Harris Institute of Technical Training

I have a sangamo single phase ct'd meter that a contrator installed, and I am trying to figure out how he came up with the multiplier for it. He said he changed the register on the meter to an Rr of 27 7/9 and could not remember what the old one was. The meter is a Sangamo class 10, 240v, 3 wire, type J4s, TA 2.5, and Kh 0.6. I have 400:5 ct's and he is telling me the multiplier should be 12. If any body can explain this to me i would greatly appreciate the help.

There is a simple way to find the multiplier for a mechanical meter. You take the Kh x Rr x Rs then divide it all by 10,000. I have a handy chart for Rs (first gear reduction) and it lists a J4 having an Rs of 50/1. When I worked this out I got a multiplier of .08 for the meter. Which seems kinda hokie. Usually you end up with something greater than 1. So then you just take the meter multiple times the CT multiple .08 x 80 and you get 6. I would bet that he used 100/1 for the Rs instead of 50/1. Which would make the multiple 12. The J4s' GE counter part (I-30 through 70) all have a Rs of 100/1. The list where I get my information can be found at www.uomschool.org, just click on the big yellow box, then go to the links tab and then under basic metering for the lineman you will see a Rs shaft reduction list. Hope this will help you out.

Starting with the billing multiplier of 12 (as noted in the original question), this does not match with the billing multiplier math that should be used. Below is my reply, based on the information provided, as to what I believe Steve has there and what I see as the billing multiplier with the new register. At the bottom of my explanation I suggest a couple of register ratios that would make a lot more sense for this billing multiplier question.

Assuming that this is probably a single phase, 240 Volt, Three Wire installation I would expect that the 400:5 CT has both energized conductors in it. This is how Single Phase, 240 Volt, Three Wire CT installations are done. With that as my expectation I expect the following to be true:
The two energized phase conductors are put into the CT in opposite directions so that the current flowing in them will add together. This might not sound right, but this is true and correct. With both conductors in the CT (adding their currents together) then the CT ratio needs to be divided by two because of the two turns caused by the two energized conductors in the Current Transformer. For example: the 400:5 CT with an 80:1 ratio would end up with an actual CT billing ratio of (80:1 divided by 2) or 40:1.

Steve was given 12 as the new billing multiplier by the contractor. Trying to prove this, the meter multiplier(Kr) is, as Kristen suggests, equal to the Kh x Rr x Rs divided by 10,000. Filling in the blanks of this formula we have: (Kh = .6, Rr = 27 7/9, Rs = 50/1)/10,000 thus (.6 x 27 7/9 x 50) /10,000.
Solving for the meter Kr with the new register ratio, the meter multiplier would be .083333… (the 3’s being infinite). I agree that this is a hokie meter multiplier, but it is what the meter multiplier math and new register gives us. Next we solve for the billing multiplier by taking the meter Kr of .08333…. and multiplying it by the CT ratio (40:1). Solving the formula we get .083333… x 40 = 3.3333… Making the new billing multiplier equal to 3.3333… (with infinite 3’s) not 12 as provided by the contractor.

I suspect that the original register ratio was either a 166 2/3 or a 333 1/3.
Using the 166 2/3 register ratio the meter multiplier would be: Kh x Rr x Rs divided by 10,000 (Kh = .6, Rr = 166 2/3, Rs = 50/1)/10,000. Which would give you a meter multiplier(Kr) of .5. With a meter Kr of .5 and a CT ratio of 40:1 the billing multiplier would be equal to (.5 x 40) or 20.
Using the 333 1/3 register ratio the meter multiplier would be: Kh x Rr x Rs divided by 10,000 (Kh = .6, Rr = 333 1/3, Rs = 50/1)/10,000. Which would give you a meter multiplier(Kr) of 1. With a meter Kr of 1 and a CT ratio of 40:1 the billing multiplier would be equal to (1 x 40) or 40.

There is also another possibility to consider, based upon my knowledge and awareness of the use of register ratios that fit well with these type of billing formulations. What they (metermen of the past) have done was to manipulate the register ratio to fit with the billing formulations. So, based on that thinking, there is an outside chance that the original register ratio was possibly 8 1/3 and if that is the case, then this meter multiplier would be: Kh x Rr x Rs divided by 10,000 (Kh = .6, Rr = 8 1/3, Rs = 50/1)/10,000. Which would give you a meter multiplier(Kr) of .025. With a meter Kr of .025 and a CT ratio of 40:1 the billing multiplier would be equal to (.025 x 40) or 1.

Kristen, I commend you on stepping up to answer this question. I admire your courage and willingness to help out a fellow craftsman. Your formulation of the problem was correct; however I recommend that you use full answers when determining your equations. For example 6.4 being the full correct answer to .08 x 80 would have provided you better information in solving for this problem.

I encourage further discussion here if anyone has additional information they feel is relevant to this posting or feel free to contact me directly. You can use the “Contact Us” button above or call me at 503.901.6132.
Take Care and Be Safe All Ways, Brad

Thanks everyone for your imput. Sorry it has taken so long to get back but my wife is having our first child. I am new to the intrusment rated meters and no one here at my company knows anything about them so I am pretty much on a trial and error basis. We wound up just installing a new electronic meter since our contracor could not figure out how he came up with the multiplier. Again thanks for the imput.

Steve! Congratulations and Blessings to you and your wife on the arrival of your little Blessing of Joy! Good luck with your progress at work. Again, if you have any questions regarding metering and want a more direct and quick answer, you are welcome to contact me directly at 503.901.6132
Be Safe All Ways,
Brad

Dear Steve, Kristen, & Brad.---Steves information indicates a 3 wire meter at 240v and ct's [ plural ]. I believe he is talking about a form 4 with 2 cts, not a form 3 with 1 ct.. I recently ran into a J4 [form 2s ] that was being billed with a multiplier of 2. I think the installer used the wrong Rs. Any thoughts?-------Earl

PS: Congratulations Stevel