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Discuss If you can't split a circuit? in the Electrical Engineering Chat area at

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I am a retired electrician and I've been out of the game for a while. My son asked me a question the other day and I wasn't too sure how to answer it so thought you lot might.

He wants to use rails to supply 5 modules, each module will have 40 small actuators that operate at 24VDC at 0.9As. Normally I said he would split each module up into a separate circuit with each one on an RCBO but as they are all attached to the one rail he can't do that. Is the only option to have a huge RCBO?

Interested in what innovative ideas you can come up with?
That is totalling about 5kW so not a trivial load, though possibly less on average depending on the usage. So you might be OK with a 25A C-curve RCBO, but:
  • What does the Manufacturer's Instructions say about supply side protection?
  • Do they need RCD protection, or is MCB sufficient? (i.e. is it hard wired and low risk of shock, or in area where additional protection is needed)
  • If they need RCD protection, what sort of total leakage current will the whole thing have? (back to the MI spec again)
A very general comment, without knowing the actual application, but wonder if the control circuitry should be separated from the load circuitry. e.g. one circuit running control gears and relays, and then the actuators powered in groups by individual circuits.

(I'm also intrigued where the 24vdc is coming from, as it may need to be multiple sources)
Presumably the (5x) Module is the source of the 24v dc for each (5X) set of 40 actuators?

Is this "One Rail" a Din rail that the Modules are clipped onto, or is it a Bus Bar as a common feed to each Module?

Is all this in a control cabinet?
Is it for commercial or personal use?
Have I got this right?
5 modules x 40 actuators x 0.9A = 180A at 24V DC
That's a lot of current. Battery supply?

I would certainly split the system into 5 modules and fuse each, probably at 32A. That's just for basic safety. No excuses as it protects against a screwdriver in the wrong place. A sixth fuse would feed any control circuit, if required.

Normally I wouldn't consider earth leakage protection on a 24V DC system, although it can be done. It's not a cheap option on DC systems.

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