Theoretically... cables must be fused down when a lower size cable is connected to a larger sized ca

[assegayer]

Now I completely understand why cables must be fused down when a lower size cable is connected to a larger sized cable. To ensure the cable does not burn out from current that it cannot take.
Yes i know this

Now current doesnt go anywhere it isnt in demand for so if a spur off of say a 6mm for a aircondition unit someone was to take a 1.5mm off that for a light.In my thinking it would work fine as none of the current being pulled by the airconditon unit is going to go down the cable for the light.

Again i know you have to fuse down but im just speaking theoretically

 

[Andy78]

Haven't fully read the thread so don't know if this has been mentioned, but the regs allow a change in cable size without fusing down at the point of size reduction if the circuit ocpd is rated to protect the smallest cable size in the circuit. This could be the easiest way to protect the 1.5mm cable in this situation.

 

[Darkwood]

@Andy78 ... Yes I brought that up in a recent post although it's an unlikely option when the 6mm is probably running a heavy load to start with but acknowledge we are talking theorectical here.

 

[Andy78]

@Andy78 ... Yes I brought that up in a recent post although it's an unlikely option when the 6mm is probably running a heavy load to start with but acknowledge we are talking theorectical here.

Ah sorry, that's me skim reading. I thought the situation was a repurposing of a former 6mm sitcom supply.

 

[ElectroChem]

So, if we were to hypothetically say that I had already done this dodgy spur, what sort of hypothetical justifications should I use to hypothetically convince myself I haven't left a firetrap behind?

 

[Richard Burns]

So, if we were to hypothetically say that I had already done this dodgy spur, what sort of hypothetical justifications should I use to hypothetically convince myself I haven't left a firetrap behind?

There are times when theory and practice meet; it is at this point that everything goes wrong! (hypothetically)

 

[davesparks]

hahaha, mate i understand why we use fuses. But no one can ever give mean answer other then the one there college tutor gave them oh its because in fault conditions, what fecking fault conditions can cause a 1.5mm cable to melt supplying one light.

It's is very unlikely that a fault of this type will occur, but the problem would be defining when this could be allowed to be done and when it would not. If one light is ok then why not two? Or if one 100W light is ok then why not 10x 10W lights?

 

[davesparks]

The situation i was thinking was if someone wanted a light outside and the house inside is all concrete ceilings and walls etc which do not want to get wrecked. But you had a perfectly good ac unit outside with its dedicated circuit it would be much easier and less hassle to just stab of that. And as mentioned earlier a fcu would jsut not be practical.

For a start you would no longer have a dedicated circuit for the AC if you extend it to do other things!

 

[Deleted member 26818]

If there were a dead short on the 1.5mm2 lighting spur, would the Over Current Protective device selected to protect the 6mm2 air con circuit protect the cable?

 

[StephenRowley]

hahaha, mate i understand why we use fuses. But no one can ever give mean answer other then the one there college tutor gave them oh its because in fault conditions, what fecking fault conditions can cause a 1.5mm cable to melt supplying one light.

Someone pieces the cable with a screw/nail, small rodent crews though cable. A Led bulb or CFC has been fault that causes a short. The fitting it self gets damaged or bulb its head knocked off and shorted, some child/thick adult sticks something into light fitting. to name but a few.

 

[Pete999]

The situation i was thinking was if someone wanted a light outside and the house inside is all concrete ceilings and walls etc which do not want to get wrecked. But you had a perfectly good ac unit outside with its dedicated circuit it would be much easier and less hassle to just stab of that. And as mentioned earlier a fcu would jsut not be practical.

What would happen when the A/C unit is switched off for the winter? no supply to the FCU you have connected to it

 

[Pete999]

Someone pieces the cable with a screw/nail, small rodent crews though cable. A Led bulb or CFC has been fault that causes a short. The fitting it self gets damaged or bulb its head knocked off and shorted, some child/thick adult sticks something into light fitting. to name but a few.

Blimey Stephen can I get some of the stuff you are on?

 

[Dave OCD]

Like !