Is this a good cable route?

[spannerintheworks]

(Posted something similar on another forum, but only got one definitive response, so posting here for a second opinion...)

I'm looking to chase in a cable for a 230V domestic interlinking smoke alarm. The previous owner has this installed in surface trunking when they rented the house.

I started making a chase in its original position last year - i.e. ~10cm to the right of an existing light switch. This is what we have now (see photo below).

I later realised that this is not in a proscribed cable zone (i.e. it is not running directly above/below the existing switch). Would you:

1) Stick with what is there - as it's very close to a proscribed cable zone, or
2) Make a new chase to add the smoke alarm cable alongside the light switch cable.

If it's relevant, there is a chance we ourselves may well be renting the property out at some point in the future, so I'm less confident someone will be aware where the concealed cabling is.

 

[EFLImpudence]

There is no prescribed zone for a cable not connected to the light switch.

Put back the trunking???

 

[flameport]

may well be renting the property out at some point in the future

If the rest of the electrical installation is the same age as that light switch, it's several decades overdue for replacement.

 

[JohnW2]

I later realised that this is not in a proscribed cable zone (i.e. it is not running directly above/below the existing switch).

As EFLI has said, it would not be in a 'safe zone' even if it were directly below the light switch, since it isn't connected to that switch.[That's not as daft/pedantic as it may sound - it's not impossible that someone might one day remove the light switch {e.g. move it to somewhere else}, leaving nothing to indicate thatthere was a buried cable.

Would you: ...
1) Stick with what is there - as it's very close to a proscribed cable zone, or
2) Make a new chase to add the smoke alarm cable alongside the light switch cable.

What any of us might do is not really the issue - any of us could decide to 'break the rules'. All we can reasonably do is make sure you are aware of what the regulations say - namely that any cable buried buried less that 50mm deep in a wall must be routed in one of the prescribed 'zones' . It's then for you to decide whether you want to comply with that regulation.

If it's relevant, there is a chance we ourselves may well be renting the property out at some point in the future, so I'm less confident someone will be aware where the concealed cabling is.

As EFLI has also suggested, why not just leave it in the surface trunking? Particularly if the property is going to be rented out, I've seen far (aesthetically) 'worse' things than that in rental property!!

Kind Regards, John

 

[sparkwright]

One option would be to be put the cable in earthed metal conduit, to avoid making another chase.

However, finding a CORRECT way to earth the conduit may not be easy.

Another way round this may to be fit a flush metal box and blanking plate in line with the chase.

Why is the existing conduit you have so damaged?

 

[JohnW2]

... Another way round this may to be fit a flush metal box and blanking plate in line with the chase.

Theoretically only if the cable were in some way terminated (i.e. 'joined') within the box (since otherwise the box and blank plate could be removed at some point in the future, leaving the cable not in a 'safe zone').

Kind Regards, John

 

[sparkwright]

Theoretically only if the cable were in some way terminated (i.e. 'joined') within the box (since otherwise the box and blank plate could be removed at some point in the future, leaving the cable not in a 'safe zone').

Kind Regards, John

Well, this is where the common sense bit comes into play.

It would be ok if the cable was cut, and a joint consisting of connectors was made within the box, and a blanking plate over it.

Another solution might be to fit a smoke detector test switch over the box, up high. I'm fairly sure they can be fitted anywhere on the 3 core and earth part of an alarm circuit.

 

[spannerintheworks]

Thanks for all the replies - very interesting to read through, and some aspects that I hasn't considered.

There is no prescribed zone for a cable not connected to the light switch.

Put back the trunking???

As EFLI has said, it would not be in a 'safe zone' even if it were directly below the light switch, since it isn't connected to that switch.[That's not as daft/pedantic as it may sound - it's not impossible that someone might one day remove the light switch {e.g. move it to somewhere else}, leaving nothing to indicate thatthere was a buried cable.

It sounds like you saying there is no 'proper' way to chase in a a smoke alarm cable between floors (at less that 50mm depth, or without earthed conduit)? If that is the case, this would affect other scenarios too - for example, a desire to chase in a dedicated loft lighting/socket circuit (where the consumer unit is on the ground floor, and the loft is above the first floor).

Another way round this may to be fit a flush metal box and blanking plate in line with the chase.

I've been tempted to implement this approach previously, with a blanking plate close to floor level. Both the lighting and smoke alarm cable would pass through the back box/

Theoretically only if the cable were in some way terminated (i.e. 'joined') within the box (since otherwise the box and blank plate could be removed at some point in the future, leaving the cable not in a 'safe zone').

Joined in the box, or running through the box? That way, in order to remove the back box, someone would have to make an active choice to cut the cable, join it, and bury into the wall.

Why is the existing conduit you have so damaged?

Well spotted! This is because the current conduit was installed without disconnecting the smoke alarm cabling. The process was to i) Remove the smoke alarm cable from the surface trunking, ii) carefully make a chase, iii) Make a vertical cut in the current oval conduit to insert the cable, iv) Clip oval conduit containing the cable into the chase.

If the rest of the electrical installation is the same age as that light switch, it's several decades overdue for replacement.

The property was build in 1970. I've found no evidence of any substantive modifications to the installation in my 3 years living here, and all cabling that I've come across under floorboards etc looks in good condition. All curcuits have RCD protection and the property passed an EICR when I moved in.
Do electrical installations have an inherent 'lifespan'? I know 50 years old isn't new, but I'm sure there are a lot of other older installations around.

 

[JohnW2]

Well, this is where the common sense bit comes into play.

Indeed.

It would be ok if the cable was cut, and a joint consisting of connectors was made within the box, and a blanking plate over it.

That's what I said, isn't it?

Another solution might be to fit a smoke detector test switch over the box, up high. I'm fairly sure they can be fitted anywhere on the 3 core and earth part of an alarm circuit.

Yep, provided the alarm cable was 'cut' and connected to the test switch (so that the switch could not just be removed, and the cable 'plastered over),that would effectively be the same as the blank plate with cable cut and joined behind it.

Kind Regards, John

 

[JohnW2]

It sounds like you saying there is no 'proper' way to chase in a a smoke alarm cable between floors (at less that 50mm depth, or without earthed conduit)? If that is the case, this would affect other scenarios too - for example, a desire to chase in a dedicated loft lighting/socket circuit (where the consumer unit is on the ground floor, and the loft is above the first floor).

I suppose that's essentially true - both for the alarm cable and lighting circuit (and any other similar situation). If the cable simply 'passes through' a room, without being 'connected to' anything visible within the room, then to satisfy regs, the cable would have to be buried deeper than 50mm, be enclosed in earthed metal conduit or have an earthed metallic outer covering. To what extent people adhere to that is anyone's guess.

I've been tempted to implement this approach previously, with a blanking plate close to floor level. Both the lighting and smoke alarm cable would pass through the back box ... Joined in the box, or running through the box? That way, in order to remove the back box, someone would have to make an active choice to cut the cable, join it, and bury into the wall.

Yes, certainly in terms of common sense, running through the box would be as good as 'jointed within the box'. However, once one has run it through the box, I suppose one might just as well 'cut and join' it within the box, so as to be certain of keeping everyone happy!

The property was build in 1970. I've found no evidence of any substantive modifications to the installation in my 3 years living here, and all cabling that I've come across under floorboards etc looks in good condition. All curcuits have RCD protection and the property passed an EICR when I moved in.
Do electrical installations have an inherent 'lifespan'? I know 50 years old isn't new, but I'm sure there are a lot of other older installations around.

Assuming the cables are PVC (and haven't been 'abused') they are likely to last for a very long time, probably at least 100 years. If accessories (switches/sockets etc.) are undamaged and still working OK, they can just be replaced individually if/when the need arises. In view of the progressive 'tightening' of regulations, an 'old' installation is unlikely to be fully compliant with current regs - but there is no compulsion to 'bring it up to current standards' and, provided nothing has 'gone wrong' it will be no less safe now than it was when it was installed (before 'new-fangled' requirements appeared in the regs).

Just as some some people seem to feel compelled to 'upgrade' their iPhone, computer, car immediately a new model/version appears, or to 'invest in' some new-fangled way of turning lights on the moment it becomes available, some will feel the need to 'upgrade' their electrical installation every time the regulations think up some new 'requirement' - but that's their choice. Others are more inclined to only 'mend' things if they are broken

Kind Regards, John

 

[sparkwright]

It would be worth checking to see if your lighting circuit has earth wires.

You mention your house was built in 1970, but if that is only an estimate, and your house is a little older, it was normal for lighting circuits not to be earthed.

Have a look behind a few light switches, and at ceiling roses.

Wiring of your age is also prone to produce green slime which emerges from the ends of the cables.

 

[JohnW2]

It would be worth checking to see if your lighting circuit has earth wires. You mention your house was built in 1970, but if that is only an estimate, and your house is a little older, it was normal for lighting circuits not to be earthed.

Good point -although, even if there are no earths, that isn't necessarily a compelling reason to re-wire.

Wiring of your age is also prone to produce green slime which emerges from the ends of the cables.

Another possibility. IIRC, 'green slime', due to inclusion of anti-oxidants in the PVC rose in cables manufactured in 60s and early 70s. However, the OP will probably be aware of that problem if he is suffering from it. I certainly know of houses with early-70s PVC cables that seem to have 'escaped' the problem.

Kind Regards, John

 

[spannerintheworks]

It would be worth checking to see if your lighting circuit has earth wires.

Thankfully, the lighting circuit does contain earth wires, and these all appear to be terminated correctly in back boxes and pendant fittings in all the accessories that I have inspected. Albeit without earth sheathing, which I have added whenever changing a fitting/switch.

Wiring of your age is also prone to produce green slime which emerges from the ends of the cables.

Not seen any evidence of this. Looks like this was one of the lucky properties not be be affected, or there has been a rewire since original construction.

 

[EFLImpudence]

It sounds like you saying there is no 'proper' way to chase in a a smoke alarm cable between floors

There is a proper way.

You should use the general prescribed zones of within 150mm. of a corner - either between two walls or between a wall and the ceiling.

Electrics:walls

www.diynot.com

 

[sparkwright]

Thankfully, the lighting circuit does contain earth wires, and these all appear to be terminated correctly in back boxes and pendant fittings in all the accessories that I have inspected. Albeit without earth sheathing, which I have added whenever changing a fitting/switch.


Not seen any evidence of this. Looks like this was one of the lucky properties not be be affected, or there has been a rewire since original construction.

Sounds like you're lucky .