BS 7856:2013 pdf download
BS 7856:2013 pdf download.Code of practice for specialde sign and other features of alternating current watthour meters for active energy(MID accuracy classes Aand B) for use in the UK.
Annex C Long-term overcurrent test requirements (normative)
Before the application of currents above the registration errors of the meter (on each circuit for multi-circuit, single-phase meters. and for each phase for polyphase meters) should be determined under reference conditions (ambient temperature, supply voltage and frequency) at load currents of 10 1, at PF = 1. (See BS EN 50470-3:2006, Table 10.)
With reference voltage at reference frequency applied, the meter should then be subjected to a load current of 1.4 ‘,a, (÷01-5%), PF = 1 (+01-0.05) for a period of 2 h (+51-0 mm), after which it should be left connected to the voltage supply for a period of 6 h (±30 mm) with load current = 0.
The sequence of application of current should be as shown in Table CI.
The test current should pass through the phase conductor circuit of the meter, and also the return path in the meter (neutral or another phase conductor circuit), as appropriate, so that all heating effects are taken into account.
For multkircuit, single-phase meters, a number of tests should be undertaken, each addressing a different split of incoming phase current between the different phase output circuits. The amplitudes of the currents in each phase output circuit should match those that could flow continuously through the protective device that the meter manufacturer recommends for that circuit: for example, a “2SA’ output circuit which the meter manufacturer requires to be protected by a 25 A-rated fuse, should be tested with a current of 1.4 * 25 A. For each of these tests, the total current flowing into the meter’s phase circuit input terminal and flowing through the meter’s neutral conductor circuit should be 1.4 ‘mar
As an example, for a two-circuit meter with an ç rating of 100 A. a first output rated l,_, = 100 A and a second output rated 25 A, the second test given for the meter in Table Cl would be conducted with 25 x 1.4 = 35 A flowing through the second phase conductor circuit 105 A flowing through the first phase conductor circuit and 140 A flowing through the meter’s neutral circuit.
During the tests, the meter should be exposed neither to draught nor to direct solar radiation.
The tests should be conducted with the meters in “free air. The volume of the enclosure in which the meter is mounted for the tests should be sufficiently large to ensure that the ambient temperature of the air inside the enclosure does not rise above reference temperature during the tests.
When tested again under reference conditions (ambient temperature, supply voltage and frequency) at 10 l, and PF = 1. the additional error should not exceed a critical change value of ±1.5%.
Annex D Performance criteria for a load switch (normative) incorporated into a meter
NOTE Load” in this context generally refers to the total consumer demand passing through a meter, which ought to be related to the meter’s However, in some equipment there are switches related to specific loads less than l,,,,, e.g. space and water heating installations.
Any switch incorporated into a meter should be able safely to break the load for which it is intended, as well as withstand the passage of any fault current with which the meter is able to cope, as given in Table D.1.
