length of circuits

[swift2]

hello could somebody please help me...I i was wondering what the maximum length for a lighting circuit wired in 1.5mm sq cable protected by a 6 amp mcb...also the maximun length of a ring final circuit wired in 2.5mm sq protected by a 32 amp mcb.

A ring may serve up to 100 m sq of floor area and, in theory, may have any number of sockets outlets or fused connection units directly connected to it. There is a limit to the length of cable permissible in a ring circuit. Assuming that the surrounding temperature does not exceed 30 degrees centigrade and that cables are not bunched together or covered with insulation of any kind, this is 68 metres for circuits protected by a cartridge fuse and for circuits protected by an MCB.

With 1 mm sq. cable, one circuit may serve up to 1200 Watts and must not exceed 83 m of cable length measured without the switch length. However, where there are long cable lengths, use 1.5 mm sq. cable instead which allows a maximum cable length of 126 m measured without the switch length


could somebody tell me if these statements are true please

 

[bongos]

Sounds like a college question?

Work it out here. You are limited to 3% voltage drop on lighting circuits and 5% on other final circuits.

What answer do you get?

 

[Spark123]

If you have an on site guide there is a section which details conventional circuit maximum lengths. The limits are either owing to volt drop or earth fault loop impedance.

 

[swift2]

thank u for ur replies...lol left college about a year ago now but not been working in the trade that regular. I get 45 metres at 1200 watts but surely that cant be right as lighting circuits do probably exceed 45 metres in the real world ?? i changed the options to 25 degrees for ambient temp and clipped direct as the rating would increase by doing this.

for the ring final I got 36 metres at 4kw, do rings finals really be 36 metres long in cable ? that sureley cant be right or maybe be right but not practised in the trade.

now I have tried to work this out could you confirm this with me please or give me your expertise opinion. thank u for your help.

 

[swift2]

If you have an on site guide there is a section which details conventional circuit maximum lengths. The limits
are either owing to volt drop or earth fault loop impedance.

could you tell me where abouts I would find this in the osg please

 

[Spark123]

Table 7.1 on page 44 onwards.

You are wasting your time using the calculator as all your load isn't usually at the furthest part of the circuit, also for a ring final you have a parallel path.

 

[swift2]

thank u spark for your help, appreciate it mate.