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MCB's

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    #32
    Philistine
    Registered Users Posts: 159 ✭✭Philistine


    NoseyMike2010 wrote: »
    Phil,

    Did you manage to get those bits and pieces sorted? Cheers.

    NoseyMike2010

    Hi, I'm working abroad at the moment so I don't have as much free time as usual. I'll get the info to you soon


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    #33
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Randyleprechaun wrote: »
    Cant agree:

    You consider the load when sizing the cable, and then,

    You consider the cable size when sizing the breaker.

    Id have to say i would consider the load when sizing the breaker, then the breaker when sizing the cable.

    If a load is 35 amps then surely you would say ok a 40 amp breaker, and the next size cable now capable of continously carrying > 40A.

    Because if you size a cable now to carry 35 amps then maybe you could pick a cable that can carry 38 amps,,, now what size breaker will you use?


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    #34
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    2011 wrote: »
    let's say you have a circuit that under normal operation it should draw a maximum of 8 amps. To protect the circuit you would then install a 10 amp fuse. If all is well the fuse will not blow.

    Imagine you had no fuse or protective device. If the circuit were to develop a fault and as result draw 30 amps you may have an issue because the load is melting but the selected can only safley rake 15 amps!

    But if you had a fuse or MCB it would simply cut the power.

    Think of fuses as being like insurance, you only need them if something goes wrong. When nothing goes wrong they may as well not be there.

    Fuses can protect against overload and short circuit conditions. If protection against electric shock is your main concern start thinking about RCDs. Remember 0.05 amps at mains voltage has the potential to kill. Most domestic fuses are rated far above this. It is not normal to select fuses alone to protect against electric shock.

    It could also be said fuses offer better high current short circuit protection/interruption than MCB`s, which is why fuses are still used in MCB boards etc.


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    #35
    M cebee
    Closed Accounts Posts: 4,431 ✭✭✭M cebee


    robbie7730 wrote: »
    It could also be said fuses offer better high current short circuit protection/interruption than MCB`s, which is why fuses are still used in MCB boards etc.

    'traditionally' yes but i notice a lot of standard mcb's are gone up to 10kA now


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    #36
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    M cebee wrote: »
    'traditionally' yes but i notice a lot of standard mcb's are gone up to 10kA now

    Are they, i never noticed that myself. I wonder how they manage that. Does something move between the contacts.


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    #37
    NoseyMike2010
    Registered Users Posts: 420 ✭✭NoseyMike2010


    Can u guys draw up a circuit diagram to explain what you are talking about please.


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    #38
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,591 Mod ✭✭✭✭2011


    'traditionally' yes but i notice a lot of standard mcb's are gone up to 10kA now
    Yes but HRC fuses are about 80kA


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