Three phase meter socket/single phase service

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rojay

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Chicago,IL USA
Is there any reason a POCO would refuse to connect to a three phase meter socket being used in a single phase service application?

A customer requested 120/208 3 phase 4 wire service and then decided against the idea when finding out it wasn't readily available in their residential neighborhood without added expense.
Unfortunately, this was after three phase meter and disconnect switch were already installed.

We returned, removed the third phase leg and left existing three phase service equipment intact. POCO is refusing to set meter :cry:
 
Three phase disconnect should not be a problem, but the meter socket limits what POCO can install. If it is like single phase meters, it assumes that neutral is equidistant from all three phases and does not even make a voltage or current connection to the neutral wire.
That cannot work with single phase with the third meter leg either open or grounded.

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GoldDigger said:
That cannot work with single phase with the third meter leg either open or grounded.

That's interesting that you say that. I had a similar situation to this a while back only in reverse.
We had a single phase feeder going to a rooftop transformer (50 kva 480/120-240 volt).
The feeder originated in a 3 phase 4 wire 277/480 volt tenant meter stack in the basement.
Only needing single phase 480 and a ground for our transformer- we had an open position in the meter socket and the POCO refused to set a meter.

The solution they required was to pull a third leg. Fortunately we had used a three phase disconnect on the primary side of the transformer. We landed the third leg at the line side of the disconnect- and that "solved" the problem.

The 7 terminal meter needed to see a third open leg to function properly? Confused:?
Click to expand...
 
I'm not getting it. From the meter's point of view, what's the difference between an open third leg and no load on the third leg? Doesn't the meter need to measure power accurately on the other three wires regardless? Also I thought three phase meters did have a connection to the neutral.
 
jaggedben said:
I'm not getting it. From the meter's point of view, what's the difference between an open third leg and no load on the third leg? Doesn't the meter need to measure power accurately on the other three wires regardless? Also I thought three phase meters did have a connection to the neutral.
Click to expand...
The difference is in the voltage on the unused leg. And the meter cannot depend on a neutral connection if it is designed to work with either wye or delta service.
However I have not really worked with one. "This looks like a job for *meternerd*!"

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In other words, as long as the third leg is bought to the meter to measure voltage, it doesn't matter if it goes further. I think I get that.

I can see how this is a problem now for the OP.
 
jaggedben said:
In other words, as long as the third leg is bought to the meter to measure voltage, it doesn't matter if it goes further. I think I get that.

I can see how this is a problem now for the OP.
Click to expand...

In the OP's case the service is 120-0-120, not two wires out of a three phase, so there is no third wire source to connect to the meter. There is a slight theoretical possibility that with the right design choices made in the meter it would be sufficient to connect the third leg to the single phase neutral.

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jaggedben said:
I'm not getting it. From the meter's point of view, what's the difference between an open third leg and no load on the third leg? Doesn't the meter need to measure power accurately on the other three wires regardless? Also I thought three phase meters did have a connection to the neutral.
Click to expand...

Two legs of a 208/120Y service does not equal a single phase service. Phase to neutral voltages are fine but phase to phase is 208V, not 240V. I'm not surprised that the POCO doesn't want a service that looks like single phase but isn't.
 
ggunn said:
Two legs of a 208/120Y service does not equal a single phase service. Phase to neutral voltages are fine but phase to phase is 208V, not 240V. I'm not surprised that the POCO doesn't want a service that looks like single phase but isn't.
Click to expand...

Just to clarify- this was initially completed as a 120/208 three phase 4 wire service. When the customer called POCO for hookup they learned that 3 phase power was not readily available in their mostly residential area without a considerable added expense. The whole 3 phase idea was then scrapped. In an attempt to salvage the existing service equipment and save the customer some $ as well- the third phase leg was removed.

Customer is now seeking a 120/240 volt three wire single phase service and the POCO will not place a meter in the existing three phase socket.
 
ggunn said:
Two legs of a 208/120Y service does not equal a single phase service. Phase to neutral voltages are fine but phase to phase is 208V, not 240V. I'm not surprised that the POCO doesn't want a service that looks like single phase but isn't.
Click to expand...

I was trying to tease out if there is any electrical theory reason why the 3-phase meter wouldn't accurately measure energy consumption, or if the reasons for utility refusal here are essentially just bureaucratic.

I understand that 2-leg 208/120V services do exist, although I've never seen one.
 
rojay said:
Just to clarify- this was initially completed as a 120/208 three phase 4 wire service. When the customer called POCO for hookup they learned that 3 phase power was not readily available in their mostly residential area without a considerable added expense. The whole 3 phase idea was then scrapped. In an attempt to salvage the existing service equipment and save the customer some $ as well- the third phase leg was removed.

Customer is now seeking a 120/240 volt three wire single phase service and the POCO will not place a meter in the existing three phase socket.
Click to expand...

They must have pulled a permit for three phase power to get an inspection and get it called in.

The service now requested is single phase. I would think they would need a new permit and a new inspection and get it called in for a single phase hook up. I would say the metering equipment at least would need changed out.

I just wonder who the idiot was that didn't check this out before doing the work.
 
growler said:
They must have pulled a permit for three phase power to get an inspection and get it called in.

The service now requested is single phase. I would think they would need a new permit and a new inspection and get it called in for a single phase hook up. I would say the metering equipment at least would need changed out.

I just wonder who the idiot was that didn't check this out before doing the work.
Click to expand...

Perhaps the same idiot who wired up an entire apartment building near here giving every unit alternating two phases of a 208 three phase service only to find that the transformer feeding the building was 240V delta high leg. Oops.
 
Meternerd to the rescue....

Meternerd to the rescue....

GoldDigger said:
The difference is in the voltage on the unused leg. And the meter cannot depend on a neutral connection if it is designed to work with either wye or delta service.
However I have not really worked with one. "This looks like a job for *meternerd*!"

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Click to expand...

Well, in my humble but absolutely always correct opinion.....if it's solid state (which most likely it will be), the meter will meter accurately whether there is a missing phase or not...but....there will be a "loss of phase" alarm which will likely drive the techs and the billing department nuts. Also, I programmed the meters to stop transmitting (for remote read meters) on a loss of phase, so the meter tech (me) had to go out and verify all three phases and clear the alarm to restart the transmission. It's mostly because of CT meters, since the service would still supply normal power even if one of the phases of the meter wiring failed due to a bad connection, blown PT fuse, etc., but the POCO would meter only 2/3 of total usage. If it was me, I'd definitely put the Kabosh on a 3 phase socket with single phase connections. Plus, I loved to "p**s off" the contractors. :lol: By the way, 3P 4W meters always depend on the neutral for metering. All three phase four wire meters have three phase jaws and one neutral jaw for the voltages. Delta meters can't be used on a Wye service.
 
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meternerd again...

meternerd again...

jaggedben said:
I was trying to tease out if there is any electrical theory reason why the 3-phase meter wouldn't accurately measure energy consumption, or if the reasons for utility refusal here are essentially just bureaucratic.

I understand that 2-leg 208/120V services do exist, although I've never seen one.
Click to expand...

3P 4W Wye (Form 9S) meters will register accurately on a missing phase because they are three phase three element meters, meaning each phase in independent of the others. No bureaucrats lurking in the POCO. That's not the reason they aren't used on single phase. They are more expensive and have "loss of phase" alarm functions which would require special programming to disable.

208/120 3 leg services are very common. No such thing as 120/208V 2 leg. You need two phase legs to get the 208V and a neutral for the 120V. Used mostly in apartment services where a 3P 4W 208/120 service feeds a multi-meter bank of 120V 3W single phase meters (Form 12S).
 
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Uh OH!....typo glitch...

Uh OH!....typo glitch...

A 3P 4W meter can be a Form 9S 20A (for CT's) or Form 16S (200A) for direct connection. Also, the newer 3P 4W meters can meter either Wye or Delta, but they internally reconfigure to do so. Just trying to avoid any flaming arrows.....:ashamed1: Remember......If guns kill people, I can blame my keyboard for misspelled words!
 
meternerd said:
208/120 3 leg services are very common. No such thing as 120/208V 2 leg. You need two phase legs to get the 208V and a neutral for the 120V. Used mostly in apartment services where a 3P 4W 208/120 service feeds a multi-meter bank of 120V 3W single phase meters (Form 12S).
Click to expand...

When I said 2 legs I meant two hot legs. But 3-wire 208/120 services are common, that's what you're saying, right?
 
jaggedben said:
When I said 2 legs I meant two hot legs. But 3-wire 208/120 services are common, that's what you're saying, right?
Click to expand...

No...I didn't intend to say that. I'm saying that it's common to find 208/120V 3P 4W services where the service is set up to feed multiple single phase 208/120V meters. I doubt you'll ever see a three phase Wye bank that feeds only one single phase service. Some utilities may allow several separate residences to each use two phases of a three phase bank, but we would not. The standard 4 jaw meter sockets require a fifth jaw added at the 9:00 or 6:00 position and connected to the service neutral, since they meter line to neutral, rather than line to line, as in a 120/240 service. It's called "network metering". Not sure why.
 
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rojay said:
Is there any reason a POCO would refuse to connect to a three phase meter socket being used in a single phase service application?

A customer requested 120/208 3 phase 4 wire service and then decided against the idea when finding out it wasn't readily available in their residential neighborhood without added expense.
Unfortunately, this was after three phase meter and disconnect switch were already installed.

We returned, removed the third phase leg and left existing three phase service equipment intact. POCO is refusing to set meter :cry:
Click to expand...

Hi There JoRay,
I've got an almost identical situation, How did you solve this problem?
Thanks,
Jon
 
jbullock508 said:
Hi There JoRay,
I've got an almost identical situation, How did you solve this problem?
Thanks,
Jon
Click to expand...
Old thread has been revived. I will only say POCO can do what they want for the most part.

If you keep three phase meter, they may want three phase input to it - keep in mind high leg systems often require the high leg to be in the right position of the meter.

Otherwise if you supply the two outer positions and leave center position open - a single phase meter will physically match up to those jaws and will work.
 
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