does this comply?

[ianmacd]

as you well be aware, I am not an advocate of the ring system for many reasons, one of which is highlighted in this scenario, we have a cable designed to carry at max 27amps but in some circumstances(rings) we allow it to carry 32amps.

+1. I can see a time when they are no longer acceptable. Aren't er the only country that still uses them?

 

[wozz]

the only difference in your two examples is distance is it not?

 

[Andy™]

right, I answered that as a de-factoin theory,

you have a cable designed for 27amps max protected by a device rated at 32amps,

and this circuit has been designed in that manner,

that is why I am saying it is in non compliance.

but it does comply. that is the point you fail to accept. yes, the breaker is 32A and max current of cable is 27A, but its protected against overload by the FCU and its protected against fault current by MCB.

 

[Andy™]

+1. I can see a time when they are no longer acceptable. Aren't er the only country that still uses them?

i think we were the only country to ever use them?

 

[steptoe]

yes, I think we are the only country in this modern age to think it acceptable to protect a cable that is only capable of carrying 27a with a device of 32 amps,

MADNESS when you think about it.

its the design that is not in compliance,

the circuit has not been designed in compliance with 7671,

I really dont see how that can be argued with.

I dont know who is at fault, but IMO the designer needs his throat tightened.

 

[Andy™]

yes, I think we are the only country in this modern age to think it acceptable to protect a cable that is only capable of carrying 27a with a device of 32 amps,MADNESS when you think about it.

its the design that is not in compliance,

the circuit has not been designed in compliance with 7671,

I really dont see how that can be argued with.

I dont know who is at fault, but IMO the designer needs his throat tightened.

it may be madness, and its not something i would generally do myself, but the fact still remains that it is fully compliant with 7671

there was a thread/post a while back (may have been Deke?) about a circuit connected directly to incoming supply going to a water pump. similar situation - may be dangerous if there's a fault, but still compliant with 7671

 

[wozz]

i dont get your argument anymore. you told me this is simple stuff but cant give me a reg that it contravenes but you keep saying it does not comply. the only difference in your examples is distance.

Im the designer of the circuit i thought of it, i couldnt think of why it didnt comply, i didnt say i was going to use it i was thinking aloud. The NIC statement voltimax posted even quotes the reg i was interested in when talking about moving overload to the acessory.

 

[kme]

Don`t think I ever said "simple stuff" mate. Regs, as has been adequately demonstrated in the past, can be read & interpreted in many ways.

If there is some ambiguity, look at it from a different point of view. IF you installed it like that, and IF something happened, AND you ended up in a court of law, do YOU believe that your circuit design would not be held as a contributary factor? Lets take a "for instance". One of these cables gets gnawed by a rodent. The rodent catches fire, and sets the house alight. Could a different circuit design have potentially prevented this occurence?

The discussion degenerated somewhat into "ring / no ring; what`s the difference". The difference is, one is an accepted final cct by BS7671; and the other isn`t. That is the bit that is "simple".

HTH

KME

 

[Graham Lister]

Rats chewing cables cables/ending up in court etc has nothing to do with the question. If you have spurred off a ring for anything you have done exactly the same circuit design as wozz suggested. No decent sparky would install a circuit as wozz suggested but the only reason is because scaremongers like steptoe upon seeing it would say your house will burn down as its a bit of a leftfield design.

It complies with regs and even if the length was over 3m then I fail to see how the 32A RCBO would fail to deal with a fault. That it's not listed as a standard circuit means nowt I am afraid. That the spurs could be changed for sockets also means nowt. Hopefully someone will prove me wrong.

 

[ianmacd]

Anyone thinking that this is acceptable, I'm sorry to say, is living with the faries.

The circuit described is NOT a ring. It could never be seen as a ring. It has no possibility of having r1,r2 & rn. If it was a ring then it should have 2 other accessories to have 2 spurs anyway. It IS a radial and as such the overcurrent device is NOT acceptable.

What about the argument about the overcurrent protection being at the end of the cable? Until Wozz wants to tell us how long the runs are then thats not a real argument either and in my mind would only hold true for the FCU as the socket does not have a perminantly connected overcurrent device (it can be unplugged easly loosing its protection).

Bottom line: It does not comply. Its not a ring and both ends do not have permanent overcurrent protection.

Wozz. Please do not see this as people ganging up on you, its not. Can you explain why you designed the circuit this way?

 

[Lee321]

those are your opinions ian only.

if the 3m rule on omisssion of ocpd applied to all radials then it would have been highlighted at the start of "omissions of protection against overload"

I believe it to apply ONLY to where a reduction (or tap off) of CCC has taken place from a supply that has a design to supply something else/bigger

as i said a 600a busbar riser in a office block and on the 3rd floor in the riser cupboard there is no db in a reasonable distance i could connect 1.5mm to the 600a supply provided max 3m and mechanical protection provided.

where talking about a complete circuit originating at a db

not nicking a supply from a bigger one

if you look at the headings of those it says POSITION OF and the reason its on about postion is it describes a scenario where a opcd is needed that NOT at the source of supply i.e a db

 

[ianmacd]

[quote name='Lee

 

[Lee321]

thumbsupsmilie

 

[Badger]

my take on this is regarding rin mains when installed correctly you would 2 earth paths and to conductor paths under fault current and over load, because you have 2 cables to the cu and 2 cables to each socket, therefore you have double the 27 amps capability ie 2 x 27 = 54 the size of the cable is 2.5 and you have 2 x those cables for the conctors therefore making 5 in total, and the earth is 2 x 1.5 making 3 in total, which would therefore allow easily 32 amps to pass through, now with regards to spurring from a ring main i dont think it should be alowed as you only have one return path back to the supply through the ring main where it connects to, and so should be classed as a radial circut from the ring main, i think ring mains are pefectly safe when not spurred from, but spurring from a ring main is when it becomes a bit dodgy. and should be not done, thats my take on ring mains as for this problem of 2 radials being from one 32 amp breaker, then imho thats a big no no because there is only one earth path so the earth and current conductors cannot share the loading therefore the resistance will be higher, no if these were connected between the 2 ends of lines and made into a ring main, then no problem for those 2 items, my self id run them in 4 or 6mm though and have each appliance seperatly if it needs a combined 32 amp trip, or run each radial froma 20 amp mcb, job done all compliant

 

[ADS]

my take on this is regarding rin mains when installed correctly you would 2 earth paths and to conductor paths under fault current and over load, because you have 2 cables to the cu and 2 cables to each socket, therefore you have double the 27 amps capability ie 2 x 27 = 54 the size of the cable is 2.5 and you have 2 x those cables for the conctors therefore making 5 in total, and the earth is 2 x 1.5 making 3 in total, which would therefore allow easily 32 amps to pass through, now with regards to spurring from a ring main i dont think it should be alowed as you only have one return path back to the supply through the ring main where it connects to, and so should be classed as a radial circut from the ring main, i think ring mains are pefectly safe when not spurred from, but spurring from a ring main is when it becomes a bit dodgy. and should be not done, thats my take on ring mains as for this problem of 2 radials being from one 32 amp breaker, then imho thats a big no no because there is only one earth path so the earth and current conductors cannot share the loading therefore the resistance will be higher, no if these were connected between the 2 ends of lines and made into a ring main, then no problem for those 2 items, my self id run them in 4 or 6mm though and have each appliance seperatly if it needs a combined 32 amp trip, or run each radial froma 20 amp mcb, job done all compliant

That is why you are only allowed one double or one single socket on an unfused spur - because the current is then restricted to 26 A by the plug top fuses.

With a fused spur the current is restricted by the fuse - e.g. 5 A

So, spurs are perfectly safe

This is the whole point of the Ops argument - why isn't it still as safe, without the ring final attached??

It isn't as simple as doubling the current carrying capacity of the two 2.5mm cables, by the way, because at different points on the ring varying amounts of current will be drawn down each leg - if that makes sense.

 

[kme]

This is the whole point of the Ops argument - why isn't it still as safe, without the ring final attached??

OK. So, on the one hand, we have regular posts on here, which are NOT argued with, that the OCPD is protecting the cable, not the appliance.

But Wozz`s OCPD isn`t.

Why is that such an issue? Sod the bit about rings & spurs - it bears no relation to the OPs question mate.

As has been said. IT DOES NOT COMPLY. (Unless you know of a "secret reg.", which is only in special copies of the BRB??? ] )

KME:C

 

[ADS]

It's protecting the cable against short-circuit, just not against overload.

The overload protection is coming from the plug top fuse or the FCU......just like it does with a spur off a ring final.

So, in the ops scenario - short circuit protection....yes, overload protection...yes (not possible to overload the cables), and, as he's using a RCBO, earth fault protection....yes.

So what's the problem??

As I said earlier, I still wouldn't do it - I'd use a 20A RCBO

 

[Andy™]

^ what he said. it complies with the regs, but is not good practice

 

[Badger]

no i disagree it DOES NOT comply by the regs full stop!! .

 

[ianmacd]

I would love to know what the weather is like on the planet you are living on if you think that complies. It does not. It's not a ring it's a radial end of story. Anyone who thinks otherwise really should get a copy of the brb the rest o us use (BS7671:2008).