This topic contains 5 replies, has 2 voices, and was last updated by Todd Lommen 3 weeks, 4 days ago.
This is a fairly common question that comes up. What happens if I find a 2S meter installed in a network 120/208 service. The answer is you have been under registering usage. In a 2S, 3S, or 4S service the phasors between legs is 180 degrees (direct opposite). In a network service it is actually 2 phases out of a 3 phase system which means they are 120 degrees apart. Because a 2S or for that fact 3S or 4S meter are not Blondel compliant they can’t register multiple phases properly. To put it simply the best registration you will see on your meter is 70% if the load is very well balanced. The more unbalanced the load is the more the registration will suffer in a situation like this.
Now if a 12S meter is installed in a single phase of 120/240 volt there isn’t anything you need to do in terms of rebill. There is an element on each leg of the power and the meter is registering correctly with no issue.
Also note if you need to have a CT rated service in a network 120/208 service you need to use a 2 element meter which would be a 5/35/45S type meter.
We run into this sometimes. Usually is a result of a Lineman changing a meter out and not putting the correct meter back in when it is not reading AMR/AMI.
We’ve seen the same thing happen with us. We have also seen where a single phase transformer was taken down and the meter got connected to a near by 3 phase bank. Most of the time when this happens we have our voltage alarms on our meters set in a tight enough tolerance that they start alarming about low voltage and a quick check of the voltage reading usually lets us know what the problem is.
Jason – What would be the registration difference in this scenario –
We have a 3 Phase 3 Wire Delta 480V- Ground is a Common –
Meter put in was programmed to be a 3 wire Network –
It probably should be programmed to be a 3 Phase 3 Wire Delta –
So if you are metering this with a 12S meter and your voltages you are measuring are L-N then you are only recording about 70% of what is actually going on. you are basically just metering 2 of the 3 legs. In this scenario with a 12S meter you need to have the common be referencing the 3rd power wire so you are getting line to line voltages. By doing the line to line voltage reference you are now accounting for the power flow in the 3rd power leg that isn’t going directly through the meter. Typically to do this requires a little modification of the 5th jaw in the socket since it is typically designed to go to the bonded neutral in the socket instead.
What we have done in the past sometimes is convert it to a 4 wire setup and measure it with a 16S, just the customer doesn’t bring the neutral in past the socket since they don’t need it.
So it’s a 9sCL200 socket, so we have a 9sCL200 meter installed here (this installation was put in 20 years ago). KV2c Fitz-All programmed as a 3P 3W Delta vs Network –
I figured we were maybe around 86% give or take depending on the load – But I think it’s just an irrigation pump – I was thinking it maybe wouldn’t be off as high of percentage if they are using an ungrounded motor load – 3 phase motor utilizing only equipment ground
I guess I won’t know for sure until I can see a season of usage this summer – This is the only service like this on our system – Motor load is around 20KW
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