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Author Topic: Is it just me or is there some really dangerous stuff going on here...  (Read 4259 times)

Mike Sokol

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Re: Is it just me or is there some really dangerous stuff going on here...
« Reply #10 on: March 12, 2014, 05:55:55 pm »

If the neutral and safety grounds are connected at the generator (or power source) and the drill is dropped in the water (or audio gear fails), then the circuit protection would trip.

Well, if the isolated transformer or generator (really the same thing) have the neutral and ground bonded together, but no earth ground rod connection, then dropping a drill in the water WILL NOT cause the circuit protection to trip, especially if it was a double-isolated drill without a ground wire. Instead, the transformer or generator neutral-ground bond and anything connected to it will become energized above earth potential and present a shock hazard. Now in a perfect world, a GFCI on the circuit feeding the primary failure should trip, thus protecting the secondary person in the mix. Remember, the GFCI feeding the secondary circuit isn't in the mix since the GROUND wire is what's energized. And we all know that GFCI's are often bypassed for iive shows due to nuisance tripping. That's why hot-grounds are so dangerous. There's nothing to disconnect you from them, no circuit breaker or GFCI or even a power switch. That's because according to code there must be no interruption of the safety ground back to the service panels G-N-E bonding point. And that's exactly what's missing from the isolated transformer scenario in the initial post.

I've thought about mocking this up and gathering some data for a demonstration, which I think would be very interesting. My plan was to do this with a generator once Honda supplies the EU2000i for my experiments. I can also try it with an isolation transformer and show that as well.

Getting interesting, isn't it?  ;D
« Last Edit: March 12, 2014, 05:59:00 pm by Mike Sokol »
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BobWitte

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Re: Is it just me or is there some really dangerous stuff going on here...
« Reply #11 on: March 12, 2014, 07:51:24 pm »

Ok, got my mind wrapped around that. So, awhile ago there was a discussion about whether generator needed a ground rod? Sounds like it should always have one. My next concern is that the portable stage the "city" provides - it is a trailer that opens up to a stage, needs the metal stage itself to be grounded - hopefully is via the power connection, ground to chassis to the generator. If not, then that could float even with a ground rod at the generator….. Very interesting. We bought the Fluke voltage detector (name escapes me - volt alert?) to check power, guest gear, etc. but the stage continuity to ground can be checked with an ohm meter I assume?


Now, to explain that to the city crew that drops off the generator and barely know how to start it….


Thanks
 

Mike Sokol

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Re: Is it just me or is there some really dangerous stuff going on here...
« Reply #12 on: March 12, 2014, 08:30:52 pm »

Very interesting. We bought the Fluke voltage detector (name escapes me - volt alert?) to check power, guest gear, etc. but the stage continuity to ground can be checked with an ohm meter I assume?

While you can use a Fluke VoltAlert (or similar Non Contact Voltage Tester) to find a "hot" metal stage. It will not detect one that's just floating, but not grounded. The fall-of-potential testers I have uses a short grounding rod about the length of a screwdriver. So sticking a screwdriver in the ground and measuring between it and the stage should give you a pretty low reading, typically between 25 and 100 ohms. Now remember that you can't have any power applied to the stage during this test since that could blow up your ohmmeter. However, measure it for AC voltage first. If there's more than a volt or so difference between the stage and your grounded screwdriver, I would get very suspicious of the grounding. As I've posted on other threads, even an overhead high-tension power line can induce voltage in an ungrounded stage. So I expect there will be SOME residual AC voltage on an ungrounded stage. But I'm not sure exactly what the "normal" voltage would read to a grounded screwdriver. I do know that if your stage is 40 volts AC above ground it will cause a standard sensitivity Fluke VoltAlert to beep/flash, and that a 40 volt shock to wet feet could be deadly.

More to think about, but I believe that ALL portable generators should be earthed to a ground-rod, and have one point of ground-to-neutral bonding. That's how I've always done it for concert power, and that's how I interpret the code. Don't confuse this with the NEC allowance of a floating neutral on the generators under 5 KW. Anything over 5 KW is supposed to be G-N bonded at only ONE point, which can be inside the generator itself, or inside your CB-distro panel.  Same goes for an isolation transformer, except in this case you carry the neutral and ground from the main service panel through your "isolated" power transformer. And yes, they need to remain separated there since the incoming service panel performs the single-point G-N-E bond.

BobWitte

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Re: Is it just me or is there some really dangerous stuff going on here...
« Reply #13 on: March 12, 2014, 09:16:03 pm »

100% agree. Now to convince the city folks with there 55KW diesel Wacker generator that a ground rod is needed. I should find a Wacker owners manual. I assume that the requirement would be in it. They do not understand the unit at all. I have made adjustments on it when the voltage control was set to its lowest setting and we were having issues with power.


Anyways - this forum is awesome!

Mike Sokol

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Re: Is it just me or is there some really dangerous stuff going on here...
« Reply #14 on: March 13, 2014, 12:54:38 am »

100% agree. Now to convince the city folks with there 55KW diesel Wacker generator that a ground rod is needed.
Remember that before you drive any ground rod(s) you need to check for any underground utliities. Of course if this is a city crew they should know already, correct?  ;D

BobWitte

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Re: Is it just me or is there some really dangerous stuff going on here...
« Reply #15 on: March 13, 2014, 08:39:37 am »

Remember that before you drive any ground rod(s) you need to check for any underground utliities. Of course if this is a city crew they should know already, correct?  ;D


They should, BUT I will fully inform them of what they should do.... We place the stage the same place for 5 different Tuesday nights so this should also help them put the stage in the same location every time.

Keith Broughton

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Re: Is it just me or is there some really dangerous stuff going on here...
« Reply #16 on: March 13, 2014, 08:55:06 am »

Having followed this thread, it seems that even when using a small, portable Honda 3000 watt genny, a ground rod would be a good idea.
I don't see any ground connection point on these small gennys.
Thoughts or experiences?

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BobWitte

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Re: Is it just me or is there some really dangerous stuff going on here...
« Reply #17 on: March 13, 2014, 09:09:47 am »

I downloaded a couple of Wacker operator manuals. Proper grounding is in the manual. I then searched a bit and found this thread. Note the comments about a ground rod providing "no iota of safety".


http://forums.prosoundweb.com/index.php?topic=135427.0


How can mis-information be purged....

Mike Sokol

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Re: Is it just me or is there some really dangerous stuff going on here...
« Reply #18 on: March 13, 2014, 09:41:18 am »

Having followed this thread, it seems that even when using a small, portable Honda 3000 watt genny, a ground rod would be a good idea.
I don't see any ground connection point on these small gennys.
Thoughts or experiences?

Here's my thoughts, but I'm going to run this by my Honda technical support contact first. If you look at my article about neutral bonding Honda generators at http://www.noshockzone.org/generator-ground-neutral-bonding/ you'll see that I've made a simple Edison kludge plug with a jumper between the Ground and Neutral screws. This has been tested lots of times by hundreds of RV owners running Honda 2 and 3 KW generators, and Honda tech support has admitted (off the record) that it's a workable fix. Now imagine adding one more wire coming from this G-N bonding point to a piece of #6 stranded wire that's connected to a properly earthed ground-rod. That's exactly how your home or business system is "earthed" by the PoCo. You should also run a heavy (#6) wire from from the metal stage (big clamp) to the same ground rod bonding point as well. This is all electrically valid and to code (as far as I can tell), but I don't like the fact that kicking out the G-N kludge plug accidentally opens up both your G-N bond as well as the Earth connection.

If you all agree that this is a workable solution, I'm going to run it by my code monkeys at Mike Holt's forum to get the NEC spin on this. But the NEC does NOT require grounding of small portable generators ONLY because they're considering you'll only have one thing at a time plugged into it, such as the drill at the construction site example I used at the top of this thread.

This is exactly the type of experiment I want to do with the EU2000i that Honda has promised to send. Once I get that done and vetted by my NEC contacts, I'll publish it as an official fix. In the meantime, this is all experimental guessing on my part. An educated guess, to be sure, but until I set up the test and gather data I don't want anybody risking their lives. So please, let's critique this proposed fix rigorously.   
« Last Edit: March 13, 2014, 09:45:55 am by Mike Sokol »
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Stephen Swaffer

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Re: Is it just me or is there some really dangerous stuff going on here...
« Reply #19 on: March 13, 2014, 11:47:26 am »

Mike,

I agree that your solution is NEC compliant.  I am trying to remember and will check code later today (book is the office),but do non-bonded gennies also have to have gfci protection?

I am not sure of the purpose for not bonding the neutral to ground.  A 3-5K genny is plenty to run multiple pieces of   equipment, and if you are using a drill with a grounded case that shorts hot to the case, you now have energized the genny with no path to trip OCPD.  Touching another piece of equipment that uses a polarized plug could potentially put you in the circuit with 120 V between neutral and "ground".  Seems dangerous to me without a GFCI to detect an imbalance between hot and neutral on a given circuit?

IMO the ground-neutral bond is the most critical, but a ground rod still plays an important part in safety-especially in wet conditions.  Though lightning protection is the primary purpose, keeping the frame/ground of the genny bonded to earth should prevent any significant voltage difference between the two.

Slightly OT but relevant.  Yesterday I dealt with a farmers bin that had had some bad things happen-arced the bus on a QO panel,burnt a contactor coil, etc.  I finally realized the panel was fed 3 wires-2 hots and a neural, the EGC had not been carried to the bin.  There was no neutral bond to the panel and all wiring relied on conduit to panel for EGC. bottom line, no metallic fault path from ground to neutral. I found where a rodent had chewed through insulation, but with no metallic path things just arced and burned instead of tripping the OPCD.  Out of curiosity, I dropped one probe of my voltmeter in a puddle against the concrete pad of the bin (the bin/pad should be equivalent to a concrete encased electrode and arguably equivalent to a metal stage sitting on damp ground)) and measured 1.56 volts-but that was with things running and no faults.  I do not think I would want to touch the bin with a wire shorted to the conduit!  Rewiring the bin was already in the works, and though I do not have to have ag jobs inspected, you can bet there will be grounding changes.
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