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Safe Zone And Dry Lining Boxes


revor

Question

A dry lining box only has cable entries top bottom and back not side. How much wider than the box height can a safe zone be  to allow a horizontal cable run to enter the box at the top or bottom. The "extra" only needs to be the width of  the cable. It is not possible to come into the back of the box as the wall is a sound reducing wall constructed with resilient bars and insulation filled cavity. The gap between the studding and plasterboard created by the resilient bar is convenient for the cable and makes it possible to ensure the cable is kept clear of the insulation. Coming into the back of the box would mean coming through the insulation. Thanks

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21 answers to this question

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do you have a modified q-max that makes a perfect T&E shaped hole

 

i really wouldnt be surprised if you did...

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do you have a modified q-max that makes a perfect T&E shaped hole

 

i really wouldnt be surprised if you did...

If not then 20mm hole and a Wiska gland with a T & e adaptor in it......all,bases covered. BUTmit would be a BIATCH to fit

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Thanks everyone the solution in the end was very quick and simple. I simply cut the corner off the box stopping a few mm short of the front flange. This gave a flat slot as opposed to a hole ideal for T&E and kept well within the safe zone.

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well the safe zone does go vertically from the box along with horizontal, so whats the problem?

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Technically just outside the very corner of the box is not a safe zone  which is where the cable would pass to go from the horizontal to enter the top of the box. So the question boils down to what is the tolerance on the safe zone around the box. I am being to exact? I will have LABC first fix pre plaster inspection soon so don't want to fall foul on anything.

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well if someone is stupid enough to drill a hole <10mm from a socket then they deserve a darwin award...


and dont forget that a dry liner box is smaller than the front of the accessory, so you should be able to fold it flat on the corner and have it fully within the accessory

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Drop the cable behind the box & bend back up into the box

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Technically just outside the very corner of the box is not a safe zone  which is where the cable would pass to go from the horizontal to enter the top of the box. So the question boils down to what is the tolerance on the safe zone around the box. I am being to exact? I will have LABC first fix pre plaster inspection soon so don't want to fall foul on anything.

Leave the back boxes out.  All the cables just exiting a square hole cut in the plasterboard. All 100% in safe zones.  Job done.

 

In the real world in a dry lined wall cables will stray out of zones. But then the risk of drilling a cable when drilling a dry lined wall is minimal, usually the cable will just push out of the way instead.

 

If you are really pedantic, you can drill your own entry hole in the side of a DL box above or below the fixing clip.

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TBH, I have no issues making my own entries into boxes!... ;)

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Thanks everyone some really good sensible ideas there, will see which I think works best with my situation.

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I'm familiar with the diagrams in for example the IET and NICEIC building regs guides that show 150mm in the corners or from the ceiling down but not seen this "suggestion" before from a quick search on the subject about a 150mm wide zone being acceptable, horizontal or vertical from a 1 or 2G fitting assuming I'm reading it right. I always thought you had to keep the zone to the depth / width of the fitting:

 

https://books.google.co.uk/books?id=A9MliSeQYxsC&pg=PA196&lpg=PA196&dq=width+of+cable+safe+zones&source=bl&ots=eOKOFXYaRy&sig=nT1vWNwtWjyc003hbQzGdP65YT4&hl=en&sa=X&ei=NdGKVZ-XI6zW7Aaf45DIAg&ved=0CGAQ6AEwDA#v=onepage&q=width%20of%20cable%20safe%20zones&f=false

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This is more definitive as it is the green OSG.

post-9512-0-48716000-1435172986_thumb.gi

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is there anything stopping you drilling a 20mm hole in the side of the box under or over the the fixing lugs??

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Why 20mm?

However no reason AFAIAC not to make a cable entry in the side of the box of your own.

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20mm sounds a bit drastic on a dry lining box, there wouldn't be much left of a 1g box but at least you could get a grommet on ;)

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i only said 20mm cos thats the standard knockout size in most electrical boxes, could be any size but if for any reason he wants to put a grommet in the drilled hole its the ideal size.

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Plastic box though, grommet needed?...

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Also he doesn't mention cable size, how do we know its not 4mm or 6mm t/e? try getting that through a 10mm hole :innocent

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just remove the back of the box...

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Also he doesn't mention cable size, how do we know its not 4mm or 6mm t/e? try getting that through a 10mm hole :innocent

 

I could probably legitimately make 100 holes of a defined size between 10 & 20mm, drill bits in 0.1mm increments anyone?... :)

So no one said 10mm dia. either davey. ;)

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I think you'e being a bit pedantic  Revor ,  no offense intended ,  we can get bogged down with all these rules & regulations if we are not careful . 

 

And its usually best to avoid rear entry cables (  Standby for inuendos )   unless you have the deeper boxes .  Sometimes struggle to get the accessory on with , say ,  a couple of 2.5s  shoved in the back .

 

As Andy says ,  the zone is horizontal & vertical .

 

Rules are made by office chair polishers ... its us that actually do anything . 

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