Positioning of a protective device.

[BillyBoBob]

Ok. we gotta install a fuse wher we have;
A reduction in the size of cable
Where the wiring system has changed
There is a change of environment
Where the cable type has altered.

Example;
A lighting circuit wired in 1•5mm T/E to a connector block, from there in 0•75mm to a light.

I know this is ok because of the amount of clik roses iv'e used. can someone tell me WHY it's ok.

 

[Risteard]

Overload protection is not required if, due to the nature of the load, an overload cannot occur.

 

[mechelec]

0.75mm^2 is good for 6 amps so ok for a 6 amp breaker the problem is volt drop over longer runs with the 0.75mm^2

 

[BillyBoBob]

Overload protection is not required if, due to the nature of the load, an overload cannot occur.

Can I assume then that that would be the reason for some flou fittings having an internal fuse due to the possibility that the ballast unit may burn out causing an overload.
Normal ES or bayonet lamps inc GU10 arn't going to overload so the fuse is not needed.

 

[pushrod]

Can I assume then that that would be the reason for some flou fittings having an internal fuse due to the possibility that the ballast unit may burn out causing an overload.
Normal ES or bayonet lamps inc GU10 arn't going to overload so the fuse is not needed.

I don't think that a ballast burning out would cause an overload. If the PF correction capacitor failed that would lead to an increase in current but it would have to a pretty sensitive and finely selected fuse to be affected by the relatively small increase in current you would get from that.

I think that i have read somewhere that flourescent lights fed by transformers need overcurrent protection (but could have been something else). TBH i have not noticed fuses in the fluorescent lights that i have looked in.

 

[trebor]

Can I assume then that that would be the reason for some flou fittings having an internal fuse due to the possibility that the ballast unit may burn out causing an overload.
Normal ES or bayonet lamps inc GU10 arn't going to overload so the fuse is not needed.

The reason some flues have internal fuses is simply for circuit continuity, normally foond in large offices etc where a fault on one flu is then prevented from operating the prot device at the db

 

[Andyfm]

And also allows lighting circuits to be on larger mcbs than 6 amp

 

[Adam W]

I seem to remember there's some reg which says you can reduce the csa of the cable without fusing if only for the last 3m.

 

[Sintra]

The reg you are thinking of is 433.2.2 (ii) which basically states that the overload protection can be placed along the length of cable and not just at the point of change if the length does not exceed 3M etc.