Cables in parallel

[Nicc]

Hi all, brilliant forum and loads of useful and interesting information.

An example question wrt cables in parallel: If you happened across an installation with a 10mm earth cable and wanted to uprate it to 16mm; what is to stop you placing another 10mm in parallel, all marked up with 'safety earth connection etc etc', and routed and terminated in the same places?

I just wondered where in the regs it expands on this or whether it is acceptable? Havent been able to find anything myself on this as yet.

Thanks in advance.

 

[truckster]

As long as the cables are of equal size and length and follow substantialy the same route theres no problem. I would crimp the ends together before making the termination to prevent seperation

 

[KINKY]

I know you can run cables in parallel but does an earthing conductor not have to be ONE continuous cable?

 

[truckster]

It should not be broken at joints etc. So if you are daisy chaining from board to water to gas then it should be continuous so when the plumber removes it to replace a stopcock for instance you don't lose the connection to the gas.

 

[KINKY]

It should not be broken at joints etc. So if you are daisy chaining from board to water to gas then it should be continuous so when the plumber removes it to replace a stopcock for instance you don't lose the connection to the gas.

What im saying is, does an 'Earthing Conductor' not have to be ONE cable, as appose to cables run in parallel?

 

[truckster]

Sorry read post wrong thinking of bonding conductors.

Anyway I dont think so, others may correct me!

 

[KINKY]

I dont think so, others may correct me!

I may have made it up hahaha, I just have this thought in my head it has to be one cable.

 

[KINKY]

Trying to find the asnwer in the regs but no luck.

 

[Des 56]

Trying to find the asnwer in the regs but no luck.

543.2.2(!) referenced from 542.3.1 brb obviously,cant afford the pretty green one just yet lol

 

[truckster]

Trying to find the asnwer in the regs but no luck.

Yeah you made me get the BRB out and there is no requirement for it to be one cable as far as I can see. BTW if you are able to get another 10mm in why not just replace the existing with a 16mm

 

[truckster]

543.2.2(!) referenced from 542.3.1 brb obviously,cant afford the pretty green one just yet lol

Hi Des, that refers to a protective conductor An earthing conductor is different by definition.

 

[Des 56]

Hi Des, that refers to a protective conductor An earthing conductor is different by definition.

Thats why I quoted where it was referenced from

 

[Darkwood]

as already pointed out if its the same size same length and run and the ends are crimped or clamped in a way they wont become seperated then its ok, i would also label both ends up as to their function, if they are both main earths to the MET i would accept seperate terminal clamping as long as they are clearly marked as its only a qualified electrician who should have access, if bonding to gas and water id take the extra steps of making sure other trades cannot seperate them apart if say removed off a pipe by a plumber. Again i would clearly mark up their function at both ends as its not a common practice used and will be clear to the next electrician to come across it.

 

[KINKY]

543.2.2(!) referenced from 542.3.1 brb obviously,cant afford the pretty green one just yet lol

Sorry lads im struggerling with this one.

I only have the red cover 17th.

543.2.2 does not mention cables in parallel, has this been revised?

 

[truckster]

No, the BGB is the same

Damn now you have made me get both books out

 

[Engineer54]

A cable run in parallel is classified as a Single cable!! The rules are that both cables must be of the same CSA and of the same type/construction, be the same length, (run in the same containment or follow the same route). Though what your suggesting is compliant, it is somewhat on the over kill side of things...lol!!!

 

[Darkwood]

Approach this from another angle you have a swa cable and your armour isnt large enough for the earthing required, solution is to run a seperate earth with it to make up the additional earthing needed, in this case you dont have to match size to size and all your required to achieve is the csa of earthing needed is met. The earth is usually only carrying a large current in a short circuit and this will be for a very short period (hopefully) so assume it need not follow the same rules placed on load bearing cables in parallel in that they must match size for size to equally distribute the load, or you may end up running a oversized earth with a 120mm swa when you may only need a 25mm to make up the difference.

 

[Engineer54]

Errr, you don't run a separate earth to make up the difference of a non-compliant SWA cable, you install a separate CPC of the correct size to meet compliance of the line conductors!! You don't mix steel and copper as a CPC at any time...

 

[Des 56]

The seperate earth conductor would need to withstand the full fault current


If you use a separate g/y with an swa then it must be capable of carrying that full fault current,it cant be added for size purposes

 

[KINKY]

Have a read of this, interesting.