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Why no main fuse in meter box?

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  1. #1
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    Default Why no main fuse in meter box?

    Am looking at an old switchboard (WA, 1950s), and notice the main switch rated at only 36A, but six circuits with fuses and CB totalling 88A.
    It could easily draw 50A in practice, e.g. aircon, oven, grill, kettle, washing machine, ... (cooktop and water are gas at least.)

    With a drop at the meter box of 4V/10A (measure on one cct while loading another), 0.4ohm from 40m each way to the grid, I'm guessing it's only around a 4mm2 supply cable (normal?)
    An 80A load would cause around a 32V drop.

    Am wondering if there is any fire hazard with the main supply cable running through the roof cavity, and why they do not use a fuse to protect the supply side?
    It would be interesting to turn everything on, and measure how far the cable droops over the street )

    If upgrading my meter box, should I ask the sparky to use a main MCB instead of just a switch? Say 40A? 50A?
    Or would I have to get the supply cable to the street upgraded as well?

  2. #2
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    There would be a service fuse on the pole of fascia. There will be no way you can get much help here as the electrician has to look at it in detail. You can send us a photo and we may be able to give some advise but you will end up with an electrician but we may be able to give you some questions you can ask.

  3. #3
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    You may well find that everything is in order if you apply maximum demand calculations to the circuits. Maximum demand takes into account "diversity factor", which recognises that it is unlikely for everything to be on at the same time.

    For example, cooking appliances can be loaded at 50%, air conditioners 75%, power 10A for up to 20 outlets, etc. So, typically your potential 80A load might well result in a maximum demand calculation of less than 36A. Your electrician can advise you according to the actual rating of the appliances etc. AS3000 Appendix C covers this in detail although if your installation is unique specific calculations may apply.

  4. #4
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    That is how it was done in earlier days.
    Although it doesn't comply with today's standards if you don't alter it or have any other electrical work done in the house then it can remain.
    You will probably find a 50 or 63a fuse at the point of attachment.
    If you have the board upgraded then you will have to have a current limiting cb installed as a main switch, the size of that will depend on the mains from the point of attachment to the Meter panel.
    Keep in mind that if you upgrade your mains from the point of attachment to the meter and you have an old wooden Meter panel then that will have to be replaced aswell. (At least it does in vic but this is part of the SIR's not AS3000). Here in vic the supply authority won't accept it.


    Sent from my SM-G900I using Tapatalk

  5. #5
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    Default

    Thanks for the replies. That seems to cover it. I'll have a look inside the roof next time I'm up there.

    Quote Originally Posted by chalkyt View Post
    Maximum demand takes into account "diversity factor", which recognises that it is unlikely for everything to be on at the same time.
    "unlikely" is fine if you have fuse protection. But if there is no fuse, we should be concerned about the actual maximum.

    Thanks Muzza. Guess I'll leave it as is until forced to replace the whole lot.

  6. #6
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    Not really related to a main fuse, but something funny i came across yesterday in a switch board which i had to rectify upon finding it.

    Main switch had the line active (supplied from meter) in the top, as well as the feeds out to the circuit breakers as well. The bottom side of the main switch had nothing. Rendering the main switch useless. @@@@ that could have gone wrong for somebody

  7. #7
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    Quote Originally Posted by Brian7886 View Post
    Not really related to a main fuse, but something funny i came across yesterday in a switch board which i had to rectify upon finding it.

    Main switch had the line active (supplied from meter) in the top, as well as the feeds out to the circuit breakers as well. The bottom side of the main switch had nothing. Rendering the main switch useless. @@@@ that could have gone wrong for somebody
    Maybe the switch went faulty and was someone's idea of a temporary fix.

  8. #8
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    Quote Originally Posted by phild01 View Post
    Maybe the switch went faulty and was someone's idea of a temporary fix.
    switch was fine

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