T
Thenitwentbang
This week, I finally decided to get on with rejuvenating the supply to my garage. This was in place when we moved in and, in all honesty (and on the face of it) is not a bad job. Notwithstanding this, I do probably put more demand on the circuit than the original installer probably intended, so I want to make sure it's all tickety boo and up to the job.
As I say, the existing supply to the outbuilding (which was in place when we moved in) is not actually a bad job - on the face of it. It is a spur from the downstairs ring (lounge - not kitchen) and leaves the house through a 30ma RCD protected FCU. It then makes it's way down the garden in 3 core 2.5 SWA, within black PVC conduit, which has been clipped to fence posts (with additional horizontal supports to stop sagging). There is a reasonable IP 55 CU in the garage already and someone has done a fairly neat job of adding sockets and lighting in the garage. I intend to move the supply from the existing FCU spur to a dedicated RCBO in the CU. Probably worth pointing out at this point that we are TN-S.
One thing does concern me, however, is that the route of the SWA from the spur to the garage makes it's way into my garage through our neighbour's garage (we are the centre garage in a block of three). I can see that it runs through my neighbour's garage within a very old piece of steel conduit - the end of which is just visible as it enters my garage. I don't like the fact that I have not yet seen how this is fixed in the neighbouring garage - or what state it's in. This is one of the key reasons I want to refresh it all.
Before I get on with changing anything, I decided, last night, to start with a few basic tests; to establish the health and integrity of the existing circuits.
An IR test on the external part of the circuit (SWA from the house to the garage) all checked out OK; seeing a reading >1000M Ohms on L-N, L-CPC and N-CPC.
Testing the continuity of the earth on the existing external wiring (disconnected from spur at house, line and CPC linked at garage CU) shows 0.39 Ohms. Naturally, that's not a full R1+R2, but some indication of the health of the existing external line and CPC conductors in the external SWA up to the garage. Notwithstanding this, a full Zs test from the sockets in the garage is more concerning at 3.6 Ohms!!! It's now disconnected and I'm definitely having all the sockets out to find out what's going on there. I'm sure that moving the garage feed onto it's own RCBO will play a part in rectifying this as the fault may well have been down to a poor connection at the FCU.
Given my concerns about the health of the piece of steel conduit in my neighbour's garage (that I have not yet been able to inspect) I also checked to see if there was any difference in potential between this and my own installation. After probing the exposed end that enters my garage with a voltage tester (and getting a reading of 36 volts) I'm glad I did that. What was more worrying was a reading (using my MFT) of 41V between the neutral and CPC in my garage and the exposed end of the conduit in my garage. Naturally, I have now fully disconnected the external circuit at the FCU. Even with this fully disconnected, I still see an indication of voltage at the exposed end of the conduit - and the MFT confirms 50 HZ.
I also see similar readings on the armour of a short length of SWA that comes from the afore-mentioned adaptable box, up the outside garage wall and through the neighbouring garage. I should point out that the armouring has not been used as CPC or bonded; it is terminated into plastic SWA glands at the adaptable box where it leaves the house, at an adaptable box on the external garage wall (junction point of long cable run from house and shorter run through the neighbouring garage into mine) and at the existing garage CU. This would indicate to me that the external insulation on the SWA is damaged as it makes it's way through the steel conduit in the neighbouring garage - so that is very high on the replacement list, also.
As I say, the circuit is now fully disconnected, pending further investigations - and a look at what's going on next door. I suspect that one of two things has happened - either the steel conduit has been bonded to the earth in the neighbouring garage and is becoming live through a fault in that circuit or it's making contact with something in there that is introducing the voltage. Given that I can see voltage present even with the supply disconnected from the spur, I know that this is not coming from the spur wiring - the IR tests would also seem to bear that out. Equally, I'm not blind to the fact that I may be missing something.
My big concern with this is the increased risks posed by the potential for much higher potential differences between line conductors in neighbouring properties, fed from different phases by the DNO.
My personal preference (if I can not find another reasonable route for the new external cable to take) will be to replace the existing metal conduit within the neighbouring garage with some very heavy duty plastic - fully enclosing the SWA from the point of entry to the point of exit. If I can realistically satisfy height requirements, I may actually opt for a catenary wire - rather than the existing route through the neighbouring garage. Additionally, I will be using proper brass SWA glands and bond to the armouring.
Any thoughts or ideas would be greatly appreciated - just conscious that my concerns over the path through the neighbouring garage may be giving me a bit of tunnel vision here!
As I say, the existing supply to the outbuilding (which was in place when we moved in) is not actually a bad job - on the face of it. It is a spur from the downstairs ring (lounge - not kitchen) and leaves the house through a 30ma RCD protected FCU. It then makes it's way down the garden in 3 core 2.5 SWA, within black PVC conduit, which has been clipped to fence posts (with additional horizontal supports to stop sagging). There is a reasonable IP 55 CU in the garage already and someone has done a fairly neat job of adding sockets and lighting in the garage. I intend to move the supply from the existing FCU spur to a dedicated RCBO in the CU. Probably worth pointing out at this point that we are TN-S.
One thing does concern me, however, is that the route of the SWA from the spur to the garage makes it's way into my garage through our neighbour's garage (we are the centre garage in a block of three). I can see that it runs through my neighbour's garage within a very old piece of steel conduit - the end of which is just visible as it enters my garage. I don't like the fact that I have not yet seen how this is fixed in the neighbouring garage - or what state it's in. This is one of the key reasons I want to refresh it all.
Before I get on with changing anything, I decided, last night, to start with a few basic tests; to establish the health and integrity of the existing circuits.
An IR test on the external part of the circuit (SWA from the house to the garage) all checked out OK; seeing a reading >1000M Ohms on L-N, L-CPC and N-CPC.
Testing the continuity of the earth on the existing external wiring (disconnected from spur at house, line and CPC linked at garage CU) shows 0.39 Ohms. Naturally, that's not a full R1+R2, but some indication of the health of the existing external line and CPC conductors in the external SWA up to the garage. Notwithstanding this, a full Zs test from the sockets in the garage is more concerning at 3.6 Ohms!!! It's now disconnected and I'm definitely having all the sockets out to find out what's going on there. I'm sure that moving the garage feed onto it's own RCBO will play a part in rectifying this as the fault may well have been down to a poor connection at the FCU.
Given my concerns about the health of the piece of steel conduit in my neighbour's garage (that I have not yet been able to inspect) I also checked to see if there was any difference in potential between this and my own installation. After probing the exposed end that enters my garage with a voltage tester (and getting a reading of 36 volts) I'm glad I did that. What was more worrying was a reading (using my MFT) of 41V between the neutral and CPC in my garage and the exposed end of the conduit in my garage. Naturally, I have now fully disconnected the external circuit at the FCU. Even with this fully disconnected, I still see an indication of voltage at the exposed end of the conduit - and the MFT confirms 50 HZ.
I also see similar readings on the armour of a short length of SWA that comes from the afore-mentioned adaptable box, up the outside garage wall and through the neighbouring garage. I should point out that the armouring has not been used as CPC or bonded; it is terminated into plastic SWA glands at the adaptable box where it leaves the house, at an adaptable box on the external garage wall (junction point of long cable run from house and shorter run through the neighbouring garage into mine) and at the existing garage CU. This would indicate to me that the external insulation on the SWA is damaged as it makes it's way through the steel conduit in the neighbouring garage - so that is very high on the replacement list, also.
As I say, the circuit is now fully disconnected, pending further investigations - and a look at what's going on next door. I suspect that one of two things has happened - either the steel conduit has been bonded to the earth in the neighbouring garage and is becoming live through a fault in that circuit or it's making contact with something in there that is introducing the voltage. Given that I can see voltage present even with the supply disconnected from the spur, I know that this is not coming from the spur wiring - the IR tests would also seem to bear that out. Equally, I'm not blind to the fact that I may be missing something.
My big concern with this is the increased risks posed by the potential for much higher potential differences between line conductors in neighbouring properties, fed from different phases by the DNO.
My personal preference (if I can not find another reasonable route for the new external cable to take) will be to replace the existing metal conduit within the neighbouring garage with some very heavy duty plastic - fully enclosing the SWA from the point of entry to the point of exit. If I can realistically satisfy height requirements, I may actually opt for a catenary wire - rather than the existing route through the neighbouring garage. Additionally, I will be using proper brass SWA glands and bond to the armouring.
Any thoughts or ideas would be greatly appreciated - just conscious that my concerns over the path through the neighbouring garage may be giving me a bit of tunnel vision here!
) is inspect the installation in his garage and disconnect that conduit from it if possible and thus removing the chance of it become live under fault conditions.
