Can a single power supply provide power to multiple current loops?

brinocerous said:

You definitely can power multiple 4-20 mA loops with a single PS, and this is extremely common. Essentially, the loops are connected in parallel to the output of the PS. Consult the documentation of your input module for details. You are correct that as long as you don't brush up against the output rating of the PS, voltage drop will not be an issue.

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defcon.klaxon said:

Hi all,

Had an interesting question sent my way, and thought I'd ask you guys for some input.

New project I'm working on has two ultrasonic liquid level sensors, both are loop powered 4-20mA. Simple enough. My question is, can a single 24V power supply provide power for multiple loops and other gear in the panel (radio, lights, etc) or does each current loop require a dedicated power supply?

I can look at this two ways. First, it would seem that each circuit, whether it's a loop powered circuit or not, is its own "loop". Power supply provides as much current as each loop needs and all is well. But second, while that seems fine ideally is the reality more complicated, and weird things can happen in the real world if they're not isolated? I'm worried about things like voltage drop, but since they're all separate "loops" as long as I spec a power supply with enough wattage, wouldn't that mitigate the issue?

Thanks for any help!

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daba said:

Just check on the specs of the devices you want to supply power to, and add them up. Allow at least a 20% margin, and choose a power supply that will deliver.

Power supplies are cheap, so don't be afraid of buying one that will deliver 5A when all you need is 200mA. In fact it would probably be hard to find a power supply just above your requirements.

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Saffa said:

I had exactly that happen a few weeks ago at a plant where a remote panel was fed from the PLC cubicle with 24V. A piece of equipment was changed in the remote panel and the installer managed to wire a relay contact wrong such that the 24V was shorted to zero volts. The original installation 20 years ago had been done with a well undersized multi core cable and there was enough volt drop in the cable that even with the short it was only pulling 5A. So the PSU was current limiting and the output voltage was sitting at 12V instead of 24V. There was a 6A fuse fitted for that... on a PSU only capable of supplying 5A.

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