ML0030 August 2009 Copyright 2009 Bitronics, LLC
−
15
−
5.0 QUESTIONS AND ANSWERS
1. What happens if the applied CT signal exceeds 5A?
The WATT/VAR meters are accurate to twice the normal full scale limit (to 10A).
The unit will operate at 100% overload without damage, however on some CT/PT
settings the display will over-range, causing the display to flash with 1999. The 0-1
milliamp output is still accurate even if the display overanges, provided the load
resistance is low enough to support the increased current.
2. Can modules be removed under power?
Yes. Neither input signals nor power need be disconnected to remove or rescale
the Electronics Module. Removing the module DOES NOT open the CTs or PTs.
3. Is routine calibration necessary?
No, nor is it recommended. More problems are caused by improper calibration than
by faulty meters. A calibration check every few years in the field is good assurance,
however. If there is a question about the meter, exchanging a module may help
verify performance.
4. HI and LO are marked on the inputs. Does polarity matter?
Yes! Correct wiring with proper polarity is essential for proper operation.
5. Can I put WATT/VAR meters in an outdoor cabinet?
Yes. Many Bitronics meters are installed that way. The temperature range of -20C
to 70C covers most applications. The case is gasketed, but not waterproof, so it
must be placed within an enclosure that provides ingress protection acceptable for
the application in accordance with IEC 529, UL 840 or the equivalent NEMA
Standard.
6. How long will WATT/VAR meters save the CT/PT ratio without power?
The data is saved in a nonvolatile memory (EEPROM) which does not require
battery backup. Retention is estimated by the manufacturer to exceed 10 years
without refreshing. In any event, long enough to exceed an outage, or for any
inactive storage period.
7. I have a low voltage circuit, can I operate WATT/VAR meters without the use of CTs
and PTs?
Although the WATT/VAR meter has been optimized for use with CTs and PTs, it can
be connected directly to a load provided that the voltages and currents do not
exceed the rating of the device. The internal CT should be set to 5 (5:5) and the
internal PT should be set to 1 (120:120).
