Earthing or bonding ?

Thank you for the great responses. Here is another example. 3 phase feeds local isolator using swa as the cpc. However as you can see flyleads have been added to join all the SWAs together even though they are earthed at the Supply. I’m aware this may not fall under BS761 but wouldn’t this be supplementary? 

No you say yourself they are the circuit CPC as they are Earthed both ends. Even if there were another G/Y they all together would form the CPC. Supplementary bonding joins things that are not part of the electrical installation to the installation for example in a bathroom to the pipes. In large installations it may sometimes be used to reduce Ze, for example using structural steelwork, but in reality this becomes part of the CPC.

The enclosure appears to be of an insulating type. The armoured cables are electrically joined together as they would be if terminated in a metal electrically conducting box/enclosure. It all looks good to me.

Z.

No, I don't think that that is the case. The cables from the banjos join the CPC, which is the armour, to the metal back-plate so they are part of the CPCs which "earth" the plate. Failing that, should there be a fault to the plate, what would be its path back to the transformer?

but surely this isn't needed (red circle) as they are earthed back at the supply? the GY to the back plate is the cpc for the power circuit (yellow). The other SWAs are just control cables which have been all connected again at the bottom of the enclosure (red) 

The linking under the enclosure may not be needed BUT, perhaps the original installer did not know the function of the S.W.A. cables and wanted to ensure good earthing at the load end. Also Zs at the load end will be low due to multiple earth return routes. The linking of the cables may be overboard, but does no harm, and may even increase safety. Even if the S.W.A. cables are correctly glanded at the supply end it is good practice to correctly gland the cables at the load end as well. As the big enclosure appears to be of the insulated type the installer may have considered that linking the S.W.A. cables together compensated for this in some way.

Z.

MrJack96 said:

but surely this isn't needed (red circle) as they are earthed back at the supply?

'Why would this be done?' is the question, I guess.

First, electromagnetic compatibility, especially for signal cables (bonding at BOTH ends is recommended by BS IEC 61000-5-2, which is referenced for this purposes from BS 7671). There are occasions where bonding at both ends is not recommended, particularly where cables have extremely long runs, but the designer would often address that.

Second, taking a step back from this, imagine a single multicore SWA supplying a distribution board, with outgoing circuits in SWA. Imagine also zinc-plated (colour passivated) gland plates on the DB, and fixings of the gland plate that provide good electrical connections to the enclosure itself (which is connected to the earthing terminals in the DB). So, do we actually need any additional earthing connections at all to the gland plates? It may well be the case that the cross-sectional area of the DB enclosure is not, on its own, suitable for the prospective fault currents and disconnection times possible in circuits downstream, and a suitably sized copper conductor is required between earth terminal and the SWA glands, to reduce the current flowing in the enclosure itself. In companies that often come across this situation, it quickly becomes a "company installation practice" to always provide sufficient copper conductors between enclosure earthing terminal and SWA glands, so a mistake is never made.

MrJack96 said:

but surely this isn't needed (red circle) as they are earthed back at the supply?

'Why would this be done?' is the question, I guess.

First, electromagnetic compatibility, especially for signal cables (bonding at BOTH ends is recommended by BS IEC 61000-5-2, which is referenced for this purposes from BS 7671). There are occasions where bonding at both ends is not recommended, particularly where cables have extremely long runs, but the designer would often address that.

Second, taking a step back from this, imagine a single multicore SWA supplying a distribution board, with outgoing circuits in SWA. Imagine also zinc-plated (colour passivated) gland plates on the DB, and fixings of the gland plate that provide good electrical connections to the enclosure itself (which is connected to the earthing terminals in the DB). So, do we actually need any additional earthing connections at all to the gland plates? It may well be the case that the cross-sectional area of the DB enclosure is not, on its own, suitable for the prospective fault currents and disconnection times possible in circuits downstream, and a suitably sized copper conductor is required between earth terminal and the SWA glands, to reduce the current flowing in the enclosure itself. In companies that often come across this situation, it quickly becomes a "company installation practice" to always provide sufficient copper conductors between enclosure earthing terminal and SWA glands, so a mistake is never made.