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

Question

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?

gkenyon · Accepted Answer

haeyun kim said: Q) I am wondering where does (iii) refer to, 
 In my house, which is TN-C-S, the green-and-yellow cable from the service head goes to an earthing block, rather than the earth terminal in the consumer unit. The main bonding is connected to this block, an a connection taken to the consumer unit. This is not uncommon. This illustration is from Figure 4.9 of IET Guidance Note 8 Earthing and Bonding , and I've circled in red the separate MET: 
 
 haeyun kim said: and why it is necessary to install the warning notices there? 
 So no-one disconnects the earthing arrangement, or the connection to the consumer unit, as this may well cause exposed-conductive-parts to have a voltage of 110 V AC from leakage currents in the installation (which can sometimes be fatal). The warning notice can be a durable label applied just above or below the MET, for example as this picture (which is a part of a setup I use to demonstrate a method for testing a consumer's earth electrode): 
 'Durable' of course depends on the external influences pertaining to the particular installation, so it's not uncommon in commercial/industrial installations to have a more durable plastic, or engraved laminated, notice, perhaps secured with screws.

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

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