spurs

[Guest123]

I'd say the Appendix 15 example is a ring final, while the traditional distribution ring would be a ring main.

Have a look at 'ring final circuit' definition in part 2 of BS 7671.......

 

[malcolmsanford]

Have a look at 'ring final circuit' definition in part 2 of BS 7671.......

As this is a caravan site lenny you have installed a distribution circuit reg 708 So you have wired the distribution circuit in a form of a ring.

But if it's a ring final circuit how did you manage to comply with reg 708.553.1.12 where it called for each socket to have an individual overcurrent device. As well as 708.553.1.13 individual for RCD protection.

I don't think Lenny you can get away with what you did as a fing final circuit mate.

 

[IQ Electrical]

Yes, the term 'final circuit' is 'the devil in the detail' and in my opinion is the difference between the 2 different types of ring.

 

[davelerave]

As this is a caravan site lenny you have installed a distribution circuit reg 708 So you have wired the distribution circuit in a form of a ring.

But if it's a ring final circuit how did you manage to comply with reg 708.553.1.12 where it called for each socket to have an individual overcurrent device. As well as 708.553.1.13 individual for RCD protection.

I don't think Lenny you can get away with what you did as a fing final circuit mate.

i'm sure each caravan socket outlet will have separate rcbo

 

[Guest123]

I don't think Lenny you can get away with what you did as a fing final circuit mate.

And I never said it was......just stimulating debate.


As you say a ring 'final' circuit or any type of 'final' circuit must be directly connected to current using equipment. The ring circuit I installed connects to overcurrent & earth fault protection devices, not directly to the socket outlet.

I've come across large factories & hospitals also have large ring circuits supplying secondary DB's, in the region of 800A or more.

Slightly off topic but relevant I felt.

 

[IQ Electrical]

So what's your opinion then Lenny

 

[Guest123]

Well it isn't a ring 'final' circuit for the above reasons, therefore a simple ring circuit or main, whichever you prefer.

 

[malcolmsanford]

Well as the Lenny knows it can not be classed as a ring final circuit as it's not a final circuit. The final circuit is the one after the individual protection device for the socket outlet.

So as he says it;s a ring circuit but not a ring final circuit, think the words little tinker springs to mind Lenny

 

[Guest123]

I just like debating topics with others in the know.

 

[malcolmsanford]

And I never said it was......just stimulating debate.


As you say a ring 'final' circuit or any type of 'final' circuit must be directly connected to current using equipment. The ring circuit I installed connects to overcurrent & earth fault protection devices, not directly to the socket outlet.

I've come across large factories & hospitals also have large ring circuits supplying secondary DB's, in the region of 800A or more.

Slightly off topic but relevant I felt.

When I was at home I did a lot of work for a company near me .............the old blue pill maker ..............and they had a fantastic ring main system. Though it was the domain of the HV guys I did a lot with them. on the ATS side of things.

They had a about 20 odd transformers around the place and if they lost one the ATS system would reroute and restore power via the ring main, another British invention used through out the world

 

[davelerave]

ok -i got this -it's a ring main

 

[johnboy6083]

just a question regarding lennys job, am i right in saying that you would be allowed to tap off the ring with a single cable to each caravan, rather than the usual two sets of conductors terminated at the equipment/accessory. As lenny has wired his ring main in 25mm2 SWA, then as long as the branch conductor is rated to the same current, or fused down then can you do it. Also if you tapped off at a smaller conductor size, if you then fitted a smaller rated fuse/mcb ect downstream then that would protect the cable. please correct me or confirm my thoughts.

John

 

[IQ Electrical]

I don't see any reason why not, as always, it comes down to current carrying capacity and protection, that protection can be upstream OR downstream.

 

[Guest123]

Using the rule of thumb factor of 0.67, I could have used 16mm SWA for my ring circuit i.e a 100A OCPD x 0.67 = a CCC of 67A, then you could not do what you suggest.

As I used 25mm though, then yes you could do what you are suggesting as the CCC of the cable exceeds 100A.

As for 'backfusing' it is done, think of tapping off a busbar chamber for instance, it may be a 400A per phase chamber but you could tap off in 16mm singles to a 60A switchfuse as that would be the maximum drawn. I believe there is a maximum distance of chamber to SF though, I'll have to check.

 

[johnboy6083]

i was aware of backfusing (never heard it called that though) with regards to switchgear, but was not sure if same principles are applicable to normal installations. Come to think of it, the DNO use backfusing with their supplies, because they are protecting their tap off to your installation, and their ring will be rated to more than 100A