SLC 5/05 Fault

[Cotton]

I'm randomly getting a 1F5A (Hardware Interrupt) fault on my SLC 5/05 PLC. AllenBradley stated it was a grounding issue, however the equipment has been in operation for 6 weeks before this occured. I have added another ground to the cabinet for the PLC racks and DC power supplies, with no effect. Has anyone ever seen this fault and how did you correct?

Any help will be appreciated.

 

[Skogsgurra]

They always tell you it is a ground problem. Or a mains problem. And - in fact - it sometimes is!

What does your ground look like? Another wire to same point as your first ground? And how good is that ground?

Any frequency inverters in the vicinity?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Cotton]

The 1st ground was suspect. The contractor did not bond the control cabinets together, nor did they bond the panel back panels to the frame. The PLC racks were grounded to the back panel, underneath the screw that secures a rack.

The second ground was brought off of a building column ground cable and attached to the PLC rack and DC power supplies.

Yes we do have inverters in the vicinity, however they are located in the adjacent panel. This control panel is composed of 2 panels, bolted together. In the left section is all the 480V mains, heater solid state relays, inverters and motor breaker & contactors and 9 inverters. In the right section, 3 PLC racks, DC power supplies and I/O terminal blocks.

 

[gcaudill]

Are the inverters grounded via the enclosure sub-panel or is there a an actual ground conductor? In my opinion, all devices in an industrial control panel should never utilize the sub-panel or enclosure as the grounding path. To do so opens the door for common mode noise and stray voltages.

Instead, all devices should have a dedicated grounding conductor to a ground bus bar. The ground bus bar should be solidly connected to the building electrical distribution ground grid.