Originally Posted by
RobertZA
then "6.9.2.2 In the case of a single-phase circuit, the disconnecting device shall disconnect live and neutral." Now what does this refer to ? If it refers to the DB main disconnecting device then fair enough. But it says circuit … so I may interpret a normal 16A lighting circuit as a "circuit" then then this "circuit" must have a double pole disconnecting device?
I suggest the full reading of 6.9.2 gives us the context.
6.9.2 Disconnection of neutral conductors
6.9.2.1 A neutral conductor shall not have a single-pole disconnecting device.
6.9.2.2 In the case of a single-phase circuit, the disconnecting device shall disconnect live and neutral. In the case of a multiphase circuit, the disconnecting device shall disconnect all the phase conductors but need not disconnect the neutral conductor in an installation connected to a supply system in which the neutral conductor is earthed direct (see the TN system in annex J).
6.9.2.3 A disconnecting device used in a supply system in which there is no direct connection between earth and any live conductor shall disconnect all the live conductors (see the TT and IT systems in annex J).
NOTE In a safety supply, none of the conductors are connected to earth, so any disconnecting device in such a circuit has to disconnect all the conductors.
There is no instruction here that every circuit requires a disconnecting device. The purpose is to instruct which conductors any disconnecting device must disconnect given the situation in which they have been placed.
An observation on disconnecting the neutral in 3 phase circuits - the neutral should* be the last conductor to break and the first conductor to make. If this isn't written into SANS 10124-1 somewhere already, I suggest it should be.
*Note that "should" becomes "must" per the requirements of some power supply authorities for cross-over switches in installations with alternative supplies.
Reply With Quote
Did you like this article? Share it with your favourite social network.