Earth connection via SWA

[bigegg]

Am I correct in thinking that if I run, say, 10m of 3 core 6mm <edit:10mm> SWA to my shed DB(20A welder, 32A ring, 6A lighting MCBs) from the house DB (63A MCB), (actual load is likely to be <40A total - if i have the oven on at the same time as the plasma cutter, and compressor) then:

If I use the armour as an additional earth path, then I don't *have* to make it a TT install, as long as the Zs is within limits?

 

[brightspark]

your using a core as the earth and the steel brade is just bonded . is the shed metal with gas and water services in it and have you pme supply at house ??

 

[mtt.tr]

Depends if you are pme, if pme you need to run a 16mm earth

 

[bigegg]

your using a core as the earth and the steel brade is just bonded . is the shed metal with gas and water services in it and have you pme supply at house ??

No services.
Concrete shed.
I specifically want to use the SWA armour as the earth.
College homework i did last week gave me an example that implies it's possible to do it this way.
The homework was using a 4 core SWA to carry 3ph+n, and the armour as the CPC - I wondered whether it was specifically disallowed by other regs?)

 

[brightspark]

6.0mm isn't rated at 63 amp only 42 your changing the goalposts by stating you want 3 phase and neutral and using the wire braiding as the earth

 

[Screwdriver]

I think if you ask ten different people you will get ten different answers.

 

[bigegg]

Depends if you are pme, if pme you need to run a 16mm earth

Tncs system

 

[brightspark]

I think if you ask ten different people you will get ten different answers.

if u state the facts on whats going in theres only one answer

 

[Screwdriver]

if u state the facts on whats going in theres only one answer

Go on then. What is “the answer”?

 

[bigegg]

6.0mm isn't rated at 63 amp only 42 your changing the goalposts by stating you want 3 phase and neutral and using the wire braiding as the earth

Ignore the 6mm.
I wrote the first post, working from memory.
I actually bought 10mm, even though i was led to believe i needed 16mm earth - because i was going to use a TT.
So i've confused the figures.

It's 10mm 3 core.
Manufacturer data says its armour is ok as a CPC, and is 39mm² actual csa

 

[bigegg]

Depends if you are pme, if pme you need to run a 16mm earth

Why?

<Edit: by which i mean, is that a "written in stone" reg, or is it a guideline if you don't want to do the calcs?>

 

[bigegg]

6.0mm isn't rated at 63 amp only 42 your changing the goalposts by stating you want 3 phase and neutral and using the wire braiding as the earth

Sorry.
I want to use the wire braiding as an earth on my actual installation to *my* shed - single phase, 3 core 10mm, 63A MCB, 40A designed maximum.


I was using the "3ph+n" example, because that was what was used in my homework, and gave me the idea of using the armour, instead of installing an earth rod.

 

[dobbslc]

Use the inner core and just bond the swa at the house end if you have 3 core on a single phase supply. You must ground any spare unused cores to stop induced voltages floating around.
PME / TNCS requires a rod at the shed end. 16mm minimum if unprotected.

 

[mtt.tr]

Why?

<Edit: by which i mean, is that a "written in stone" reg, or is it a guideline if you don't want to do the calcs?>

I'll find the book and show you

 

[steviec_lj]

Why do you want to use the SWA as an “earth”?

You bought 3 core, use the spare core you’ll have, otherwise it may pick up voltage or short out.

I did mine in 16mm 2c SWA and used the SWA as the bonding.

 

[RWD3M]

Just drive an earth spike into the ground next to your shed (and connect to it) and be done with it?

Is that a thing? Genuine question.

 

[steviec_lj]

Just drive an earth spike into the ground next to your shed (and connect to it) and be done with it?

Is that a thing? Genuine question.

Yes, but you’d still need to bond the SWA at source

 

[RWD3M]

Thanks Steve.

 

[bigegg]

Why do you want to use the SWA as an “earth”?

You bought 3 core, use the spare core you’ll have, otherwise it may pick up voltage or short out.

I did mine in 16mm 2c SWA and used the SWA as the bonding.

I'll be using the 3rd core as the earth.
I want to know if i can use the armour as an additional earth path to reduce the Zs.
I may not need to, but want it as an option.

 

[daedalusminos]

If you use the SWA to export the earth don't forget to factor in its steel and therefore higher resistance.