Another stupid sparky question

[Legion]

A guy on gumtree is selling "2.5mm 3C+E" cable for a good price. I need new extension cables. Online US-centric charts indicate that 2.5mm diameter cable is ~AWG 10 and under the "maximum amps for power transmission" column AWG 10 is 15A.

Two questions:

- given my devices are only ever going to be pushing 10A constant at full output, surely these cables are more than enough? There's a picture and they look pretty big, but nowhere near as big as my existing stupidly big extension cable that's about a 50c piece in total diameter and came with 50A Clipsal socket/plug.
- is it disingenuous to put 32A sockets/plugs on a cable like this, even though I'm the only one using them, if the cables themselves aren't capable of 32A?

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[BobL]

It doesn't matter that just you will be using it, if someone was to "borrow" the extension cord and do themselves a mischief then you would be liable .

[Legion]

So you need to choose the plugs to be less than the cable rating? So if I have a 32A wall socket I can only have 32A capable cable? (I think 32A and the 10/20A size are incompatible)

And exactly how many amps can this "2.5mm" cable carry? E.g. it looks like the cable is thicker than my welder, which came with a 32A plug on a cable about half the diameter of my current extension cable. The online tables have "maximum power transmission" and "maximum amps for chassis wiring" and "NEC copper wire ampacity" etc but all these seem very US-biased. Is there an Australian standard measurement I need to look up for flex cable size for 400V 32A three phase transmission?

Again, I could just ask my sparky which is who will be wiring up things in the end, but if I can get classified cable at 1/10 the price I'd pay the sparky shop that's what I'm looking to do, and then they're happy to wire it up for me if it is fit for purpose. But if I choose the wrong cable and fittings then they won't and I blow my money.

[Vernonv]

And exactly how many amps can this "2.5mm" cable carry? E.g. it looks like the cable is thicker than my welder, which came with a 32A plug on a cable about half the diameter of my current extension cable.

The welder is a known load and the cable can be sized accordingly. An extension lead could have any load up to the circuit design maximum.

[Legion]

Yeah, that makes sense.

So I need ~AWG 6 or greater? ~4mm diameter per wire? That's rated to 37A for power transmission.

[Vernonv]

Not according to the info I found :2014-10-14_1603.png

[Legion]

In that chart the first column is areas, I was talking diameters. Actually, according to your chart the 4.0mm^2 cable is rated to 25A and that is ~2.26mm diameter so from that chart maybe 2.5mm diameter cable is borderline 32A.

I'd rather a 32A cable, sized big enough without being ridiculously big. If I can get away with 2 or 3 or 4mm rather than 10mm per cable that would be great. My current cable is a pig of a thing to move around. I figure 40m is probably about 50kg+.

[Vernonv]

In that chart the first column is areas, I was talking diameters.

I'd bet that the cable you are looking at is NOT 2.5mm diameter, rather 2.5mm2 CSA.

Electrical cable in Australia (well certainly in these situations) is always quoted in CSA, not diameter.

[Legion]

Oh, good point. You're probably right. Here it is:

http://www.gumtree.com.au/s-ad/perth...ase/1057225566

[Vernonv]

The other thing to consider is if this cable is actually flex cord, which is what should normally be used for extension leads.

Also looking at the info I have, flex cord only goes to 4mm (that is info from only one supplier though).

[NCArcher]

Oh, good point. You're probably right. Here it is:

http://www.gumtree.com.au/s-ad/perth...ase/1057225566

That cable is not suitable for what you want. Talk to your electrician and ask him to recommend a cable size then search for it online for the best price.

[Legion]

Thanks everyone for the help and advice! You saved me $.

[Karl Robbers]

There is a brilliant little free app for android phones, (maybe apple as well), called electro droid that has a section for calculating voltage drop for DC, AC single phase and AC three phase circuits. You input the length of the cable run, the voltage, load amperage, current type and wire gauge and it will then calculate the drop. It is my understanding that you should aim for less than 5% drop for a constant load and sub 10% for surge loads such as starting motors etc. Obviously the lower the voltage drop the better.
Lots of other handy tools in the app as well.

[Legion]

Installed. Thanks! Looks cool.

[soundman]

Just for those that may be interested.
There are some things that have changed with the use of extension cords according to AS standards.....how do I know...I've just coughed up about $1200...yeh that is right, one thousand two hundred dollars......( don't get me started)...for the standards I need to carry.....and I am swatting up because I am due for the 5 yearly exam to reknew my licence.

It is not and has not ever been legal, to use anything other than flex for extension cords or cords to connect equipment to a plug...it can also be argued that flex should be used to connect machines that are permenently wired..may be moved ( even a bit) or involve vibration

yeh I know there is a lot of orange circular out there doing jobs that should be done by flex....but that is just bad bananas.

Now there are two matters to consider with extension cords.....current rating and voltage drop.

If you are talking about electrical matters in Australia we work in mm2, and we work off different considerations to overseas......so talk in the manner described in the standards and use australian tables.

In fact if the cable is marked or discribed in guage.....it will not be Australian approved.

here is a rough regirgitation of what is in the tables in the standards..tables I can not reproduce because of copyright....(ya cant know the rules unless you pay your money..told ya not to get me started)

Equipment like compressors, fridges anything with a motor and welders produce high start currents.

10 amp cables...that is cables with 10 amp plugs.
1.0mm2 is permissable up to 25meters for general use and 15 meters for equipment with high start currents.
1.5mm2 is permissable for general use up to 35 meters and 25 meters for high start currents
2.5mm2 is permissable for general use up to 60 meters and for high start currents up to 40 meters
4mm2 is permissable for general use up to 100 meters and high start currents 60 meters

15 or 16 amp cables...15 or 16 amp plugs
1.5mm2 is permissable general up to 25meters and high start current up to 15 meters
2.5mm2 general up to 40 meters, high start current up to 25 meters
4mm2 general up to 65 meters, high start currents up to 45 meters

20 amp leads..20 amp plugs
2.5mm2 general up to 30 meters, high start current 20 meters
4mm2 general up to 50 meters, high start current 30 meters.

the above is worked on 5% volatge drop

This may explain why 30 meter builders leads have shrunk to 25 meters

AND this applies to total length between the outlet and the machine.

There was word out that they ( whoever "they" are) where trying to make it illegal to plug one extension cord into another......and it actually may be so in some situations.

cheers