Wanted - two pair cable for 12VDC and RS485

Thanks, Roger. I spoke to Lee at FSC. He didn't know about combined power/data but he recommended a cable with two screened twisted pairs of 18AWG at =A30.61/metre. I'm guessing that this cable might do the job OK

Hmmm. 18awg has a resistance of three ohms for 80m there and back. This is voltage drop of 1.5V for 500mA, which is too much for a 12V supply voltage. I'm going to check whether my loads really require that much current...

Why not just use one of the standard multi-core cables?. You can double up the pairs for power, and given the cores are twisted pair, and the power is DC, there should be insignificant crosstalk between the data and power pairs. Something like 9503, and use two pairs for the power. The same could be done with 8777, which has individually shielded pairs. Realistically if you want 12v at the far end, you would be much better off sending 24v, and regulating locally. Have you tried FSC?. When I wanted to source some Belden cable in the UK, they were able to help. They also do their own range of cables, that combine power and data in one cable.

Best Wishes

The 'silly' thing is that combined data/power cables, seem to have become less common. I seen to remember Farnell, doing one with a heavy pair and a single twisted pair, but could not find it. There are usually 'thicker' versions available for servo applications (have one heavy pair for the motor drive power, and usually a shielded pair, or two pairs, for the shaft encoder outputs, and/or the zero sensor), but because they are designed to be very flexible, they are usually expensive. £0.61/m, sounds reasonable if you only want the 80m mentioned.

Good Luck.

Why not use just a single twisted or straight pair of wires. You can get your DC power to run over the same pair of signal wires using chokes and capacitors in the form of a filter.

But two separate cables will be the most economic solution. Any old stuff will do for the power cable provided it has a low enough DC resistance.

---- Reg.

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Cat5

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