ECN Forum Forums General Topics of the Trade General Discussion Area Faulty kWh meters

I have worked 12+ years in on site meter testing, calibration of electromechanical kWh meters and electronic ones.

Running fast, not often but is due to the weakening of the brake magnet. Around 1998 we still took out in Devonport, Auckland NZ, Ferranti FDb meters and Chamberlain & Hookham 10 Amps LR meters which were last tested in 1926. These had an average error of around 7 % at 10 Amps Inom. Considering the normal peak house loads of 40 to 60 Amps + @ 230 Volts the meter would be on overload anyway and the current coil in saturation with a meter error of - 20%. I have proven that on a test bench.

A lot of current coils had shorted turns where the varnish and insulation had burnt of and the metal cased meter was live at mains potential.

On older meters the weakening of the brake magnet and the wearing out of the rotor bearings tend to cancel out each other a little.

The Floton bearing meters 1970's ( Sangamo series ) did not have any major problems at all except Jamming jumping dials.

Most meters up to 50 years old are in general very accurate and overall errors are well wirhin the ±2½ % margin.

Some electronic meters do run fast, we had certain batches of meters around 1994 with capacitors on the circuitboards going faulty and the meter taking off. errors of 600% were found. This affected 1Ø and 3Ø meters. It was quite visible on the meterdial that the meter had a problem with hardly any load the led was blinking like crazy and the numbers of the dial rolling over. :