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.

 

[Pete999]

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!

Sorry Mate how on earth are you going to cover lengths of conduit in PVC, it's just not a practical option, OK in the world of theory, but totally impracticable.

 

[bailes1992]

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 ...

Installation time isn't an issue as I will be installing myself.

There's also the other issue of getting data out to the garage. I could run a seperate PVC tube underground for the data, but I would still run galv up the side of the house as PVC never looks as good as galv conduit in my opinion.

 

[Pete999]

Installation time isn't an issue as I will be installing myself.

There's also the other issue of getting data out to the garage. I could run a seperate PVC tube underground for the data, but I would still run galv up the side of the house as PVC never looks as good as galv conduit in my opinion.

I'm out

 

[Toneyz]

Well the O.P. has asked what the forum thinks and has a consensus answer that this is a bad idea.

 

[willy fixit]

I'm glad the PME/Equipotential zone issue has been clarified.

 

[snowhead]

Well the O.P. has asked what the forum thinks and has a consensus answer that this is a bad idea.

That won't stop him.

 

[Toneyz]

The run cannot be that long SWA can't cost that much.

 

[Pete999]

That won't stop him.

Good quals in building services, makes you wonder if all that studying was worth it.

 

[bailes1992]

The run cannot be that long SWA can't cost that much.

The run is approx 30 meters.
I will have to purchase either 30m of 10mm² 3c SWA and a consumer unit for the garage.
Or, 30m of 1.5mm² 3 Core for lighting, 30m 2.5mm² for heating and another 30m 4mm² for power.

Not a huge issue I admit, but if there was a way I could use the materials I have then I'd probably keep the few hundred quid in my pocket.

Shame I don't have any stainless conduit.

 

[bailes1992]

Good quals in building services, makes you wonder if all that studying was worth it.

Difference between having an idea and seeing if anyone else has experience in it than going right ahead and just doing it!

After all someone may have said they've buried a galv conduit wrapped in denso tape and it was fine 10 years later. In which case I'd probably give it a go myself.

 

[Strima]

The run is approx 30 meters.
I will have to purchase either 30m of 10mm² 3c SWA and a consumer unit for the garage.
Or, 30m of 1.5mm² 3 Core for lighting, 30m 2.5mm² for heating and another 30m 4mm² for power.

Not a huge issue I admit, but if there was a way I could use the materials I have then I'd probably keep the few hundred quid in my pocket.

Shame I don't have any stainless conduit.

What about voltage drop and maximum impedance for disconnection times?

Also derating factors for circuits run together.

SWA for the power and armoured CAT5/6/7 for the data. Much less to go wrong.

 

[westward10]

Just whack it in and be done with it as it is what you intend to do or is this just a carrot and stick thing.

 

[KEV 1 N]

Good luck pulling all those cables through 30 metres of conduit! Don't use washing up liquid as a lube, it contains salt, so will aid the inevitable corrosion of the conduit

 

[Toneyz]

Good luck pulling all those cables through 30 metres of conduit! Don't use washing up liquid as a lube, it contains salt, so will aid the inevitable corrosion of the conduit

30mtrs and two bends good luck

 

[Darkwood]

I am starting to assume the OP is ignoring all advice because they cannot terminate SWA or as is common that the conduit etc has already been purchased and damned doing there hardest to recoup any losses...

My advice is take the losses and prevent costs further down the line.

 

[static zap]

The conduit may corrode rapidly due to galvanic action with other earthed metalwork. .....................

Just like how old batteries work --Zinc- and Iron
do better it they are in air , not underground .
Next stupid idea , how long would 22mm copper-last ! .... But more expensive than SWA ?

 

[westward10]

My advice is lock the thread it seems like a wind up.

 

[Squid]

Why bother just nail the cables to the fence and run it that way saves on the cost on conduit and if the foxes gnaw at it then a pest exterminator so its a win win situation.

 

[HandySparks]

If you feel that you must use the conduit, then use it to protect the network cable and run a suitable length of SWA adjacent for the power.

 

[Sparkie30]

I think the OP has a great idea. Please report 5 years later.

All the best