# Questions on generators and lightning



## rgm1982 (Aug 4, 2013)

On film sets in the event of a lightning storm safety protocol is to shut down the generator immediately - running the genny when there is lightning is considered even more dangerous than having lights up on stands, even if all the lights are safely set up inside a building the genny must be powered down. I've always wondered why that is? Does something about the generator producing it's own electricity somehow attract the lightning?


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## José_Fuentes (Aug 8, 2014)

As far as I can tell, there's no difference regarding lightning due to the generator powering itself and the loads. If the electrical system is safe from lightning, for instance, if it's completely indoors with no conducting path to the outside (Apart from the earth/soil, of course), then there's no reason to shut it down. The only exception is radio equipment, which may pick the high electromagnetic noise and the powerful electromagnetic pulses from the thunderstorm may endanger it.

On the other hand, if the generator is connected to the grid or part of the system it feeds is outdoors and prone to be hit by lightning, then it makes sense to *disconnect* it (Not only shut it down) and ground *all* the conductors. This way if there's a lighting strike in a conductor most of the energy will pass directly to earth.

As far as I can tell, simply shutting down equipment won't protect it from lighting. Lighting is dielectric breakdown of kilometers of air, and won't have any problem passing through an _open_ switch or relay to get a path to earth through an electrical apparatus, should it hit a normally hot wire (Even if it's unenergized). Furthermore, most appliances are electronic and are keep a part of their electronics powered even when ostensibly powered off. This is the system responsible for receiving the power up input from the user (Button push, etc.) and activating the device for the intended function, and also to keep the real time clock running and the LEDs glowing. There's no benefit in shutting down such a device in a thunderstorm AFAIK, because those electronics could be damaged in the event of a lighting strike, and the whole device would be rendered unusable.

My advice for lighting protection is to shut down all devices and disconnect the conductors that feeds them (Physically disconnecting the cables, not just setting a switch to _off)_, then ground all conductors; if downtime is not acceptable, devices should be protected in advance with an UPS and use the same procedure in the case of a thunderstorm, but keeping devices powered by the UPS battery (Or flywheel, Diesel fuel, fuel cell, etc.) while the thunderstorm lasts.

Regards.


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## Meadow (Jan 14, 2011)

rgm1982 said:


> On film sets in the event of a lightning storm safety protocol is to shut down the generator immediately - running the genny when there is lightning is considered even more dangerous than having lights up on stands, even if all the lights are safely set up inside a building the genny must be powered down. I've always wondered why that is? Does something about the generator producing it's own electricity somehow attract the lightning?


I have no idea. And no it doesn't attract lightning.


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## macmikeman (Jan 23, 2007)

Brilliance of safety officers and regulation writers.


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## Meadow (Jan 14, 2011)

macmikeman said:


> Brilliance of safety officers and regulation writers.


I've actually read on the internet that some people are afraid of running their air-conditioner or pool pump during a storm because increases the chance of those getting hit by lighting under those conditions.


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## rgm1982 (Aug 4, 2013)

The electrical system is not safe from lightning, these are outdoor only, diesel powered portable generators, typically either tow or tractor mounted plants, usually 500-2000 amps, smaller ones about 6' high, large ones up to 12'. They are always outside. Lights might be either set up inside, outside, or both. Main feeder cable, usually 4/0, runs from the genny to one or several distro boxes, then breaks out from there to power the lights. I've just always wondered about the safety protocol because common sense wise it never made sense to me - they always make it a point to turn off the large genny first and worry about lights high up on metal stands later which seems more dangerous, and they never seem concerned about disconnecting the cable which is capable of carrying current and surrounding the entire set...sometimes they will still power a few things on smaller putt putt gennies (2000-6500 watt, usually of Honda make). They tell me it's standard protocol and I'm just following orders so I take it for granted that they know why they're doing, but in my current position I'm the one in charge of all that and would like to have a better idea of why safety protocol is what it is or otherwise know of a better solution to keep things safe.


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## dmxtothemax (Jun 15, 2010)

It's just another urban myth !

View attachment 38304


:thumbup:


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## bobelectric (Feb 24, 2007)

It's a Union thing. Maybe because of poor grounding.


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## Bad Electrician (May 20, 2014)

rgm1982 said:


> they always make it a point to turn off the large genny first and worry about lights high up on metal stands later which seems more dangerous, a.



I do believe they have it bass ackwards, those light stands are more likely to be hit, that a lower generator. 

The general rule is a higher metal structure is more likely to be hith that anjacent lower metal objects.

THOUGH lightning can and will do what it wants.


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## Big John (May 23, 2010)

Yeah, this is safety-nazi BS. If the risk of lightning strikes is severe enough to start disconnecting and shutting off equipment, then it's severe enough to simply stop production and wait for the storm to pass.

Some places we work have requirements that we can't be in their substations if there has been a lightning strike within 25 miles.


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## Bad Electrician (May 20, 2014)

Big John said:


> Yeah, this is safety-nazi BS. If the risk of lightning strikes is severe enough to start disconnecting and shutting off equipment, then it's severe enough to simply stop production and wait for the storm to pass.
> 
> Some places we work have requirements that we can't be in their substations if there has been a lightning strike within 25 miles.


When I did MCI work their standard was to transfer to generator if there was the slightest hint of a storm. They had no faith in the utility.


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## Big John (May 23, 2010)

Bad Electrician said:


> When I did MCI work their standard was to transfer to generator if there was the slightest hint of a storm. They had no faith in the utility.


 There's an AOL server farm in Maryland (or at least it was AOL back in 2000) and we were there to provide support because they were terrified of Y2K causing grid disruptions so they put the whole place on emergency generator power until they were sure the grid was stable. 

Double-time-and-a-half to raid their New Years Eve party buffet. :laughing:


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