I saw an interesting statement in a tender:
The meter must be capable to carry permanently 120 % of the maximum current without loss of performance.
Actually, an energy meter has certain specifications, including maximum current. This is the base for all kind of meter type tests. So it would be more reasonable to choose a meter with the next higher current rating. Some consultancy for the customer is here necessary.
The IEC62052-11 Ed.2 gives us a very clear idea:
The specified operating range is from Imin to Imax while the limit range of operation is 0 to Imax.
The Imax is the highest current the meter can carry continuously and remain safe, and at which it purports to meet the accuracy requirements of the relevant standard.
The internal load switch, terminals and other components are dimensioned with a safety margin for the maximum current stated on the nameplate. For example, the load switch for CLOU meters can always carry 20 A more than the stated maximum current. This is for security and not for abuse with higher currents on long durations.
Any electrician will rely on the information printed on the meter and choose the wiring dimensions and protection fuses accordingly.
A higher current will reduce the manufacturers safety margin. So, stick to the specifications.
Two other things are crossing my mind in this context.
I have an energy meter with Imax = 60 A. The gradation for miniature circuit breakers (MCB) is 63 A.
So, why does the meter not also have a rating of 63 A?
And for curiosity, an MCB and also Molded Case Circuit Breaker (MCCB) has only one terminal screw per conductor for carrying the same current.
Why do most of the energy meters still have two screws to fix each conductor?
Thank you for reading and for sharing your ideas.
Editor's note: This article was originally published in August 2020 and has been updated for comprehensiveness.