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.

[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/uploads/2018/06/Cables-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]

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?

[ians]

Since back when we didnt even have TV's ( a flippen long time ago)

I would use the general rule for wire size

1.5 mm - 10amps
2.5 mm - 20 amps
4 mm - 30 amps
6 mm -40 amps
10 mm - 50 amps
16 mm - 60 amps
25 mm - 80 amps
35 mm 100 amps

I dont know of any issues ... i am still doing work for customers since tha 90's

I have identified more issues (thermal) with loose connections and and dogdey equipment than under rated wire size ... make no mistake i do have find issue with under size wiring ... in fact today ... the aircon which was relocated last week ... the wire size is only 1.5 mm between the indoor unit and compressor ... it is showing signs of over heating ... by discolouring on the copper core and the plastic is not as felxible and the sheat is difficult to remove ... I will create a report and email it to the customer.

[AndyD]

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?

[ATTACH=CONFIG]8131[/ATTACH]

The length or the run becomes a problem because of volt-drop. Yes, if the cable doesn't enter conduit anywhere along its run then and no there derating factors are applicable then a 10mm cable will suffice for a 65A load.

[ians]

The length or the run becomes a problem because of volt-drop. Yes, if the cable doesn't enter conduit anywhere along its run then and no there derating factors are applicable then a 10mm cable will suffice for a 65A load.

Talking about derating ... I had to do the calculations for an 800 amp supply ... 150 metres long ... everything was on track until the cables got to the underground duct ... that 30 m piece in the ducts makes a huge difference to the cable calculation.

[Frans400]

Interesting questions, am I aloud to use silicone insulated wire or panel flex in a db? Some people reckon than you only allowed to us gp wire.

[ians]

Interesting questions, am I aloud to use silicone insulated wire or panel flex in a db? Some people reckon than you only allowed to us gp wire.

I dont see why you cant use panel flex (so long as it is rated for the the voltage).

There is some confusion with flexible cables ... panel flex ... welding cable ... automotive cable ... its all about the rating (voltage) some cables are only insulated for up to 50 V other cables up to 1000 V and higher.

YOu can use flexible cables for just about anything so long as it is correctly rated for the applications ... you can wire inside the DB to motors/ pumps / controls ... you can even use flexible busbars.

Maybe one of the smart fellas could do a write up expalining the difference.

[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-catalogue/electric-cables/general-wires/general-welding-cable.pdf

[Derlyn]

Ok, so I measured the cross sectional area of the commercially available busbars pictured above.

On the left is for dinrail. Top section between breakers 7mm sq.
Pins going down into breakers 4mm sq.

On the right is for samite. Top section between breakers 18mm sq.
Pins going down into breakers 10mm sq.

So from the above, as far as dinrail is concerned, It seems as if self made bridges using 6mm sq house wire will do a better job than the commercially available buzbar, I also know that if a product has been especially designed for a certain purpose, then it should be used.

What sayeth the other toppies ?

Peace out ... Derek