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Ground rod for container kiln?

Started by Marshall, April 22, 2018, 09:44:50 PM

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Marshall

I'm bringing a 50 amp feed with ground to a new container kiln I just bought. It's a Woodmizer 250 kiln. Does anyone know what the bonding and grounding requirements are for this container?  Should I also sink a ground rod or two near it? And is there a special method for bonding to the metal parts of the container?  I really want this thing to be safe but this doesn't seem to be covered in the NEC 2014!  Thanks for any help anyone can give me.  John (Marshall's my middle name!)

Runningalucas

Quote from: Marshall on April 22, 2018, 09:44:50 PM
I'm bringing a 50 amp feed with ground to a new container kiln I just bought. It's a Woodmizer 250 kiln. Does anyone know what the bonding and grounding requirements are for this container?  Should I also sink a ground rod or two near it? And is there a special method for bonding to the metal parts of the container?  I really want this thing to be safe but this doesn't seem to be covered in the NEC 2014!  Thanks for any help anyone can give me.  John (Marshall's my middle name!)

 
Yes, it's a separate building, you'll need grounding electrodes, the deal with ground rods, is they're supplementary; meaning if you have building steel, or concrete encased electrodes, like rebar, you go there first.  if that's not available, then go to the supplementary electrodes=ground rod; usually 2, 6' apart.  If you do this, then yes you need to still bond to building steel, any water lines, etc.  #6 copper will be the minimum size bonding conductor.  This is an outdoor building with power, any receptacles will need to be GFCI's, and per code a light inside, and out illuminating any man door entrances.
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Southside

John,

Welcome to the Forum.  In the book for your kiln it tells you how close your ground rod has to be to the kiln in order for the probes to read correctly, I think it's something like 20 feet max.  I just drove a new ground rod at the kiln and ran #4 from the rod to the junction box I built inside of the "nest box" holding the controller.  I then ran a home run to each of the fans, the kiln unit, light, etc - every one has it's own # 12 THWN ground inside of CPVC and liquid tite.  Rather than buying three rolls of the stuff I just went with orange and color striped each lead like you would for three phase.

Hope that helps.    
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YellowHammer

Yes, ground rods are required.  If in doubt call your county inspector and have him point you to the code.

Funny story, at work we had one of the big metal portable office trailers that had lost its ground.  We later learned the air conditioner had shorted out and the buldling ground was loose.  No plumbing and the portable was electrically isolated being on wooden and concrete blocks.  One of the guys opened the door and and got shocked when he grabbed the door knob.  Not bad, but it woke us up when he screamed.  We shut the power off and called in a work order and a few hours later a Facilities repair man, kind of a know it all, showed up, and we told him the building was electrified and he said it was impossible.  We were just dumb engineers and he was a "certified" electriction, so he knew everything.  So we told him to go ahead, flip on the power and grab the DanG door knob and see what happens.  By this time quite a crowd had gathered to watch the show.  One of our electrical engineers had already put a meter on the building to ground and proven it was hot, but this guy wouldn't listen.  Guess what?  I can still, to this day, remember with perfect clarity him grabbing the door knob with a sneer in his face, only to be lit up like a Christmas tree.  He didn't get hit with the full 220V, only a little bleeder voltage so he was able to let go and not get smoked.  When he was able to stand back up, and we had stopped laughing, he was a little more careful.  
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PA_Walnut

Quote from: YellowHammer on April 23, 2018, 01:29:18 AMHe didn't get hit with the full 220V, only a little bleeder voltage so he was able to let go and not get smoked.  When he was able to stand back up, and we had stopped laughing, he was a little more careful.  


LOL! That's awesome! Another electrician story to behold: I had one, who worked at a faith-based business that I was doing work for, INSIST that I get involved with him in video-production of his PORN side business. He finally opted-out when I asked him what my daughter might say if her dad was involved in it.  :-X

I have done a lot of research on this topic and have found that some locales call for a single ground rod and others a double, six feet apart. Every time I have to drive another one of them in, I hit the liquor store first! ;)

I've found a disparity of direction on whether the sub-panel ground still needs tied back to the main panel ground. I do it, since it's not a big deal and seems reasonable. To further cramp the brain, the main panel's ground and neutral can be bound, but the sub needs them isolate.

I would like know some of the science logic about how/why this is. I know it's something about grounding loops, etc.
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Don P

Right, the only bond between neutral and ground happens back at the main panel, keep Neutral and ground separated all the way back to the main panel, do not bond neutral to case inside a subpanel, otherwise neutral and ground won't "know" which line to run on. Yup black magic to me too.

YellowHammer

Driving multiple rods is sometimes required, and the same effect can also be accomplished by driving them deeper, with multiple rods screwed together.

Lots of theory with proper grounding, but it can generally be boiled down to all earth ground isn't the same.  In order to insure a true ground at the remote and also the main panel box, ground rods must be driven locally.  Local grounding also allows safe grounding if the remote ground fails.

Case in point, I ran 1600 feet of wire to a pump in a cool water spring, with the only electrical ground coming from the breaker.  However, there was a measureabe difference of 7 ac volts, measured from the pump casing attached to the panel ground wire so far away and to the creek water if the pump was lifted clear of it.  Of course, the pump was locally grounded when it was in the water, but only remotely grounded when lifted clear.  These 7 ac volts was enough to feel, but not enough to bite.  The issue was that there was a difference in the ground plane over the 1600 feet distance.  The solution was to simply drive a local ground rod into the creek bank and wire the pump casing to it.  So a local ground rod is always useful as a safety.  If you ever want to see if a ground rod is doing its job, especially one a distance away from the main panel, attach a meter lead to the unwired local ground rod, and the other end of the meter lead to the ground wire coming from the electrical panel a distance away.  Many times, you will measure a slight voltage difference between the two grounds planes which is why the local grounding and rods are so important.    
YellowHammerisms:

Take steps to save steps.

If it won't roll, its not a log; it's still a tree.  Sawmills cut logs, not trees.

Kiln drying wood: When the cookies are burned, they're burned, and you can't fix them.

Sawing is fun for the first couple million boards.

Be smarter than the sawdust

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