Protection When Changing CSA

I have always went by the rule " when changing (lowering) csa of cable/wire then insert protection device",

The regs have traditionally worded it something like that - although I prefer to think about it the other way around - i.e. insert a protective device any any point where the cable would no longer be protected by the upstream protective device. These days it's more about the cable's current carrying capacity rather than its c.s.a. - as installations methods (esp. thermal insulation or ambient temperature) can make a significant difference.

 

and further to that the second rule was "if its only a small run perhaps <2M then first rule need not apply".

Regs say 3m rather than 2m - but it's not a blanket exception - you also need to ensure that the chances of a short circuit are minimised, the consequences of any short circuit are acceptable and overload protection is provided (if downstream).

This particular application in design phase has an incoming 95mm cable in through a a switch disconnector which requires distribution to many smaller branch circuits. usually this application for me in control panels is simple as small currents (<30A) are in use but this larger requirement means the terminations get tricky having many different wire sizes.

Sounds like the sort of problem the distribution board was invented for.


   - Andy.

I have always went by the rule " when changing (lowering) csa of cable/wire then insert protection device",

The regs have traditionally worded it something like that - although I prefer to think about it the other way around - i.e. insert a protective device any any point where the cable would no longer be protected by the upstream protective device. These days it's more about the cable's current carrying capacity rather than its c.s.a. - as installations methods (esp. thermal insulation or ambient temperature) can make a significant difference.

 

and further to that the second rule was "if its only a small run perhaps <2M then first rule need not apply".

Regs say 3m rather than 2m - but it's not a blanket exception - you also need to ensure that the chances of a short circuit are minimised, the consequences of any short circuit are acceptable and overload protection is provided (if downstream).

This particular application in design phase has an incoming 95mm cable in through a a switch disconnector which requires distribution to many smaller branch circuits. usually this application for me in control panels is simple as small currents (<30A) are in use but this larger requirement means the terminations get tricky having many different wire sizes.

Sounds like the sort of problem the distribution board was invented for.


   - Andy.