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IET Wiring Regulations, 18th Editions, Amendment 4 - Clause 536.4.202

RAW42

When reading this new clause, it appears to apply to all switchgear, which means diversity can no longer be used in the design of electrical distribution switch / control gear assemblies.

I am aware of the necessity, where multiple sources of supply are connected in parallel, to ensure main switchgear / distribution boards are sized for the sum of supply capacities, but the above new clause does not reference multiple sources of supplies.

Could i get the communities thoughts on this new clause please?

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  • 0

    See here: engx.theiet.org/.../clarification-on-section-536-4-202

    Diversity CAN be used, at least for Option (a) of the Regulation.

    For multiple sources of supply, see Regulation 5541.7.2.2.

    Guidance is available in IET Guidance Note 6 Protection against overcurrent

  • 0 in reply to gkenyon

    My concern with the item a) is the wording which states  The rated current or current setting of the upstream protective device (In) is less than or equal to the rated current of the assembly (InA) and any outgoing unit (Inc). 

    specifically the that the upstream protective device should be rated less than any outgoing unit?

    ive got to be misreading this but words are not clear to me eg if you had a 6amp outgoing breaker then the upstream protective device should be less!

  • 0 in reply to RAW42

    I have put my interpretation in the other parallel thread.

  • 0 in reply to RAW42

    But Inc isn't the rating of your actual outgoing devices - NOTE 2 gives the example of an RCCB - so think 100A split load CU with a couple of 80A RCCBs in it - you'd need an 80A (rather than 100A) upstream fuse to ensure the RCCBs weren't overloaded (or a sum of MCBs downstream of the RCCB <= 80A, or load curtailment, or ... - just not relying on diversity alone).

       - Andy.

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  • 0 in reply to RAW42

    But Inc isn't the rating of your actual outgoing devices - NOTE 2 gives the example of an RCCB - so think 100A split load CU with a couple of 80A RCCBs in it - you'd need an 80A (rather than 100A) upstream fuse to ensure the RCCBs weren't overloaded (or a sum of MCBs downstream of the RCCB <= 80A, or load curtailment, or ... - just not relying on diversity alone).

       - Andy.

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