Earth bonding on SWA

[TomDurham2013]

Earth Clamps for Armoured cable

Due to a restriction on the entry point into the supply area it is virtually impossible to fit a standard earthing gland assy

Is there a none damaging clamp that can be used to link up the outer sheath to the CU , normal bonding clamps will crush the inner/outer cable (Bit of a Spoonerism)

The cable is 6mm SWA and has tested at inf on 500v from sheath to earth.

Tom

 

[plugwash]

do you have a picture of this area?

could you screw the gland into a galv through box and pick off the earth from the terminal in there?

 

[TomDurham2013]

As it was drilled in via an 18mm hole through a cavity wall the only way to fit any form of gland would be to withdraw the cable from the wall and then make off a mechanical earth link.

It was a cock up on measurement really as the wall was 60mm thicker than the length allowed for the tails.

There is a portion of the sheathing showing heance the request for info on clamps.

Being very picky really as most of my 17th edition mates tell me to make a bonding joint where it is not seen but can be tested !!

 

[Spark123]

You could take it back out, resin joint a new piece of cable onto it.

 

[TomDurham2013]

Thanks for the thought

As there seems to be no easy fix I will get a big bolster out and knock seven shades of sh*t out of the inner wall, that will allow me to unhook the supply and fit a gland which will be plastered back into the wall

The other consideration was to put an earth rod on the garage end of the cable but I need to check the rest of the property to see what the original installers put in ?.

The house is about 20 years old and was built by a local businessman who employed jobbing builders and sparky's to do the work.

Had to fit new rose and pendants in the toilets and bathroom because they had put in glass globe fittings, they then used bare brass jointing strips (They must have snapped them out of existing roses) to connect the ring and the switching.

These strips were hanging un-insulated inside the globe where anyone changing a bulb could have been given a belt, cables were not sheathed in heat resistant material so that they were baked hard.

Having said that there is a stables near by so they had somewhere to park and feed their transpost.

Tom

 

[ban-all-sheds]

As it was drilled in via an 18mm hole through a cavity wall the only way to fit any form of gland would be to withdraw the cable from the wall and then make off a mechanical earth link.

If you can withdraw the cable, why not replace it with one the right length?

As there seems to be no easy fix I will get a big bolster out and knock seven shades of sh*t out of the inner wall, that will allow me to unhook the supply and fit a gland which will be plastered back into the wall

Surely SWA glands should be fixed through a flat surface, not just plastered into the wall? You could gland into a 45mm flush box...

The other consideration was to put an earth rod on the garage end of the cable

How does that remove the need to earth the armour?

 

[TomDurham2013]

The fixing gland normally goes through a hole in the mounting box (either metal or ABS) and on the other side there is a brass eyelet supplied which in theory you should tighten down between the surfaces and then bolt the earth cable too.

If the gland is clamped up on the outer cable there should be enough mechanical strength when the cable is encased in plaster or cement up to the base of the gland

Leaving out the mounting box is not going to cause any visual grief because now the whole lot will be cased in behind a sheet of chipboard.

Using an Earth rod at the garage end should in theory dispense with the earth at the CU end, as according to the comics you should only earth one end of the sheath to prevent eddy currents.

 

[Spark123]

The banjo you mean? A non permanent joint such as this really needs to reamain accessable.
Is this a 6mm data cable or something? Not sure on your eddy current idea!
You can either export the earth or not, however you would need to consider how the armour and the cable is going to be protected.

 

[TomDurham2013]

Is that a Cockermouth type of Banjo? or one for the people with stumpy arms?.

Yes I take your point and will do a metal termination box inside, just means ripping out more woodwork.

No it is a 6mm supply for a couple of lousy sockets and a light in a shed and the same in a garage , neither of which will exceed 13amps or be used simaltaniously and they are MCB fused down to the bare minimum but because of the length of the runs I have beefed up the cables to meet the 6% voltdrop rule.

Last post

The use of an earth rod at one end was to eliminate the need for an earth termination at the CU or have I missed something

 

[Spark123]

Doesn't everyone call the brass thingy's banjos?
If the SWA was to be connected to an earth rod at the far end then you need to take into consideration what is protecting the cable. Is the supply a TN system? Where is the RCD protecton? How are you testing this earth rod?
If there are no extraneous conductive parts in the shed then, assuming a TN system, there may be little point in using an earth rod. Exporting the supply earth may be more viable.
The volt drop on the consumer premises is meant to be 4% max.

 

[TomDurham2013]

Sorry

The eddy current bit was dropped on me by a fiesty Jock that I used to employ.

He has just done his 17th and states "SWA outer sheath only needs to be bonded to earth at one end according to the regs because of possible ringing and eddy currents which may develop if both ends are bonded down ".

He is not known to be a bull ****ter so I took it on board

 

[ban-all-sheds]

You might be missing a perfectly good earth....

Cut a recess in the wall to take a 45mm flush box - dual will give you more space.

Gland the cable into it, and take a flylead from the banjo or Piranha.

Take the flylead and cores to a choc-clock and then from there run whatever cable you planned to to the CU. If the wood that then covers the area will not be easily removable then use crimps inside the box, not choc.

 

[TomDurham2013]

Typo, should have said 4

Calculations done by

http://www.pandpelectrical.com/mpm/voltcalc.htm

Am off to North of Scotland in the morning, if it turns out to be bullshit I may divert to the SW find a use for the earth rod after all, may come in handy if his backside is struck by lightning .