24VDC Control Circuit Intermittent Fault

[gar]

220801-1720 EDT

beck693:

Anything new?

Reading back thru the posts I see many comments that make no sense.

For example, how can you expect a power supply to be the problem when the problem only occurs in a small portion of the total circuit? Many other circuit portions from that same power supply operate with no failure.

With very high probability the problem is in a small region of the total circuitry. Changing from a DC relay to an AC has no advantage. But using sealed contact reed relays would have a great benefit in a dirty environment.

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[TimWaldner]

I had the same problem in a coal fired boiler control panel. One of the VFD driven fans would just shut off for no apparent reason. The problem was the relays; just like gar said. They were 10 or 15 amp GP relays. I replaced all the control relays with (3A max) gold plated bifurcated contacts . Problem solved.