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?

 

[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