Electrical wiring getting warm is usually caused by either excessive current draw on an inadequate conductor cross section or a poor connection/dry joint leading to a high resistance.
In both instances you should carefully examine the wiring and confirm that its capable of handling the demand with some safety factor. There is a formula to work out exactly what you need. Also, always buy the best quality within your budget.
blue skies
tony
The above statement is correct in every sense.
High resistance inhibits the flow of current. Therefore, given that the supply voltage isn't changing, high resistance cannot be the cause of a melted connector.
Tom
Automotive electrical circuits are designed and specified in accordance with the current draw of the consumers been powered. The greater the current draw, the thicker the wire must be. Consider the difference in conductor thickness between battery cables and those of an average stereo head system.
Laws of physics determine that the resistance of a wire varies based on its physical thickness – the thinner the wire, the higher its resistance. Thicker wires must be used to accommodate a higher current. The cross-sectional area of a wire is inversely proportional to its resistance – if the wire is doubled in thickness, then its resistance is halved. Using thinner wire to support large current draw will result in the wire heating up and eventually melting both itself and its connector housing as well as possible damage to the consumer it is connected to.
Clear evidence of “hot” wiring can be found in a car cigarette lighter which uses a high resistance coil to glow red hot by applying a high current. The lighter pop’s-out when heat sensitive tabs within its body expand and release the lighter which then begins to cool. Another example is by using thin cables to jump start a car will result in the cables getting hot – hence the use of substantially thick cables!
The weak link in any electrical circuit is the physical integrity of its terminations – the connectors. Connectors are not only subject to vibrations and periodic handling, but the connection itself deteriorates over time and begins to oxidise. A connection that is not mechanically tight will begin a failure process that will increase its resistance and consequently will increase in heat. As this process continues, the joint will become less tight, higher in resistance and hotter. As this cycle continues, the joint will attain a sufficiently high temperature that will damage the connector housing and the conductor itself. This will also have the effect of sporadic operation of the consumer. Good electrical connections are made by solid mechanical crimping methods and using terminals rated for the current being applied. It may come as a surprise to many that a fusible link will not detect a high resistance and overheated wiring, and will not protect the circuit until there is a short circuit as a result of heat damage, which by then is probably too late.
To work out the correct wire thickness (gauge) we need to know the current (Amps) draw for the consumer. Using Watts’s law;
I = W/V or current = watts/volts
A typical headlamp rated at 60 W will require approximately 5 Amps.
I = 60/12, therefore, I = 5Amps
Using this formula, we can now specify the correct AWG (American Wire Gauge) for the conductor.
Note please that the VOLTAGE always remains constant in a typical automotive application at 13.2Volts – commonly rounded to 12Volts.
Providing a secondary wire to an electrical circuit in parallel may allow for some current drain but as electricity flows down the route of least resistance (much like water), it is likely that the bulk of the current will travel via the shorter wire.
I hope this helps and addresses misconceptions surrounding basic electrical principles.
blue skies
tony
any other ideas would be great. I've unplugged it at the moment incase it catches fire!!
