- Thread starter Ade1309
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- Nov 30, 2021
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- If you're a qualified, trainee, or retired electrician - Which country is it that your work will be / is / was aimed at?
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Ahh the IF word makes a difference.
But yes agreed, and it’s another reason to try and avoid using an upfront rcd.
- Sep 24, 2013
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- If you're a qualified, trainee, or retired electrician - Which country is it that your work will be / is / was aimed at?
- United Kingdom
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- Practising Electrician (Qualified - Domestic or Commercial etc)
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- Dovecote Electrical
I wonder if I might throw an SPD-shaped spanner in the works here?
If the guidance in the On-Site Guide (section 3.6.4, page 41 of the little brown book) is that dual RCD metal boards are not suitable on TT systems due to the risk of the single-insulated L feeds to the RCCBs making contact with the metal box, presumably the same argument could be made for situations where the L feed to an SPD inside the metal DB is in the form of a single-insulated cable? In which case a time-delayed RCCB acting as a main switch might be a good idea. 534.4.6 (concerning fault protection of SPDs), and figures 16A2 and 16A3 of Appendix 16 refer. Of course, your SPD will not protect your upstream RCCB in this case.
If your SPD is fed directly from the bus bar - such as the single module Wylex SPDs - then this is equivalent to having all RCBOs, a situation that the OSG says an upfront RCD would not be required (though of course it may be needed, or desired, for other reasons).
If the guidance in the On-Site Guide (section 3.6.4, page 41 of the little brown book) is that dual RCD metal boards are not suitable on TT systems due to the risk of the single-insulated L feeds to the RCCBs making contact with the metal box, presumably the same argument could be made for situations where the L feed to an SPD inside the metal DB is in the form of a single-insulated cable? In which case a time-delayed RCCB acting as a main switch might be a good idea. 534.4.6 (concerning fault protection of SPDs), and figures 16A2 and 16A3 of Appendix 16 refer. Of course, your SPD will not protect your upstream RCCB in this case.
If your SPD is fed directly from the bus bar - such as the single module Wylex SPDs - then this is equivalent to having all RCBOs, a situation that the OSG says an upfront RCD would not be required (though of course it may be needed, or desired, for other reasons).
- Sep 24, 2013
- 1,519
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- If you're a qualified, trainee, or retired electrician - Which country is it that your work will be / is / was aimed at?
- United Kingdom
- What type of forum member are you?
- Practising Electrician (Qualified - Domestic or Commercial etc)
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- Dovecote Electrical
... and reading a bit further on in the big brown book, 534.4.7, SPD installation in conjunction with RCDs:
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