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 Maximum circuit current: assume for current estimating purposes that
q
1 horsepower = 1 kW = 1 kVA. Determine CT ratio if load is above
meter class rating.
Mounting: socket (S) or bottom-connected (A).
q
Register: 4-dial or 5-dial pointer; 4-dial or 5-dial cyclometer;
q
cumulative demand register with 15-minute interval.
Frequency: check value.
q
q Compliance
to standards:
ANSI C12.10, Watthour Meters.
Special features: pulse device.
q
2.1.4
Watthour Meter Register. A register of a watthour meter is a
geartrain designed to count the number of revolutions of the disk
(Figure 9-5). Rather than displaying the number of disk revolutions directly,
the register derives kilowatthours by the number of disk revolutions.
Registers are either pointer type or cyclometer type (Figure 9-6).
2.1.5 Meter Terminology. To facilitate an understanding of operation,
testing, and accuracy of meters, it is helpful to recognize the meaning of
certain abbreviations in common use:
Kh =
The number of watthours represented by each revolution of the
meter disk.
The register constant. This is the value that a register reading
K r=
must be multiplied by to obtain the correct kWh registration.
Refer to Figure 9-5. A ratio of the number of revolutions of
Rr =
first register shaft (A) to each complete revolution of the first
pointer shaft (B). The gear marked A is driven by the disk shaft.
Gr =
Gear reduction ratio between the disk shaft and the gear (A in
Figure 9-5) which meshes with it.
TF =
Transformer factor which is the product of the current transformer
ratio (CTR) and the potential transformer ratio (PTR).
Primary meter constant
PKh =
=
Kh x TF
2.1.6 Meter Nameplate. The meter nameplate provides important information in
addition to totalized watthours (Figure 9-7).
2.1.6.1 Class. Modern meters will measure accurately up to 800 percent of
full load calibration test amperes. This is denoted by "CL", or class, on the
nameplate. Use Class 20 meters with instrument transformers to obtain
9-13
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