Cable `safe` Zones ?


Postby bb700 » Sat Dec 18, 2010 2:50 pm

This is part of a total re-wire to new 17th ed. regs. & everything with RCD protection.
The sparky told me that he couldn`t take a horizontal run from one socket outlet to another ( only 18" apart ). He would take a vertical to the ceiling void go across then down to the finished socket position (on every socket).
I didn`t question his method but could not find this info. in the 17th ed. regs. book or the on-site guide book.
In the ECA guide to the Wiring Regulations 17th edition by Darrell Locke figure D 5.1 page 109 (section D) it shows cable safe zones. This page shows a horizontal safe zone band from a socket to 150mm corner wall area with verticals. Is this info. deceiving as it seems you can put sockets along this horizontal band (but can you run cables in this zone).
Thanks
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Postby ericmark » Sun Dec 19, 2010 11:54 am

You are correct as to horizontal being permitted. However in my house the extension was wired in my absence and so I never saw the cabling go in.

My wife bought a new fridge / freezer which required a water supply. Lucky the loo was above this so handy cold water supply, just needed chasing down the wall, so two hack saw blades with spacer between them would cut two lines allowing me to remove the plaster with ease.

However you can imagine my shock in more ways than one, to find the two way light switch had been run horizontal, around a corner through the outside wall and to position of new switch.

And this is really the point. Would you expect wires to be run that way? From the cooker isolator to the connection box one expects the cable to run vertical and horizontal, in fact one would even check for diagonal in that case. However from socket to socket one does no expect a horizontal link.

Having said that with the 1/3 rule on drilling beams, running a ring main with less than 106 meters of 2.5mm cable can be a challenge, and one has often to consider methods to reduce the cable run. I have seen houses wired side to side, instead of upstairs and downstairs, to reduce the cable required to keep the earth loop impedance to within limits. With this in mind, to not return the cable into ceiling space would assist in reducing the earth loop impedance, and of course increasing the prospective short circuit current.

522.6.6 (v) be installed in a zone within 150 mm from the top of the wall or partition or within 150 mm of an angle formed by two adjoining walls or partitions. Where the cable is connected to a point, accessory or switchgear on any surface of the wall or partition, the cable may be installed in a zone either horizontally or vertically, to the point, accessory or switchgear. Where the location of the accessory, point or switchgear can be determined from the reverse side, a zone formed on one side of a wall of 100 mm thickness or less or partition of 100 mm thickness or less extends to the reverse side.

Above is the bit referred to. And from what I here there are to be some changes with amendment 1, and where RCD protection does not exist one is to be allowed to add without RCD protection, so this section is likely to change.

However with all installations the guy who has the final word is the one signing the paperwork. And with Part P to have designer, Installer and tester as three different signatorys is costly as it has to then go through the local authority building control, and not through the scheme operator. And of course some scheme operators also impose their own rules, so although the IET/BSI may permit it, that does not mean the Electrician can do it, and still sign off the work with scheme operator.

When I took my 17th Edition exam there were no on-site guides so never bought the new one. And to be honest the whole idea of a guide to how to use a guide does seem a bit of over kill anyway. The old one had minimum number of sockets for each type of room. It was very rare to find a new house with so many sockets. Also how many wires in a conduit, we all know this is very little help as to knowing if they will fit and if the temperatures will be within limits, as it has no reference as to current carried be each cable. So although it may help the young apprentice with 60 turns to my coil not really interested in guide.

It of course comes down to why keep a dog and bark yourself? What is the point of employing an electrician then doing it your own way anyway?
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Postby sparx » Thu Dec 23, 2010 5:23 pm

Hi, perfectly acceptable to run horizontally between outlets, much preferable to long vertical runs as ERICMARK says, also as so close together much less chance of getting 'spiked' by kitchen fitter installing top cupboards.
Some people who should know better will insist in their own version of the regs.
bet he's an niceic 'domestic installer' god help us!

Extra: just looked at my copy of this excellent book and no deception, you can indeed run in the zones shown, also not shown it is additionally considered a 'Safe zone' 150mm at sides of door frame.
The aim being that it is unlikely anyone would hang a picture say in the area as it would over hang the door way.
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