Item #078-31LJ-QR-C6, AC Varmeters (Switchboard) - Crompton
The Crompton Instruments switchboard series of AC wattmeters and varmeters incorporate a DC moving coil, pivot and jewel indicator with a micro-circuit watt transducer PCB to read power on single or three-phase systems. The most frequently selected wattmeter scale marking for common current and voltage transformers are listed on the following pages. In addition, these instruments may be supplied with zero-left or center-zero scale.
Crompton Switchboard Meters offers two case types; models 007 and 078
- Model 007 is a one piece flame retardant polycarbonate moulding with a black matte finished bezel area, and a specially contoured window to minimize reflection from adjacent light sources.
- Model 078 is high shock hermetically sealed and all models have heavy gauge pressed steel cases.They have a die-cast bezel and a projecting moulded toughened glass window, which incorporates a gas tight zero adjuster.
- 250° Linear Scale
- AC Instruments with True RMS Circuit
- Rugged Pivot & Jewel Movement
- IP54 Front
- c-UL-us Certification
Wattmeter and VArmeter current circuits should have equal carrying capacity because they are frequently connected in series. This means that the sum of the left and right end-scale values of the VArmeters should be equal to or greater than the full scale value of the Wattmeter (or have higher end-scale values if the instruments are center or offset-zero). Instruments measuring 10,000 kilowatts and over are marked in megawatts. Center-zero or offset-zero Watt and VArmeters are marked “IN” for left deflection and “OUT” for right deflection.
For full load value of Watts or VAr, assuming unity power factor:
- 1-phase 2-wire Watts = amps x volts
- 3-phase 3-wire Watts = amps x line-to-line volts x √3
- 3-phase 4-wire Watts = amps x line-to-neutral volts x 3
Minimum scale values are obtained by multiplying resultant Watts, using the above formula x 0.7 and selecting next higher standard scale. For maximum scale value, multiply x 1.3 and select the next lowest standard. If scale calculates to an exact listed value, use this value rather than the next higher or lower value.
Note: When ordering Wattmeters and VArmeters, please specify CT ratio, VT ratio and required scale. Wattmeter and VArmeter scales will be calculated, the nearest preferred scale will be offered from the charts in the catalog. Custom scales are available but at an extra cost.