Grounding Laser Exhaust

[Brian Leavitt]

There's a fairly sizable thunderstorm going here right now, which got me thinking... What would happen if lightning struck my laser exhaust fan?
The fan is in a steel enclosure on the roof which is 25 feet up and the tallest object that's really nearby. It's connected to metal ducting, which is connected to the metal laser bodies. The lasers are sitting on carpeted concrete. So what do you all think? Is there anything to worry about here?

[Kev Williams]

IMO there's always something to worry about with lightning nearby!

Safest thing to do with lightning nearby is power down the machines, or the whole house, and wait for it to pass.

Back in the 80's lightning hit this place, we think it hit the CB antenna but never did know for sure- It took out 3 stereo's, the microwave, 1 of 2 TV's, and the data board in the AppleIIe computer that ran my Concept 2000. Not sure exactly what was or wasn't energized by the hit, but it wasn't good! Then (true story) the first time my soon-to-be-and-still-is wife called me after we met a few days before. I had my 2 kids with me that day, and while on the phone a bolt of lightning hit. Like before, never found out where exactly but it was close enough that "it looked like a laser light show" according to my son, the four florescent tubes in a fixture in the living room lit up for about 5 seconds, all my stereo equipment lit up like a Xmas tree even though all of it was turned OFF, and my daughter, sitting in the middle of the living room, said she felt it 'tingle', and her arms were red as if sunburned. I was on a cordless phone and felt nothing, not sure why! Since that day the time delay hasn't worked in the stereo (a first-year Carver C2000 preamp) and the power button doesn't work, it's always on.

I Don't Like Lightning! If it hits something, there's no telling what it will or won't do. I can attest to some of what CAN happen!

[John Lifer]

I don't know how you could really ground it. Lightning will do what it wants. You could have a ground wire down to the ground, you could put another wire just before it comes inside. Doesn't matter. Lightning will follow its own path. I was hit about 20 years ago, hit second story nail sticking out of a roof joist. Blew out about 2ft if the joist. It travelled around some Christmas lights around the entire house, then down and jumped across to my phone line and into a computer, telephones, answering machine. Nothing else. Strange stuff. I'd shut down and wait it out.

[Keith Outten]

Disconnect your laser from the electrical outlet, your network, metal piping and any ground wires when there is lightning in your area. Anything that conducts electricity presents a danger to your machine.

[Lyle Cheredaryk]

Personally I would replace a section of the exhaust ducting with non-metallic tubing, either flexible or rigid, then ground the first section connected to the fan. Electricity usually takes the path of least resistance. Not always though. If you use a flexible section it also helps cut down noise from vibration. We have used it in doing duct work for many years.
Lyle

[Bill George]

Grounding helps. Years ago when I had my ham radio tower neighbors told me a couple times they saw lighting hit it. When I installed I drove a copper pipe ground rod in the hole for the base and connected to the tower steel with heavy #6 copper wires. Poured concrete around the base section in the ground. Static electricity builds up in the air (ionizing) before an actual strike the ground rod helps also to provide a "drain" for it, instead of your house or nearby tree.

[Brian Leavitt]

Thanks for the input, fellas. In the 13 years we've been in this industrial park I've never had a strike on the fan up there, and I never really even took it into consideration before recently that it could happen. I'm not sure how I would ground the ducting, though. From the roof, it routes above the drop ceiling and splits into three just above where the lasers are, then it comes through the ceiling and to the lasers. As far as I can tell, the only way I could ground that would be to drill through the concrete next to the lasers and punch a grounding rod through there. I think I may just call the HVAC guys who installed the system and see what they think.

[Keith Outten]

A ground wire is great for normal operation (Bleed Static Charge) but in the case of lighting strikes they are not effective. You want to totally isolate your laser engraver from everything when there is lightning in your area. You cannot afford to purchase a wire large enough to handle a direct lightning strike and a residential or light commercial ground rod will not work.

[Kev Williams]

Anything you do- grounding ductwork, the blower itself, or anything short of a radio tower like Bill mentions, is pretty much useless. I read a story years ago about lightning facts and myths, one myth being 'a car will protect you because the tires are rubber'. The author explaned 'a billion volt bolt of lighting that traveled 3 miles from the sky isn't going to be put off by 3 inches of rubber'... -what protects you is the metal roof. Just don't touch anything in the car!

A grounded radio tower is about the best protection you can get, very tall, very grounded usually. Not protection for the radio tower, but for the house and occupants connected to or next to the tower. It simply provides a path to ground for a lightning strike.

Your grounded blower or ductwork will also provide a path to ground, but right thru the building, exactly what you DON'T want! A bolt can travel sideways thru a building hitting people, things and can start fires.

The best protection is a lightning protection system, basically a lightning rod, a big ground rod buried in the ground, and really big cable to connect the two. And even then the protection is probably best described as 'better than nothing'

Another weird thing to be aware of in lightning storms, concrete-- because of the steel mesh or rebar that's in it.

[Bill George]

You want the bonding ground wire to be attached at the roof, not at the machine. I would contact someone who does lightning protection for a living. Lighting rods and grounds work.

[Brian Leavitt]

On my way in this morning I was kind of thinking the same things to myself. Why would I want to give lightning an easier path through the building? I'm going to look into a lightning protection company. I may just go up on the roof. Maybe there's already some kind of protection in place I don't know about. Only problem is the ladder to the roof is kind of coming away from the building right at the top. Not reassuring climbing up that thing.

Thanks again for the input.

[Bill George]

Correct, if the only ground the lightning charge finds is your electrical system that is where its going. Putting the ground wire on the sheet metal at the roof will help, but no 100% guarantee with lighting.