This is a question about (iii) of 514.13.1 of BS 7671:2022

This is a question about (iii) of 514.13.1 of BS 7671:2022.

 

BS 7671:2022

514.13.1 A durable warning notice with the words 'Safety Electrical Connection - Do Not Remove' shall be securely fixed in a visible position at or near:

(i) the point of connection of every earthing conductor to an earth electrode, and

(ii) the point of connection of every bonding conductor to an extraneous-conductive-part, and

(iii) the main earthing terminal; where separate from main switchgear.

 

Q) I am wondering where does (iii) refer to, and why it is necessary to install the warning notices there?

Parents
  • we seem to have lost a reply from Graham, but I'll have a go.  the MET is any sort of marshalling block where the green and yellow wires come together that is not inside another box. although the regs don't make it very clear there is often more than one - perhaps in the basement of a block of flats, and then again inside each flat. this sort of thing. The warning is because taking the site off-earth without isolating the supply first may well allow all the earthed metalwork to drift to a  painful voltage.

    Mike.

  • we seem to have lost a reply from Graham

    Yes, not sure why?

    EDITED ... but it has reappeared, perhaps popped onto the moderation queue?

  • And now the original post has re-appeared, I can link the two responses, which just happen to be complementary, by pointing out that the picture in the post from   clearly shows a more durable plastic notice, secured with screws ...

  • I love the wee flags!

    Most SP CUs nowadays seem to have a couple of terminals in the earth bar for bonding, but I am not sure that it was always so.

    The other thing is that my (ex-) TN-S supply has 4 weedy looking strands for insertion into the MET. They are not long, but do have a diameter of about 2¼ mm. It follows that a junction block (even with no bonding) was required.

    With modern TN-C-S service heads, there is a terminal for the earthing conductor.

    Should that have a warning notice?

Reply
  • I love the wee flags!

    Most SP CUs nowadays seem to have a couple of terminals in the earth bar for bonding, but I am not sure that it was always so.

    The other thing is that my (ex-) TN-S supply has 4 weedy looking strands for insertion into the MET. They are not long, but do have a diameter of about 2¼ mm. It follows that a junction block (even with no bonding) was required.

    With modern TN-C-S service heads, there is a terminal for the earthing conductor.

    Should that have a warning notice?

Children
  • With modern TN-C-S service heads, there is a terminal for the earthing conductor.

    Should that have a warning notice?

    The service head is not part of the consumer's electrical installation, and isl also outside the scope of BS 7671 ... so perhaps a question for the relevant DNO ?

  • Equally well, the earthing conductor is part of the consumer's installation, so where do you draw the line?

    The earth terminal is not sealed, in fact there is nothing more than a sort of dust cover over the terminals.

    I had never thought about this before, but the OP prompted the question.

  • I thought the N/PE cover on most cutouts was normally sealed - and even if it isn't it is rather more obviously part of electrical equipment that even ordinary persons shouldn't be tempted to mess with (similar to the earth bar in a CU not needing a label). Some larger (industrial) METs do look rather more mechanical than electrical to the untrained eye.

    Don't over estimate non-electrical types. I've seen an example of a plumber doing exactly what the label said, when replacing a gas pipe - they left 6" of the original pipe hanging in mid-air just so they didn't have to remove the original bonding clamp. Maybe the wording could have been better... (e.g. ensure it remains connected, rather than do not remove perhaps).

       - Andy.

  • ve seen an example of a plumber doing exactly what the label said, when replacing a gas pipe - they left 6" of the original pipe hanging in mid-air just so they didn't have to remove the original bonding clamp.

  • I love the wee flags!

    Permitted by 514.5.2 even if they contain only numbers, provided those numbers pertain to the relevant circuit for circuit identification ... The main purpose of 514.5.2  being to stop someone numbering the PE conductor and using it as a live conductor, and 514.4.2 of BS 7671:2018+A2:2022 aligns with this to prevent "oversleeving" of the PE in a multicore cable to use it as a live conductor, as well as using GNYE single-core cables for any purpose other than PE or CPFE (the latter being combined protective and functional earthing).

  • I am sure that Mike will tell us, but it does seem sensible to label water bonding, gas bonding, etc.

  • I thought the N/PE cover on most cutouts was normally sealed

    This is after the N/PE split, so it is just the PE.

    I shall post pictures tomorrow.

  • This is after the N/PE split, so it is just the PE.

    Usually, at that point, it's often the same block for N and PE ... at least at the service head itself.

    So, perhaps labelling it as "PE" alone is not quite right?

    However, at my sister's house, there is a DNO earthing terminal, that's brought off the Neutral, and has a DNO earth electrode connected ... because it's PNB.

    Again, all belongs to the distributor, but ...

  • I see what you mean. I had not quite remembered the service head properly. However, the PE terminals are accessible to an ordinary person.

    Perhaps the terminal constitutes the MET? "The terminal ...provided for the connection of protective conductors ... to the means of earthing."

  • However, the PE terminals are accessible to an ordinary person.

    In some designs of service heads. In others, even from the same manufacturer, you need to remove a screw that is accessible only when the service fuse carrier is removed from the head (in fact, there is one of those Series 7 with a fixed block and no access to the consumer on the demo board I pictured earlier in the thread).

    Perhaps the terminal constitutes the MET?

    Not in my opinion, it's not part of the electrical installation.

    In my opinion, in BS 7671 speak, the earth block on the service head is the means of earthing, see Fig 2.1 in BS 76771 ... but if I remember correctly, in ESQCR it's the Distributor's Earthing Terminal.