed for the service is coming from some switchgear located in the basement of a 5 story building(three phase 4 wire 120/208). The previous contractor has installed a three phase meter and a fed it three phase to the line side and went single phase out of the meter through the disconnect and to the load. Does anyone have any thoughts as to why I would want to mirror this kind of setup vs. using a single phase meter and disconnect?
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I believe you need the 3 phase meter socket because the POCO's meter has to be a 3 phase meter to record the values at the 120/208v. Plugging a single phase socket set for values 120/240 would probably read the wrong kilowatts at 120/208. They probably use a 3 phase meter with one phase not being used.
 
Mulrooney said:
I believe you need the 3 phase meter socket because the POCO's meter has to be a 3 phase meter to record the values at the 120/208v. Plugging a single phase socket set for values 120/240 would probably read the wrong kilowatts at 120/208. They probably use a 3 phase meter with one phase not being used.
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:thumbsup:
A standard 129/240 meter does not need a neutral connection because it assumes that the line to neutral voltages are equal and opposite in phase. A three wire delta can assume that the line to line voltages are equal and 120 degrees out of phase and so could measure two line currents and one line to line voltage, although the design for an analog meter is easier if all three voltages are available.
But although a three phase four wire meter could "cheat" and not measure voltages relative to the neutral, it is both more accurate and easier to design if it has access to all four wires.



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