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Smoke Alarm Connection Confusion?

AncientMariner

On getting the odd false alarm on our BRK 670MBX Mains powered, wired interlinked Ionisation Smoke Alarms, batteries OK, blew out minimal dust but still bleeping, so time to replace.

Found that Ionisation type alarms were now out of favour, looked for suitable replacements. The HiSpec Fast Fix PE?FF10 mains Interlinked Optical Smoke Alarm from our local Screwfix (907RG) looked promising at first, but the wiring diagram https://www.free-instruction-manuals.com/pdf/pa_3632041.pdf is unclear regarding wiring.

Like our existing alarms, there are three terminals, Live, Neutral and Interconnect  on a plug in connector, but also an Earth Terminal, which seems strange since these alarms are Class II Apparatus.

In our case there are just three wires visible, possibly the then unused ecc wire was cut short where the 3-core+E was connected to the pre-wired 3-pin connector.

Possibly (likely) that this Earth Terminal is just a terminal to anchor the unused ECC, but is it required for interlinking?

Clive

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    but also an Earth Terminal, which seems strange since these alarms are Class II Apparatus

    And a very good thing too - since BS 7671 requires (in domestics at least) a c.p.c. to run to and terminated at each point in wiring. Much better than trying to squeeze in a floating terminal into a space whose designers hadn't considered it.

       - Andy.

  • 0 in reply to AJJewsbury
    AJJewsbury said:
    And a very good thing too - since BS 7671 requires (in domestics at least) a c.p.c. to run to and terminated at each point in wiring.

    At least in 17th and 18th Edition, only where ADS is used (Regulation 411.3.1.1 in Section 411).

    It is therefore not a specific requirement for PELV (which is Section 414).

    I suppose PELV systems could have an effective PEM conductor in theory ... for example a combined '0 V and cpc or ground'. In the past I've also in the past been witness to debate on whether this is permitted in the UK in consumer's installations (because of ESQCR). It has, arguably, certainly been used, for example in 3-wire unscreened EIA-232 (RS232) where PG and GND are bonded at both ends, or where GND is connected to PG at one end and PG is not used at the other. Effective PEM conductors may also appear in parts of PELV control systems, but often the wiring is enclosed in exposed-conductive-parts or metallic containment, which are connected to PE (or in machinery, the protective bonding circuit, which is the same thing).

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  • 0 in reply to AJJewsbury
    AJJewsbury said:
    And a very good thing too - since BS 7671 requires (in domestics at least) a c.p.c. to run to and terminated at each point in wiring.

    At least in 17th and 18th Edition, only where ADS is used (Regulation 411.3.1.1 in Section 411).

    It is therefore not a specific requirement for PELV (which is Section 414).

    I suppose PELV systems could have an effective PEM conductor in theory ... for example a combined '0 V and cpc or ground'. In the past I've also in the past been witness to debate on whether this is permitted in the UK in consumer's installations (because of ESQCR). It has, arguably, certainly been used, for example in 3-wire unscreened EIA-232 (RS232) where PG and GND are bonded at both ends, or where GND is connected to PG at one end and PG is not used at the other. Effective PEM conductors may also appear in parts of PELV control systems, but often the wiring is enclosed in exposed-conductive-parts or metallic containment, which are connected to PE (or in machinery, the protective bonding circuit, which is the same thing).

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  • 0 in reply to gkenyon

    At least in 17th and 18th Edition, only where ADS is used (Regulation 411.3.1.1 in Section 411).

    Also 412.2.3.2 (double or reinforced insulation).

    And Clive's link seems to be to a typical 230V powered variety ... so not PELV either (at least not the L/N/PE bit...I suppose the interlink might be).

       - Andy.

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