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What does BS7671 mean by an "installation coupler" 411.3.3 Note 5?

JHFE

What does BS7671 mean by an "installation coupler"  411.3.3 Note 5?

Is this a proprietary connector or standard connector used in a singular and specific way purely for a particular installation application?

I will be providing a new circuit in a domestic setting which supplies power to a yet-to-be-installed garden office pod.

 

The Pod supplier/builder has specified a 32amp 230v BS EN 60309-2 Commando socket at the end of the circuit.  They then deliver and build their pod and connect a flexible lead from the back of the pod to the socket/circuit I provide.  This in turn powers a 40A 30ma 2-way consumer unit, pre-wired at the pod building factory. In other words, outlets and lighting in the pod are RCD protected.

 

My circuit will come from CU (DB2) which I will fit and SWA will run from DB2 all the way to the outlet near the garden pod. (15-18 metres on 6mm2 SWA)

 

My question relates to RCD requirements.

 

In the interests of Selectivity, I could run the SWA from just an MCB, as the SWA negates RCD protection for the cable itself.  However, if the 32amp commando I fit is classed as a "socket outlet", I could be failing to provide RCD protection where BS7671 requires it.

 

411.3.3 Note 5 pg65 A2:2022 - states that an "installation coupler" "is not regarded as a socket outlet for the purposes of this regulation"

 

Would it be fair to class this connection between pod and circuit as an installation coupler?  It is unlikely to be accessed by lay persons to, let's say, power a lawn mower and will be behind the pod and not readily accessible to lay persons, once the pod is installed.  It will more than likely be connected once and stay permanently connected for many many years without interference.

 

Or

 

The 32amp outlet used to connect the pod to power is without question a socket outlet and therefore 411.3.3 must be obeyed and the cable run from DB2 to the outlet must be RCD protected?  Even if I sacrifice selectivity as the lesser of 2 evils and have 30ma upstream and downstream?  (or fit time delay upstream)

 

Any advice is much appreciated. Thumbsup tone1

 

Cheers

James

 

Other info.  single phase, domestic setting, TNCS, 8-year-old property, "17th edition" dual RCD (AC wave) split board for the main house, no existing SPD.

  • +1

    An Installation Coupler is a product to a specific standard. BS 7671 also talks about lighting support couplers and cable couplers as well as socket-outlets.

    In addition to Regulations 411.3.3 and 411.3.4, have a look at Regulations 521.201, 559.5.1, 551.5.4, and 553.2.1.

    Tricky regards 553.2.1 - I think that BS EN 60309-2 "free plug" and "free socket-outlet" combination, used to extend a cable, could potentially be classed as a cable coupler according to Regulation 553.2.1 - but a fixed BS EN 60309-2 socket-outlet would be exactly that, and Regulation 411.3.3 ought to apply.

    However, overall regarding selectivity, how different is this arrangement (30 mA RCD supplying socket-outlet that feeds a unit of some description with 30 mA RCDs inside it) to a Caravan, or other mobile and transportable unit, with the same sort of RCD requirements for the supply socket-outlet and installation in the unit?

  • 0 in reply to gkenyon

    Great input thanks.

    From a risk point of view, my feelings are that RCD on both ends is a "better" means of compliance.

    My understanding is that selectivity considerations exist to mitigate against unwanted tripping (correct me if I'm wrong).  If there's a trip here, it takes out one circuit going back to a one-circuit CU (+ SPD), while potentially preventing injury or fatality.

  • +1 in reply to JHFE
    JHFE said:
    My understanding is that selectivity considerations exist to mitigate against unwanted tripping

    I am tempted to ask whether there is such a thing as wanted tripping, but I won't. Tripping should be a rare, or even very rare event.

  • 0 in reply to Chris Pearson
    Chris Pearson said:
    am tempted to ask whether there is such a thing as wanted tripping

    Joy

    Yes, agreed, wording in the standards world appears very odd sometimes.

    The use of the term 'unwanted' in this case - where we used to talk about 'nuisance' - actually aligns with the International Electrotechnical Vocabulary unwanted operation of protection entry. By the looks of things, we ought to have been using unwanted tripping instead of nuisance tripping since 1996 (entry December 1995).

  • 0

    I would hard wire the pod distribution board to the circuit without the plug and socket.

  • +1

    Installing a plug and socket then supplying a permanent installation with a trailing flex rather than just hardwiring the pod consumer unit to the circuit SWA cable is very difficult to justify, it adds cost and complexity, decreases safety and is hard to justify from a regulatory point of view.

  • 0

    Wanted tripping is where it saves a life surely.

    I think the pod manufacturers specify a socket so that they can treat the pod as an appliance and not as an extension to the electrical installation, in spite of providing a CU within it. Also that the people doing the installation wouldn't necessarily be trained electrically, so couldn't wire it into a provided box.

    TNCS, are there metallic parts external to the pod?

    Can you give us a link to their site and show us which model it is?

  • 0 in reply to OlympusMons

    For the hot tub guys I just leave the SWA already made off with a gland, along with an earthing nut and earth fly lead, so they can just secure it and connect the conductors.

    If they cannot do that they should leave the electrical work alone.

  • 0 in reply to OlympusMons

    PDF

  • 0 in reply to JHFE

    Load of twaddle.

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