Earthing SWA

[Knobhead]

Right I’m going to throw a rock in the water.

There’s been a lot of debate about earth clamps and SWA. To my mind, conventional clamps shouldn’t be used. But I kept on thinking back to cable jointing and constant pressure springs. I had a dig around and found 3M can supply the springs and copper braid separately from joint kits.

This could save a lot of time and trouble for you guys.

• SB1 12mm
• SB2 19mm
• SB3 25mm
• SB4 38mm

Don’t even think of putting you’re standard bonding wire in to the spring, it has to be braid.

 

[oxocube]

Yes, but they are a designed and proven system that is completely sealed in rock hard resin.

 

[Knobhead]

Why do you think they sell them separately? No joint involved (unless your smoking it). It is a legitimate and safe way of doing the job so long as you follow the instructions. Although I don’t agree with their instructions, I can do it neater.

This subject has been niggling me for a while, I’ve done it with old VIR / Jute DWA cables using lead under the armours to protect the inner serving, instead of the clip we used Jubilee clips! I never had one fail.

 

[Engineer54]

Your right Tony, they use the same spring constant pressure coils on many manufactures heat shrink jointing kits for both MV and LV where SWA is present.

Some use the conventional type screw clamps, onto a purpose made split galvanised tube to protect the inner serving and conductors. Both SWA terminations are perfectly sound and safe....

 

[Knobhead]

I do like the split galvanised tube, a sound conection

 

[pencilpusher]

Different question but linked to the OP's original point; I have seen a debate (argument actually!) on another forum where sparks are discussing the earthing of SWA.

In my case I have a 16th edition installation and am planning a CU change for assessment. The detatched garage has a distribution circuit from my house CU. It starts at a 16a CB with T&E through the house wall behind the CU and in to an adaptable box where it meets SWA for a short run out to the garage (2 meters or so). The garage has its own TT system. The house is TNCS. The SWA is earthed at one end to the garage TT system but not at the adaptable box end. I suppose thats so the earth is not exported to the garage?? Is this correct? The argument on another forum is that it should be earthed at both ends but in this case that would surely export the TNCS sytsem which for some reason was not designed for when the house was built in 2001.

I just need to be sure my thinking is correct as I am about to get rid of the adaptable box and run SWA the whole way so 17th Edition is complied with in relation to avoiding the need for RCD protection on garage dist circuit in the house CU.

Thanks

PP

 

[telectrix]

Different question but linked to the OP's original point; I have seen a debate (argument actually!) on another forum where sparks are discussing the earthing of SWA.

In my case I have a 16th edition installation and am planning a CU change for assessment. The detatched garage has a distribution circuit from my house CU. It starts at a 16a CB with T&E through the house wall behind the CU and in to an adaptable box where it meets SWA for a short run out to the garage (2 meters or so). The garage has its own TT system. The house is TNCS. The SWA is earthed at one end to the garage TT system but not at the adaptable box end. I suppose thats so the earth is not exported to the garage?? Is this correct? The argument on another forum is that it should be earthed at both ends but in this case that would surely export the TNCS sytsem which for some reason was not designed for when the house was built in 2001.

I just need to be sure my thinking is correct as I am about to get rid of the adaptable box and run SWA the whole way so 17th Edition is complied with in relation to avoiding the need for RCD protection on garage dist circuit in the house CU.

Thanks

PP

as the garage has its own earthing system, the SWA armour needs to be bonded only at 1 end. it's usual to do this at the supply/house end.

 

[pencilpusher]

Thanks. Will that be the best thing for me to do? Its defo done at the garage end and that has thrown me to be honest. This has not been touched since the original installation and I cannot work out why this would have been done this way round.

 

[malcolmsanford]

The discussion of extending a TNC-S earth to an outbuilding is heated, long and fraught with myths. There is a sticky on here with an attachment that explains all.

As for what you have a TNC-S at the house and a TT at the garage is entirely acceptable. Why both ends are not connected is simple you would not ideally want to introduce 2 earthing systems into either the garage or the house as you will have 2 potentials, so you separate them.

Normally it would be done the other way, ie you would earth the SWA from the TNC-S from the house as this will protect the SWA without the need of an RCD, and then when you terminate it at the garage you would isolate the earth by either using appropriate glands or a non ferrous enclosure.

 

[pencilpusher]

At the moment the earth from the CU is terminted in a connector block within the adaptable box. The SWA termination in the same box is earthed back to the MET in the garage CU. (Strange)

 

[pencilpusher]

Another querie. If the garage has a TT arrangement and I am filling in the Shedule of Test Results for the house CU, how do I measure ZS for the garage distribution circuit. It has its own earthing system and I am not sure how I can show a ZS for this circuit. Advice gratefully received.

PP

 

[Deleted member 26818]

You use the armour of the SWA as the earth conductor.

 

[pencilpusher]

Sorry, do you mean for the ZS test only as it wil be isolated at the garage CU end?

 

[SPARTYKUS]

Right I’m going to throw a rock in the water.

There’s been a lot of debate about earth clamps and SWA. To my mind, conventional clamps shouldn’t be used. But I kept on thinking back to cable jointing and constant pressure springs. I had a dig around and found 3M can supply the springs and copper braid separately from joint kits.

This could save a lot of time and trouble for you guys.

• SB1 12mm
• SB2 19mm
• SB3 25mm
• SB4 38mm

Don’t even think of putting you’re standard bonding wire in to the spring, it has to be braid.

Hi Tony,

this is very interesting, do you have a link I can look at ?

Cheers

Spartykus

 

[Deleted member 26818]

Sorry, do you mean for the ZS test only as it wil be isolated at the garage CU end?

What is it you are confirming with your Zs test of the distribution circuit?