SWA test results

[haptism]

Hi hope someone can advise; ive not done alot of testing or filling out eic's and am a bit stumped on this. I have run the usual dead tests on a 3 core swa cable used on a final circuit all tests are good. However the amour (which needs to carry the full fault current), does it not need to be accounted for its continuity on an eic ? For example if there are 4 sockets on a radial wired in swa it would be possible to forget to link out each pair of banjo's.

So do you calculate the resistance of the armour (although I know this would be up to standard if its smaller than 50mm or something), or do you just tick a box confirming continuity. I cannot find any info on example eic's where this situation is accounted for, so im probably missing something and would like to find out ! Thanks

H

 

[telectrix]

if the armour is used as cpc, then the banjos need to be linked to provide a continuous cpc. even if a core is used as cpc, the armout must be earthed at the supply end at least and must also be continuous. a wander lead and R2 reading would confirm.

 

[haptism]

if the armour is used as cpc, then the banjos need to be linked to provide a continuous cpc. even if a core is used as cpc, the armout must be earthed at the supply end at least and must also be continuous. a wander lead and R2 reading would confirm.

Telextric, yes I know the amour must be earthed and linked to provide a continous cpc even if a core is being used as cpc; the issue im having is what tests does the armour need and what do i identify it as on the eic ?.

Would I put "socket radial armour" in the circuit description box, and work out the the resistance of the armour and put this result in the R2 column ? Although its not strictly R2 is it if the core is being used as cpc ??

 

[telectrix]

measure it. R2 with a wander lead. you only need to enter on the cert R1+R2 or R2 at the last oultlet. measuring it at intermediate points is not necessary.

 

[haptism]

Okay I get it, measure R2 with wonder lead at the last socket, this is what i have already done. If you could be a diamond and tell me where I put the result on the EIC!

Do I put it in the same row where all the other test results are for that circuit in the R2 box ?

Or do I put the R2 result in a separate Row titled "socket radial amour" ?

 

[telectrix]

if it's used as cpc, or part cpc with a core,then put the value in the R2 box ( or the R1+R2 box) for that circuit. if it's not a cpc but just earthed, there's nowhere to enter the value. so maybe a comment in the comments section to enter the value as proof that it's continuous.

 

[Deleted member 26818]

What you have is parallel CPCs.
Measure the third core and the armour together, to obtain the R2.

 

[haptism]

I that case all amoured cables have parallel cpc's, so by that reasoning all armoured circuits are recorded as an R2 value, not R1 + R2.

 

[Deleted member 26818]

No, not all SWA cable installs use the armour as a CPC.
You can record R1 + R2, saves having to get a wander lead out or R2, up to you.

 

[haptism]

if it's not a cpc but just earthed, there's nowhere to enter the value. so maybe a comment in the comments section to enter the value as proof that it's continuous.

This is what im getting at, you only use R1 + R2 or R2, not both,

 

[haptism]

No, not all SWA cable installs use the armour as a CPC.
You can record R1 + R2, saves having to get a wander lead out or R2, up to you.

But all amoring is earthed, as in this case, the swa has the 3rd core as cpc

 

[Deleted member 26818]

If you use the armour as a CPC, then you need to record it's resistance R2 or R1 + R2.
If you are using the armour as a CPC along with one of the cores, then you need to record the combined resistance, again R2 or R1 + R2.
If the armour is not being used as a CPC, there is no need to record it's resistance, though you do need to check that the resistance is such that the protective device will operate.
Where it becomes problematic, is when you are using the armour as a second CPC for high integrity circuits.

 

[Simonslimline]

Edit, missread.

 

[westward10]

What you have is parallel CPCs.
Measure the third core and the armour together, to obtain the R2.

I agree that if you use a separate core as the cpc the armour still becomes a parallel earth or cpc. To record R2 as the separate core resistance maybe the design of the circuit and to be honest doesn't matter, is the same with cpcs within steel conduit. Under fault conditions however that armour will become part of that fault path and thus also becomes the make up of R2.

 

[Wilko]

I do as Tel says loop impedance measure R1+R2 from final socket and put it in the column marked Continuity (R1+R2) which is col. 13 on the generic forms in GN3. The row could be called 'Radial - Sockets in Garage' and the Remarks could be 'SWA buried in garden' for example. And I make sure armour is continuous and earthed. Hope that helps.

 

[Simonslimline]

If you use the armour as a CPC, then you need to record it's resistance R2 or R1 + R2.
If you are using the armour as a CPC along with one of the cores, then you need to record the combined resistance, again R2 or R1 + R2.
If the armour is not being used as a CPC, there is no need to record it's resistance, though you do need to check that the resistance is such that the protective device will operate.
Where it becomes problematic, is when you are using the armour as a second CPC for high integrity circuits.

Regarding the high integrity circuits you mentioned, this is how its been done in a commnercial project I am on at the moment. Can you possibly give a bit of detail as to how it can be problematic spinlondon? Purely for my curiosity is why I ask.

Cheers.

 

[westward10]

If the circuit was singles in steel conduit with a separate cpcs you would not be considering recording the conduit resistance, this is no different.

 

[telectrix]

I agree that if you use a separate core as the cpc the armour still becomes a parallel earth or cpc

and what about if the armour is only earthed at the supply end to comply with the fact that it must be earthed, if not used as cpc? it's not a parallel cpc then.

 

[haptism]

If the armour is not being used as a CPC, there is no need to record it's resistance, though you do need to check that the resistance is such that the protective device will operate

Cheers Spin; I cant find mention of this situation in any books (x7) or online anywhere, and so was a bit concerning. Im surprised that there is no tick box or anything else to confirm the continuity or resistance of the SWA on the EIC; continuity of swa could easily be missed and the standard range of tests would not identify it.

 

[Deleted member 26818]

With High integrity circuits, you need two separate readings, one for each CPC.
Some people just use the highest reading, others try to squidge two readings into one box and others use a second line for the second CPC.
Not come across anyone using the R2 box for the second CPC, but I guess it could happen.

 

[sparksburnout]

If the armour is only connected at the supply end then its not a parallel path, and nothing to do with the R1+R2 values. However, it is a good point, that it needs to be of a good enough value to operate the OCPD when someone shoves a spade through the cable?

 

[westward10]

I agree that if you use a separate core as the cpc the armour still becomes a parallel earth or cpc

and what about if the armour is only earthed at the supply end to comply with the fact that it must be earthed, if not used as cpc? it's not a parallel cpc then.

Depending on armour length/csa it should be earthed both ends to prevent any potential difference.

 

[Simonslimline]

With High integrity circuits, you need two separate readings, one for each CPC.
Some people just use the highest reading, others try to squidge two readings into one box and others use a second line for the second CPC.
Not come across anyone using the R2 box for the second CPC, but I guess it could happen.

Thanks. I will ask how they recorded the results in this case.

 

[haptism]

If the circuit was singles in steel conduit with a separate cpcs you would not be considering recording the conduit resistance, this is no different.

Yes thats a good point, didn't think of it like that.

 

[westward10]

Yes thats a good point, didn't think of it like that.

If the design intends the separate core to be the cpc then record that size and it's R2. Check continuity of the armour and forget it, don't over think this.

 

[Deleted member 26818]

You have to remember that the purpose of a CPC is to connect exposed-conductive-parts of equipment to the main earthing terminal.
The armour of an SWA cable, and also earthed conduit or trunking concealed in walls is intended to provide an earth path if the cable or conductors are penetrated by a metallic object.
Sometimes the armour, conduit or trunking is used as a CPC.

 

[Deleted member 26818]

Depending on armour length/csa it should be earthed both ends to prevent any potential difference.

Unless of course it is supplying a TT'd outbuilding.

 

[sparksburnout]

Depending on armour length/csa it should be earthed both ends to prevent any potential difference.

Could you explain that? Potential difference between what??

 

[westward10]

Unless of course it is supplying a TT'd outbuilding.

True but you would have to contain the armour at the TT end.

 

[haptism]

Thanks for the responses it really helpfull and bear in mind that I have not done much testing so not too familiar with the test sheet yet !

 

[westward10]

Could you explain that? Potential difference between what??

A few years back I tested a circuit consisting of a 1.5 4-core SWA using a separate core as the cpc. Earthed at dist board end, from here it went to an external light a considerable distance from the board, terminated at an all insulated enclosure. Zs between the separate cpc and armour was greatly different.

 

[westward10]

True but you would have to contain the armour at the TT end.

No it isn't, record the R2 of the separate core.

 

[telectrix]

A few years back I tested a circuit consisting of a 1.5 4-core SWA using a separate core as the cpc. Earthed at dist board end, from here it went to an external light a considerable distance from the board, terminated at an all insulated enclosure. Zs between the separate cpc and armour was greatly different.

it would as the resistance of the armour will be > the copper core.

 

[sparksburnout]

A few years back I tested a circuit consisting of a 1.5 4-core SWA using a separate core as the cpc. Earthed at dist board end, from here it went to an external light a considerable distance from the board, terminated at an all insulated enclosure. Zs between the separate cpc and armour was greatly different.

Yes it quite possibly was but why is this a problem?

 

[westward10]

it would as the resistance of the armour will be > the copper core.

I know.

 

[westward10]

Yes it quite possibly was but why is this a problem?

The armour and cpc should be bonded together to prevent potential differences under fault conditions

 

[telectrix]

The armour and cpc should be bonded together to prevent potential differences under fault conditions

but they are at the supply end if the armour is not connected at the load end. where would this PD come from?

 

[sparksburnout]

I am a bit confused here westie! Now, I just want to get this straight as I am bit concerned. Taking your example, a remote accessory (or DB) powered from an armoured cable using one of the cores as the CPC. I have to say I have also terminated the armour at both ends but then thought "why the hell am i doing this?" If you just leave the remote end un-terminated then the cable is protected against damage by virtue of the armour being earthed at the origin. Under fault conditions then yes the armour and CPC could be at a different PD but there is no possibility of the armour being able to introduce this? Surely it is better to use the Zs of the CPC provided by the core alone rather than with the armour providing a parallel path, as this might degrade over time?

 

[westward10]

Everything is possible.