24VDC Grounded or Floating


Thread Starter


In DCS, we are using external Weidmuller/Phoenix 230VAC to 24VDC PSU as an interrogation supply for Digital Inputs. + from 24VDC PSU is extended to the field limit switch contacts, and return supply is connected to the DI module having -24VDC from the PSU as reference. Please advise the best industrial practice either (-) of the 24VDC needs to be grounded or floating.
I prefer to ground the negative otherwise you may get an accidental ground on positive which would send all the negative rail to -24V DC and you would never know it.
Sometimes pushing an A/D negative plays havoc with the converter

Solidly grounded with lots of individual breakers or fuses gets my vote. If a circuit get's grounded the breaker trips and you can quickly isolate the fault.

BTW, make sure your power supply has more than enough capacity to pop the breaker (or fuse) otherwise it may just pull the Voltage down on the "Over Current" protection. You should have a separate supply for the processor of course, you don't want to stall it.