Larry, it's an interesting issue. I recently had an electrician tell me that 110 volt AC electrical signals contained in EMT or BX are supposed to shield energy gnerated from within unlike Lumex etc. Both EMT and the outer sheath of a BX cable are considerably substantial and contain a lot of metal mass that could absorb the energy.

. In the reverse scenario involvong a balanced microphone signal, the shield around the inner conductors absorbs the external interferance and by the time it reaches the inner conductirs it is of equal intensity as it travels in the same direction towards the primary side of the balancing transform subsequently cancelling itself out inside the transformer. But I'm not qualified enough to say whether a shield around a 70 volt pair will prevent induction from eminating into adjacent data or tel conductors. I don't see how it possibly can effectively.

Data / Tel as you well know can be corrupted by such interferance, that while not preventing it from communicating, can reduce it's performance by causing packets to be lost as processors interpret the corrupt data. in the case of Tel. it might just be manifest in some noise, or even the presence of the 70 volt audio program.

With more and more platforms moving to data cable wiring protocol, I have really become much more sensitive to the concerns regarding proximity of these runs to all other signal conductors.

I once experienced a serious 70 volt interferance problem in a large hotel that had separate hallway and guest room zones. The rooms were onl;y to recieve emergency paging,, the hallways were to recieve emergency paging as well as full time background music. I rann all of these conducxtors together. There were four wings to the comlex ( over 200 rooms) Well,, needles to say,,, you could hear a faint bleed of music in all of the rooms which was being induced by the hallway zones. I ended up having to build a relay system that both shorted out (terminated) the 70 volt conductors going to the guest room speakers as well as disconnecting these wires from the amplifiers so as not to cause the amplifier to see a dead short. When a page was activated, the relays un shorted the conductors, and re connected them to the amplifier channels allowing the page to be heard in the rooms. Prior to this,, I spent at least a day looking for a crossed wire not ever suspecting induction.