Adequate cable amperage rating?

[dogfonos]

Would appreciate guidance/advice on suitable amp rating for a cable I wish to use to wire an external PIR and an associated 20W LED light.

Normally, I wouldn't need to ask such a simple question but I'm a bit unsure about my house wiring and think it may affect the current rating of wiring I should use. I have wired several external PIR LED lights and LED + PIR combinations before but always used an individual 3 amp fused spur for each light and used cable rated at 6 amps.

An extension was built a few years ago and I've never taken the trouble to fully understand the new wiring circuits - until a combined LED/PIR unit (added when the extension was built) failed the other day. I intend to replace the combined unit with a separate PIR and an LED light. I discovered that the 13 amp fused spur I thought was solely for the PIR/LED light actually supplied my garage too. The fused spur is on the circuit (maybe ring main, maybe radial) that supplies kitchen and utility room sockets and is protected by a 32A MCB in the distribution box. I've removed the failed PIR/LED light, and associated wiring, which just leaves the external junction box, with its mains supply, ready for re-wiring the new PIR and separate LED light.

Question is: should I use 13+ amp rated cable to wire the PIR and LED light because of the 13 amp fused spur that feeds it? I can't down-rate the fuse in this spur as I need it to be 13 amps for the garage sockets. Thanks for your time.

 

[EFLImpudence]

To be ultra cautious you could fit 13A cable but 6A will be fine.
The PIR and light is not going to overload it and a short will blow the fuse.

Can you fit another Fused Spur Connector Unit (the cable is the spur) with a 3A or 5A fuse?

 

[dogfonos]

Can you fit another Fused Spur Connector Unit (the cable is the spur) with a 3A or 5A fuse?

That's an idea. The only place I could access the spur, without disruption and considerable additional cost, would be where the external junction box is sited. So maybe one of these could replace the external junction box? Or be positioned alongside it?


I remember an electrician telling me that a fuse protects the wiring, rather than the appliance, which is why I was wary of using 6 amp cable when the preceding switched spur has (and needs to have) a 13 amp fuse. Would I be going against the IET Wiring Regulations by using 6 amp cable?

 

[JohnD]

6 amp cable?

What do you mean by 6A cable? Some sort of flex?

 

[EFLImpudence]

That's an idea. The only place I could access the spur, without disruption and considerable additional cost, would be where the external junction box is sited. So maybe one of these could replace the external junction box? Or be positioned alongside it?

It could be.

I remember an electrician telling me that a fuse protects the wiring, rather than the appliance,

That is true.

which is why I was wary of using 6 amp cable when the preceding switched spur has (and needs to have) a 13 amp fuse.

Yes, I realise that.

Would I be going against the IET Wiring Regulations by using 6 amp cable?

Not in my view if you read the section on "omission" of overload protection.

As I said, the tiny load will not overload the cable and a short circuit or fault current will blow the fuse.

 

[dogfonos]

What do you mean by 6A cable? Some sort of flex?

Yes. The LED lamp has a sufficient length of attached cable (of unknown rating) and I intended to use 3 core, 6 amp flex to wire the PIR - just because I already have some - even though the PIR has no earth connection.