watt-hour meter specs? EH?

Discussion in 'The Projects Forum' started by Lightfire, Apr 17, 2011.

  1. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    21
    Hello,

    I looked at our watt-hour meter at our house.

    It's rated as follows;

    240V 15A

    So means, it can only supply 240 volts and 15 amperes???

    But our circuit breaker is rated as follows;

    240V 30A

    So means, it's rated 240 volts and 30 amperes???

    What if we exceed 15 amperes? Is it OK? Or the whole electric will break? How? :( Because the circuit breaker rated as 30 amperes. :( Or the meter will stop measuring?

    Eh? Would somebody explain me???
    p.s. sub-meter? i heard most apartments using that. :) is the line seperate from each room? :D
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    Probably the meter will get on fire :cool:
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    932
    The meter only requires a 'fraction' of the power being used in order to 'meter' it.

    The circuit in your house is capable of 100 to 150 amps depending on the breakers in the access panel, and the wire gauge coming from the pole transformer. The FULL power does not pass through the meter, only a small fraction does.

    It is probably something around 10%, so your 15 amp rating would only be exceeded if your house needed more than 150 amps.
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    The full load current must pass directly through the meter. Otherwise the energy consumption can't be properly monitored for the dwelling. The only exception would be where current is coupled into the meter via a current transformer. In that case there would be some scaling factor applied to correctly measure the actual energy consumed. This would be unusual in a small domestic situation, but perhaps this is what is installed in this case.

    I would be very surprised if the maximum demand at the house was only 3600W. This may be a 3-phase system with a meter designed to measure 3-phase power.

    Sure, the meter itself only consumes a very small fraction of the total energy consumed in the dwelling. But would be very much less than 10%.
     
  5. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    804
    If you exceed 15 amps, the wires inside the meter will melt.
    The 30amp breaker has nothing to do with it, as 30 > 15, so your meter will be toast long before the breaker acts.
     
  6. Lightfire

    Thread Starter Well-Known Member

    Oct 5, 2010
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    21
    Ahhh. means thats why our circuit breaker is rated as 30 amps for safety reasons????
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Let me correct myself.

    The full load current passes, AND a small amount is used in the meter. BOTH currents are needed to make it a watt/hour meter.

    There is a series and a shunt portion to the 'windings' of the meter.

    With the new SMARTmeters this no longer applies completely.
     
  8. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    www.cdfa.ca.gov/dms/programs/devices/EPO39.pdf

    Basic conclusion is: the numbers you found on the face of the meter are not necessarily to be taken as 'ratings' of current allowed in your house, and are not related to breaker amps. The total of all breaker amperages in your breaker box is much more important and tells what 'capacity' service you have.
     
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