need help from electrician, EE , psychiatrist

[John Bush]

I finished planing a bunch of pine and as I was scooting the planer(5hp-220V) into it's resting spot, the frame made contact with the metal DC duct, big spark/pop, tripped the breaker(50A--for welder too) in the shop subpanel and the main house panel(50A) 160 ft. away. I have ~~10 ft of vinyl flex pipe from planer to metal DC main run. I was pushing the planer by hand and didn't feel even a tingle, but I almost did tinkle. Is it remotely possible static build up could have caused this? I can't imagine there would be enough juice to pop a big breaker like that, but don't know the physics of electrons in DC current mode. Hasn't happened before.

I now have issues with WWing equip. that plugs in--shrink's comments would be appreciated as well. Thanks, JCB

[Ken Fitzgerald]

John,

Did you see a spark fly?

The metal ductwork..is it attached directly to the DC?

Here's the thing. The ductwork connected directly to the DC should be at the same ground potential as the DC. So if the DC is 220 vac..there should be 2 - hot leads and 1 ground attached to it. So it's body/metal housing should be grounded and so should the ductwork.

Now the planer...same scenario. It 's 220 vac.....2 hot leads....1 ground....it's chassis/body should be grounded.

Therefore, there shouldn't be a potential difference between the ductwork and the planar chassis.

The plastic tubing can build a charge but you said you pushed the planar chassis against the DC ductwork....

Static discharge voltages can easily be in the tens of thousands of volt range.....

Do you have a multimeter?

It would be interesting to check the grounds to both the planer and the DC.....and then check at the end of the ductwork where the tubing attaches ...check it for ground......

[Chris Strizver]

Definitely *NOT* static. My guess is that your metal ductwork is energized somehow. You can verify this by taking a volt meter reading from the metal ductwork to ground prong of any outlet that is within reach. I would recommend not touching any metal while your breakers are on.

[Dan Friedrichs]

Definitely *NOT* static. My guess is that your metal ductwork is energized somehow. You can verify this by taking a volt meter reading from the metal ductwork to ground prong of any outlet that is within reach. I would recommend not touching any metal while your breakers are on.

+1. Either the planer or the ductwork is not properly grounded.

[JohnT Fitzgerald]

Also +1

Are any of these items powered by a subpanel? the neutral/ground setup in a subpanel might be improperly bonded - they should be separate and bonded only at the main panel.

[Chris Strizver]

+1. Either the planer or the ductwork is not properly grounded.

The planer is properly grounded. If it wasn't, we'd be at best getting a hospital report... The ductwork isn't an electrical part, so grounding it wouldn't normally be done.

Does your ductwork share mounting brackets with electrical conduit or otherwise come in contact with conduit? You could have wires that got scraped while pushing through. A particular machine doesn't seem to be likely...you'd need a short to a case, a ground failure on that machine, plus a direct connection to the ductwork. A scraped wire creating energized conduit seems more likely.

[Ken Fitzgerald]

Chris,

Not necessarily. You can hold a hot wire as long as you aren't grounded.

But...You are probably right.


There is a ground problem.........

I have seen some really strange static problems too and you can't rule them totally out as a possible cause but the most likely problems....bad ground to either the DC or the planer...

[David Epperson]

If there was a GFI (Ground Fault Interrupter) Breaker involved, then a large static burst could very well trip this breaker, I've seen 200 amp @ 13,800V Subpanels get tripped from less. But it should not have tripped a standard load limiting circuit breaker.

[John Coloccia]

Without getting into a treatise on this, don't assume that anything is safe because you didn't feel a tingle. If you where touching another piece of grounded metal, you may have felt a heck of a lot more than a tingle.

It does certainly sound like something is really wrong, and you need to be extremely careful with what you do and what you touch until you figure it out. Don't count on your luck not running out. If it turns out to be nothing (unlikely), then fine, but until you know that for sure you need to assume that EVERYTHING in your shop that's plugged in is energized and dangerous. If it's a general grounding problem somewhere, you can't even assume that just flipping off the breakers will make it safe. If the ground has broken and shorted with a hot somewhere, then everything that's grounded is now hot, and who knows which breaker is the right one to kill it?

Don't dismiss that. When I moved into my current house, the fan in the bedroom stopped working a few weeks after we moved in. When I got around to debugging it, I found that the romex was DRILLED through. It must have happened when they built the house, and finally, 10 years later, it shorts out. This was a VERY dangerous situation, and it's a good thing I had my wits about be as I tracked it down. The fan's chassis was energized. One stupid move would have been a serious mistake.

[John Bush]

Thanks for all the info. I'll do some investigating, call my electrician, make an appointment with a shrink, and make sure my insurance is up to date so my widow can start living the high life!

[Dan Hintz]

For future reference... normal breakers work via heating of a bi-metal strip. Even at tens of thousands of volts, a static discharge simply does not have the current or longevity to trip a normal breaker. Also, that current wouldn't flow through the breaker, it would flow from whatever had the charge down the neutral or ground wire, not the hot (which is what the breaker controls, or two hots in the case of 240V).

[Ken Fitzgerald]

Dan,

I have seen the closest thing you can see to St. Elmo's fire without seeing the real thing.....4 times in one morning. You can't always predict what static will do. I saw it.

[Rod Sheridan]

Either the dust collector, planer or your receptacles have a wiring problem.

One of them is grounded properly, the other has an energized structure which means a wiring mistake probably.

If either had been properly grounded and developed a line to ground fault, the breaker would have tripped when the machine was running.

If you have an ohmeter, unplug the planer and measure from the ground pin of the plug to the planer bed. You should have under 2 ohms resistance.

Same for the dust collector, measure from the ground pin to the dust collector and you should have less than 2 ohms resistance.


Start there and let us know what you find.

regards, Rod.

[Andrew Joiner]

Thanks for all the info. I'll do some investigating, call my electrician, make an appointment with a shrink, and make sure my insurance is up to date so my widow can start living the high life!

John, Your course of action sounds good and my laughter after reading it felt great!

[Dave MacArthur]

Good read.
I thought of this thread today while shopping... Walking around the grocery store, concrete floors and wearing some Cabela's sandals (leather with rubber soles), I was getting HUGE shocks every time I touched anything. Didn't matter what it was, even items on shelves, grabbed some artichoke hearts in a can and ZAP. Wierd thing is, I've never had that happen before... I'd think the grounding characteristics of rubber soled sandals I was wearing would be the same as all the other shoes I wear just about, weather was the same... but SOMETHING was letting a big static charge build up while walking around the store.

About the third big shock, like I was my own portable van der graff generator, I thought of this thread and NOW I understand your consternation totally!

The wife's birthday dinner did go off without a hitch though.