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RCBOs and lighting?

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    #62
    tomplate
    Closed Accounts Posts: 63 ✭✭tomplate


    Bruthal wrote: »
    Presumably an mcb will assist that, unless the non-REC forgets to connect the neutral supply tail while there's a nice little earth neutral fault....

    Overall I'm not heavily against rcd protection on lighting. But shock risk from lights is extremely low. Sockets though, have people plugging all sorts of devices into them and operating them in hand.

    That was always the distinction, luminaires are 'fixed'

    You could plug into a socket and be gone half a mile up the road in the rain with an extension lead


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    #63
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    Ironically enough, it would be extremely unlikely a person making contact with a phase in a house would trip an RCD unless they also have contact with an earthed point.


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    #64
    tomplate
    Closed Accounts Posts: 63 ✭✭tomplate


    Bruthal wrote: »
    Ironically enough, it would be extremely unlikely a person making contact with a phase in a house would trip an RCD unless they also have contact with an earthed point.

    I had an electrician friend who used to grab hold of the phase on an upstairs domestic circuit

    You'd then stick a phase tester on his arm and it would light up

    I never liked the idea myself


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    #65
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,595 Mod ✭✭✭✭2011


    Bruthal wrote: »
    Ironically enough, it would be extremely unlikely a person making contact with a phase in a house would trip an RCD unless they also have contact with an earthed point.

    ....with the 30mA RCDs that are normally used for socket circuits in a domestic installation.

    So should the “logical progression” be for 10mA units?


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    #66
    tomplate
    Closed Accounts Posts: 63 ✭✭tomplate


    2011 wrote: »
    ....with the 30mA RCDs that are normally used for socket circuits in a domestic installation.

    So should the “logical progression” be for 10mA units?

    That will probably happen too

    The 10mA protects against let-go currents afaik

    The 30mA only protects against fibrillation


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    #67
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,595 Mod ✭✭✭✭2011


    tomplate wrote: »
    That will probably happen too

    If so there will be a dramatic increase in nuisance tripping.


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    #68
    tomplate
    Closed Accounts Posts: 63 ✭✭tomplate


    2011 wrote: »
    If so there will be a dramatic increase in nuisance tripping.

    It shouldn't be too bad, it will be rcbo

    Installations having them fitted will be largely free of wiring faults and there is less leakage now with appliances


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    #69
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,595 Mod ✭✭✭✭2011


    tomplate wrote: »
    It shouldn't be too bad, it will be rcbo

    Reducing the sensitivity by a factor of 3 will have to increase this occurrence significantly.
    Installations having them fitted will be largely free of wiring faults and there is less leakage now with appliances

    Nope, the opposite applies.
    Nuisance tripping has nothing to do with faults and everything to do with nonlinear loads such as switched mode power supplies which are on the increase.


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    #70
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    2011 wrote: »
    ....with the 30mA RCDs that are normally used for socket circuits in a domestic installation.

    So should the “logical progression” be for 10mA units?
    I think 30 is fine. The idea of 30 is that it's the area of danger, magnitude wise. 10ma would cause too much nuisance. If a person receives 15 or 20 it's not very severe. It's quite nice at 30 though. An RCD more limits the time of exposure than the current level also.


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    #71
    tomplate
    Closed Accounts Posts: 63 ✭✭tomplate


    2011 wrote: »
    Reducing the sensitivity by a factor of 3 will have to increase this occurrence significantly.



    Nope, the opposite applies.
    Nuisance tripping has nothing to do with faults and everything to do with nonlinear loads such as switched mode power supplies which are on the increase.

    You make it sound like nuisance tripping is a big problem when it's not

    It's quite uncommon in modern domestic installations


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    #72
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,595 Mod ✭✭✭✭2011


    Bruthal wrote: »
    I think 30 is fine.

    So do I.
    My reccomendation would be replace a single socket RCD with RCBOs per circuit as is the standard in industrial installations.


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    #73
    tomplate
    Closed Accounts Posts: 63 ✭✭tomplate


    2011 wrote: »
    Reducing the sensitivity by a factor of 3 will have to increase this occurrence significantly.



    Nope, the opposite applies.
    Nuisance tripping has nothing to do with faults and everything to do with nonlinear loads such as switched mode power supplies which are on the increase.

    I should have said wiring leakage rather than faults

    I'm not sure that leakage from power supplies is a big issue either

    My understanding is that leakage is low from power supplies, in the order of 300 micro Amps max.


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    #74
    tomplate
    Closed Accounts Posts: 63 ✭✭tomplate


    The old calculation on PCs was 3.5 mA leakage

    It was then recommended have no more than 4 on a 30mA device

    I think they now have a lot less leakage than that


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    #75
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,595 Mod ✭✭✭✭2011


    tomplate wrote: »
    The old calculation on PCs was 3.5 mA leakage
    I’m not sure to be honest. There are now switched mode power supplies in TVs.
    It was then recommended have no more than 4 on a 30mA device

    If that is the case it would be less for a 10mA unit.


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    #76
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    tomplate wrote: »
    I had an electrician friend who used to grab hold of the phase on an upstairs domestic circuit

    You'd then stick a phase tester on his arm and it would light up

    I never liked the idea myself

    Nothing at all is perceived with phase only contact in those circumstances.


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    #77
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    2011 wrote: »
    Rubber mats under the distribution board in the hall?

    Rubber mats are a bit of a placebo at 230v.


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    #78
    2011
    Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,595 Mod ✭✭✭✭2011


    A typical domestic distribution board may contain the following:

    ⦁ A main neutral bar and a neutral bar for the RCD for the socket circuits. Connecting to the wrong neutral bar will of course cause issues.

    ⦁ A bus bar for all sockets not fed through the RCD. An RCD for the socket circuits.

    ⦁ A busbar for all sockets not fed through the RCD.

    ⦁ A 2nd busbar for the socket circuits that are fed through the RCD.

    ⦁ An RCBO for an instantaneous shower. This device is wired differently to everything else in the board.

    The above is not rocket science, but it tends to confuse many that have limited electrical experience which often keeps them away from it (thankfully).


    Installing RCBO's on every circuit in a domestic installation would simplify the distribution board. This is especially the case when a suitable RCBO type phase / neutral busbar is used (like the one in the image below).

    product34.jpg

    This simplifies the distribution board considerably. In this case the wiring for every circuit would be identical and the device protecting every final circuit would be identical (apart from the rating). To those with limited electrical experience this "dumbed down" distribution board would encourage them to "have a go" at just about any modification.


    I am not for one minute suggesting that this alone is a valid reason for not installing RCBO's on every circuit. I am just saying that it will have unwanted consequences, so be careful what you wish for!


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    #79
    Bruthal
    Closed Accounts Posts: 13,422 ✭✭✭✭Bruthal


    2011 wrote: »
    To those with limited electrical experience this "dumbed down" distribution board would encourage them to "have a go" at just about any modification.

    Even qualified non REC persons might have a go:pac:


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