Wednesday, Mar 03, 2004 at 14:44
There is no difference in the electrical resistance of AC or DC wire, its all down to the size of the wire (ie. 6.0mm2 cross sectional area) not the number of strands or size of individual strands. Copper wire has a resistance of 0.0000017241 ohm-cm (volume resistance at 20C)
Copper wire resistance is a function of cross-sectional area and say a 1.0mm2 cross sectional area (csa) wire is availble as either 1 strand of 1.13 dia or 32 strands 0.2 dia. Both have a csa of 1.0mm2 and both have a resistance of 0.019 ohms per metre and both are rated at 10 amps (for 12v dc).
AC wire is generally rated differently to automotive DC wire as AC wire has significantly longer cable runs compared to automotive DC wire. Remember, resistance is a function of distance and an automotive wire is rarely longer than 6 metres, unlike the 100's of metres in AC wire. AC wire also has twin insulation, unlike automotive DC wire which has single insulation. But a good automotive electrician will always put the dc wire in convoluted tubing to help protect it.
The 32 strand wire in the above example will be far more flexible than a single strand wire, but there is no electrical difference. Thicker individual strands generally suffer stress fatigue (vibration) and can lead to breaking. But a
well supported thick strand wire will not simply break.
Also, crimping is favoured compared to soldering as a soldered joint is more prone to stress fatigue. However, the cheap crimping
tools seen in discount stores give a poor crimp connection and you would often be better off soldering the connection. The proper crimping tool leaves an imprint of the connector size in the plastic cover, one easy way to tell if the proper crimping tool has been used.
In a nutshell, if wire of sufficient diameter has been used there is no pratical difference between AC or DC wire for 12V automotive use, apart from the ease of use of multi strand wire.
Cheers
Mark
(NOTE- do not apply this "general" advise to high voltage AC applications, insulator resistance becomes significant, amongst other factors).Nissan 2003 GU 3.0TD
Windsor Rapid Offroad
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