Swa earthing

[Gary latto]

Hi all hope everyone is keeping ok under the current circumstances,
I've got a 6mm swa to my garage cu, its glanded to plastic cu but no earth to armoured if I put a banjo on to it and crimp a cpc to banjo what size cpc cable do I need to use ?
Still learning so any advice appreciated,
Also no rcd in garage cu, but rcd in main board in house should I look at fitting rcd to garage board ??
Thanks everyone ?

 

[SJD]

Use a piranha nut, much easier than banjos.
E.g. Piranhna Earth Nuts - Pirahna - https://www.tlc-direct.co.uk/Main_Index/Earthing_Index/Piranhna_Earth_Nuts/index.html

I'd tend to use 6mm earth, same as the SWA cores.

It would be better to have the RCD in the garage, rather than in the house CU, and feed the SWA with an MCB. But don't have two 30mA RCDs in series, it will be somewhat random which trips.

 

[radiohead]

A minimum 2.5mm cpc should be sufficient for an earth link. No point in having two RCD's in series, if there is one at the supply end then that will suffice.

 

[Gary latto]

Use a piranha nut, much easier than banjos.
E.g. Piranhna Earth Nuts - Pirahna - https://www.tlc-direct.co.uk/Main_Index/Earthing_Index/Piranhna_Earth_Nuts/index.html

Cheers yes I've seen them ? just that due to isolating and I've got banjos would save a trip going out, any idea on size I should use or stick with same size of swa ie 6mm

 

[radiohead]

Cheers yes I've seen them ? just that due to isolating and I've got banjos would save a trip going out, any idea on size I should use or stick with same size of swa ie 6mm

2.5mm or greater. As a rule of thumb if you are unsure think of the cpc CSA in flat PVC cables of the equivalent size, ie 6.0 T/E has a 2.5mm cpc

 

[Gary latto]

A minimum 2.5mm cpc should be sufficient for an earth link. No point in having two RCD's in series, if there is one at the supply end then that will suffice.

Cheers for that appreciated ? so the rcd supplying the swa would be ok ?

 

[radiohead]

Cheers for that appreciated ? so the rcd supplying the swa would be ok ?

In most cases (except on a TT system) an SWA distribution circuit will not require RCD protection. Best practice is to supply the distribution circuit from a fused isolator, and have RCD/MCB protected circuits in the garage. This means a fault in the garage will not affect other circuits in the house. But as long as the garage circuits are protected by an RCD at the supply end then the requirements for additional protection have been met, just not necessarily in the ideal way.

 

[telectrix]

But as long as the garage circuits are protected by an RCD at the supply end then the requirements for additional protection have been met, just not necessarily in the ideal way.
all the right notes bits, but not necessarily in the right order.

 

[Gary latto]

Cheers tel ,so if I earth the armour in garage despite garage cu is plastic and no rcd just main switch and mcb's but swa on rcd in house cu ,
When I do a bit of practice testing do I test main earth like doing a ze or do I do as a zs and compare results in onsite guide for size of mcb in house board ?
[automerge]1588792754[/automerge]

2.5mm or greater. As a rule of thumb if you are unsure think of the cpc CSA in flat PVC cables of the equivalent size, ie 6.0 T/E has a 2.5mm cpc

Cheers Radiohead makes sense ?

 

[telectrix]

your SWA should be earted at the supply (house) end. if you have a conductor as cpc, then it does not require earthing at the other end, but it would do no harm. if you have extraneous parts in the garage (gas/water) that's a whole new ball game re bonding.

you would do a Zs at the garage CU and record as such ( some call it Zdb). then Zs readings on the garage circuits as normal

 

[Gary latto]

your SWA should be earted at the supply (house) end. if you have a conductor as cpc, then it does not require earthing at the other end, but it would do no harm. if you have extraneous parts in the garage (gas/water) that's a whole new ball game re bonding.

you would do a Zs at the garage CU and record as such ( some call it Zdb). then Zs readings on the garage circuits as normal

Cheers tel yes one core used for cpc at garage end , earthed at house end but will do at garage too , no extraneous parts so nothing to worry about on that one, cheers for advise re ze/zs .
Thanks again take care gary
[automerge]1588795085[/automerge]

your SWA should be earted at the supply (house) end. if you have a conductor as cpc, then it does not require earthing at the other end, but it would do no harm. if you have extraneous parts in the garage (gas/water) that's a whole new ball game re bonding.

you would do a Zs at the garage CU and record as such ( some call it Zdb). then Zs readings on the garage circuits as normal

Cheers tel yes one core used for cpc at garage end , earthed at house end but will do at garage too , no extraneous parts so nothing to worry about on that one, cheers for advise re ze/zs .
Thanks again take care gary
[automerge]1588795181[/automerge]
Thanks for all the advice everyone ?
I'll remove post now to save wasting anybody's time etc ?

 

[pc1966]

One issue with having something like a garage system off your main house RCD is the extra opportunity for spurious trips, more so from a N-E faults that the house MCB cannot disconnect as it only switches the live.

That aspect, along with the difficulties of achieving selectivity on overload between the garage protection and the house MCB, are reasons for preferring a separate fused-switch at the sending end. Obviously then you need RCD protection in the garage for the final circuits.

With SWA cable (as for the Flexishield style) you don't need RCD protection for the cable run as it will short out and trip the OCPD in the event of an accident involving a nail in the wrong place, etc. All that is needed for that cable is short circuit protection.

The feed fuse/MCB can also provide overload protection but that need not be done at the feed point, as you also have the option of doing that at the load (garage CU) end but limiting what the circuits there can pass before the local MCB(s) trip.

 

[davesparks]

Cheers tel yes one core used for cpc at garage end , earthed at house end but will do at garage too ,

If it is already earthed at the house end then that is OK and it doesn't necessarily need to be done at the garage end.

If you are fitting a banjo to a gland in a plastic enclosure then remember you need to fit the banjo between two locknuts/rings on the gland inside the enclosure, not have the banjo fitted between the gland and the enclosure as you would with a metal enclosure.
Plastic is a soft material which can move over time so the earth connection would become loose if the banjo is not properly secured between two locknuts.
Likewise the bolt for connecting the flylead should not pass through the enclosure as you would again have a soft plastic part included in the connection.

 

[pc1966]

That is a good reason to use the Earthing nuts - you lock them in place after fixing pysically so material compression is less of a concern, and they have tapped holes and a stud/screw arrangement for a ring tag to connect to them.

 

[davesparks]

That is a good reason to use the Earthing nuts - you lock them in place after fixing pysically so material compression is less of a concern, and they have tapped holes and a stud/screw arrangement for a ring tag to connect to them.

Plus they are a more substantial nut to screw the gland in to, better than the paper thin locknuts with half a thread in them that come with glands these days.

I'm not 100% happy with the screws for the earth connection that come with the 20/25mm sizes, but thankfully they are M4 so a besa box screw fits.
The 32mm+ sizes are better with the stud and nut arrangement.

 

[pc1966]

I'm not 100% happy with the screws for the earth connection that come with the 20/25mm sizes, but thankfully they are M4 so a besa box screw fits.

I have only used the bigger ones so far, but a standard thread and screw would get round any issues with the hex grub screw used (assuming they are same as the bigger ones) for the ring tab.

 

[davesparks]

I have only used the bigger ones so far, but a standard thread and screw would get round any issues with the hex grub screw used (assuming they are same as the bigger ones) for the ring tab.

No, the 20 and 25 have a pan head screw with a (usually) badly formed head on them.