Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: Triton on January 02, 2011, 02:09:30 AM

Title: AWG Current Limits
Post by: Triton on January 02, 2011, 02:09:30 AM
Hi,

I'm confused by the current limits for the AWG cable system.

I did a Google search and came up with a table but it has different limits for "chassis wiring" and "power transmission". I'm guessing the former refers to cable in air (as in a model boat) and the latter to applications such as windings on a transformer, where heat would be a significant factor.

Anyhow, as a short cut, does anyone know what current 22 AWG would be good for in a model boat application?

Thanks,

John
Title: Re: AWG Current Limits
Post by: derekwarner on January 02, 2011, 03:57:20 AM
Triton......you will find the answer to your question in the following table....... O0 Derek

http://www.powerstream.com/Wire_Size.htm

[22 0.0254 0.64516 16.14 52.9392 7 0.92 42 kHz ]

There is als a ready reckoner table to back check or calculate requirements .... :-))
Title: Re: AWG Current Limits
Post by: wombat on January 02, 2011, 10:23:04 AM
The limits are also affected by the ambient temperature and the way the cables are bundled. I always allow a significant overcapacity toallow for this. Always be more generous

Wom
Title: Re: AWG Current Limits
Post by: malcolmfrary on January 02, 2011, 11:26:54 AM
When the power has got where it is going to, i.e. the "chassis", you can live with rather more voltage drop per unit length, because there is very little, as it were, length.
When you are transmitting power from one place to another, there is plenty of length, but you don't want to lose too much voltage in the line over that length, so the same current needs a thicker wire.  This is one of those cases where more is actually more, and better.
Title: Re: AWG Current Limits
Post by: oldiron on January 02, 2011, 12:42:45 PM
  From Derek's posted URL, in case you missed it, the qualifier relative to chassis wiring and transmission wiring and taking into account the effects of air and bundling:

In careful engineering the voltage drop, insulation temperature limit, thickness, thermal conductivity, and air convection and temperature should all be taken into account. The Maximum Amps for Power Transmission uses the 700 circular mils per amp rule, which is very very conservative. The Maximum Amps for Chassis Wiring is also a conservative rating, but is meant for wiring in air, and not in a bundle.
John
Title: Re: AWG Current Limits
Post by: andrewh on January 03, 2011, 07:46:02 PM
 - and most important of all -  the insulation material

The current any wire can take (in the short or long term) is set by the allowable temperature of the insulation, and that depends on whether it can get any cooling.
The wire (conductor) heats up because it has a (small) resistance, and loses the heat thru the insulation.
PVC insulation, for example should not be used at more than about 80degC, Silicone can go to around 350 degC continuous. PTFE kills you above 405 degC

So the question has to include what the wire is insulated with :}
andrew