spurs

[JUD]

I'm not being pedantic.

I'm just curious as to which regulation you would mark it down as a departure from.

As you said, you are not making it any less safe by reducing the size of the OCPD and as for NEW INVENTIONS....what new inventions, it's still a ring circuit.

 

[malcolmsanford]

Jud I do actually agree with you to the extent that the appendices are informative but saying that they have no context in the regs is not quite right.

As I noted the nominal design for a ring is outlined in appendix 15 and for the sake of design that is what 99.9% of designers stick to. If your making a ring final circuit 20 amps then your departing from regular design and that should be noted somewhere. As you said someone following you seeing a 20amp protection device with 2 x 2.5mm will not think it is a ring final circuit.

The only place on the EIC where you can put it is either the departure section or The comments on the existing installtion. I suppose you could put it there, but as your the one altering the installation by down sizing the protection device then it can't be something on the existing installtation. The bit I would mark in there would be the spurs not conforming.

It's great that these sort of thing bring out discussion and I fully appreciate what your saying and in many respects think your right. But it as to be noted somewhere and that is where I would note it. As a departure from normal design if you so want to call it.

 

[JUD]

I would probably note it on the schedule of test results in the special notes section.

 

[nick611]

yeah note it.but in the end our job is to make it safe.de-rate it /fuse lower than cable capacity job done.safety is our priority and surley our main concern

 

[telectrix]

my original thoughts exactly

 

[Sintra]

I'm not being pedantic.

I'm just curious as to which regulation you would mark it down as a departure from.

As you said, you are not making it any less safe by reducing the size of the OCPD and as for NEW INVENTIONS....what new inventions, it's still a ring circuit.

Probably referring to 433.1.5 but i would interperate that as a 30 / 32 being the highest OCPD that can be used. I can't see a problem with derating to 20A

 

[IQ Electrical]

Though if it was me you have no need to do anything really. As your fitting a new CU then all you need to do is make your work in line with the 7671. Again on your EIC you note in the part comments on existing installation the spurs and advise the client that they do not come up to the Regs and you advise them to have them upgraded.

And me!

 

[Guest123]

Just as a side note on the ring circuit issue, I installed a 100A ring circuit in 25mm 3C SWA in a caravan park not so long ago. The way I see it as long as CCC is taken into account and also all other circuit constraints i.e, VD, loop impedance etc and also equal spread of loading on the ring is achieved, a ring circuit can be of any size.

Neither NIC nor ECA had anything at all to add on the subject other than what I had taken into account above.

In this case the load will not be equally shared as it is overloaded at one point so needs down rating to a 20A OCPD, but as you are responsible only for the CU upgrade technically you need not do anything about it. Having said that you're installing new anyway so put a 20A OCPD in and note it just to make the customer aware and to cover yourself more than anything.

I know I would if it were me in your position.

 

[malcolmsanford]

Just as a side note on the ring circuit issue, I installed a 100A ring circuit in 25mm 3C SWA in a caravan park not so long ago. The way I see it as long as CCC is taken into account and also all other circuit constraints i.e, VD, loop impedance etc and also equal spread of loading on the ring is achieved, a ring circuit can be of any size.

Neither NIC nor ECA had anything at all to add on the subject other than what I had taken into account above.

In this case the load will not be equally shared as it is overloaded at one point so needs down rating to a 20A OCPD, but as you are responsible only for the CU upgrade technically you need not do anything about it. Having said that you're installing new anyway so put a 20A OCPD in and note it just to make the customer aware and to cover yourself more than anything.

I know I would if it were me in your position.

Would you class that as a ring final circuit or a ring main ?

 

[Guest123]

Would you class that as a ring final circuit or a ring main ?

Can you give a definition of the difference between the 2???

BS 7671 doesn't seem to be able to.

 

[rocker]

If you're that worried about down-rating the MCB (IMO if an overload is unlikely it would be fine) regs wise, (or in fact overload-wise) could you split the ring at the spur point and use a spare way in the board for another 16A breaker, thus creating 2 radials?

Couldn't you just put a properly fated FCU at the first spur??

 

[IQ Electrical]

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

 

[malcolmsanford]

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

Beat me to it IQ

Yes appendix 15 gives you a ring final circuit. I think what you have done Lenny is a Distribution Circuit in the form of a ring.

Both rings I grant you. Isn't this electricary wonderful.

 

[rocker]

Eh? A ring main and a ring final are exactly the same thing, just old and new names, surely?

 

[malcolmsanford]

Eh? A ring main and a ring final are exactly the same thing, just old and new names, surely?

The national Grid is a ring main that is why the Regs introduced the ring final circuit to stop the confusion.