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Surge Protection Failure 7

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fosrich

fosrich

Electrical
Oct 8, 2020
3
We had a surge protection device fail, and injure someone with the shrapnel, minutes after being wired up by an electrician. The device may have been wired incorrectly by the electrician. The system is 480 VAC corner grounded delta. Below is an email from the manufacturer of the SPD. I believe what he's saying but I'm kind of confused with some of the device ratings. I assume there's a duration element with some of the ratings that I don't know. Maybe some of you that know more about these could help me understand the ratings. Also, he doesn't mention but the SCCR of the device is 200 (kA). How would that come in to play or not?

The device is an ICM Controls 531, see attached photos, I tried to attached two photos.

"When you connected the Neutral to your corner grounded Delta configuration, you put 480 volts across a 350 VAC rated TMOV. This will blow it sky high as you have seen. The Thermal protection on the TMOV will allow the TMOV to safely fail during a surge event when the limit of the TMOV is reached (50KA per TMOV). However, in your case with the Mis-wire, the current was not a fast acting transient but constant and way over the rating of the TMOV. No thermal protection was going to help that. The Outgassing of the TMOV pressurized the interior and popped the top cover off which likely prevented further issues. The ICM531 is designed to outgas in such an event but your extreme situation caused by the miswiring allowed more than normal outgassing which popped the cover off completely."

Thanks for any help, just trying to make sure I understand what happened.
 
 https://files.engineering.com/getfile.aspx?folder=72305930-0330-42be-bbc0-e33daa420fa5&file=ICM_Surge.jpg
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The surge protector is designed to deal with short duration high transient voltages by switching on and conducting the current to ground. Yours had a Maximum Continuous Operation Voltage (MCOV) of 350 V. With 480 V from line to ground (corner grounded delta), its MCOV was exceeded and it failed. It is not intended to protect against a continuous overvoltage in excess of its rating. When a SPD is applied to a system voltage well in excess of its MCOV, it will fail, often catastrophically, as in your case.

The "delta" ratings on the nameplate would apply to an ungrounded 480 V delta, not a corner-grounded system. My conclusion as a certified random Internet guy, is that the device was misapplied and you need one with a higher MCOV. I'd say at least 1.25 x 480 V.

I once heard an engineer who worked for an arrester division say that "arresters are a very simple product - no moving parts. And if it ever has moving parts, you need to get out of the way."

I hope the injury wasn't too severe.

Dave
 
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I have the following opinion for your consideration
1. I fully agreed with the learned advice by Mr dpc. "...The "delta" ratings on the nameplate would apply to an ungrounded 480 V delta, not a corner-grounded system. My conclusion as a certified random Internet guy, is that the device was misapplied and you need one with a higher MCOV. I'd say at least 1.25 x 480 V...".
2. "...the device may have wired incorrectly by the electrician..." is wrong to blame the electrician. It root cause is WRONG SPD selection. See Mr dps learned advice.
3. Suggestion: a) select a higher rated SPD say with Y rated L-N > 480V or 1.25 x 480V. b) Attention: following suggestion may need extensive study. Remove the corner earth, i.e. making it a simple D without any earthing. BTW replacing the SPD with a higher rating would be simple and cost little instead of removing the corner earthing which need costly study if at all feasible.
Che Kuan Yau (Singapore)
 
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From the ICM 531 installation instructions "...There will be a white wire which is only used in the Wye configuration and which needs to be capped off in the Delta configuration...".
And there is a diagram showing corner grounded delta as an option.

Looks like "may have been wired incorrectly" is a possibility.
 
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It sounds like the electrician wired it line to neutral configuration, where it’s only rated for 350V.

I agree, sounds like a miswire.

Casey

 
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RTFI?
Read The Free Instructions

--------------------
Ohm's law
Not just a good idea;
It's the LAW!
 
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