DB Wire Size

[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?

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.

[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.

[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.

[AndyD]

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.

Not sure why you'd want to use silicone insulated wire, it would work out expensive and is unnecessary from a temperature rating point of view...

The regs mention the voltage rating of the insulation must be higher than any voltage found in the DB, they don't specify it must be PVC as far as I know.

The problem with using silicone wire or any panelflex type wire would be that it's fine stranded conductors which may be against the manufacturers instructions for the types of wire the circuit breaker cage clamp terminations or the neutral bar screw terminations are suitable for....although using it in conjunction with bootlace ferrules may be acceptable.

[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