How thick does steel protection have to be?

[dingbat]

I don't understand why earthed steel conduit is deemed sufficient protection for cables outside prescribed zones.

Read regs 522.6.5/6/8 again and you'll see that each refers to earthed cable coverings, conduit, ducting and trunking as options which give protection by the method you describe.

Each of these are also often used to provide simple mechanical protection against various forms of impact damage (see 522.6.1) where cables are not concealed.

 

[dingbat]

Some have it that it's also to protect cables from the edges of plasterer's trowels and floats etc, but I'm more inclined to believe the plasterers who say that a good edge on those tools is so important that it's ludicrous to suggest they'd risk damaging them by hacking at cables.

It's not the skim that's the problem; by then the cables are well-buried. I can assure you that plenty of damage is caused to unprotected PVC cable by common practices in applying and levelling the bonding - for instance, keying the bonding surface with a piece of batten with nails in it!

 

[mfarrow]

Solder copper to steel?

Silver solder (5%) or braze it, but brazing usually means more heat.

 

[ajrobb]

Is there any requirement for bonding purely mechanical protection? (As long as it is not an exposed extraneous metal part.)

 

[Chri5]

Is there any requirement for bonding purely mechanical protection? (As long as it is not an exposed extraneous metal part.)

Yes- It needs to be earthed.

 

[Chri5]

OP why not use shielded cable to comply ?

http://tpwcc.com/features.html

(flexisheild)

 

[dingbat]

Is there any requirement for [earthing or] bonding purely mechanical protection? (As long as it is not an exposed [or] extraneous metal part.)

Yes- It needs to be earthed.

No it doesn't. (Remember this is 522.6.6 (iv) and not to do with section 411.)

 

[h00tsman]

Does the plate need to be earthed if it's in no contact with the cable at all. For instance the cable is buried 20mm and filled over, then the plate is over this..

 

[RF Lighting]

Why don't you stop all this fannying about and just avoid running the cables it the one part of the house that almost guarantees the cables WILL get damaged by the penetration of screws / nails?

 

[AdamWatson]

Hi.

The safeplates you get for covering cables across joist are 3mm thick if I recall correctly. The TLC ones are supposedly approved by the NIC or ESC. Would prefer to chase out myself, could be a right faff, not to mention the cost of getting the sheet steel made up.

Regards.

3mm! What are they protecting from? Bullets?

Safe plates are at most 18g (1.25mm, .049") doesn't sound like much but without a nail gun you'll do well to get a nail through it and hit it with a drill and it'll slow you down enough to notice, a masonry drill won't get through easily

 

[RF Lighting]

If you can get through it with a nail gun, then it doesn't satisfy the regs. Simple.

 

[JohnD]

Scaffold pole makes a nice sturdy conduit.

Bit difficult to plaster in the chases, though.

 

[Geps]

If you can get through it with a nail gun, then it doesn't satisfy the regs. Simple.

To play devils advocate though, I could come along with a powder actuated nail gun and put holes in the 3mm plate. So how exactly do you define adequate protection?

I really don't think you can.....

 

[RF Lighting]

Exactly, which is why every one has being saying that it is very difficult to make the use of mechanical only protection compliant with BS7671, and one of the other methods such as using earthed steel conduit or using safe zones and RCDs is a much easier way of ensuring your installation is compliant.

 

[Geps]

Sorry, it wasn't a question directed at you, just meant to pick up what you said. It's seems so absurd to have a regulation that realistically can't be put into use.