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Discuss Mechanical protection in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

D Skelton

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Just out of interest, how many steel capping lengths stacked on top of each other would you consider to be suitable to provide mechanical protection to switch drops on non-RCD protected lighting circuits?

I've always been lead to believe that 3mm of steel is thick enough to be defined as mechanical protection against screws and nails which by my measurement would make it about 5-6 steel capping lengths stacked. Would you stack more or less? Would you even consider it suitable?

And before you mention it, lets say for example that steel conduit is out of the question.

Debate... :D
 
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As it's layered perhaps some could be surplus to requirements. A penetrating object would have it's velocity reduced by the first layer, then the second slows it some more etc etc. Wouldn't like to try it though
 

Des 56

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I suppose you could judge "how many" whilst fitting
If you can easily bang your fixing nail through the sheathing you may need more :smile5:
 
S

Silly Sausage

I've always been lead to believe that 3mm of steel is thick enough to be defined as mechanical protection against screws and nails which by my measurement would make it about 5-6 steel capping lengths stacked. :D
Not with my Hilti used in anger! :smiley2:
 

D Skelton

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I suppose you could judge "how many" whilst fitting
If you can easily bang your fixing nail through the sheathing you may need more :smile5:
Fixing nail??? Steel capping??? lol

No, I would probably drill the stack me thinks and combine with screws and plugs :D
 

Des 56

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Fixing nail??? Steel capping??? lol

No, I would probably drill the stack me thinks and combine with screws and plugs :D
Ah,you are now copying my usual method,but we need to use capping nails for the considered opinion of "how many"
Bringing drills and such to the issue would be infecting the experiment with high technology, that would render the result invalid
 

Richard Burns

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Take a piece of steel conduit and cut in half lengthways and drop over the cable, fix with pipe clips, sorted!!
 

Strima

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Take a piece of steel conduit and cut in half lengthways and drop over the cable, fix with pipe clips, sorted!!
Plenty of lube and good blades then... :) Sounds like a good night out in Liverpool.
 
G

Guest55

How can steel conduit be out of the question , but 6 layers of capping is a considered alternative ?
Fit as many as you want lol , bs7671 still wont recognise it as proper mech protection ;-)
its not just thickness either , conduit steel is considerbly harder than capping tin-foil.
 
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D Skelton

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How can steel conduit be out of the question
Coz it is :D

but 6 layers of capping is a considered alternative
6 layers of capping would only be about half the thickness (overall width wise) of the diameter of 20mm steel conduit. If mounted on a wall, it is just as thick as 1/2" plasterboard and can easily be plastered over. Steel conduit would protrude too much to plaster over.

bs7671 still wont recognise it a proper mech protection ;-)
Correct me if I'm wrong but as far as I'm aware, BS7671 has no guidance for what can and can't be considered mechanical protection, only that mechanical protection must be suitable for each individual situation.

its not just thickness either , conduit steel is considerbly harder than capping tin-foil.
Hence why I said 6 layers. I've used 3mm steel plate to protect cables before and you aint never getting a nail through that unless you're using a Paslode! Then again, with a Paslode you could quite easily penetrate galv conuit as well :D I just wondered if enough capping was stacked together to an overall thickness of 3mm, surely that wold be the same as 3mm plate steel anyway?
 

D Skelton

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Dreaming of a solution to a problem that doesn't involve steel plate :D
 
G

Guest55

and youre wrong about bs7671 guidance on mech protection.
dont want rcd's ? then its EARTHED steel conduit or swa. thats your lot.
gonna be earthing your 6 layers of capping then ?
thought not lol.
 

Strima

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Epoxy resin between capping sheets and you'll have the poor mans version of Chobham armour... :lol:
 

D Skelton

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I'm thinking of other scenarios as well biff, although you're right on the RCD front.

What about cables not in safe zones?
 
G

Guest55

stop being lazy and chase out the conduit drops.
we both know thats the real reason lol.
 

D Skelton

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stop being lazy and chase out the conduit drops.
we both know thats the real reason lol.
Ah, with regards to that, the block was waaaay too thin to chase, hence why I asked.

With regards to the other situation, I was thinking of CU changes that involve moving the CU thus rendering the cables buried in the wall out of their safe zone.

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option b - swa
I never would, tis way too easy to penetrate with nails IMHO

Edit: I should add, these are hypothetical future situations that could potentially be made easier with steel capping than when I've been faced with these same situations in the past.
 
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G

Guest55

Ah , no worries.
just make up the solutions as you go along , works for me. ;-)
as for swa , its a permitted type for rcd free circuits so dont discount it.
 
G

Guest55

is micc / pyro allowable for rcd free circuits ? hmm not sure , might be.
 

D Skelton

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is micc / pyro allowable for rcd free circuits ? hmm not sure , might be.
I should hope not. Might be indestructable to a hammer and flames but it would be pretty easy to ram a nail thru it.
 
G

Guest55

I should hope not. Might be indestructable to a hammer and flames but it would be pretty easy to ram a nail thru it.
It doesnt have to , as with swa , neither will stop a nail but they are allowed because having a completely surrounding metallic covering guarantees to activate the circuit device on penetration.
 

D Skelton

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It doesnt have to , as with swa , neither will stop a nail but they are allowed because having a completely surrounding metallic covering guarantees to activate the circuit device on penetration.
Not if the nail creates a path between earth and neutral :D

No in all seriousness, I totally get what you're saying and I'm aware of the reasons why SWA is considered suitable mechanical protection for a non-RCD protected circuit, however in my mind, I like to either protect a cable with an RCD, or I like to protect it from damage all together.

I'm not saying you're not right, I just don't like using SWA to protect buried cables, underground or in walls unless RCD protected also, this is purely down to personal preference :)
 

Richard Burns

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is micc / pyro allowable for rcd free circuits ? hmm not sure , might be.
I raised this one on here a while ago and was told NO.
However the csa of the metallic sheath is suitable for use as a cpc, so I think, but should not say, that you could use this to omit RCD protection.
This is only my opinion and is not supported by others.

DS have you never touched earth and neutral together on an isolated circuit and tripped the RCD?
 
M

madmac

1 Layer of earthed metallic sheathing is all that is required to meet the old "EEBADS" method of protection for vulnerable cables.
As long as it's earthed, it provides EEB.
And as long as the the circuit is protected by the correct rating of fuse/circuit breaker then it is protected by ADS.
It also has a degree of mechanical protection for ordinary persons using tacs etc for fixing pictures, but if a drill is used or heavy nails etc then it will be pierced but that just brings us back to making sure it is "earthed".
It behaves in exactly the same way as an swa cable.
It's mentioned in the regs about conduit or swa or "earthed metallic protection".
 

D Skelton

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DS have you never touched earth and neutral together on an isolated circuit and tripped the RCD?
I was talking about making a connection between neutral and earth on a non-RCD protected circuit. My point was that nothing would disconnect.
 
G

Guest55

I raised this one on here a while ago and was told NO.
However the csa of the metallic sheath is suitable for use as a cpc, so I think, but should not say, that you could use this to omit RCD protection.
This is only my opinion and is not supported by others.
i agree with that , and i've put that assessment into to practice this week.
tidying up wiring in grans house this week including re-jigging circuits in CU.
noticed that garage supply is actually pyro cable fed from the ring main mcb on the rcd side of split board.
Wanted to put garage on its own mcb ( plenty of spare ways ) but on the non-rcd side so freezer in garage doesnt trip the whole house if fault.
May not comply strictly speaking but did it anyway as its the most practical solution without spending big money.
i did a mental risk assessment and micc in ducting under block paving is unlikey to get damaged anytime soon :)
 
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D Skelton

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i agree with that , and i've put that assessment into to practice this week.
tidying up wiring in grans house this week including re-jigging circuits in CU.
noticed that garage supply is actually pyro cable fed from the ring main mcb on the rcd side of split board.
Wanted to put garage on its own mcb ( plenty of spare ways ) but on the non-rcd side so freezer in garage doesnt trip the whole house if fault.
May not comply strictly speaking but did it anyway as its the most practical solution without spending big money.
i did a mental risk assessment and micc in ducting under block paving is unlikey to get damaged anytime soon :)
It's all down to common sense most of the time aint it. Regs are regs.. but from time to time, we all realise that sections of the regs were never written by people living on this planet :D

Given that situation, I would have probably done the same thing, but I would still have used an RCBO.
 

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