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dp main switch

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  • 17-09-2020 5:54pm
    #1
    lostman666
    Registered Users Posts: 19 ✭


    in what scenario are these fitted and is there any benefit to fitting one where a upstream overcurrent device is fitted


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    #2
    Restrooms
    Closed Accounts Posts: 20 ✭Restrooms


    lostman666 wrote: »
    in what scenario are these fitted and is there any benefit to fitting one where a upstream overcurrent device is fitted

    Well in nearly every new domestic installation the Main Switch has an upstream overcurrent device which is the Main OCPD in the meter cabinet but DP is not required here afaik( neutral reliably at earth potential)

    In the UK they'd be required for TT installations so afaik DP main isolation is standard for Main DBs , I think

    I've used them here for an outbuilding DB where I had to wire off an RCD protected socket circuit, helps isolate the outbuilding if there's an RCD trip , that's not Main Isolation only Isolation

    I'm not sure if that's helping or I'm missing something obvious?


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    #3
    Risteard81
    Registered Users Posts: 2,567 ✭✭✭Risteard81


    Restrooms wrote: »
    In the UK they'd be required for TT installations so afaik DP main isolation is standard for Main DBs , I think
    BS7671 requires them for single phase installations which are not under the control or supervision of a skilled or instructed person, which is explicitly stated to include all domestic installations. This includes TN systems.


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    #4
    lostman666
    Registered Users Posts: 19 ✭lostman666


    Restrooms wrote: »
    Well in nearly every new domestic installation the Main Switch has an upstream overcurrent device which is the Main OCPD in the meter cabinet but DP is not required here afaik( neutral reliably at earth potential)

    In the UK they'd be required for TT installations so afaik DP main isolation is standard for Main DBs , I think

    I've used them here for an outbuilding DB where I had to wire off an RCD protected socket circuit, helps isolate the outbuilding if there's an RCD trip , that's not Main Isolation only Isolation

    I'm not sure if that's helping or I'm missing something obvious?


    i bought an old house last year and was in the process of doing it up, then covid hit fast forward to about a month ago and we were getting the bathroom renovated and preparing for a shower. all fine and grand electrician came out and did all the required testing and everything prefect, but i need a new connection outside for a shed he said grand no probs but said something about 20% in the consumer unit and it would need to be upgraded, which im fine with as the house is 50 ish years old. this is what i dont understand he said as we had neutral, earth and live going through the overcurrent device a double pole main switch has to be added. so why do i need another main switch if the overcurrent device is a switch as well.


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    #5
    Tuco88
    Registered Users Posts: 1,051 ✭✭✭Tuco88


    I've seen GE 100amp 3 pole isolators installed in meter cabinets before (The type with the clear sort plastic). I'm not sure if this is being done with the digital meter upgrades? Pretty sure its not in the regulations to do so to.


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    #6
    Restrooms
    Closed Accounts Posts: 20 ✭Restrooms


    Tuco88 wrote: »
    I've seen GE 100amp 3 pole isolators installed in meter cabinets before (The type with the clear sort plastic). I'm not sure if this is being done with the digital meter upgrades? Pretty sure its not in the regulations to do so to.

    3-pole?


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    #7
    Restrooms
    Closed Accounts Posts: 20 ✭Restrooms


    Risteard81 wrote: »
    BS7671 requires them for single phase installations which are not under the control or supervision of a skilled or instructed person, which is explicitly stated to include all domestic installations. This includes TN systems.

    Thanks I stand corrected

    I should have figured it was a regulation for all supply types as all the DBs have 2 pole isolation I think?


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    #8
    Tuco88
    Registered Users Posts: 1,051 ✭✭✭Tuco88


    Restrooms wrote: »
    3-pole?

    Yes.

    This is not the norm from my understanding other lads here will most like agree on this, Its a while now that I have been in the domestic work so this might be new? I can't remember where I crossed this, I am pretty sure it was after a meter upgrade.


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    #9
    Restrooms
    Closed Accounts Posts: 20 ✭Restrooms


    Tuco88 wrote: »
    Yes.

    This is not the norm from my understanding other lads here will most like agree on this, Its a while now that I have been in the domestic work so this might be new? I can't remember where I crossed this, I am pretty sure it was after a meter upgrade.

    I've wired a lot of them

    I refer to isolator poles as the number of switched poles?

    Maybe I'm mistaken


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    #10
    Restrooms
    Closed Accounts Posts: 20 ✭Restrooms


    They're on the go for 10 or 20 years them ones


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    #11
    Restrooms
    Closed Accounts Posts: 20 ✭Restrooms


    lostman666 wrote: »
    i bought an old house last year and was in the process of doing it up, then covid hit fast forward to about a month ago and we were getting the bathroom renovated and preparing for a shower. all fine and grand electrician came out and did all the required testing and everything prefect, but i need a new connection outside for a shed he said grand no probs but said something about 20% in the consumer unit and it would need to be upgraded, which im fine with as the house is 50 ish years old. this is what i dont understand he said as we had neutral, earth and live going through the overcurrent device a double pole main switch has to be added. so why do i need another main switch if the overcurrent device is a switch as well.

    It's difficult to understand what you mean there


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    #12
    Restrooms
    Closed Accounts Posts: 20 ✭Restrooms


    Risteard81 wrote: »
    BS7671 requires them for single phase installations which are not under the control or supervision of a skilled or instructed person, which is explicitly stated to include all domestic installations. This includes TN systems.

    What's the reasoning behind the DP main isolation for TN there

    I could never see any reason not to do it, i heard it has happened where the supply was connected up reverse polarity and a person died connecting an appliance after switching off the SP main isolator


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    #13
    lostman666
    Registered Users Posts: 19 ✭lostman666


    Restrooms wrote: »
    It's difficult to understand what you mean there

    which part?


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    #14
    Risteard81
    Registered Users Posts: 2,567 ✭✭✭Risteard81


    Restrooms wrote: »
    What's the reasoning behind the DP main isolation for TN there

    I could never see any reason not to do it, i heard it has happened where the supply was connected up reverse polarity and a person died connecting an appliance after switching off the SP main isolator

    It seems that the idea is to protect DIYers working on the installation as it doesn't apply to non-domestic installations where the neutral can be reliably considered to be at Earth potential (i.e. TN systems) or for non-domestic installations. The latter has users protected by legislation e.g. the Electricity at Work Regulations etc.


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    #15
    Restrooms
    Closed Accounts Posts: 20 ✭Restrooms


    Risteard81 wrote: »
    It seems that the idea is to protect DIYers working on the installation as it doesn't apply to non-domestic installations where the neutral can be reliably considered to be at Earth potential (i.e. TN systems) or for non-domestic installations. The latter has users protected by legislation e.g. the Electricity at Work Regulations etc.

    The non-domestic you can expect trained personnel to "prove dead", not so much for DIY

    I often wondered why they don't have DP isolation on domestic boards here, I can't think of any reason not to

    I mean strictly speaking local isolation can also be achieved with single pole isolation according to ET101 but they we use DP


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    #16
    Risteard81
    Registered Users Posts: 2,567 ✭✭✭Risteard81


    Restrooms wrote: »
    The non-domestic you can expect trained personnel to "prove dead", not so much for DIY

    I often wondered why they don't have DP isolation on domestic boards here, I can't think of any reason not to

    I mean strictly speaking local isolation can also be achieved with single pole isolation according to ET101 but they we use DP
    I meant to add to that that three-phase TN installations in domestic premises (although unusual) do not require the neutral to be broken. It's only for single phase.


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