In 2019, my company lost 13 Allen-Bradley 5069-IF8 analog input modules over the course of several months. These losses always corresponded to lightning activity in the area (a common issue here in south Florida), but often did not correspond to direct hits on the facility or the loss of any other equipment. A few times we lost one or two transmitters as well when the strikes were more direct. All panels have upstream surge protection, so I think it's fairly clear the lightning was inducing surges from the field side, even when occurring over half a mile away. I was convinced these modules had a design flaw that was allowing this to happen so easily. Since that period time I've installed Phoenix Contact analog surge protectors on each AI circuit (part number 2906767). This completely solved the issue until last month, when we lost an additional module that had the field-side protection. Again, no other device was damaged. These SPDs are expensive, and it roughly doubles the IO cost for analog inputs if I were to bake the cost in to future designs. The protection is also not as complete as I thought since it happened again, although the failure rate is vastly improved. Has anyone experienced a similar issue or have any insight into this problem?
Lightning strikes damaging AI modules
- Thread starter EC Dan
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petersonra
Senior Member
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- Northern illinois
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- Semi-retired engineer
is the negative side of the power supply that feeds the transmitters grounded?
mikeames
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- Gaithersburg MD
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- Teacher - Master Electrician - 2017 NEC
I don't have experience with that but is an opto-coupler out of the question?
There are no external connections between the negative of the power supply and ground. Is that a common practice?
I actually tested two solutions, one was the Phoenix Contact part number above and the other was a 4-channel signal isolator. The signal isolator was a lot more expensive and cumbersome, and recently had a failure one of the channels, so I was pretty convinced the Phoenix Contact SPD was the way to go.
petersonra
Senior Member
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- Northern illinois
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- Semi-retired engineer
Yes
I haven't seen it since 24 VDC is generally not considered dangerous and isolation is usually desired, but my experience is somewhat limited. Would a ground connection to the 24 VDC common help or hurt in this case?
winnie
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- Springfield, MA, USA
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- Electric motor research
Something to check if you are having problems with nearby ground strikes damaging equipment:
Do you have earth electrodes that are not properly bonded together. As the strike is spreading through the ground, current can enter through one electrode, pass through your equipment, and exit through another electrode.
Jon
Do you have earth electrodes that are not properly bonded together. As the strike is spreading through the ground, current can enter through one electrode, pass through your equipment, and exit through another electrode.
Jon
petersonra
Senior Member
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- Northern illinois
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- Semi-retired engineer
I think what could be happening is some induction on the DC power supply when the lightning hits. Could be elevating the DC voltage well above the level the AI modules are rated for. If it is tied to equipment ground, the amount the voltage can rise above ground is limited. I think the isolation rating on the module itself is only about 500 V.
You might want to run this past AB. Get the product manager involved if you have to.
A lot of times I see equipment mounted poorly. For instance putting a level sensor on top of a tank. What is the tallest object? In this case a simple “mast” such as a stick of strut bonded to the tank or ground shields the sensor from getting hit.
Another issue I’ve seen is when the analog system is well grounded but the tank farm itself is not structurally grounded. Lightning would utilize the nearest good ground (the PLC system).
Another issue I’ve seen is when the analog system is well grounded but the tank farm itself is not structurally grounded. Lightning would utilize the nearest good ground (the PLC system).
We had the plant grounding system evaluated by a lightning protection systems company after these occurrences. They did find a few instances of >25 Ohms at ground rods, but did not comment on any potentially improperly bonded electrodes except to say "continuity was found between electrical components". Each SDS has one or two electrodes, and if there are two they are close together and bonded.
I did talk with AB in depth when this happened and they were basically no help. Among the companies I reached out to to get guidance, Phoenix Contact was the only one that really worked with me towards a solution. This is the first time I've heard it suggested that grounding the common might help, although what you're saying makes sense.
We do have a very tall SS tank with a radar level sensor on top. The sensor itself has not been damaged, but interestingly the AI module connected to this sensor was the module that was damaged in this latest incident. The tank is somewhat grounded, in that an agitator motor is at the top with an EGC, and the motor is bolted with all metals parts to the tank. I have to imagine if lightning actually did strike this tank, a burnt out AI module would be the least visible damage that would occur.
petersonra
Senior Member
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- Northern illinois
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- Semi-retired engineer
Who did you talk to at Allen Bradley? talking to the average tech support guy or some sales weenie is not going to cut it.
Is there an alarm contact or regular checking of the Phoenix SPDs? I believe they can only take a hit or two and then they're toast and need replaced.
We've had good success with them, but you have to make sure they are in good standing or the next surge will wipe out what it's protecting.
We've had good success with them, but you have to make sure they are in good standing or the next surge will wipe out what it's protecting.
It was an applications specialist. I was unfair when I said they were no help. Looking back through our correspondence, they recommended doing the site ground evaluation (which I had already initiated) and surge protection/isolation on the individual circuits. But the Phoenix Contact specialist I talked with really went the extra mile to help me identify a specific product and to integrate it.
These have an indicator on them, and when the AI module was lost I checked the block of SPDS but none of them were any different. The manual isn't super clear about this, but I believe that empty rectangular hole on the front should show orange or red when it has popped.
Lost an another AI module last night at the same location as the previous loss. All the analog signal circuits are contained within the building except for one that goes to the top of an outdoor stainless steel tank to a level transmitter. Although the SPDs are not giving an indication of failure, I replaced the one protecting the tank level transmitter since it's the most likely source of lightning induced surges. I did some testing on the removed SPD but couldn't determine any signs of failure (I would except some continuity to ground when it fails). If another module gets taken out I will try grounding the common side of the DC circuit.
Edit: My assumption of expecting continuity to ground may be mistaken. The failure mode could be that it is no longer able to make continuity to ground during a voltage surge.
Edit: My assumption of expecting continuity to ground may be mistaken. The failure mode could be that it is no longer able to make continuity to ground during a voltage surge.
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petersonra
Senior Member
- Location
- Northern illinois
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- Semi-retired engineer
Most likely the mov would just open up so you wouldn't see any continuity at all
These are using gas discharge to operate, so I'm thinking based on what bwat said above that maybe the gas gets less sensitive or depleted after one or more activations? I'm waiting to hear back from Phoenix Contact.
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