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The Value of R.C.D.s

Zoomup

There have been many discussions recently about R.C.D.s, whether they really are necessary, and is an installation necessarily unsafe if it is old and has no, or insufficient, R.C.D. protection.

 

Well consider this please. If you are driving and need to brake hard to save somebody from injury or death does that incident ever get reported. If you knocked somebody over due to having bad vehicle brakes then it might.

 

If an R.C.D. operates correctly and saves somebody from injury or death, does that every get reported? There may have been 10s, 100s or even thousands of cases where an R.C.D. has saved somebody from injury or death, but we will never know the numbers because of a lack of reporting of the cases.

 

Personally I like the idea of R.C.D. protection

 

Z.

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  • 0

    whjohnson: 
     

    Look at it like this Zoom - if a BS3036/BS3871/BS60898 device disconnects within 0.4 seconds then yes RCDs are nice to have but are they necessary?

     

    Will an OCPD disconnect within that time if someone touches a live conductor from a severed flex? (Lawnmower often quoted, but vacuum cleaner, pet or other accidental damage can also result in the same.)?

    Answer … NO

    The requirements in BS 7671 are for additional protection to be provided (411.3.3, 411.3.4), not fault protection. In fact, additional protection is supposed to operate if fault protection fails (as well as basic protection)

    The distinction is important, because of the wording in 415.1.1:

    415.1 Additional protection:RCDs
    415.1.1 The use of RCDs with a rated residual operating current not exceeding 30 mA is recognized in AC systems as additional protection in the event of failure of the provision for basic protection and/or the provision for fault protection or carelessness by users.


    (See underlines)

    Basic protection might effectively fail for many reasons, not just direct “damage” - perhaps temporarily for example due to spilling water (or wine/beer/vodka etc.) on an appliance or extension lead, and being fortunate enough for this not to operate the OCPD …

    Not flagging lack of additional protection by RCD, at least for the serious attention of the installation owner, I think puts the inspector in a difficult position.
     

     

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  • 0

    whjohnson: 
     

    Look at it like this Zoom - if a BS3036/BS3871/BS60898 device disconnects within 0.4 seconds then yes RCDs are nice to have but are they necessary?

     

    Will an OCPD disconnect within that time if someone touches a live conductor from a severed flex? (Lawnmower often quoted, but vacuum cleaner, pet or other accidental damage can also result in the same.)?

    Answer … NO

    The requirements in BS 7671 are for additional protection to be provided (411.3.3, 411.3.4), not fault protection. In fact, additional protection is supposed to operate if fault protection fails (as well as basic protection)

    The distinction is important, because of the wording in 415.1.1:

    415.1 Additional protection:RCDs
    415.1.1 The use of RCDs with a rated residual operating current not exceeding 30 mA is recognized in AC systems as additional protection in the event of failure of the provision for basic protection and/or the provision for fault protection or carelessness by users.


    (See underlines)

    Basic protection might effectively fail for many reasons, not just direct “damage” - perhaps temporarily for example due to spilling water (or wine/beer/vodka etc.) on an appliance or extension lead, and being fortunate enough for this not to operate the OCPD …

    Not flagging lack of additional protection by RCD, at least for the serious attention of the installation owner, I think puts the inspector in a difficult position.
     

     

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