SWA earthing

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Hi, 

I had a discussion with another electrician on a job regards earthing an SWA on a metal isolator and consumer unit. . 

I installed the SWA , 3core using the 3rd core as the earth, using banjos both ends as u normally would. 

He insists as the SWA is glanded to a metal enclosure both ends I don't need to use banjos as the enclosures themselves are providing the SWA with an earth. 

Is he right? 

 

Sidewinder

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Only IF, the banjo's are not through a gland plate, and, IF, there is adequate and reliable continuity that can be guaranteed, between the banjo & fixing and the earthing bar in the board.

Else fit, at least, a half size flylead, preferably IMHO a full size, or else in accordance with tables in the regs, or MI's.

 
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Evans Electric

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The original purpose of a banjo ....we were told many years ago....was the meeting face of the gland was not big enough in surface area for adequate earthing so the banjo increases this area , plus fitting a bolt through the banjo .   To my mind that was enough but a fly lead is expected now to the earth bar. 

We were also taught to file the paint off from around the gland hole , but no one does that today.

I think the surface area was ballcocks really,  as  the same did not apply to a 20mm conduit bush ....specially today where bushes are so thin you can't even grip them  properly.   

I came upon a new industrial board a while back with the banjo,s on the INSIDE which I'd never seen in 50 years , but some members on here were doing it that way .

 
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Sidewinder

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Yeah Deke,

Banjo's on the inside, bend them down and tag the fly lead on internally.

It's the way I do it out of choice.

1. Don't need to drill an extra hole.

2. Greater surface area between the locknut & the banjo than the gland.

3. As no extra hole, less chance of compromising the IP rating of the board.

4. Connection is protected.

5. Less chance of some idiot trying to unscrew the banjo bolt from the outside and the nut falling into the board.

-1. Can't do this with separate cpc where this is run with the SWA, and lugged off to the banjo.

-2. Can't inspect the banjo securing screw from outside the board.

-3. Can't tell if there is a banjo fitted from outside the board.

-4. Locknut is galv, not brass, but, brass contains enough zinc, imho for the electro chemical difference to be negligible, especially within the DB, which obviously is adequate for the internal influences...

 

Evans Electric

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We all have our preferable modus operandi  .   

Personally I'd say one earth strap onto the top plate with all the banjos bolted down would be an adequate job.   And as in times of yore ... I always chisel the locknuts on , specially when theres a return edge on the top plate to stop you getting the grips in. 

We all have our ways and they all work ..whatever the book says .

 

Tony S

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To my mind, only one fly lead is required for any number of SWA glands in a metal gland plate. Proper metal to metal contact between each gland and the plate is more than adequate.

The fly lead to suit the largest cable.

 
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Sidewinder

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To my mind, only one fly lead is required for any number of SWA glands in a metal gland plate. Proper metal to metal contact between each gland and the plate is more than adequate.

The fly lead to suit the largest cable.


Tony,

That is OK, when, you are responsible for the whole install.

For those of us who are contractors, IMHO we need to ensure that our bit complies regardless of what others have done, or do.

Thus I always install my cables to comply, regardless of what else is there, because I believe that the installer of other cables and the original all cable bond, could remove that when if they took their cable out, this, leaving my install non-compliant.

Now I KNOW that it is not for us to have a crystal ball and see what others are going to do.

However, IF we do our bit totally compliant including the bonding fly leads etc. and then someone else undoes this, that is not our issue.

 
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As pointed out by Evans elec you are meant to remove the paint from around the gland/conduit hole, no one seems to do that these days but you will get better continuity doing that than a banjo. I never understood why so many sparkies religiously bolt a banjo down when it still is relying on how tight the bush/lockring is tightened anyhow.

I recently did a board change where the conduits were the cpc. I dusted off my R2 extension lead before  starting, and tested again afterwards  before other tests. I got better , perfectly acceptable readings  after but very difficult cleaning the paint off the consumer unit.

 

roys

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I always put banjos on outside of the enclosure then fix a flying lead from that to an 0BA brass set screw and double nut that I had drilled and bolted on the enclosure, then on the inside another fly lead from screw to the earth bar, that way IP is not affected, usually there would probably be another fly lead on the outside connected to the "new" Earth screw from the likes of metal trunking or Unistrut, in some cases the manufacturer would have fitted the earth screw but not always, this was in industry and the way I was taught many many years ago.

 

Tony S

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Tony,

That is OK, when, you are responsible for the whole install.

For those of us who are contractors, IMHO we need to ensure that our bit complies regardless of what others have done, or do.

Thus I always install my cables to comply, regardless of what else is there, because I believe that the installer of other cables and the original all cable bond, could remove that when if they took their cable out, this, leaving my install non-compliant.

Now I KNOW that it is not for us to have a crystal ball and see what others are going to do.

However, IF we do our bit totally compliant including the bonding fly leads etc. and then someone else undoes this, that is not our issue.


Sorry Paul. Yes I did have direct control of the distribution system and the installation methods.

Larger boards would have 3x25mm copper tape between the top and bottom gland plates picking up the main body of the board on its way.

 

steptoe

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Only issue I see with @binky method is the sharp point if the screw protruding,

and, if being very pedantic, you don't get many brass self tappers,

one place I work at you would be threw off site for anything other than brass bolts.

 

binky

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Only issue I see with @binky method is the sharp point if the screw protruding,

and, if being very pedantic, you don't get many brass self tappers,

one place I work at you would be threw off site for anything other than brass bolts.
I tend to use the Orbix type screws, which are pretty blunt, but they certainly don't come in brass versions

 

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