what is the minimum size wire that can be run to a out side flood light?

[lee2lee]

500w flood light, coming out of its spur what is the minimum size cable, round and flat cables.



Also, on a seperate question.

does an outside flood need a spur ? i have found a lighting cable in my lounge and dont really want an ugly spur sitting on the wall, can i just take it into a light switch and out to the flood ?


Thanks

 

[Mark_Burgess]

Ohms law and page 282 in the big red book will give you the answer to your first question

 

[JUD]

No problem coming off lighting circuit.

However, as you're altering the circuit, it will need to be RCD protected if it isn't already.

I would probably go for 0.75mm² flex to light. I hate seeing T&E on the outside of buildings.

 

[Deleted member 9648]

Why will it need to be RCD protected ?.....If the alteration itself requires RCD protection under Bs 7671 (which it possibly wont) it can be provided to that alone.There is no requirement to provide additional protection to the existing if it complied at the time it was installed.

 

[JUD]

The guy said he doesn't want ugly spurs. As he wants to run it off a light switch, what would you suggest???

 

[Deleted member 9648]

Still dont see what thats got to do with RCD's....unless the newly installed cable comes under the buried less than 50mm deep regs then there is no requirement for an RCD.

 

[JUD]

Sorry, I'm with you now.

I was just assuming that if the OP doesn't want ugly spurs then he wouldn't want ugly cables/trunking on his wall.

Once again......more info needed

 

[jeremy]

The light will be outside, therefore outside the equipotential zone. Will the Zs achieve req disconnection time and if cable outside is visible, is it UV stable?

 

[Deleted member 9648]

The light will be outside, therefore outside the equipotential zone. Will the Zs achieve req disconnection time and if cable outside is visible, is it UV stable?

...........not sure of the significance of the first part of your post,fixed equipment outside does not require additional protection by RCD.....the Zs would have to meet the disconnection time regardless of inside or out.

 

[jeremy]

equipment outside is out of the equipot zone so surely should have a 0.4 sec dis time whereas the inside lights only need a 5 sec dis time if my occasionluy failing memory serves me well (for once)

 

[JUD]

equipment outside is out of the equipot zone so surely should have a 0.4 sec dis time whereas the inside lights only need a 5 sec dis time if my occasionluy failing memory serves me well (for once)

411.3.2.2 Circuits ≤ 32A require a 0.4s disconnection time on TN systems and 0.2s on TT

Anyway guys, it's getting a bit off-topic. How about some advice for the OP.

 

[jeremy]

funny how I can remember stuff from 10 years ago but can't remember last Friday night!

 

[Deleted member 9648]

Has gone a bit off topic .............as far as the OP goes,minimum cable size depends on the rating of the protective device...but if from the fused side of a FCU 1.0mm would suffice in most circumstances.
Yes you can feed off the lighting circuit...but other facors come into play, like whether the circuit will be overloaded...(quite likely if you are adding a 500w T/H light).

 

[lee2lee]

So what was the minimum cable to the flood from a spur, is 0.75 flex ok?

Thanks

 

[Deleted member 9648]

From the load side of a FCU 1.0mm or 0.75mm fused at 5a wiil be fine assuming the legnth is only a few metres.