Mechanical protection/ Safe zones

[sparrrrk]

Hi all,

Just after a bit of advice from all you domestic installers out there.

I've been asked to do a job in a house which involves running a cable in a wall. The cable needs to run vertical the entire height of the wall. However I cannot run it where the walls meet at an angle due to obstructions. This wall is at the base of stairs so quite small.

Can I utilise the thermostate as an acessory and run behind it (obviously taking it off wall and mounting back on after filled) to fullfill the requirementof running to an accessory. Or is this not allowed as it isn't actually supplying the accessory.

If not can I just cap the cable with metal capping at least 3mm thick. I know meeting the requirement to prevent nail penetration is hard to meet.

The circuit is covered by a 30ma rcd. Just a little confused as my domestic regs knowledge is not up to scratch. Don't want to install a cable unsafeley.

Any advice would be appreciated. Thanks

 

[telectrix]

the thermostat is an accessory and assuming it has a LV supply, then it can serve as a pointer for a prescribed zone. won't do if it's a wireless stast.

 

[sparrrrk]

It's definitely Lv. There's surface trunking supplying it. Was even thinking I could bury these supply cables as well If pos. Get rid of the unsightly trunking. What do ya think?

 

[telectrix]

go for it. but remenber thst buried cables need RCD protection.

 

[Leesparkykent]

What's the cable for? LSX cable could be an option.

 

[gnselectricals]

Or bury some steel conduit for a lovely job, don't forget to earth it tho

 

[Deleted member 26818]

Mechanical protection is not required to be earthed.

 

[davesparks]

Mechanical protection is not required to be earthed.

That's a rather sweeping generalisation! There's plenty of times when mechanical protection is required to be earthed and occasionally bonded

 

[Deleted member 26818]

There is no requirement in BS7671 for mechanical protection to be earthed.
So not a sweeping generalisation, a simple statement of fact.

 

[infinity]

Only earthed mechanical protection needs to be earthed

 

[Gavin A]

I'd be dubious about running it using a supposed safe zone from a room thermostat that itself has got surface mounted cable. The room stat is something that's likely to get moved / replaced at some stage, and anyone would assume that the only cable run to it / likely to be in that safe zone would be the one that's surface mounted.

technically it's arguable, but going with the spirit of the regs, it wouldn't seem a wise move to me.

 

[davesparks]

There is no requirement in BS7671 for mechanical protection to be earthed.
So not a sweeping generalisation, a simple statement of fact.

Steel conduit and trunking are mechanical protection and require earthing
Any mechanical protection which is an extraneous part needs to be bonded

 

[Gavin A]

Steel conduit and trunking are mechanical protection and require earthing
And mechanical protection which is an extraneous part needs to be bonded

how's it an extraneous conductive part if it's buried in the wall?

mechanical protection and earthed metal capping are 2 separate protective measures, it doesn't need to be earthed as long as it actually does provide protection against nail penetration.

 

[davesparks]

how's it an extraneous conductive part if it's buried in the wall?

mechanical protection and earthed metal capping are 2 separate protective measures, it doesn't need to be earthed as long as it actually does provide protection against nail penetration.

He made a blanket statement about mechanical protection, nothing specific about it being buried in anything

 

[Deleted member 26818]

It doesn't matter whether it's buried or not, there is no requirement in BS7671 for mechanical protection to be earthed.
You want to earth it carry on, I'll get you some PVC conduit to earth.

 

[Gavin A]

He made a blanket statement about mechanical protection, nothing specific about it being buried in anything

ah fair enough, I was assuming the conversation was referring to this situation.

 

[davesparks]

It doesn't matter whether it's buried or not, there is no requirement in BS7671 for mechanical protection to be earthed.
You want to earth it carry on, I'll get you some PVC conduit to earth.

Wtf? Steel conduit and trunking is mechanical protection and I'm pretty damned sure it requires earthing.

 

[andyb]

Mechanical protection is not required to be earthed.

That is a sweeping statement Spin, you've just told the op and anyone else reading this, including trainees and diy'ers that you never need to earth mechanical protection regardless of the situation which is not true.

As it happens, in this case the way I read it is that one option being considered is to run the cable in the wall outside of a safe zone with a metal covering.

In this case the mechanical protection does need to be earthed.

 

[davesparks]

That is a sweeping statement Spin, you've just told the op and anyone else reading this, including trainees and diy'ers that you never need to earth mechanical protection regardless of the situation which is not true.

As it happens, in this case the way I read it is that one option being considered is to run the cable in the wall outside of a safe zone with a metal covering.

In this case the mechanical protection does need to be earthed.

I can see where he's going with it, but it didn't come across right.
In your example it will depend on the type of mechanical protection. Steel conduit would need earthing, but a solid steel plate resistant to penetration by nails etc likely wouldn't need it

 

[andyb]

The reg dealing with cables buried in walls mentions various scenarios from >50mm and several 'ors' but the ones mentioning metallic protection all say earthed.

It's the statement 'There's no requirement in bs7671 for mechanical protection to be earthed' that I find misleading.