Main disconnector - single phase

[Andrew_van_Zyl]

My assessor and I developed a difference of opinion at my assessment today.

He suggests that in a single phase installation that a single pole main disconnector that disconnects only live is sufficient?

10142 - 6.9.2.2 - "In the case of a single phase circuit, the disconnecting device shall disconnect live and neutral."

I've always replaced single pole with a double pole that disconnects both live and neutral.

Have I interpreted 10142 correctly?

[Dylboy]

That is interesting. That quoted reg is about the disconnecting of the neutral conductor and not about main switch.

The main switch bit in the book just states that it must isolate a supply.

If the symbol of the single pole CB states that it is suitable for isolation then I think a single pole is ok.

Interesting point and keen to get some clarity too.

I always have a double pole mains witch in my boards as I like to disconnect the neutral for testing of things and then I know it isolated proper.



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[GCE]

My assessor and I developed a difference of opinion at my assessment today.

He suggests that in a single phase installation that a single pole main disconnector that disconnects only live is sufficient?

10142 - 6.9.2.2 - "In the case of a single phase circuit, the disconnecting device shall disconnect live and neutral."

I've always replaced single pole with a double pole that disconnects both live and neutral.

Have I interpreted 10142 correctly?

Going through the regulations and maybe understand why the assessor says so , but disagree with him completely

The intention under 6.9 clause if read in full is clear that a single phase supply is both live and neutral
If you look at 6.6.1.1 and 6.9.1.1 which both call for a switch disconnector at the D/Board and then 6.9.2.2 calling for live and neutral to be switched on single phase then I don't see the grey area.

I have had a rant before on assessors that seem to think there interruption is correct and they teach the guys incorrectly .This is what then causes and addendum to SANS to clarify something when it has always been acceptable practice and as per OHSA " designed with good engineering principles "


3.79.2
switch-disconnector
switch that, in the open position, satisfies the isolating requirements
specified for a disconnector
NOTE A switch-disconnector was known as an "on-load isolator".

6.6 Distribution boards
NOTE This clause describes the minimum safety requirements for the construction
and installation of distribution boards. The symbols to be used in distribution boards are
stipulated in annex N.
6.6.1 General
6.6.1.1 Each distribution board shall be controlled by a switch-disconnector
(see 6.9.4). The switch-disconnector shall:
a) be mounted in the distribution board or adjacent to the distribution board in
the same room,
b) in the case of the main or first distribution board of an installation, be
labelled as "main switch",
c) in the case of a sub-distribution board, be labelled as "sub-main switch" "or
main switch" if the board is labelled "sub-board…",
d) in the case where an alternative supply is installed (emergency supply,
uninterruptible power systems (UPS), etc.), be labelled as required in
7.12.2.1, and
e) have a danger notice on or near it. The danger notice shall give instructions
that the switch-disconnector be switched off in the event of inadvertent
contact or leakage.


6.8.1 Circuit-breakers used as main or local switch-disconnectors
A circuit-breaker that is used as a main or local switch-disconnector
(see 6.9.4) shall comply with the relevant requirements of a standard given in
clause 4 for switch-disconnectors, or, alternatively, a switch-disconnector
shall be positioned on the supply side of the circuit-breaker.

6.9 Disconnecting devices
6.9.1 General
6.9.1.1 Each installation shall have one disconnecting device to disconnect
the entire installation, except in the case of multisupplies or more than one
transformer supplying the installation where each supply shall have its own
disconnecting device. There shall be a notice fixed next to each such
disconnecting device indicating that the installation has more than one main
switch-disconnector.
6.9.1.2 If an installation consists of separate parts, each part shall be
controlled by a sub-main switch-disconnector to disconnect
a) that part of the installation, or
b) individual circuits and appliances.
6.9.1.3 A disconnecting device that is intended to disconnect equipment for
repair, maintenance, or inspection shall have at least the safety isolating
requirements of a switch-disconnector.
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 K).

6.9.4 Main switch-disconnectors
The main switch-disconnector on each distribution board shall be easily
accessible. (See also 6.6.1.1(b), 6.6.1.1(c), 6.6.1.6 and 6.6.1.9). If, owing to
the nature of the installation, it is necessary to be able to interrupt the supply
immediately, the switch-disconnector shall be so installed that it can be rapidly
identified and operated.

[Thys LOW Elektries]

I guess in the event you have a sub db and a double mains in the supply db one can settle for an one pole but I prefer a two pole mains for obvious reasons

[GCE]

I guess in the event you have a sub db and a double mains in the supply db one can settle for an one pole but I prefer a two pole mains for obvious reasons

I disagree with your statement - 6.9.1.2 requires a disconnector and 6.9.2.2 requires neutral to be disconnected in single phase supply .
I know they are different clauses but to me if you read section 6.9. the clauses are all relevant to each other



6.6.1.1 Each distribution board shall be controlled by a switch-disconnector
(see 6.9.4). The switch-disconnector shall:

6.9.1.2 If an installation consists of separate parts, each part shall be
controlled by a sub-main switch-disconnector to disconnect
a) that part of the installation, or
b) individual circuits and appliances.


6.9.2.2 In the case of a single-phase circuit, the disconnecting device shall
disconnect live and neutral

[mygoggie]

I disagree with your statement - 6.9.1.2 requires a disconnector and 6.9.2.2 requires neutral to be disconnected in single phase supply .
I know they are different clauses but to me if you read section 6.9. the clauses are all relevant to each other



6.6.1.1 Each distribution board shall be controlled by a switch-disconnector
(see 6.9.4). The switch-disconnector shall:

6.9.1.2 If an installation consists of separate parts, each part shall be
controlled by a sub-main switch-disconnector to disconnect
a) that part of the installation, or
b) individual circuits and appliances.


6.9.2.2 In the case of a single-phase circuit, the disconnecting device shall
disconnect live and neutral

I think you misunderstood @Thys LOW Elektries as my interpretation of what he is saying is that if the sub-DB has dual pole disconnector than the disconnector in the main DB that feeds the sub-DB can only have a single pole (L) disconnector.

This brings me to my presence here.

My question maybe hijacks this thread, but please bear with me as I do think it is relevant.

Where in the regs can we find the specification that stipulates whether this disconnector in the main DB (isolating the cable feeding the sub-DB) must be a dual pole or be a single pole disconnector?

[GCE]

Where in the regs can we find the specification that stipulates whether this disconnector in the main DB (isolating the cable feeding the sub-DB) must be a dual pole or be a single pole disconnector?

The main switch an the Main DB will be a disconnector - The C/Breaker feeding out (single phase) can be single pole to protect the cable - Feeding out will not be a disconnector .
When the cable feeds into the sub DB it will terminate in a disconnector D/Pole - The disconnector will have to be suitable rated against the CB protecting the cable

[mygoggie]

Thanks @GCE this make sense if I read the definitions of the regs. Much appreciated.

As I read the regulations (2020 (not the latest)) then I have to agree with you that a main switch or a sub-main switch must be a disconnector as per §6.9.1.1 and §6.9.2.2.

[Isetech]

Inverter sub panels and changeover switches bring in a new set of challenges.

Would the changeover panel mounted next the the inverter be regarded as a sub DB which requires a double isolator or can the changeover switch be used as the D/P islotor?

In some cases there is no changeover switch only a supply to the inverter and the output which will then either feed a sub DB feed back into the changeover "sub DB".

Throw in a bi directional hybrid inverter just to confuse everything.

[Dylboy]

Been pondering that myself with regards to the change over board being a Sub DB or a change over switchgear assembly ?

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[mygoggie]

I am not a specialist on the regs, but here we are looking at "point of control" requirements. Best explained in Figure P.1