"skin current"

G

g-and-h_electric

Senior Member
Location
northern illinois
Occupation
supervising electrician
Hey guys, need some help with the concept of "skin current".

I fully understand that the electric current flows on the outside of a solid conductor (AKA skin current). The technicians at TRANE CO ( HVAC equipment) told our service manager that the 2 wire CAN BUS data leads from a communicating heat pump cannot be spliced with a wirenut, as twisting the ends together disrupts the skin currents. This I do not understand, I can understand if it has something to do with the twists and all like a 4 pair CAT 5 cable, but just a simple twisted splice??? The tech, did not offer an alternative splicing method.

Anyone have any ideas? Is the tech a bit mistaken?


Howard
 
Has nothing to do with skin effect. Skin effect causes current to flow along the surface of the conductor. The amount of current in a CAN bus circuit is low enough that it just does not matter.

A splice made with a wire nut will likely work at least most of the time, especially if it is a short distance, but the splice may also create reflections in the conductors that can interfere with communications.
 
If both wires in the pair are cut to the same length, and twisted into 2 wire nuts the same amount so that the twist of the wires are generally laid the same, and twist mostly maintained, it will work fine.

CAN bus is a very resilient method and you can get away with a lot worse than this.

It would be no different than a branch/stub teed off the pair that goes to some device/node, and those taps are a lot longer than the length of a wire nut.
 
Back to the original question...
The "skin effect" or skin current is directly related to the frequency- a DC current will use the entire cross-section of the conductor whereas at 60Hz the skin is about a third of an inch (so is almost irrelevant to most line voltage wiring). A high-speed CAN bus could be up to 1mb/s or a skin depth of about 0.0026", and a 24g wire is about 0.0220".

That aside, as the other folks say it won't matter much it it matters at all.
 
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