Adding Light to Power circuit.

[Bender]

Adding a light to a Radial Power Circuit - the circuit is wired in 2.5mm and on a 20A MCB

Now if I add a FCU to my Radial and then wire my light in 1.5mm this should be safe?

But what if I don't use a FCU but wire the light with 2.5mm cable? what dangers are there.

 

[telectrix]

none. but bettr to use a 5A FCU so as to be able to isolate.

 

[Bender]

Thank you for your Reply I'm a student and trying to better understand Overcurrent.

So im making notes, so apart from Isolating the light there is no danger in the second method as the MCB would safely protect the 2.5 cable from overload?

 

[littlespark]

If your light is being controlled through a normal light switch, these are generally rated at 10A and can be difficult to terminate 2.5 mm into.

Switched fused connection unit with 5A fuse, using the switch to control the light is a good suggestion

 

[Bender]

Ok so the switch itself might not have the Load carrying capacity? and in theory could be dangerous with the conductors inside reaching a dangerous level of heat before the 20A MCB tripped?

 

[Cid]

It won't be a problem. Just not conventional

 

[Bender]

I guess what im driving at is as I understand the MCB is protecting the cable from Overload but Lighting circuits usually run of a lower rating MCB so apart from the wires is anything else being protected from a lower rated MCB that im missing?

This is all hypothetical and just trying to understand overcurrent, MCB rattings and Cable CSA size

 

[Cid]

Theoretically possible to overload the light fittings if you're planning on running multiple lights.

The main issues with doing unconventional installations is that it can cause confusion for the 'next guy'.

 

[ipf]

In most domestic situations, I wouldn't want to be connecting 2.5mm cable into a light fitting terminals, either, they aren't designed for it.

edit. Just seen #4, sorry LS.​

It's not just about protection, there's the basic common sense factor

 

[Wilko]

Hi All - see Reg 559.5.1.204 which limits some lampholders to 16A OLCP. I was expecting to see 6A for pendants somewhere thereabouts, but can't.

 

[SJD]

In most domestic situations, I wouldn't want to be connecting 2.5mm cable into a light fitting terminals, either, they aren't designed for it.

Neither would I. But it is not uncommon to find a builder has wired up downlights in 2.5mm T&E. With all the exposed basic insulation hanging out of the fittings, of course!

 

[Bender]

Further trying to understand Overcurrent - In europe you have a Radial power circuit protected by a 20A MCB but all sockets are 13A and no fuse in plug so how is the cable of the 13A appliance protected from overload if the MCB is 20A?

Whats the current carrying capacity of flex for most appliances?

We have fuses protecting the flex from 32Amp on a ring but what about 20Amp on a radial?

So the original scenario could be dangerous with a pendant Light the flex not protected from overload by 20A MCB? so a fuse would be needed in this situation - unless pendant is of course wired in 2.5mm flex.

 

[Yozza19]

Don’t forget volt drop on power is 5% lighting is 3%

The 20a or 32a only protects the permanent installation from over current the fuse in a plug top would provide the protection for the cable

 

[Wilko]

Further trying to understand Overcurrent - In europe you have a Radial power circuit protected by a 20A MCB but all sockets are 13A and no fuse in plug so how is the cable of the 13A appliance protected from overload if the MCB is 20A?

Whats the current carrying capacity of flex for most appliances?

We have fuses protecting the flex from 32Amp on a ring but what about 20Amp on a radial?

So the original scenario could be dangerous with a pendant Light the flex not protected from overload by 20A MCB? so a fuse would be needed in this situation - unless pendant is of course wired in 2.5mm flex.

Hi, just my late night thoughts :
- I expect the appliance should not be able to overload its own flex and maybe in Europe they have an internal fuse if it was required.
- appliances have flex with various current carrying capacity to suit their draw. Could be 0.5mm (3A) up to 1.5mm (16A) from Table 4F3A.
- in UK its expected that 13A outlets will use plugs with an internal fuse of 3A to 13A. The circuit overload protection rating is a separate issue.
- if wiring some lights off a circuit with power outlets I would always fuse it down as per the original advice from @telectrix . Looking in some lights their internal conductors don't fill me with confidence, just saying.

 

[Bender]

Thanks for your replys so this is what im going with yes it should be ok with the increase in CSA of the cable but because we don't know anything about the conductors in Switches and the Lights themselves and may have a rating below the CSA of our cable and could reach a dangerous level of heat before the MCB tripped from overload, a fuse would definitely be a good idea

The European and worldwide Radial and plugs not being fused I can only guess that a 0.5mm 3A rated flex on a 16A or 20A MCB is not realy ever been much of a concern although there does seem to be potential there for the conductor in the flex to fry before the MCB trips.