Security Floodlights

[JasonW]

Hi - hope someone can help with this.

I was hoping to add a light to the downstairs circuit. On investigation I notice that this circuit has 9 normal bulbs (say 900W), and the mains halogen lighting in the kitchen (8 x 50W). That's 1300W total on my 6A MCB - no problem.

However, there are also two security floodlights on this circuit, which I think are 500W each, although only on briefly when activated by PIR.

Is this ok as it stands? Is it ok enough to add another couple of normal bulbs as I originally wanted? If not, is it ok to limit it by adding a switch so that you can only have security lights OR new lights, not both (I figured out the circuit for this).

So many questions ...

 

[plugwash]

are you sure the security lights are on the lighting circuit.

 

[Job_n_knock]

Just what I thought....2.2Kw of potential load on the 6A MCB ??

 

[Steve]

the outside lights should be taken off the lighting circuit and fed from a 13A FCU in 1.5mm² hi-tuff or arctic.

 

[JasonW]

the outside lights should be taken off the lighting circuit and fed from a 13A FCU in 1.5mm² hi-tuff or arctic.

13A? Even when both activated they can only draw 5A, can't they?

The cables supplying the lights are currently 1mm2 T&E but run straight out of the hole in the wall and into the back of the light - should I replace with arctic?

 

[Steve]

oops i ****ed up. sorry.

yes, a 5A FCU. for some reason i was thinking of a 10A load, which would warrant a 13A fuse.

If the cable goes straight into the light, it should be ok. UV light degrades ordinary PVC cable. arctic is more resistant to UV.

 

[securespark]

You have to be careful here. I had a customer with a circuit for security lighting on a 5A breaker. It tripped madly with 2 x 500W lamps in because of the inrush.

But with a 500 and a 300 or less, it was fine.

So maybe a 5A might not be enough for 2 x 500W. You have to think not just about the steady current draw, but startup current, too.

 

[JasonW]

Hmm, but having said all that there's nowhere convenient to get into the ring. There's an existing FCU for the boiler (which bizzarely has *two* cables coming in from a junction box somewhere ...) but I read that you can't spur off a spur so that's no help to me. Problems, problems.

 

[plugwash]

iirc LS found a while back that 2x500W halogens caused problems on a B6 but were fine on a C6.


so i'd expect them to be fine on a 5A cartridge fuse as well. cartridge fuses seem a LOT less sensitive to surges than MCBs, i've had a B16 trip (with negligable other load) while the 3A fuse downstream was left intact from a bulb failure before.