converting 240V meter to 120V

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daniel3

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I have a client that has a camp ground which has a RV type panel at each camping site. This last spring he had me install meters on six of these sites, the circuits are single phase 120V @ 30A. I purchased the meters from Utility Supply Group after talking to their tech who assured me that the meters would work with 120V rather than the 240V. I was told to wire the meter by connecting the line to the line1 terminal, place a jumper between the two load terminals, and to connect the load to the line2 terminal. I found out yesterday that the meters are not reading, the power was off for the season at the time that I installed these and didn't get the chance to test them at the time of installation. Obviously I don't have a great deal of faith in USG's tech help, can anyone here suggest how to make the 240 meters work on 120V?
 
One would think that you'd just have to connect Line-1 and Load-1. It would operate no differently than an extremely unbalanced 240V service, assuming it's a singlephase 3-wire meter.

The way you're describing would cause the meter to read the same amount going both ways, cancelling each other out (I'm thinking like net metering_)
 
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Thanks Rampage_Rick, I had thought it should be something like that, I'll give it a try in the morning.

By the way, this was done last spring and the client just now got hold of me about a different matter, when I found out that the meters weren't working I asked him why he didn't call me immediately. I had traded my time for fire wood which he gets for free, and he was embarrassed to ask me because he thought that I basically worked for free as far as he was concerned. I'll remind him tomorrow how nice and warm it is here tonight.:D
 
Actually I am an electrician, I'm just finishing my first semester in the Mechatronics program at Sierra College. I have back problems that will not allow me to continue the work that I have been doing.

Mechatronics equipment integrates electronics, mechanics, pneumatics, hydraulics and computer control. Applications range from robotics to maintaining medical electronics, and from repairing ATM machines to stationary engineer positions.

The demand in our community is so high that employers are hiring students right out of the classes. The city of Roseville, Ca. hired one of our grads with a entry level pay of 52k., not bad for a two year degree.
 
If you had a true 120/240V single phase meter that met the requirements of 'Blondel's Theorem', then the system would work as Rick describes. The meter would separately meter the voltage to each 'hot' conductor, and separately meter the current to each 'hot' conductor, and then register the total power delivered. One side would have no voltage, and no current, the other side would register, no problem.

Unfortunately the common 'form 2S' meter 'cheats'. The meter makes a _single_ line to line voltage measurement, combined with separate current measurements for each hot leg. In essence, the meter operates on the assumption of perfect voltage balance between the legs. If you were to only connect one of the 'hot' legs, and not the other, then you end up with no voltage measurement at all, and thus no power delivered.

A form 2S meter can be reconnected to read properly, but this involves both different wiring for the current measurement, and different wiring for the voltage measurement. It sounds like the USG tech didn't tell you about the jumper that you need to add for the voltage measurement.

See:
basic theory:
http://www.uomschool.org/Meter_Book/Table%20of%20Contents/Blondel/Blondel's%20Theorem.htm
normal application of the meter:
http://www.uomschool.org/Meter_Book/Table of Contents/Self-Contained Diagrams/2S - 240V - 3W.htm
and finally the solution, how to use the meter at 120V:
http://www.uomschool.org/Meter_Book...lf-Contained Diagrams/2S - 120V - 2W alt1.htm

Be especially aware to connect the voltage measurement jumper to the correct terminal, otherwise you've built a short circuit into the meter.

-Jon
 
Makes sense now that I read it. Learn something new every day... Essentially Danial connected everything correctly, he just omitted a step:

Open the test link to gain access to the right end of the potential coil. Be certain you attach the ground wire to the appropriate screw on the back of the meter. Connecting to the wrong test link will create a dangerous short circuit when the meter is installed!

USG appears to be right up there with the bleeding edge of technology. They've got 'digital' meters for a song. (and you were wondering what your PoCo did with their old meters?)
Meter.gif
 
So the wiring of the socket is correct, and the jumper to be removed is on the rear of the meter itself?
 
Thanks again, I found the diagram in winnie's post. I'm going to call USG this morning and see if I can get one of their techs, they were all at an electronics show earlier this week.

Edit: I just got off the phone with USG's tech and he has confirmed the location of the test jumper and which side to attach the ground wire to.

Rampage_Rick, I wasn't aware that these meters were reconditioned units, oh well...I have the warranty and the price was right.
 
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