Can I run two circuits through the same accessory box?

[mgx]

I have a power and lighting circuit on a large room that has a concrete ceiling and floor, and breeze block walls, and a number of 5A lighting sockets (for lamps) that sit right next to 13A double sockets for the power.

I'm not sure on the best way to run the cables. Rather than run the two cables up in the top 150mm and constantly loop them down and up to the sockets, I'd like to run the cables horizontally between the sockets, but the problem would be that the cables would need to pass through each others accessory box. It's not very elegant, but would considerably save on the cable length. Is this permissible?

Are there any other solutions to this problem, e.g. having each cable run a bit lower down the wall around the opposing accessory box, but this is out size of 522.6.6 zone allowance, so it would need to run in a bit of steel conduit (seems pretty inelegant).

I can't run the cables in the floor fwiw.

 

[ericmark]

There are a number of things to consider.

Circuits for safety have to be independent from other electrical supplies but as to if your lighting sockets are safety circuits I am not sure.

There is also a labelling requirement where two separate supplies feed one appliance etc.

If the cable was not broken into as it passes through the box in same way as with trunking then likely it would comply.

 

[Taylortwocities]

I don't see a problem with doing this as long as the cable passes through the box.

You may need to consider Cg when doing cable calcs.

 

[mgx]

Thanks for the replies - yes, the cables would be unbroken as they pass through their opposing boxes. Is it relatively standard practice, would be great to hear on this point? I can't say it's my preferred option, but it will cut down significantly on the overall cable distance which matters in my case. I wanted to get a feel for (a) whether it was compliant (seems it is), (b) is it the general acceptable/best practice (if not, what is).

 

[PrenticeBoyofDerry]

Regarding the run beneath the boxes.
It would not need to be steel conduit, but would need mechanical protection or chasing 50mm in to depth of wall.
If the cable is run within the permitted zones it would be okay,
but I say if it was run through the accessory back boxes, it would tell any one inspecting the installation that other cables are routed in the direction the cables show.

 

[seasickstevie]

Your safety zone is 150mm deep/wide, so normally this would give sufficient space either immediately above or below the line of boxes for an additional circuit to run.

Better that than filling your boxes up with additional cableing.

 

[GaryMo]

Consider what hassle the somebody may have in the future if one of the fixed tags on the backbox ends up stripped and the backbox requires replacement.

I'm not a fan of running other circuits through backboxes.

 

[mgx]

Having thought about it, I won't route through the boxes - I don't like it either, and the point about if one needs to be replaced in the future is the deal breaker! I'll either need to wear the long cable run, or route just below/above, not sure on which of these yet.

The 150mm allowance applies to walls/floor/etc, but doesn't seem to apply to runs between accessories:

(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.

Since the work is going to be LABC inspected, they might be very pedantic.

 

[PrenticeBoyofDerry]

Where cable is concealed in a wall or partion at a depth less than 50mm from any surface, it must be enclosed in earthed metal conduit/trunk/ ducting or the cable shall be provided with mechanical protection to prevent damage by nails, screws etc... or installed within the permitted safe zones.
The safe zones in this case are directly between the accessories not beneath or above.

 

[ColJack]

for the width and height of the box..
so fit a cooker switch in line, but make it a vertical one so the double backbox is vertical..
this then creates a zone as wide as a double box and allows for the cables to run above or below* the singles and doubles mounted horizontal..

*depending on how you mount the cooker switch..

 

[PrenticeBoyofDerry]

does it?
It may comply to the first accessory either side, but then your back between normal sized accessory boxes!

 

[ColJack]

does it?
a zone doesn't stop merely because it hits another accessory or intersects another zone.. it continues to the corners and to the floor and ceiling..

 

[PrenticeBoyofDerry]

Interpretation?
Cable concealed in wall or partion must:
run horizontally/vertically to an accessory,
You could be right but you need two of the verticle cooker boxes as explained by you earlier for that to work, one at one end off the room and another at the other with the normally installed boxes in between to make it a safe zone.

 

[ColJack]

don't need 2 boxes to go horizontal.. it extends to the 150mm corner zones...

 

[PrenticeBoyofDerry]

Then everything becomes clear,
I love know it alls