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Well, now I've been out and looked at a few, and they don't say 138 8/9. They say 13 8/9. And there are quite a few out there with the same 7.2 Kh, but a different Rr (27 1/3, or something like that).

So Rr is not the reciprocal of Kh, nor does it have any apparent mathematical ratio thereto. I have no idea what it means.

Funny thing, though. If it did say 138 8/9, that would make sense!

That sounds similar to the 120/208 single-phase "network" service we have in certain urban areas here. Here, that type of service uses a Form 12S meter (2 current coils and 2 120V coils), which looks similar to the more common Form 2S (2 current coils and 1 240V coil).

A meter on each phase... I've only seen that once, in Mexico. It was in the corner of a small restaurant. Exposed knife switches, too!

[This message has been edited by yaktx (edited 02-16-2006).]

yaktx

Rr stands for register ratio, and is not always the correct constant, the way I understand it that it has to do something with the intermediate gears from the register train.
We have Sangamo meters here 3 Ø 40 Amps with Rr of 40 and 80, The meter in both cases was a 80 rev / kWh meter but the pitch of the worm drive was different. In case of the Rr of 40 the pitch was 1 rev of the disc is one cog advance on the register.
In case of the Rr of 80 one rev of the disc advaced 2 cogs on the register.
I have a read up through some of my metering box what the actual definition is.
I will get back to this interesting topic.
Raymond

from "Hand book of Electricity Metering" ninth edition. quoted from text on page 136.

Kh is the number of watthours represented by one revolution of the disc.

Rg The necessary gearing is provided so that the revolutions of the disc will move the first (or right-side) pointer or cylinder one full revolution (360degrees) each time the rotor revolves the number of times equal to ten kilowatt-hours of usage. This is known as gear ratio, or Rg.

Rr The register ratio, known as Rr is the number of revolutions of the wheel which meshes with the pinion or worm on the disc shaft for one revolution of the first dial pointer.

Thanks, RODALCO.

So Rr only has to do with the worm & pinion. Now it makes sense how two meters could have the same Kh but different Rr.