[RE-wrenches] solid vs stranded AC vs DC

[Jeff Yago]

I just had this "debate" with a reader of one of my articles who was a ham radio operator and a do-it-yourself solar homeowner who insisted stranded wire had a substantial lower resistance than solid wire for DC wiring.  After lots of research I discovered he was getting this from his ham radio text books.  It seems for antenna and speaker wire applications, as you increase the frequency of a current flow, the current starts to move out onto the surface of the wire, so the more strands of wire you have, the lower the resistance AT HIGHER FREQUENCIES.   

I learned that below 0.1 Mhz, this higher voltage loss does not come into play since DC electricity has a frequency of 0.0.  I think there is basically no differnce for a given current and voltage using stranded or solid wire for DC appications.  However, when you have long runs of DC wire (like to a large ground mounted array), if you allow the + and - wire to not be banded together in the trench, you will create a long narrow "capacitor" which can induce all kinds of resistance to power flow, not to mention reek havoc on nearby radios, and this may be more of a problem with DC than AC. 

I think many of these do-it-yourself types don't realize when they are wiring up some 12 volt DC solar equipment that the current for the same 120 VAC load will now be 10 times higher at 12 volts DC, and this is causing them to think the wire has a higher resistance when running DC through it and do not understand how the current drastically increases at the lower voltage and any long wire run will have a major voltage drop at low voltage.

Jeff Yago

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