120ac versus 24dc motor control


Thread Starter

old _Guy

In an effort to "eliminate the hazard" or "mitigate the risk" I have seen the introduction of 24 Vdc control power transformers in motor control. Inherently safer by design, it can be difficult for an old culture to "change" from the traditional 120 Vac wiring to 24 Vdc.

I was wondering who else has seen this shift? Or is this not a popular or wise choice? Is it not a good idea?
I don't see a safety issue with 120 VAC motor control. You need qualified electricians to work on it; but the motor will be a higher voltage 600 V - 13.8 KV and will require qualified tradesmen.

I can see stupid cheap people doing this so that they can hire less qualified cheaper labour.

The DCS side has gone to 24 VDC with interposing relays more frequently in the MCC logic section.
Hi Old guy, yes, I have also have been seen the shift of motor control design from 120 VAC to 24 VDC since safer for human that operate or troubleshoot and in my experience and easier to maintain.

Based on my experience, 24 VDC control voltage are more immune to control voltage transformer output voltage drop caused by big motor starting inrush current.

The cons is, when you need to put local manual control remotely and the distance is quite far, such as push button or limit switch , there will be significant voltage drop that will made 24 VDC relay or contactor will not be working properly.