DB Wire Size

[recre8]

Hi Guys

I just wanted to confirm if 10mm2 wire is OK for mains use (60A). I noticed that my mains wires feeding into the mains 63A MCB is 16mm2, but from there feeding into the Earth Leakage again from the EL into the first breaker it is all 10mm2. Everything else seems fine though. 2.5mm2 for all plugs and geyser (20A MCBs), 4mm2 stove (32A MCB) and 1.5mm2 for lights (10A MCB). The house has had two different COC's done over the years by two different companies. My earth wire coming into the house is oddly 10mm2 compares to 16mm2 for the live and neutral.

[Lindley]

10mm is correct wire size yes.the overall Installation is correct for stove and plugs according to wire size.

[recre8]

10mm is correct wire size yes.the overall Installation is correct for stove and plugs according to wire size.

Thank you, I was just wondering since on another forum a member claimed that 10mm2 will fail a COC because it is only rated for 52A. https://powerforum.co.za/topic/2303-...&comment=37743

[AndyD]

Wire size is relative to several factors, not just the load in Amps. The installation method, the wire/cable type and the length of the circuit should also be taken into account. A 4mm wire on a 32A breaker and a 10mm wire on a 63A breaker are a bit undersized from memory but I'd need to check the table in the regs when I'm in my office to confirm.

[ians]

Attached is an example of welding/flexible cable you cannot use for 230/400 VAC applications ... not in a DB or any other application with a voltage rating of over 100 VAC/VDC.

https://www.l-osales.co.za/download-...ding-cable.pdf

[Frans400]

I agree with Andy that 10mm^2 are to small. If im correct your electrician have the option to increase the wire size to 16mm^2 or to decrease the breaking current of the mains breaker to 40 amps.

[ians]

Thats interesting ... table 6.27
10 amps - 1 mm
16 amps - 1.5 mm
25 amp - 2.5 mm ... I remember it being 20 amp - 2.5 mm ... I see a lot of aircon installations with 25 amp MCB's ( been looking at my SANS book a lot lately )

If you look at the manufacturers table ... 10 mm can carry 61 amps ... but then there are other factors which need to be considered

https://www.voltex.co.za/wp-content/...-and-Wires.pdf

I have noticed prepaid meter installations popping up all over town using 10 mm to connect between the DB and the meter ... some dodgey looking installations ... I suppose you allow a R600 budget for an electrician to drive to site ... chase the wall or drill into the side of the DB ... mount the meter and connect ... you cant expect a COC and a quality installation ... you get what the supplier pays.

[ians]

Something to consider ... the time frame the load is present on the bussbar or any cable for that matter.

Installing a 6 mm cable for a stove for example ... which is used maybe a max of 2 - 3 maybe 4 hours a day (unless like one of my customers who does baking for a shop) ... and only 10-20 % of the rated load ...etc etc etc ... In all the years as a sparkie I personally have never seen a 6 mm stove wire burnt due to overloading ...only burnt at the connection.

How often is a 60 amp supply to a house under full load ... not very often ... I have been running load profiles for solar/inverter installs ... I can tell you that we hardly ever see anything over 30 amps.

From my experience .. .you more likely to see a burnt out terminal on a circuit breaker than a overloaded wire ... the last fire I went to ... it started at the connector block the aircon tech used to extend the calbe to the plug ... it completed guttered the granny flat ... thats where it gets interesting ... does the insurance company pay out and sue the aircon company ... what if the installation was done by a non registered installer ... the entire building was burnt ... yet the place the fire started was as clear as daylight ... you could actually see the V up the wall from the connector.

[ians]

A note - calling the ECA is not going to get you an investigation unless the contractor is not an ECA registered member (they look after their members)

I assume you need to contact the AIA or DOL ( dont know that they have suitably trained/qualitfied staff to tackle investigations ... hence the appointment of the
AIA ? )

Maybe someone who is up to date with this kind of stuff can comment ... I gave up with the ECA more than 10 years ago ... I think Brian Bilton got tired of all the calls back when I actually gave a shyte about this industry ... you can only flog a dead horse for so long.

[recre8]

Here is the table from the regs for single core PVC insulated wires. The table seems to be for longer runs of wire since the installation methods listed are all about how the wires are fixed. But I'm assuming that the "direct clipped" method in the table will suffice as a worst-case scenario compared to how they are installed in a DB board. According to the table then, 10mm2 should be able to carry 65A in a single-phase installation?