Lightning makes my saw blade move?

[Trent Shirley]

Am I wrong in thinking that these magnetic switches do not actually use a magnet to engage and require a physical push? I would think that once pushed the power activates an electromagnet that holds the switch closed and if power is disrupted then the circuit is broken, the electromagnet no longer produces a field and the spring loaded switch opens.
If my assumption is true then no matter how strong a magnetic field you get from the lightning it does not close the contacts on the physical switch and therefore there is no power to the saw.

I imagine the magnetic field generated by the lightning caused induced current in the motor windings causing a minor twitch to the blade but could never be strong enough to spin the blade fast enough to cause serious damage.

[Jason Roehl]

What about the magnetic starter become just charged enough to act as a capacitor, inducing a small amount of charge flow on the other side of the contacts in the starter, thus causing the blade to move a slight amount?

[Dan Hintz]

Am I wrong in thinking that these magnetic switches do not actually use a magnet to engage and require a physical push? I would think that once pushed the power activates an electromagnet that holds the switch closed and if power is disrupted then the circuit is broken, the electromagnet no longer produces a field and the spring loaded switch opens.
If my assumption is true then no matter how strong a magnetic field you get from the lightning it does not close the contacts on the physical switch and therefore there is no power to the saw.

Correct...

[Trent Shirley]

What about the magnetic starter become just charged enough to act as a capacitor, inducing a small amount of charge flow on the other side of the contacts in the starter, thus causing the blade to move a slight amount?

I have never read details about how these work but my assumpton has always been that it is not a starter but just a capacitor storing a little extra power for the next spin up to give the motor a little extra juice on spin up. But a capacitor charges as current is drawn across the circuit and does not discharge until it has a ground/return path so the lightning it not likely to either charge or discharge the capacitor.

Anytime a magnetic field passes through copper wire it induces current so a lightning strike producing a strong magnetic pulse can cause induced current in all the wiring of the saw but could not cause it to actually turn on the saws connection to the AC power. The magnetic pulse would have to be very strong and very close to have any effect though as magnetic fields dissipate very quickly with distance. It is recommended that people using hair dryers hold them about 4 inches from their head as the magnetic field generated by fan motor disipates within a few inches. Magnetic fields are suspected to cause long term harm to health but they dissipate so quickly that it is not generally a large risk except for large producers near your head or living right by large power stations and high voltage transormers. Whether there is any real risk is constantly debated but statistics show a lot of birth defects and developmental problems in children living near high EM fields.

Playing devils advocate on the saw magnetic switch issue, it is possible that a mechanical failure in the switch leaving the switch without any spring tension holding it in the open position could result in it powering on if enough current was induced in the circuit causing the electro-magnet in the switch to enage and pull the switch into a closed position. The odds are astronomical for something like this happening but I never discount possibility as it will always come back and kick your behind when your not prepared.
I once replaced my kitchen stove, first shutting off the only 220v breaker in the house then laying the stove down and going at it with a ratchet to release the terminal lugs of the power line. My ratchet came into contact with the body of the stove and sent a nice shower of sparks across the room and took a bite out of the bottom of my socket wrench. I spent some time investigating why there was power in the circuit even though the breaker was off and eventually found that one of the two 30 amp ganged breakers did not in fact disconnect power in the off position so there was still 110v going through the stove. I have never heard of a breaker failing that way but it taught me a lesson about making assumptions with electrical power and always using my tester before working.

[Wes Thom]

I am going with your theory. Its an unexplained possibility. I'll lower the blades in a storm. It is freaky to see that blade move......

First off, kudos for noticing something. And then having the curiosity to ask such a question. Important because I will later explain why you have described a serious problem.

Will a millimeter gap in a switch stop what three miles of sky could not? Of course not. A lighting strike could easily arc across that gap. Create a plasma path. And be done in microseconds. That is not enough energy or enough time to move a saw blade. But may have created plasma just like an inert gas becomes a conductor inside a fluorescent tube.

Once a fluorescent tube has no current, the plasma turns to gas. So tube conduct a low voltage current to maintain that plasma and to create light. Your switch did same during at least one cycle of AC power. Now it is not a microsecond current through the switch. Now a tens of millisecond (or longer) current that has higher energy maintains that plasma. The switch acts like it was closed.

Well, AC power eventually goes to zero. That is when the tiny plasma path might return to gas. Fortunate for your hand.

That plasma path and AC electric flowing through it is not your concern. You had surge energy inside and hunting destructively for earth. Fortunately some of the best protection inside every house is that inside every appliance. This time the surge was too tiny to do damage. But you were warned (because you took notice). Since you did not have a properly earthed 'whole house' protector, then energy was inside and hunting. Protection means that energy must never be inside. This time, it was too tiny to do damage. But learn from what you saw. Any wire that enters without first connecting to single point earth ground (either directly or via a 'whole house' protector) means your only protection is that inside every appliance. Eventually (typically once every seven years) a surge will be large enough to overwhelm protection inside some appliances.

Your cable connects directly to earth - best protection if the cable company did as required by Federal regulations and code. Your telephone wires have always had a 'whole house' protector installed for free. But your AC electric has nothing is you did not install a 'whole house' protector from more responsible companies such as Square D, GE, Intermatic, Siemens, ABB, or Leviton. A Cutler-Hammer solution sells in Lowes and Home Depot for less than $50. Options are many. Best protection costs the least amount of money - about $1 per protected appliance. And, of course, earthing must be upgraded to both meet and exceed post 1990 code.

BTW, induces currents from lightning do not have enough energy to move that. At best, energy content is only sufficient to push milliamps through an NE-2 neon glow lamp. To get that blade to move meant a current entering inside the building.

[Dan Hintz]

First off, kudos for noticing something. And then having the curiosity to ask such a question. Important because I will later explain why you have described a serious problem.

Will a millimeter gap in a switch stop what three miles of sky could not? Of course not. A lighting strike could easily arc across that gap. Create a plasma path. And be done in microseconds. That is not enough energy or enough time to move a saw blade. But may have created plasma just like an inert gas becomes a conductor inside a fluorescent tube.

Once a fluorescent tube has no current, the plasma turns to gas. So tube conduct a low voltage current to maintain that plasma and to create light. Your switch did same during at least one cycle of AC power. Now it is not a microsecond current through the switch. Now a tens of millisecond (or longer) current that has higher energy maintains that plasma. The switch acts like it was closed.

Well, AC power eventually goes to zero. That is when the tiny plasma path might return to gas. Fortunate for your hand.

That plasma path and AC electric flowing through it is not your concern. You had surge energy inside and hunting destructively for earth. Fortunately some of the best protection inside every house is that inside every appliance. This time the surge was too tiny to do damage. But you were warned (because you took notice). Since you did not have a properly earthed 'whole house' protector, then energy was inside and hunting. Protection means that energy must never be inside. This time, it was too tiny to do damage. But learn from what you saw. Any wire that enters without first connecting to single point earth ground (either directly or via a 'whole house' protector) means your only protection is that inside every appliance. Eventually (typically once every seven years) a surge will be large enough to overwhelm protection inside some appliances.

Your cable connects directly to earth - best protection if the cable company did as required by Federal regulations and code. Your telephone wires have always had a 'whole house' protector installed for free. But your AC electric has nothing is you did not install a 'whole house' protector from more responsible companies such as Square D, GE, Intermatic, Siemens, ABB, or Leviton. A Cutler-Hammer solution sells in Lowes and Home Depot for less than $50. Options are many. Best protection costs the least amount of money - about $1 per protected appliance. And, of course, earthing must be upgraded to both meet and exceed post 1990 code.

BTW, induces currents from lightning do not have enough energy to move that. At best, energy content is only sufficient to push milliamps through an NE-2 neon glow lamp. To get that blade to move meant a current entering inside the building.

I can't decide on what you're trying to say. Your second/third paragraph suggest arcing across the switch's unclosed contacts, but as I said earlier, if that was happening the amount of damage would be severe... you'd know it was happening. To top it off, he has seen this before, and that kind of cumulative damage would be quickly noticed via non-working equipment in the shop (and more likely, electronics in the home long before the beefy equipment failed). Any surge strong enough to ionize the air gap (i.e., plasma) would not go unnoticed.

[Phil Thien]

We're spending roughly a grand, in our new house, to get a "whole house surge protector."

Whole-house surge protectors should only run about $150 to $250, depending on brand/features. Installation cost should be negligible because they install it when they wire the panel.

I'd find out what they're installing for $1000 to make sure you're getting your money's worth.

[Dennis Ford]

A lot of guessing going on here. If the movement came from an induced current (seems reasonable to me), unplugging the machine will not prevent it from happening again. If a surge was strong enough to jump across the motor starter, I think some smoke would have been released (probably a lot of smoke).

[Wes Thom]

I can't decide on what you're trying to say. Your second/third paragraph suggest arcing across the switch's unclosed contacts, but as I said earlier, if that was happening the amount of damage would be severe...

Damage would not exist. You would not know a lesser transient existed. Protection inside all appliances would have made that transient irrelevant. The transient would have enough voltage to create that plasma. But be too short and have insufficient current to cause any damage. Don’t confuse this lesser transient with a future and more severe one that will do damage. This lesser transient was a warming that no one would have known had blade movement not been observed. It explains a one or two cycle application of AC power to that motor necessary to move the blade.

If an induced field or the transient strike alone was sufficient to move that blade, then extensive surge damage would have existed. Had the motor been unplugged, the plasma could not form across a millimeters gap in a power switch.

[Bill Huber]

If the movement came from an induced current (seems reasonable to me), unplugging the machine will not prevent it from happening again.

I guess that I just can not see it, if you unplug the machine how in the would would a lightening hit on the line casue it to happen again. The lightening would have to strick the cord laying on the ground to do anything. If the lightening hit the saw then I guess it could do it but I am sure it would take out the saw at the same time.

[Ken Fitzgerald]

If the machine is unplugged, for a lightning strike to induce a current in the motor and cause the motor to turn would require the lightning bolt to be awfully, awfully close and I'd be worried about flashburn if I was in the area.

[Charles Krieger]

I have a different theory on why the connector with thumb size conductors melted. When the lightning struck a mile away it possibly ionized the air around an exposed, metalic, area of the cable. Ionized air becomes a good conductor which possibly created a short between two legs of the power. Once shorted the power source supplied enough current to heat the point of most resistance, the connector. I think it is unlikely that unless it were directly struck by the lightning that the connector would fail from the energy of the strike. As has previously been mentioned lightning does strange things so I rule nothing out!

[Ken Fitzgerald]

Charles....the parts that melted were inside the insulation of the connector. The crew of the crash truck were sitting maybe 50' away on the same hardstand and observed the lightning strike. If as you say it was an air ionization, it would have been visible to them. I would expect ionized air to be very visible too!

[Ken Fitzgerald]

At NAS Meridian, MS thunder storms, and lightning were a frequent event starting very early each New Year. Lightning striking the ground and taking out power cables for AC power to the radar and other flight navigational aid electronics including runway lights was a fairly frequent event. I worked air traffic control maintenance and yet the civilian public works folks were responsible for maintaining and repairing those buried cables. While there, the public works guys came to us with a problem. They couldn't locate a damaged buried cable along the runway. Some of us put our heads together and we developed a "shop made" timedomain reflectometer using a known length of coaxial cable, a pulse generator and an oscilloscope. We used it often enough that we could pinpoint a damaged spot in buried cable...power cable...signal cable...video cable (radar) within 10'. Now you might say 10' isn't accurate but when you consider there could be 3 miles or 15,000 feet of cable between the air operations building and the bad spot in the cable, 10' is pretty good considering it was the early 1970's and what was available for test equipment then and the cost of same. The civilians at public works using a backhoe to dig considered 10' a pin point.

[Wes Thom]

I think it is unlikely that unless it were directly struck by the lightning that the connector would fail from the energy of the strike.

Lightning is capricious when a basic electrical nature of the beast is not first learned. For example, a direct lightning strike is maybe 20,000 amps. How many amps can an 18 AWG (ten amp lamp cord) carry? Something less than 60,000 amps. Lightning is not the high energy event so often believed in myths. Even that small wire can conduct a direct lightning strike without damage.

More often, damage is created by other high energy sources. For example, a west coast radio station was severely damaged when lightning struck incoming AC wires. Due to a failed installation, lightning formed a plasma connection from a 33,000 volt primary wire to low voltage wires into the transmitter. Lightning did not provide that high energy. Lightning only created a path - a temporary short circuit. Damage was from the follow-through current sourced by an AC utility.

Colin Bayliss describes in "Transmission & Distribution Electrical Engineering" what many do not learn:
> Although lightning strikes have impressive voltage and current values (typically
> hundreds to thousands of kV and 10-100 kA) the energy content of the discharge
> is relatively low and most of the damage to power plant is caused by 'power
> follow-through current'. The lightning simply provides a suitable ionized discharge
> path.

A trivial surge too tiny to harm any appliance can create a plasma path across millimeters inside a switch. Lightning would not cause the blade to move. But one or two cycles from a high energy source (AC electric) might be enough to more that blade.

Numbers explain how a temporary plasma path could be created when a surge, too tiny to overwhelm protection inside all appliances, does create a tiny and temporary conductor inside a switch.