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FAQ

OFGEM/MID Approved Meters

  1. How do I know if I should be using an OFGEM or MID Approved meter?
    You should use an OFGEM/MID approved meter if you intend to collect revenue from the meter readings.

All Meters

  1. Can I mega-test (Insulation test) the circuits with the meter still connected?
    No. Under no circumstances allow this to be done. This will damage the microprocessors in the meter.
  2. Do all meters have pulse outputs suitable for a management system?
    No. All meters normally have a pulse output, but it will be an “SO” pulse output not suitable for a management system. The correct pulse for a BMS system would be a volt free optically isolated pulse.
  3. Do all meters have the same pulse value?
    No. Meter manufacturers have their own constants and therefore a different pulse output value.

All CT Operated Meters

  1. What is the difference between a Direct Connected meter and Current transformer-operated meter?
    A direct connected meter is where the current carrying cables are connected into the meter terminals and is normally used up to a maximum of 100 amps.

    A current transformer-operated meter requires current transformers which fit around the cable. This is normally used on loads exceeding 100 amps.
  2. How should a three phase current transformer meter be connected?
    The correct way would be to have a four pole circuit breaker as the main isolation to the meter with three lower rated fuses to protect the electronics in the meter. The current circuit should have a shorting test block (ATB 23008) that allows the current transformers to be shorted out should the meter need to be removed in the future. Please see our full meter assembly with metal enclosure.
  3. What do I do if the meter readings do not equal that of the main meter?
    Check that all the cables have been connected into the correct terminals by referring to the connection diagrams in the installation manuals. Check that you have three line voltages present at the meter by referring to the line voltages on display in the meter.

    If you have a current transformer-operated meter check that the meter has been programmed to the same ratio as the current transformers. Check the current transformers have been placed on the cable /bus bar the correct way with P1 facing the mains. Check the circuit diagram.
  4. Can a three-phase current transformer-operated meter be used as a single phase meter?
    Normally, yes. But you must check with the supplier of the meter.
  5. Which phase should I use, if I use a three-phase current transformer-operated meter and want to use it as a single phase meter?
    Please check with the supplier of the meter
  6. If I use a three phase meter as a single phase is it important that I use the same voltage as per the phase connection?
    Yes, you must use the same current circuit as the line voltage. For example, line 1 voltage must be line 1 current circuit.
  7. Is it important that the current transformer ratio on the meter matches the current transformers fitted?
    Yes. In all cases the ratio of the current transformer must match the ratio of the fitted meter. For example, a meter with ratio 200/5 amp will require a CT with ratio 200/5 amp.
  8. What is a Current transformer shorting block & why should I be using one?
    A CT shorting block is used to enable the meter to be taken out of service at a later date. It is good practice to fit one where a current transformer operated meter is being used. It allows the current transformers to be shorted out when the meter has been removed.
  9. Do I need to short out the current transformers when taking a meter out for a period of time?
    Yes, under no circumstances leave a current transformer open circuit when power is on.
  10. Do I need to Earth the current transformers?
    No. Although you will need to check with the meter supplier because some meters must not have a common earth on the current circuits.

Current Transformers

  1. Which way round do the Current Transformers go?
    The current transformers must be fitted and connected in the correct way or the meter will not be accurate. The current transformers are marked on two sides: ‘P1’ and ‘P2.’ ‘P1’ must face the mains side and ‘P2’ must face the load side. ‘S1’ must be connected to the main side of the meter and ‘S2’ to the load side. Refer to appropriate wiring diagram of the meter for correct connections.
  2. What is the maximum distance the Current Transformers can be fitted from the meter?
    This depends on the ‘VA’ burden of the meter, the cable being used between the current transformer and the meter and the distance the current transformer is from the meter.

    Please see current transformer graph for further help.
  3. What class of current transformer should I use with a current transformer-operated meter?
    To accurately measure kWh we recommend a minimum class of 1.0; class 0.5 is better.
  4. What is the difference between a moulded case current transformer and a split core current transformer?
    A moulded case current transformer is a solid ring of steel in a plastic or resin case and can only be used when you fit the cable through the hole in the middle of the plastic/resin case.

    A split core current transformer is manufactured with the steel core in two pieces. This enables the core to be separated, allowing you to fit the cores around the cable without disconnecting the cables. The disadvantage with split core current transformers is that they can be larger than standard moulded case and the price is approximately four times more expensive.
  5. Can the current transformers be a higher or lower ratio then my maximum load?
    The current transformers should ideally be about 80% of the normal running load, thus allowing a 20% allowance of increasing the load in the future.
  6. Do I need to measure the neutral current?
    No, it is not a requirement but in offices and large warehouses it is recommended.

Metal Enclosures

  1. In the SX range of enclosures where I am using a current transformer-operated meter, what is the specification of the three voltage fuses?
    The fuses in the SX enclosures are 250 volt, 2 amp anti-surge, 5 x 20mm. The Farnell part number is 9922270.
  2. Can you design me a special metal enclosure for my installation?
    Yes, all you need to do is supply a drawing and we will advise a price and approximate delivery date.

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Electricity Meters and Power Monitoring Systems
4b Albany Road, Chorlton-cum-Hardy, Manchester M21 0AW
Tel: +44 (0)161 861 9056 / Fax: +44 (0)161 881 3745