Upgrading fuse board on system with conduit earthing
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electrician786
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Do a R2 test (long lead method) on the conduit and insert result on the Certificate.
TBH this does not sound very good, I'd at least get some BS951 clamps on those,,, et a good connection
Otherwise it's not a problem to use conduit as the CPC, just test your (R1+R2) as normal
Lillpete
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Sorry a slight misunderstanding, its boxed in so I can't see the ends of the conduit but they don't terminate into the fuseboard directly they are earthed by the twisted cable, I assume there ar appropriate clamps in place (possibly not though)
Doc Hudson
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Have you done any continuity tests to check the integrity of the existing conduit joints, such as opening up some of the accessories to check what the joints look like at the back-boxes and a long lead test?. If the conduit as CPC is dodgy have you got enough room to pull a new CPC through the conduit with the circuit conductors if you need to?
Doc H.
electrician786
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Link the correct cpc to to the line of the correct circuit, make sure you safely isolate and lock off before doing this. now test at each point on the circuit and note down the highest reading as your R1 + R2. Or do the long lead method. (R2)
Looking at your post again it seems you have only one cpc at the consumer unit, instead of two. So you can not to the cross over with cpc and line (figure 8) for ring final circuit. I would suggest you carry out an R2 test. Long lead method.
Looking at your post again it seems you have only one cpc at the consumer unit, instead of two. So you can not to the cross over with cpc and line (figure 8) for ring final circuit. I would suggest you carry out an R2 test. Long lead method.
This is just a guess , but there may have been an original metal board with the conduits bushed into it with , perhaps , earth couplers , hence the "twisted cable" looping them together .
What sort of cable goes down the conduits? T/E or 6491X ?
If you're not rewiring , I presume you take the Zs,s with conduit as earth .
What sort of cable goes down the conduits? T/E or 6491X ?
If you're not rewiring , I presume you take the Zs,s with conduit as earth .
andy_spark
Senior Member
I've been working for the local housing association recently and the sub contractor I'm working for has had us rewiring all circuits in blocks of flats using conduit as the earth, the reason being (they claim) is that it doesn't comply to 17th edition.
After rewiring a radial socket circuit I tested Zs without the new earth, conduit only, 0.19 ohms and using new earth as well 0.18 ohms. It seemed like a lot of hard work for nothing!
After rewiring a radial socket circuit I tested Zs without the new earth, conduit only, 0.19 ohms and using new earth as well 0.18 ohms. It seemed like a lot of hard work for nothing!
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The conduit is fine for the earth as long as it's in good condition.
Problems I have found before:
Conduit "snapped" at a joint where it's been stood on in a loft, breaking the CPC connection and exposing the cables to a rough edge.
Sockets only earthed through their mounting screws, no flying earth lead from the conduit back box and not even a screw in the back box to attach a flying lead to.
Ditto for light switches, but not such a concern if only plastic switches.
The only connection to the conduit is often the gland where it bolts to the old metal clad fuse box. If trying to do a CU swap it can be hard or impossible to get a decent earth connection.
So lots of things to think about if trying to upgrade a conduit system. It may be okay, but then again it may not.
And that's before you consider things like not enough sockets, and not in the right place, very hard to convert a single socket to a double etc etc.
Problems I have found before:
Conduit "snapped" at a joint where it's been stood on in a loft, breaking the CPC connection and exposing the cables to a rough edge.
Sockets only earthed through their mounting screws, no flying earth lead from the conduit back box and not even a screw in the back box to attach a flying lead to.
Ditto for light switches, but not such a concern if only plastic switches.
The only connection to the conduit is often the gland where it bolts to the old metal clad fuse box. If trying to do a CU swap it can be hard or impossible to get a decent earth connection.
So lots of things to think about if trying to upgrade a conduit system. It may be okay, but then again it may not.
And that's before you consider things like not enough sockets, and not in the right place, very hard to convert a single socket to a double etc etc.
andy_spark
Senior Member
+1 Dave
Its hard to see how these conduits could get damaged they are buried in about a foot of concrete, it seems like a money making exercise, still as long as they keep paying!!
ray
On previous jobs I've always made sure the sockets are earthed with a cpc from back box and any light fiitngs have a good cpc from conduit to ceiling rose, and also bonding clamps on the conduit with a 6mm or 10mm earth to the CU earth bar.
Provided all this is in place and the test results are Ok I personally can't see an issue.
Its hard to see how these conduits could get damaged they are buried in about a foot of concrete, it seems like a money making exercise, still as long as they keep paying!!
ray On previous jobs I've always made sure the sockets are earthed with a cpc from back box and any light fiitngs have a good cpc from conduit to ceiling rose, and also bonding clamps on the conduit with a 6mm or 10mm earth to the CU earth bar.
Provided all this is in place and the test results are Ok I personally can't see an issue.
Sharpend
"It Just Is"
I'm fairly sure that the17th requires the ring circuits to have cpc ring however is this a ring? The single cpc will loop in/out each socket as a radial and the conduit is then linked in the same way through the fixing 3.5mm screws?? Not a true ring in my book.
On the old flats that I have been upgrading always run an additional cpc. Also ensures a continuos ring should additional sockets be required.
On the old flats that I have been upgrading always run an additional cpc. Also ensures a continuos ring should additional sockets be required.
Thats right Sharpend, I was thinking in terms of an existing system and doing a PIR , conduit as earth would be a 14th edition job I would think , but if Zs is OK then its still safe .
Sharpend
"It Just Is"
So in answer to OP as your are upgrading the consumer unit then you are the last one to work on the install and have to therefore ensure what you do is compliant to 17th edition so I guess you will have to pull in additional cpc. Hope you allowed for this in the price!
When did I miss conduit not being acceptable as a cpc under regs then?
As far as I know you can still use steel conduit as a cpc as long as it meets the requirements of the relevant reg numbers, is mechanically and electrically continuous.
As far as a conduit not acceptable for a ring circuit cpc, simple, don't install a ring!
As far as I know you can still use steel conduit as a cpc as long as it meets the requirements of the relevant reg numbers, is mechanically and electrically continuous.
As far as a conduit not acceptable for a ring circuit cpc, simple, don't install a ring!
Sharpend
"It Just Is"
Side it's not that it's not compliant just not on a ring final. The powers that be!!
Not so sure I agree with you Sharpend.
I believe that it still could be installed on a ring final.
However, it is easier to just not install ring finals!
What do the powers that be have to say about not using conduit as a cpc on a ring final.
Who are these powers that be, what is the reg. no. that disallows this?
Not trying to be argumentative, but, I think this is another urban myth to be honest.
I believe that it still could be installed on a ring final.
However, it is easier to just not install ring finals!
What do the powers that be have to say about not using conduit as a cpc on a ring final.
Who are these powers that be, what is the reg. no. that disallows this?
Not trying to be argumentative, but, I think this is another urban myth to be honest.
Sharpend
"It Just Is"
I have got me BGB to hand but will look up reg tomorrow unless someone beats me to it
We have if tubes don't pull, change the ring to a radial, ensuring design meets regs.
We have if tubes don't pull, change the ring to a radial, ensuring design meets regs.
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Sharpend
"It Just Is"
Can you expand on that as don't have BGB to hand. ? Please.
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
543.2.9 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.
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
543.2.9 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.
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