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.

 

[Darkwood]

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

My bad, just going back on how I was taught but it essentially is the same answer just referred to differently, the PME stops at the cutout and is no longer classed as PME on the consumer side so you are not exporting it as commonly expressed by many.

Lets call it zone of protection ... seems even the term equipotential zone was ambiguous to some hence it was dropped to which I forgot

 

[Pat Tester]

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

3

 

[Deleted member 26818]

Having a combined neutral and earth does not necessarily equate to PME.
PME is Protective Multiple Earthing and can apply to TN-S.

 

[Darkwood]

Never implied it did @spinlondon but the term exporting PME was used to which I commented on, unless you were just making a general point regarding combined N/E and not reflecting on my post then I absolutely agree ☺

 

[bailes1992]

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

Agreed! However, this isn't particularly straight forward.

I should have probably put more detail into my initial post.

I'm currently in the middle of purchasing a new house. It's a 3 year old 4bed detached with a separate garage. Earthing system is PME/TNC-S and there's no bonding required in the outbuilding(s) concerned.

Ideally I'd have bought something older and gutted it myself and made it how I want it but my Wife is pregnant so I don't have that luxury.

I'm also maxing myself out on the mortgage of this out on the basis that it's only going to get easier.

I plan on making the current garage into a small workshop and the current 20A supply isn't going to work for me. Therefore I need to do what I can with what I have. And what I have is quite a lot of galvanised conduit & trunking along with 6491B.

My plan is to have a 6A circuit for lighting, a 16A circuit for heating and a 32A circuit for power all fed from individual RCBO's in the house consumer unit.

I also need to get data out there. Ideally a fibre or at least a shielded Cat5e/6.

I don't intend on doing anything dangerous. There is absolutely nothing wrong with using well constructed metal containment as a CPC. I personally find the installation of CPC conductors in a metal containment system where they are not required totally wasteful and makes for sloppy containment installation.

The issue here is ensuring the conduit underground will last. I have an old Land Rover Defender so I have all sorts of primers, paint and underseal about. Weirdly I also have a 100m roll of 32mm 2:1 heat shrink which would be ideal to cover a 25mm conduit.

This isn't going in for at least another 6 months. Maybe it's worth prepping a small off cut of conduit and burying it underground and seeing how it holds up?

I'll also be putting up a shed in the back garden for the lawn mower, bikes, strimmer etc and will be planning on putting a light and a socket out there using the same method.

 

[Octopus]

Covering steel conduit isn't going to stop it rusting. 6 months is not long enough to test it..........

You can lead a horse to water ..................

 

[bailes1992]

Covering steel conduit isn't going to stop it rusting. 6 months is not long enough to test it..........

You can lead a horse to water ..................

I'm not sure I can believe that it cannot be stopped rusting?

Surley if all threads are protected, the full length of the conduit is painted thoroughly and covered in PVC then it's going to last a long time? After all an SWA is just galvanised steel wires covered by a PVC sheath! Or even covered in denso tape which pipe fitters use to stop their non galvanised steel pipes from rusting!

 

[snowhead]

Or even covered in denso tape which pipe fitters use to stop their non galvanised steel pipes from rusting!

I'm not going to bother after this as I've seen how other posts go, but Steel pipe used for Heating / Gas has a much thicker wall than conduit.

 

[Octopus]

I'm not sure I can believe that it cannot be stopped rusting?

Surley if all threads are protected, the full length of the conduit is painted thoroughly and covered in PVC then it's going to last a long time? After all an SWA is just galvanised steel wires covered by a PVC sheath! Or even covered in denso tape which pipe fitters use to stop their non galvanised steel pipes from rusting!

So how do you plan to completely "seal" your conduit .....

In fact why are you just making this so complicated ....... it can't be about costs as SWA is much quicker to install, and when done properly will last for decades

unlike steel conduit

A couple of years ago I was swapping a panel heater in an out building - I did a Zs - which showed there was no earth .... a galv box, installed above ground was almost completely disintegrated ...

 

[westward10]

How will you prevent internal corrosion from condensation.