Upgrading fuse board on system with conduit earthing

[SPECIAL LOCATION]

The time where you may need an additional CPC is if you got high protective current flowing..

Thus need High integrity earth as per 543.7 pg 165 ->

What are the sockets feeding??

Guinness

 

[andy_spark]

543.2.7 Where the protective conductor is formed by metal conduit,trunking or ducting or the metal sheath and/or armour of a cable, the earthing terminal of each accessory shall be connected by a seperate protective conductor to an earthing terminal incorperated in the associated box or other accessory.

So this states that conduit is fine to use as a cpc

43.2.9

Except where the protective conductor is formed by a metal covering or enclosure containing all of the conductors of the ring, the circuit protective conductor of every ring final circuit shall als be run in the form of a ring having both ends connected to the earthing terminal at the origin of the circuit.

I would read that as conduit is fine as the cpc for a ring final, so long as continuity/R2 checks out.

thanks for the link to the regs, I'd been looking in the osg and was unable to find any reference but just read these regs now in the bgb, this will help settle an argument.

 

[Sharpend]

OK M107, I'll hold my hands up to misinterpreting the regs, read them to fast without digesting.:worship

 

[M107]

Sharpend that is something we are all guilty of from time to time.....

 

[Sharpend]

But I will read them diliegently from now on..... ]

 

[sparkytim]

What's the deal with this regards to testing etc As there is no ring circuit cpc's

The existing board appears to be connected to the conduit via a section of twisted cables (approx equivalent to 10mm2)

Last one I came across like this turned out to have large Conduit box embedded in the wall behind the Fuse box which the conduits connected to and a bare earth fly lead link to the earth bar ,( Only found after stripping Fuse box out.)

I was able to connect a 10mm 6491X to the box using a crimp Lug screwed onto a threaded hole of the box and link to the new Consumer unit earth bar.

 

[ProDave]

But it's pointless discussing the finer points of whether the CURRENT regs allow you to use the conduit as CPC of a ring final.

If you are say doing a CU change, surely you don't have to upgrade all circuits to the current spec. As long as they complied with the regs in force when they were installed and still test okay.

 

[Sharpend]

I agree Dave, I was only suggesting that the ring circuits should be upgraded due to the single earth and conduit, however as I have been corrected by M107, I now stand by the comments you have made.

 

[electrician786]

Why do we even bother installing ring final circuits. It really is a bad design in my opinion. If you ever lose a leg of the ring you will never know, causing overloading and sending possibly 32A down a 2.5mm radial circuit. At least with a 16A radial circuit you will notice power loss at a socket outlet so the customer knows something is wrong and they can call an electrician out.I used to think that ring final circuits were the only way as an apprentice but as I've got older I install more radials now.

Ive posted this in regards to a end user / customer using the sockets after all works have been completed. Obviously we as electricians would test the circuit and know that the leg had broke.

 

[Sharpend]

Radials IMHO are far superior to the Ring circuit and easier to test!!

 

[electrician786]

In glad i am not alone in my thinking, I'm glad you agree.

 

[Ash]

I've always hated Ring Finals.

I remember in college completely throwing off my lecturer asking what the point in them was.

As for the consumer unit change, I've always been under the impression when you change the consumer unit you are only responsible for the work done at the unit as long as all the circuits pass tests. Otherwise every consumer unit change would require a rewire as well.

 

[sparkytim]

Ring Final Circuits were introduced in 1948 after the War (a bit before MY time) to save on copper and deal with the problem of an increase in the number of circuits required (Radials) in the new Housing stock being built.

 

[ProDave]

Ring Final Circuits were introduced in 1948 after the War (a bit before MY time) to save on copper and deal with the problem of an increase in the number of circuits required (Radials) in the new Housing stock being built.

If I understand it (before MY time as well) previous radial circuits were only ever ONE socket on each circuit.

Nobody ever had the eureka moment of deciding to put 2 or 3 sockets on the same radial circuit. Instead the ring final was born.

I only know that from what I gather from my dad when I was a boy, and I recently did a rewire on a VERY old installation, and that had just 2 radial socket circuits, each with just one socket on them. So I stand to be corrected if indeed radials with multiple sockets were common in the 40's and 50's

 

[andy_spark]

From my experience I've found a lot of conduits supplying only 1 socket from the CU, these were wired in 7/036 or something similar with conduit as the cpc in nearly all 1950s flats I've worked in. again seperate conduit for immersion, cooker etc. In fact the lights were the only multiple point radials, with the conduit as cpc. Thinking about it these were probably safer than the 1950s houses with only twin cable feeding the lights.

In my house (1958 model) the original socket cables were seperate radials, 1 to each bedroom.

 

[SLIPSHOD & SLAPDASH]

Back to the OP, if you find the end of the conduits its more than likely they have a copper strip wrapped round them secured with a brass nut and bolt that your stranded cable is attached to. This was the only way to bond pipework up until the mid 60s. If your R2 (or R1+R2) tests ok i would note this down under departures and not worry about it.

 

[batty]

Why do we even bother installing ring final circuits. It really is a bad design in my opinion. If you ever lose a leg of the ring you will never know, causing overloading and sending possibly 32A down a 2.5mm radial circuit. At least with a 16A radial circuit you will notice power loss at a socket outlet so the customer knows something is wrong and they can call an electrician out.I used to think that ring final circuits were the only way as an apprentice but as I've got older I install more radials now.Now I have to say radials are not the be all end all of circuits. Say you have a standard 20 amp radial circuit installed by a 5WW and he doesn't connect the CPC very well at the first socket and as he is a 5WW he probably hasn't tested it very well. You could have have another 10 sockets with no earth protection and as its a radial Mrs Smith doesn't know about it. She plugs her iron into the third socket and as it has gone faulty down to earth she could get a nasty belt off it especially as she has let her RCD jam through not testing it . Know if it had been a ring circuit she may have had a chance as at least the CPC would probably have come back the other way. As you may guess I generally fit ring mains.

 

[electrician786]

Yes true, but the 5WW could also install a ring final circuit in just as bad of a way as he would with a radial circuit. There are positive and negatives to both types of circuits, but I prefer a radial over a ring final circuit any day.