Tag Archives: amps. amperage

Question: How Do I Know How Many Amps Your Cable(s) will Handle?

 

This week’s question comes from Rick H. in Iowa:
 
Question:  How can I tell what the maximum supported amperage capacity is for your cables? 
 
 
Answer:  
 
Thank you for the excellent question Rick!  Understanding the voltage and current limits of your cable(s) is absolutely critical to maintaining a safe transfer of electrical power between your devices.  All cables feature some degree of resistance to electrical energy.  
 
When electricity is forced to flow up against this resistance, it releases energy into the environment in the form of heat.  When cables are very thin, i.e. 30 AWG or smaller, the cabling cannot dissipate that heat energy into the environment fast enough, leading to a fundamental breakdown (failure).
 
The electrical breakdown of a cable assembly is not a pretty sight. During my younger years when my electronics expertise was in its infancy, I once made the horrible mistake of wiring a 12V DC switch incorrectly on a project box.  The switch connected a 12V lawn mower battery to a radio transmitter.  
 
Upon engaging the mis-wired switch, the connection created a short circuit between the negative and positive terminals of the battery — effectively dumping up to 100 Amps of current down some 18 AWG wire.  I watched in horror as the wire literally melted from the inside out, causing a flash-fire with the PVC wire insulation melting away like candle wax!  The melted wire dripped onto the carpet and nearly started a house fire.  
 
Example: Electric Blanket Fire
 
Fortunately, I was able to disengage the switch quickly before things got even worse, but literally in a matter of seconds, significant damage was done.  I learned a hard lesson that day about just how important current-handling capacity can be when it comes to cables.  What would happen if a whole bundle of wires ignited and went unnoticed?  Besides the fire risk, the burning PVC insulation contains toxic fumes that can prove deadly in their own right.
 
To prevent disaster, you should always select a cable based on the most conservative of safety ratings in mind.  The extra margin of error can be a life-saver.  So what do you need to know first?
 
#1:  You Must Know the Wire Gauge (AWG) of the Cable!
 
This value is imperative.  Our popular D-Sub Cables for instance tend to use 26 AWG insulated wire in their designs.  They are often used in custom projects and fed with a variety of both power and signal data.
 
American Wire Gauge (AWG) Chart

 

 
#2:  Is the Wire Bundled or out in the Open Air?
 
This, believe it or not, makes a huge difference.  When a wire is stand-alone and exposed to the open air, the movement of air around the cable will help cool it down, thus allowing for the transfer of more current.  
 
Example of Chassis Wiring (Free-Air)
 
When a wire is alone and exposed in free-air, we refer to it as:
 
Chassis Wiring
 
Example of Power Transmission Wiring (Bundled)
 
When a wire is bundled together with other wires, we call it:
 
Power Transmission Wiring
 
Chassis wiring refers to the wiring often found inside the chassis of an electronic device where you may have one wire in free-air that jumps from a connector on the outside of the chassis to a connector or PC board on the inside.  Again, because it is in open air, it can handle more current for its given size. 
 
Power transmission wiring refers to any wiring that is bundled together.  This is the figure you generally need to worry about most as most of the cable assemblies we make at Cables on Demand feature more than one wire bundled together.  Note: This rule applies to all bundled cable types, even those you would normally associate with data transfer and not power.  
 
As an example, if you were to open up a typical outdoor rated power extension cord, it would have three wires bundled together (hot, neutral and ground).  Since they are bundled and sealed off in a cable jacket, less current can flow through them safely.   
 
The Current Handling vs. Wire AWG Chart
 
The chart below will tell you the maximum recommended current handling capacity (Amps) for a given wire gauge in both Chassis Wiring and Power Transmission Wiring versions.  Remember to choose the Power Transmission Wiring value for most cables purchased through us and other cable vendors (bundled wire).
 
 
Amphenol Cables on Demand (www.CablesOnDemand.com) sincerely hopes this information proves useful for you and your electronics endeavors!  If you have any more questions, please call us toll-free at 1-866-223-2860 or send an e-mail to:support@cablesondemand.com.
 
 
Sincerely,
 
The Cable Guy