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Electrical distribution box?

  1. Jun 25, 2014 #1
    In my country, the Electrical distribution box has two sections
    lighting section 300 mA
    and power section 30 mA

    why the lighting section taking more current than the power ?? Shouldn't the power take more ??
     
  2. jcsd
  3. Jun 25, 2014 #2

    sophiecentaur

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    Hi and welcome.
    Those figures don't make a lot of sense to me. Where did you read them? Were they on the RCD (Earth leakage safety circuit breakers?)
     
  4. Jun 25, 2014 #3
    i didnt read them anywhere
    all i know that they are using 30 mA for power and 300 mA for lighting and am wondering why 300 mA for lighting ?? isn't that too much ?
     
  5. Jun 25, 2014 #4

    sophiecentaur

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    Bearing in mind that 30mA at 240V represents 7.2W, this is very unlikely to be true for any 'Power system'. So when you say that you "know" this fact, I have to ask where you read / heard this and what was the context?
     
  6. Jun 25, 2014 #5

    gerbi

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    30/300 mA looks like typical RCD ratings. Why select different ones for different purposes ? Less sensitive ones (higher rated residual current) are cheaper. It also depends on regulations.. in some places highly sensitive protection devices are not needed.
     
  7. Jun 25, 2014 #6
    so in other words they are using 30 ma for power because its more sensitive because power is more dangerous, and 300 ma for lighting because its less sensitive because lighting is less dangerous ??
     
  8. Jun 25, 2014 #7

    gerbi

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    Yeah.. sure. LOL. You do not have any EE background, do you ?
    30 mA are used for circuits where you (more often) can put your fingers and get hurt.
     
  9. Jun 25, 2014 #8

    sophiecentaur

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    I reckon that the standards for lighting circuits (in the UK at least) is so low ( spaghetti of wires, daisy chained all over the place) that 30mA would be quite common for general leakage, in amongst the sawdust, mouse droppings and discarded cigarette stubs. Not to mention the apparent lack of regs about light fittings in general. The build quality of the power fittings is so much better and tighter. To be more charitable, the lifetime of lamps is poor and they frequently take out fuses when they go. This could also cause a hair trigger RCD to cut out, too. (Despite the 'balance' of Live and Neutral currents).
    Also, the routing of lighting circuits contains loops of Live conductor to switches and back. Perhaps the unequal Z of some such circuits could be producing a phase imbalance which a 30mA RCD could react to.
     
  10. Jun 25, 2014 #9

    gerbi

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    Well said, +1 from me.
     
  11. Jun 25, 2014 #10

    jim hardy

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    In theory, all current that enters a healthy device by its supply wire should exit by its return wire. That's the underlying assumption of Ground Fault Interrupters, which i think is what you guys call a Residual Current Device. They operate on the difference between current sent into and current received from their branch circuit.

    Looking down a branch circuit from the breaker's end, the same assumption should hold true, current in = current out.
    However there's distributed capacitance in the wiring that bypasses a little bit of current around the breaker's current differencing transformer,
    so with long lines or electrically "noisy" loads(brushed motor for example) you can get nuisance trips.

    I own an ordinary fluorescent shop light with electronic ballast that trips its GFI branch breaker when it tries to startT12 bulbs but with T8's works just fine. I think it generates noise at the same frequency as the GFI's internal electronic IC.

    If a well meaning but inattentive handyman messes up your house wiring so that current going out one branch's "hot" returns via another branch's "neutral", well, a RCD simply won't work in either of those two spots.

    30 ma probably wont kill a person, hence that choice for residential where tiny fingers may be exploring.
     
    Last edited: Jun 25, 2014
  12. Jun 25, 2014 #11

    CWatters

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    http://www.neweysonline.co.uk/RCD/Static.raction

    .
     
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