Swa Banjo?

[Michael Bloomfield]

Hello everyone, having a debate with colleague, concerning SWA connected into metal CU. Can anyone advise the exact reason for the banjo, brass washer with cpc tag, is it compulsory rather than it just looks nice.
Any thoughts sound reasons would be nice also is it a requirement under the regs?

 

[Octopus]

I would venture to suggest its not required ............ but you could use a piranha nut if you wanted.

 

[Pete999]

Hello everyone, having a debate with colleague, concerning SWA connected into metal CU. Can anyone advise the exact reason for the banjo, brass washer with cpc tag, is it compulsory rather than it just looks nice.
Any thoughts sound reasons would be nice also is it a requirement under the regs?

The Banjo is there to provide a connection from the gland to the earth bar via a fly lead, Jeez what a question.

 

[Michael Bloomfield]

Pete 999 why is the earth connection not connected via the earth bar which is connected to the metal CU, also I would prefer simple sensible answers if it requires a "jeez" then dont bother answering. we all learnt over time I find it frustrating when someone just knew it all straight away.thanks

 

[Pete999]

Pete 999 why is the earth connection not connected via the earth bar which is connected to the metal CU, also I would prefer simple sensible answers if it requires a "jeez" then dont bother answering. we all learnt over time I find it frustrating when someone just knew it all straight away.thanks

It's a basic installation procedure, surely they taught you this during your training.

 

[Pete999]

Pete 999 why is the earth connection not connected via the earth bar which is connected to the metal CU, also I would prefer simple sensible answers if it requires a "jeez" then dont bother answering. we all learnt over time I find it frustrating when someone just knew it all straight away.thanks

It's something you should have known before attemptigany work with SWA cables, sorry you found my post not to your liking, but it really is a basic procedure.

 

[Octopus]

Pete999 - its a metal CU ................................

 

[Pete999]

Pete999 - its a metal CU ................................

So? with the stabdard of practical training these days not many people are taught to clean the SWA and conduit entry points any more, so would you not use a Banjo or Piranha nut when terminating SWAs to a Metal enclosure, and not use a fly lead from the SWA termination point to the earth bar? if the case is that SWAs are just terminated into the enclosure, then why do SWA gland manufacturers include a Banjo in their kits. In saying that I can see where the confusion may lie, with regards to a metal and a non metalic enclosure. May be the fly lead is not the B all and end all but at least use the Banjo to form a decent conectionto the metalic enclosure.
I apreciatemy initial reply may have been a bit harsh, but maybe this is not his fault, the fault probably lies with the shoddy training, I'm not sure which. OP I apologise if I erked you off.

 

[Pete999]

Pete 999 why is the earth connection not connected via the earth bar which is connected to the metal CU, also I would prefer simple sensible answers if it requires a "jeez" then dont bother answering. we all learnt over time I find it frustrating when someone just knew it all straight away.thanks

I don't profess to know it all Micheal, never have and never will.

 

[Richard Burns]

If an SWA cable is simply glanded into a metal box then it is likely that the electrical contact between the gland and box is not reliable, particularly where the box is painted, even cleaning the area may not be enough. Therefore the standard approach is to use a banjo and flying lead to ensure the continuity of the earthing of the armour.
An easier method is to use a piranha nut, these do have teeth on one side to score the surface of a metal box, but this may still not be enough so the fly lead is still connected.
All this is to ensure the cables armour is reliably connected to earth with a joint of suitable mechanical and electrical strength.

 

[cliffed]

What about the grommets,I know many who don’t.

 

[Spoon]

Pete 999 why is the earth connection not connected via the earth bar which is connected to the metal CU, also I would prefer simple sensible answers if it requires a "jeez" then dont bother answering. we all learnt over time I find it frustrating when someone just knew it all straight away.thanks

The cores of the SWA go thought the gland. The armour of the cable connector to the gland. Look up SWA glands and how to wire to them, you will understand better. You have to earth the gland properly. That's why you use the banjo or brass washer with cpc tag.

Bugger... Richard beat me to it.

 

[SJD]

How about a nice example of how NOT to terminate SWA (and this is a plastic enclosure) from an EICR I did last week

 

[Octopus]

So Pete999 - a banjo - fixed to the CU with a nut and bolt and a fly lead?

 

[Richard Burns]

How about a nice example of how NOT to terminate SWA (and this is a plastic enclosure) from an EICR I did last week

It has the banjo fitted so it must be fine!!!
What on earth did they manage to do to that gland to rip off the end of the clamp nut?

 

[Michael Bloomfield]

Many thanks for your reply Richard Burns which makes lots of sense, behind the use of a banjo.
Although i wish the locking nuts provided were just a fraction thicker to get a good purchase on when tightening but thats obviously cut backs, i quite often use piranha and flying earth lead, my companion debated that if earth continuity was present with as he said measured to 0.00 ohms on meter is that not sufficient continuity, i gracefully conceded the debate.

 

[Pete999]

So Pete999 - a banjo - fixed to the CU with a nut and bolt and a fly lead?

Could do it that way I prefer a Piranha nut a far better and neater approach.

 

[Pete999]

So Pete999 - a banjo - fixed to the CU with a nut and bolt and a fly lead?

Could do it that way I prefer a Piranha nut a far better and neater appr

It has the banjo fitted so it must be fine!!!
What on earth did they manage to do to that gland to rip off the end of the clamp nut?

They cut the Armour out of the equation Richard, because they didn't know how to do it properly, you can see from the pics that the Armour was/is /wouldn't reach thecorrect position to form a proper termination.

 

[Spoon]

my companion debated that if earth continuity was present with as he said measured to 0.00 ohms on meter is that not sufficient continuity, i gracefully conceded the debate.

I don't quite understand this bit. What did your companion actually measure between to get this reading? How accurate is his meter?

 

[Richard Burns]

It is the reliability of the connection that is the issue, with a very short distance from gland to metal it is easy to get a 0.00Ω measurement but the contact area could be only 0.5mm² and this may not withstand an earth fault current, melt and and so leave the armour disconnected at the very time it is needing to be earthed.

 

[Rpa07]

Adding onto @Richard Burns reply as I can’t quote at the moment -
. . . besides oxidation over time leading to an even poorer earthing connection. Banjo and fly or piranha - it’s the only fun we get in this game!

 

[magnoliafan89]

I use these when terminating into a plastic box. Great way to maintain earth continuity

 

[Octopus]

Interesting thread .................. especially for those who insist on using 2 core SWA and use the CPC to the outer protection .....................

I prefer to use 3 core ..........

 

[Anthony S]

Very basic stuff and some people wonder why the industry is in such a mess.

 

[Ian1981]

Interesting thread .................. especially for those who insist on using 2 core SWA and use the CPC to the outer protection .....................

I prefer to use 3 core ..........

When using swa for the ‘tails’ I use 2 core 25mm swa and a 16mm earthing conductor in parallel

 

[MDJ]

Hello everyone, having a debate with colleague, concerning SWA connected into metal CU. Can anyone advise the exact reason for the banjo, brass washer with cpc tag, is it compulsory rather than it just looks nice.
Any thoughts sound reasons would be nice also is it a requirement under the regs?

 

[Spoon]

When using swa for the ‘tails’ I use 2 core 25mm swa and a 16mm earthing conductor in parallel

So what's the price comparison between the above and 3 core SWA?
I haven't got the charts on me at the mo but isn't the armour on 25mm sufficient for the earth?

 

[Ian1981]

The armour would not be 16mm equivalent copper as I’m talking about the main earthing conductor
Also if I used 3 core then a 25mm earth conductor is way overkill

 

[Spoon]

The armour would not be 16mm equivalent copper as I’m talking about the main earthing conductor

That's what I was going on about. I will have to look that up as I thought it would be.

 

[Ian1981]

The armour can be used as a cpc but it won’t be 16mm CSA copper equivalent which is what the DNO require on a new supply

 

[Ian1981]

As a rule of thumb 85mm steel is only 10mm at copper equivalent using the formula in gn8 anyway.

 

[Leclanche]

Just returning to the banjo's how many folk use brass bolts nuts & washers to secure the fly lead to the banjo?
I've lost count of the number of zinc plated roofing/trunking bolts I've seen on jobs with swa installed probably doesn't make a lot differance but it's looks right & is right.

 

[Ian1981]

Just returning to the banjo's how many folk use brass bolts nuts & washers to secure the fly lead to the banjo?
I've lost count of the number of zinc plated roofing/trunking bolts I've seen on jobs with swa installed probably doesn't make a lot differance but it's looks right & is right.

I always use M6 25mm brass nuts, washer and bolts as it’s always the way I was tought and is my preference.
Piranha nuts are a great alternative, tho when using larger glands say 32 mm and up,I’ve not seen them made for this size

 

[westward10]

Like Ian I always use brass.

 

[Pete999]

The armour would not be 16mm equivalent copper as I’m talking about the main earthing conductor
Also if I used 3 core then a 25mm earth conductor is way overkill

The csa of the steele armour on a 25mm2 2core SWA equates to 60mm2 which in terms of CU eqates to 26.6mm2

 

[Pete999]

I always use M6 25mm brass nuts, washer and bolts as it’s always the way I was tought and is my preference.
Piranha nuts are a great alternative, tho when using larger glands say 32 mm and up,I’ve not seen them made for this size

Piranha nuts 20mm to 32mm

 

[westward10]

The csa of the steele armour on a 25mm2 2core SWA equates to 60mm2 which in terms of CU eqates to 26.6mm2

Not in terms of conductivity it doesn't.

 

[Pete999]

Not in terms of conductivity it doesn't.

What do you mean?

 

[Strima]

Brass for me as well, reduces the risk of bi-metal corrosion and you can undo them in ten years time.

 

[Richard Burns]

What do you mean?

There are two comparisons for steel and copper.

One is where the conductor is to be used as a cpc and will have to withstand a very high current for a short period of time, in an earth fault.

The other is where the conductor is a bonding conductor and may in certain circumstances have to carry a significant current for a sustained period.

Steel is ~8.5 times worse at conducting electricity than copper but steel is better than copper at maintaining its integrity under thermal stress of high current.

So the where the steel is used solely as a cpc the combination of the two factors means steel comes out at about 2.25 times worse than copper for use as a cpc.

However where the conductor may have to carry long term current only the comparative resistances are considered and steel is then about 8.5 times worse than copper.

This means that for a cpc calculation the 60mm² steel armour in PVC /ST/PVC SWA is comparable to a 26mm² copper conductor in a cable.

For a bonding conductor calculation the 60mm² steel armour in PVC /ST/PVC SWA is equivalent to a 7mm² copper conductor in a cable.

 

[Ian1981]

The csa of the steele armour on a 25mm2 2core SWA equates to 60mm2 which in terms of CU eqates to 26.6mm2

You would be need the swa steel to be 136mm for it to have the same conductivity as equal to a 16mm copper equivalent

 

[Pete999]

You would be need the swa steel to be 136mm for it to have the same conductivity as equal to a 16mm copper equivalent

 

[Ian1981]

[/QUOTE
I use gn8 tables or manufacturer data for actual CSA of the steel armour but like has been said the copper-steel ratio is around 8.5 difference in conductivity so as an example if a steel conductor was used as a protective bonding conductor then the CSA of the steel would need to be 85mm to be the equivalent of the required 10mm copper

 

[Ian1981]

I use gn8 tables or manufacturer data for actual CSA of the steel armour but like has been said the copper-steel ratio is around 8.5 difference in conductivity so as an example if a steel conductor was used as a protective bonding conductor then the CSA of the steel would need to be 85mm to be the equivalent of the required 10mm copper

 

[Tes369]

I always use M6 25mm brass nuts, washer and bolts as it’s always the way I was tought and is my preference.
Piranha nuts are a great alternative, tho when using larger glands say 32 mm and up,I’ve not seen them made for this size

I don't like it when people put earthing pigtails across tray or join swa glands by a fly and leave the brass bolt long and proud. It needs tightening and cutting off with 3 threads showing so it can't catch on anything.

-It's lazy and it catches on cables when being pulled in.

Brass for me as well, reduces the risk of bi-metal corrosion and you can undo them in ten years time.

The old bi metal corrosion debate what about using brass bushes in steel conduit or trunking ...? I've never seen any corrosion.

The only time you will see corrosion is if you introduce an electrolyte salt+water.

But that would be rare.

Cheers

 

[Michaelwgroves]

I use gn8 tables or manufacturer data for actual CSA of the steel armour but like has been said the copper-steel ratio is around 8.5 difference in conductivity so as an example if a steel conductor was used as a protective bonding conductor then the CSA of the steel would need to be 85mm to be the equivalent of the required 10mm copper

This is also covered in Guidance Note 8 Earthing & Bonding 5.2.1 pg 60.
I think it's also covered generally in Guidance Note 1, selection and Erection. I think the statement used is generally you should not use SWA for main protective bonding, but I can't recall which section this was.

 

[bonjovi]

is this question real really , as most on hear know the armourings are used as protection for the cable which is usually used when its installed in areas likely to get mechanically damaged ,ie buried ,spade digging ,and secondly a lot of sparks still use this as a cpc to keep the cost down and not include a extra core as a earth , either way the armourings need to be earthed, this is done via a gland , banjo nut and bolt for a solid earth and flylead . its beggers belief to think there are guys out there doing work not knowing such a thing

 

[Pete999]

is this question real really , as most on hear know the armourings are used as protection for the cable which is usually used when its installed in areas likely to get mechanically damaged ,ie buried ,spade digging ,and secondly a lot of sparks still use this as a cpc to keep the cost down and not include a extra core as a earth , either way the armourings need to be earthed, this is done via a gland , banjo nut and bolt for a solid earth and flylead . its beggers belief to think there are guys out there doing work not knowing such a thing

 

[telectrix]

i always use a banjo:

OK it's a UKelele. thank God it's no longer an EUelele.

 

[Ib≤In≤Iz]

I mostly use piranha nuts now, much better and neater than a banjo. Brass for me too and always a fly lead to the earth bar.