No.

The LNB (or multiswitch and LNBs) is powered as he says from the receiver through the coax. That same voltage also serves to tell the LNB or multiswitch whether to send down on that one cable the right hand polarized or the left hand polarized signals by changing back and forth from 13 to 18 volts as you go through the channels. (The RH and LH signals are duplicate frequencies so they cannot be on the one cable at the same time.) The LNB doesn't care whether it gets 13 or 18 volts for power.

That said, this is one instance where power is carried by the coax in addition to the RF signal. Its understandable then that you would want to keep the DC voltage drop on that cable within acceptable limits. That is not something you would be concerned about with coax running to an antenna or a CATV drop and wiring in a building because it doesn't handle any power.

Most coax has a center conductor that is made of steel that has a thin layer of copper plated on the outside (called "copperweld"). The steel is used for strength and the copper provides conductivity at RF frequencies because of the "skin effect". The skin effect says that the higher the frequency the more to the outside of a conductor the signal will travel. Therefore at CATV and higher RF frequencies the signal travels entirely on the outside of the center conductor through the copper plating. So using a solid copper center conductor for a cable that only handles RF is also a waste of money.

What happens when you use a cable with a steel copperweld center conductor to handle power also? As said, when it has to handle any current you need to be concerned with making sure that what ever is on the other end gets ample voltage to operate. If you look at the DC resistance specs for a copperweld cable vs a solid copper center conductor, the solid copper obviously will be lower due to the fact that copper is a better conductor than steel.

What does this mean? Really not much unless you are installing long runs where voltage drop becomes a factor. Then you would want to use a solid copper center conductor.

As far as a copperweld center conductor causing the cable to short, think about it. The center conductor would have to somehow contact the shield through the dielectric that separates the two. Usually this happens because of a staple shot through the cable. The cable can work for awhile then fail. But lets say there were no staples used. Could the center conductor become hot enough because of the current to possibly melt through the dielectric? Nope. Even with a dead short at the LNB, the receiver LNB power is current limited to probably no more than 250ma. That would hardly cause even an 18 ga steel wire to get warm.

What would cause the cable to short? An improperly grounded dish and lightning is the first thing that comes to mind. Wouldn't even have to be a close strike. Then comes crummy cable itself, as well as water migration within the cable.

If you really want to know remove the shorted cable and start examining it. Look for the obvious stuff first like pinholes, staples, etc. Then start cutting it into sections and using your ohmmeter until you find the shorted section. Then cut that apart to see what is causing it.

-Hal

CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.