Folks,
I'm looking at getting a heat pump installed at my house that uses a communicating thermostat (specifically, the Lennox iComfort S30) that uses two pair of wires: 1st pair should be shielded (per manual) and 18 to 22 awg. This is a flavor of RS485 I believe. The 2nd pair is just 24VDC to power the system. No mention of shielding or twisted pair for this cable.
Finding two twisted pair shield cables is pretty easy. Finding one with a shield twisted pair cable and two other untwisted, unshield conductors is a bit harder.
So, the question is this: Is there any problems with running DC power (low power) through shielded twisted pair? The only thing I can think of would be cost, but I am FAR from an expert. The reason I am asking is I have seen people discussing issues with not using shielded cable for the communications pair and it sometimes causing problems. I want to make SURE the correct cable is installed so I never have any issues down the road. And no, I do NOT necessarily trust the contractors to install the correct cable correctly. These are HVAC contractors after all that are still getting used to variable speed motors.
Thanks!
RRRoamer