Adding a switch to Security light.

[dishman]

I have a simple halogen pir security light.

It is wired from a spur in the garage, the cable is routed (over a long length) externally to said light.

I would like to add a switch to isolate it.

Is it a simple case of cutting the cable at an appropriate place and adding a SPST switch?

 

[EFLImpudence]

If you mean 'isolate' then fit a Switched Fused Connection Unit at the origin of the spur.

If you mean a switch for convenience at a suitable position, then, as you say, a SPST switch in the Line(live) conductor would do, although a DP switch somewhere may be useful.

 

[dishman]

Yes, I meant more for convenience.

It is currently spurred of a junction box and is permanently on.

Why may a DP switch be more useful?

 

[EFLImpudence]

Just in case the lamp develops a fault or water gets in it may be handy to be able to 'isolate' it so that the rest of the circuit may still be used.

This, though, could be achieved by a SFCU (which are DP) at the origin of the spur.

 

[dishman]

Hmm, looking at the layout more closely. The security light is just fed directly from a junction box which, from what I can see houses all the permanent live feeds for the garage lighting.

Best solution?

 

[ban-all-sheds]

Why is where the supply from the light originates relevant to putting a switch in it?

 

[dishman]

@EFLImpudence suggests putting a SFCU near the origin of the spur, I was just clarifying that is was not a spur (as I originally thought) but a junction box.

Hence I was also clarifying why putting a SFCU near the origin of the spur or junction box is a good idea. Is it just a common practice? Or is it also OK to put a SFCU at any point along the cable that feeds the light.

 

[ban-all-sheds]

It is a spur. A spur is a branch from a ring final (technically so is a branch from a radial, but most people try to stick to "spur" if it comes from a ring and "branch" if it comes from a radial).

In terms of connections it can come from a socket, or a junction box, or an FCU , or from the circuit breaker or fuse in the CU.

Sometimes an FCU is mandatory, sometimes optional.

It has become common for people to call an FCU itself a "fused spur". This was never a good idea, but it has escaped into the wild and cannot be eradicated.

If your light is on a lighting circuit you don't need an FCU. What rating is the circuit breaker for the lights in the garage?

 

[dishman]

Useful information, thank you.

The garage in which the juction box is situated is attached to the house. All the garage lighting is fed off the ground floor lighting circuit. It is a 6amp circuit breaker with no RCD.

The junction box seems to contain all the permanent live connections for the garage lighting. The security light is fed into this, hence is permanently live.



The cable for the security light is the one coming in from the right hand side of the junction box.

If a FCU is not required, then I assume a STDP switch will suffice?

 

[ban-all-sheds]

Yup - a switch is all you need, and a double pole one will provide complete isolation - a useful precaution for outside lights, even if there is no RCD on the circuit at the moment. What power is the light? It's easy to overload a lighting circuit by using large halogen lights. 6A is 1380W, and you can swallow up almost half of that with ease.

And as for that rat's nest....

It really could do with tidying up - there's exposed copper, at least one of the earth connections looks a bit iffy....

... the cables aren't clamped, and basically there's too much crammed in there.


Something like a central heating wiring centre would be better.

 

[dishman]

I added up there is about 500w on the ground floor circuit. I only use a 120w halogen for the security light.

I also thought that it looked a bit cramped and messy.

Out of interest, rather then cramming all the line and neutral into one block each, what is the best method to spread them over multiple blocks? Do you link a block together?

Or say if I wanted a new permanent live, would I create a small link from the current line and neutral to a new empty block for each?

----
Something like this?

https://www.tlc-direct.co.uk/Products/SMTRT049.html

Or this (although it does not have any clamps).

https://www.tlc-direct.co.uk/Images/Products/size_3/TL810.JPG

 

[ban-all-sheds]

So the circuit loading is fine.

Linking terminals together is a good way to avoid cramming things is - in this, for example, you can see that some of the terminals in the top row are linked, but the smaller block on the left shows the technique - you use one side of the terminal block to loop a link from one to the other, leaving you a row of terminals on the other side for individual cables.

I don't know how far to the right in your photo the space extends, but if you want to make provision for future expansion then you could create 4 sections - L/N/E and Switched Live with some unused terminals in each.

Your second example is a real C&N product - it is literally a bog standard 2 gang pattress with a bit of choc-block inside. As you say, no cable grips. Which, to be fair, aren't essential, as if the box is fixed to a surface you can use cable clips to anchor the cables to the same surface. If you were using a box like that for a socket you'd not expect it to have cable grips inside.

Love the price of it though - the same supplier will sell you a box, a blanking plate and a terminal strip for less than half that. I know a couple of quid here or there is not really important, but there are principles to uphold.

 

[dishman]

What are these pre-wired tooless boxes like?

http://www.screwfix.com/p/surewire-sw2l-mf-16a-2-way-pre-wired-junction-box-white/8676h

Are you unable to put more than one cable in each? How securely do they clamp the wire without a manual screw-down clamp?

Also, on an slightly unrelated topic.

It is always best practice to have a choc contained within a chocbox?

I have a situation where someone cut too much sheeth from some twin + earth cable for an extractor fan. I have now installed an in-line fan which is in the garage on the other side of a cavity wall. To extend the cable to reach the in-line fan in the garage I have connected the existing un-sheethed line and neutral (about 20cm in length) to a chock box, and then another length of twin and earth cable which connects to the in-line fan.

Because it goes through the cavity wall into the garage, the initial unsheathed length is long enough to be pushed into the cavity, where the choc box connects to the next length.

My concern is

1) the fact there is 20cm of unsheathed/vulnerable cable
2) no choc box

Two is pretty easy to solve. Is there anything that can be used to re-sheeth unprotected cables?

There is no space bathroom side to cut short the existing cable and hide the choc box out the way or behind the fan grill.

 

[ban-all-sheds]

What are these pre-wired tooless boxes like?

http://www.screwfix.com/p/surewire-sw2l-mf-16a-2-way-pre-wired-junction-box-white/8676h

http://www.screwfix.com/p/surewire-sw2l-mf-16a-2-way-pre-wired-junction-box-white/8676h

It is always best practice to have a choc contained within a chocbox?

They should be in something.

Is there anything that can be used to re-sheeth unprotected cables?

Heat-shrink sleeving.

 

[EFLImpudence]

Fit a new piece of cable.