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Posted By Topic: Short circuit protection in Switchboards

OctaneOutlaw
Mar 24 2019 14:16

I don't know if I'm missing something completely obvious and I'm just mind blanking but I've been reading over about over current protection and was wondering where the feeds used from the mains to the groups of sub circuits receive there shortly circuit protection

I understand that overload protection for these conductors is normally provided by the sum of the MCBs being supplied is less than the CCC of the cable but normally the boards I've seen only have an isolating switch for the main switch due to the lines company providing service protection

Is their service protection what also provides the short circuit protection for these conductors? Or should it be being provided at the origin of these conductors?

Any explanation would be appreciated as I feel like I'm missing something really obvious because I've seen a number of boards done in this way 2.5.4.2 makes me feel like this doesn't comply though? And I felt like the alternative positions and omissions didn't apply here either

Thanks in advance for your time
   

AlecK
Mar 24 2019 19:26

ESRs require linescos to provide short circuit & fault protection for mains. The next lot of cabling, within the switchboard, also needs these protections, plus overload protection. So the installer / designer must either provide it, or ensure that the protection for mains coverts them as well.


   

OctaneOutlaw
Mar 24 2019 19:45

Ah, right so basically the short circuit protection for these cables is usually provided by the short circuit protection provided for the mains? Is that basically what you're saying?

How does that comply with 2.5.4.2 saying it has to be at the origin or at the reduction in CCC? Wouldn't something need to be provided there in the switchboard where those feeds start at the reduction from the incoming mains?
   

Someone
Mar 24 2019 21:51

The exception to 2.5.4.2 points you to 2.5.4.3.2, which basically says 'except where the upstream protection protects it anyway.
   

OctaneOutlaw
Mar 24 2019 22:05

I knew I must have been missing something that is the part I couldn't seem to find

Thank you both