Ethernet Surges and Transients

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Thread Starter

Robert

We're having an ongoing issue with a project and I was curious if anyone as ever seen something like this before. Our contol panel which consists of 4 VFDs (300HP, 100HP, 30HP, and 10HP) all controlled by a PLC connected to HMI. All components are connected by ethernet cables which communicate digitally. Normally any incidents we have are isolated and normal (meaning they are infrequent and happen due to age). However, on this recent project we have noted numerous issues and have had to replace VFDs, PLC, power supplies, communication cards and the HMI all due to issues on the low voltage side.

The only thing different about this project versus every other project we have encountered is the customer has their SCADA system connected to our ethernet hub in order to remotely read alarms and status. It has been brought to my attention that this CAT5/6 cable could be sending transient voltages to our system however I wasn't sure that would cause as much damage as it has. I always thought this was the sort of thing for filtering noise.

My question is this: Has anyone seen an industrial application where a single incoming ethernet cable was the cause of internal damage to their system (similar to what we believe is happening with ours?) If so, what was done to protect the system? I have seen a number of devices that claim to protect the system but I don't know if they will actually work.
 
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Curt Wuollet

Twisted pair Ethernet is usually pretty immune to that sort of thing because it has transformer isolation built in. And I would expect their SCADA to become a smoking wreck before that much industrial gear.Still, stranger things have happened. I would look at grounding and power issues first. Especially if you are replacing power supplies. I have seen this sort of thing happen in gear where the power supply negative is not grounded and it floats around taking things outside their voltage limits. Including one system where they let the power supply float because "we get a line fault when we ground it". Hmm.....

Regards
cww
 
Thanks for the response. Very helpful.

We have added some CAT5 surge supprssors and isoltaors. Hoping that helps if its the problem.

The main power we get is 480V whereas all the problems we have seen are on the low voltage side. I would think that the power supply would be an issue if it was taking out some of the larger stuff but its not. As for grounding, I think (keyword...think) we have that covered as we actually added extra grounding rods for this. With that said, it doesn't hurt to double check all grounding points.
 
We added something similar just recently in hopes that will do the trick. Of course, only time will tell.

I'm curious...why did you install them for your application?
 
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