Burying Galvanised Steel Conduit

[bailes1992]

I was wondering if any of you have any experience burying galvanised steel conduit?

My current plan is to make up the conduit, T-Wash it and give it a couple of coats of primer and hammerite before I sink it in the ground but I'm wondering if it will be enough? My Father has suggested covering it in heat shrink before it is buried? Is it needed?

The conduit will be the only CPC to an outbuilding so it's essential it cannot corrode over time.

And yes, I could run an SWA but I don't want to.

Sam

 

[Pete999]

I was wondering if any of you have any experience burying galvanised steel conduit?

My current plan is to make up the conduit, T-Wash it and give it a couple of coats of primer and hammerite before I sink it in the ground but I'm wondering if it will be enough? My Father has suggested covering it in heat shrink before it is buried? Is it needed?

The conduit will be the only CPC to an outbuilding so it's essential it cannot corrode over time.

And yes, I could run an SWA but I don't want to.

Sam

SWA would be my choice, why the reluctance to use it?

 

[Deleted member 26818]

It will corrode.
Perhaps your precautions will slow corrosion?

 

[KEV 1 N]

If you must use conduit, then I would pull in a separate CPC. I have come across several instances where conduits buried in concrete/ plaster have failed miserably in regards to acting as an earth, although they are 40/50 years old....install a separate earth conductor.

 

[Octopus]

Why complicate matters? - SWA every time for me

 

[snowhead]

It's steel, it will eventually rust away.
The screwed joints, if any, will corrode and you'll loose your CPC.
Heatshrink could trap moisture.

 

[snowhead]

Why complicate matters? - SWA every time for me

The O.P posts on LOTS of other forums, usually car related.
He's,,, unusual in his approach to things sometimes

 

[Octopus]

The conduit will be the only CPC to an outbuilding so it's essential it cannot corrode over time.Sam

What you are proposing to do is not acceptable.

If you are a spark you should know this, if you think you will be getting a spark to sign it off - they won't

Would you fit worn out tyres to a brand new car and race it around a track?

 

[KEV 1 N]

I once came across a 95mm 4 core SWA (installed 2007) where which was ran underground in a duct from a substation, ran downhill to a building. Where it was glanded into the section board was completely corroded as were the SWA armouring strands, could only presume the outer insulation was damaged during installing in the duct, and water has got in, and wicked its way out of the gland...luckily there was a separate earth cable installed!

 

[willy fixit]

When you say "cps" do mean main earth - exporting pme? What's in the outbuilding services wise? does anything need bonding?

 

[MJPD29]

I would definitely pull in a cpc you can't stop corrosion you can only slow it down

 

[Lucien Nunes]

The conduit may corrode rapidly due to galvanic action with other earthed metalwork. I went to investigate one buried steel conduit only to find it had been completely eaten away, leaving singles buried direct in the earth. If I had to bury steel for whatever reason,I would wrap the whole length in Denso tape, but there are much better alternatives!

 

[Pete999]

The conduit may corrode rapidly due to galvanic action with other earthed metalwork. I went to investigate one buried steel conduit only to find it had been completely eaten away, leaving singles buried direct in the earth. If I had to bury steel for whatever reason,I would wrap the whole length in Denso tape, but there are much better alternatives!

Like SWA cable?

 

[Lucien Nunes]

I prefer mercury-filled sausage casings, but SWA would do.

 

[Darkwood]

When you say "cps" do mean main earth - exporting pme? What's in the outbuilding services wise? does anything need bonding?

You are not normally allowed to export the PME, I believe you mean extending the Equipotential Zone of which is something totally different.

As others have commented here, your over complicating the issue and creating problems for yourself here, the 2 common methods are to bury some ducting and pull your cabling through (usually SWA) or bury SWA directly, any other method like you suggest becomes a very expensive solution due to all the extra protection required to combat the natural corrosion and moisture ingress.

 

[willy fixit]

This seems to make it pretty straightforward:
http://www.electriciansforums.co.uk...159-good-guide-exported-pme-outbuildings.html

 

[westward10]

What's the equipotential zone then?

 

[Darkwood]

To export the PME would in essence mean continue the DNO supply method (normally concentric cable) where the N/E are combined to another location, the thread link you posted only goes to show the confusion what is exactly meant by the term Exporting PME, I totally disagree with what the thread suggests as it takes on the idea you are simply bringing an earth out of your property to say a garage from your supply origin but this is no longer classed as a PME as all wiring you do after the cutout is Seperate N/E thus not classed as PME and therefore cannot be addressed as exporting PME.
If you wished to continue the PME system then you would need to inform the local DNO as local networking conditions may require additional measures to be taken, it is not a no go solution but it is very rarely asked for or done due to the extra time and work it can involve when there are simply easier, quicker and cheaper solutions.

A buildings equipotential zone is usually the perimeter structural wall of the installation IE, if you take a supply passed this perimeter to say a remote shed with an earth then you are said to be extending the equipotential zone to that shed, it is just a descriptive change and usually makes no difference to the installation.

 

[Toneyz]

Like SWA cable?

Exactly Pete, easier and probably cheaper.

 

[westward10]

BS7671 stopped using the term equipotential zone when the 17th Edition came out.