under floor containment

[bren19]

Hi everyone, this is my first post any advice would be gratefully appreciated. I'm just starting to do my own work and have been asked to install several circuits of floor boxes in large office space. The problem is that there is no containment under raised floor which is also fully carpeted. The client does not want floor lifting to put any containment in, just to cut the floor boxes out and fish cables, is there any way this is acceptable?

 

[J&M Electrical]

This is a similar scenario to a thread a bit ago about spot lights in a ceiling and how to clip them. I would say the only way of doing it would be to fish them. If the floor space isn't accessible then there isn't much chance of damage. Would the floor sockets be RCD protected?

 

[bren19]

Yes the sockets would be RCD protected (have to be for 17th, correct?). I would be installing radials with a dual earth as the sockets are mainly for computers. So do you think no containment would'nt be a major issue?
Thanks

 

[J&M Electrical]

I was only asking about RCD protection as I'm not 100% sure about it in offices with computers. Haven't done much work on computer only circuits but I'm sure 1 of the older heads will clarify that soon. But if it is going to be RCD protected I cant see a problem with no containment. There is no other way of doing it really by the sounds of it

 

[Adam W]

You could wire them in singles in flexible conduit, then the CPC could be the same size as the live conductors.

 

[bren19]

I see what you mean Adam thanks, but due to lengths of cable runs this could be too difficult. I was looking at wiring T+E and a seperate single cpc but now looking at regs not sure what size this cpc would have to be? Any ideas?

 

[Adam W]

I think it's at least 6mm if you're not running it in containment.

*4mm as per 543.1.1

 

[Des 56]

With 2.5mm T+E rings the cpcs are permitted to act as the functional earth as well

 

[Farmelectrics]

why not run 4mm radials and run seperate earth aswell for high integraity earthing

 

[jumpin jax]

I cannot see any reason for the sockets to be on an RCD as the staff are supervised, they are not going to be used for outdoors and they are not less than 50mm in the wall. Besides, the computers with leakage will be tripping the RCD if there are too many on the circuit, unless i am missing something?

 

[UNG]

Depending on the quality of the original install you may find cable tray or basket under the raised floor for routing your cables

 

[KINKY]

you could use SY cable. Done that before feeding floor boxes.

 

[bren19]

There is definitely no containment under the raised floor this is my concern as some of the runs will be 25 m long just laying on concrete slab. Regarding RCD issue there would be upto 80 sockets throughout this space for computers and general use so was under the understanding that rcbo would have to be used on the 10 circuits I would be installing.

 

[Farmelectrics]

make sure you have plenty of circuts as you should only have about 12 pcs per circut due to earth leakege or thats what we work to each pc can have earth leakage of about 1-2mili amps just a thought

 

[sedgy34]

Hi everyone, this is my first post any advice would be gratefully appreciated. I'm just starting to do my own work and have been asked to install several circuits of floor boxes in large office space. The problem is that there is no containment under raised floor which is also fully carpeted. The client does not want floor lifting to put any containment in, just to cut the floor boxes out and fish cables, is there any way this is acceptable?

we used armoured cables on this scenario