Phil Pascoe
Established Member
I thought using the armour as the earth was a no no on current regs. anyway?
Current garage electric supply.
- Thread starter The Bear
- Start date
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phil.p":2sur4sto said:
That's an awkward question to answer Phil.
I could just quote myself with this line, "Each and every electrical installation needs proper design and correct installation."31/10/14, and probably leave it that. There isn't a one size fits all answer to be honest.
There are certain factors that make the use of the armour undesirable in some situations.
Then there are some situations, if you interpret the rules and regulations correctly, that just don't allow it to be used full stop.
A very simple example is aggressive and corrosive environmental conditions, that could cause accelerated corrosion of the armours causing the loss of the "earth"/cpc (circuit protective conductor) function it provided.
There are many factors that need the consultation of the necessary tables and technical manuals to come to the required decision.
However as in the situation of supplying a domestic garage or workshop, the use of swa as the supply cable and it's armour as the earth could be acceptable. Some factors still need to be considered.
I've tried to keep my answer simple, I (and most electricians/engineers) would have to consult the books to come to some conclusions in some instances.
You see what I mean about "Each and every electrical installation needs... blaa blaa blaa.............."
For most of the members here, if an electrician has arrived and terminated correctly a suitable swa cable to our workshops/sheds and used the armour to provide the earth, then this will probably be within the regs and be adequate for the intended purpose.
Most of my "quirks" come from real world experience and an attitude of "belt and braces".
I've seen way too many badly terminated swa cables and badly installed swa with rotted off armour.
The armour always needs bonding down anyway, but I try not to rely upon it as the only provision of the "earth"/cpc. Others will argue against this as unnecessary and maybe rightfully so but as I said it's one of my quirks.
MMUK
Established Member
phil.p":1tsue08i said:
Using armour as the sole earth has been a no-no since the 16th Edition came into force nearly 25 years ago.
Below is taken from a paper written by John Peckham. He updated it in 2012 for the 17th edition.
The full article can be found here http://www.gadsolutions.biz/regulations/swa-as-cpc
It is considered by many as definitive.
The use of internal cores, of both thermoplastic and thermosetting SWA cables, as a CPC and/or the use of separate parallel CPCs are not required for SWA cables to comply with BS7671 provided.
1. The operating temperature of the cable does not exceed 700C.
2. The CSA of conductor cores does not exceed 95mm2.
3. The cable is not installed in the floating section of any marina.
4. The cable is correctly selected for the correct value of R1 + R2, or Z1 + Z2, for the circuit protection device protecting the cable.
5. The cable does not connect different installations together which have separate means of earthing unless sized for the potential earth fault current.
6. The cable is not used as a combined CPC and bonding conductor on a PME
installation unless suitably sized.
7. The cables are properly terminated in correctly sized manufactures brass glands selected for the external influences prevailing.
8. Where a removable gland plate is present on the enclosure to which the cable is attached the earth ring (banjo) supplied with the gland is used and is connected to the earth terminal in the enclosure with a separate CPC. This CPC terminated in an eyelet to a bolted connection to the earth ring.
9. Any protective coating on the enclosure surface is removed under the contact surfaces of the gland and associated earth ring to expose bare metal.
10. All the wires of the armouring enter the gland and the gland nut is adequately
tightened. The cable is adequately supported up to the gland with cable cleats to prevent mechanical strain on the gland
As I indicated in an earlier post, many factors exist that determine whether or not the armour of SWA is suitable for use as a CPC/"earth".
The matter of using the swa as a cpc has been around and accepted (so long as the factors and conditions mentioned in the above noted document, also in many other tables and technical manuals are met) much longer than the existence of the 16th edition.
Sweeping statements sometimes lead to confusion.
The full article can be found here http://www.gadsolutions.biz/regulations/swa-as-cpc
It is considered by many as definitive.
The use of internal cores, of both thermoplastic and thermosetting SWA cables, as a CPC and/or the use of separate parallel CPCs are not required for SWA cables to comply with BS7671 provided.
1. The operating temperature of the cable does not exceed 700C.
2. The CSA of conductor cores does not exceed 95mm2.
3. The cable is not installed in the floating section of any marina.
4. The cable is correctly selected for the correct value of R1 + R2, or Z1 + Z2, for the circuit protection device protecting the cable.
5. The cable does not connect different installations together which have separate means of earthing unless sized for the potential earth fault current.
6. The cable is not used as a combined CPC and bonding conductor on a PME
installation unless suitably sized.
7. The cables are properly terminated in correctly sized manufactures brass glands selected for the external influences prevailing.
8. Where a removable gland plate is present on the enclosure to which the cable is attached the earth ring (banjo) supplied with the gland is used and is connected to the earth terminal in the enclosure with a separate CPC. This CPC terminated in an eyelet to a bolted connection to the earth ring.
9. Any protective coating on the enclosure surface is removed under the contact surfaces of the gland and associated earth ring to expose bare metal.
10. All the wires of the armouring enter the gland and the gland nut is adequately
tightened. The cable is adequately supported up to the gland with cable cleats to prevent mechanical strain on the gland
As I indicated in an earlier post, many factors exist that determine whether or not the armour of SWA is suitable for use as a CPC/"earth".
The matter of using the swa as a cpc has been around and accepted (so long as the factors and conditions mentioned in the above noted document, also in many other tables and technical manuals are met) much longer than the existence of the 16th edition.
Sweeping statements sometimes lead to confusion.
