Subpanel revisit...

[harryball]

I did a few searches and reading on previous topics.... I THINK I know what to do both short term and long term but I thought I'd ask.

My new shop has twin 200A panels. The Neutral-Ground bond is made in the meter box not in the panels. As such, the panels have split Neutral / Ground bars. (done by licensed electrician and inspected)

However, my subpanel I uninstalled and transported from my previous shop sports ONLY a ground/neutral bar and the previous shop had a Neutral-Ground bus that was bonded as one. (licensed electricians did all this and it passed inspection). In addition my bot chassis itself was grounded directly to its own ground rod. It always worked, never had comm problems.

Now I'm in the new shop and I'm not sure how to approach this.

The subpanel feed has two hots and a ground for 220V.

Option 1)
Leave it as is (was) with the neutrals from the bot (there are only two 110V breakers) bonded to ground and leave the ground bonded to the main panel. Add a direct chassis ground to drain off static and any leak currents.

Option 2)
Same as above, but do NOT use the ground wire in the feed but rather ADD a ground wire from the ground bar in the subpanel direct to the SAME grounds as the main panels. This should prevent any potential neutral feeds from leaking through the main panel grounds.

Option 3)
Replace it all with a new subpanel and 3/C+G wire. Then add a chassis ground. My least favorite option.

I'm not worried about comm problems, if I have those I'll do what's needed when I encounter them up to and including option 3. I'm more concerned about SAFE. So long as Option 1 (or 2) is SAFE and I don't have comm errors I'm fine.

Non-binding and non-accountable opinions?


/RB

[harryball]

FYI, yes I do have a licensed electrician lined up next week but I like to have ideas ahead of time on how things should be so I can spot any red flags. I'm not interested in having it done wrong nor am I interested in doing more than is needed.

/RB

[pkirby]

I recently did my new shop, and ventured down a path of curiosity similar to yours. A good friend of mine is an electrical engineer for Eaton and his primary job is specifying the requirements for industrial power applications. After several hours of discussions, I still don't know a lot about electrical theory, but I did learn that since the neutral and ground are bonded at the meter (same as my shop) then they should always remain isolated from each other.

As for grounding the machine, I had a dedicated ground rod just for the Shopbot but after he saw it, he recommended that I attach the Shopbot ground directly to the ground bar in the panel. He gave me a good explanation why it was better, but I'm not smart enough to remember the reason's why:o

I hope that helps. Also on a side note, I was paranoid about fire safety so I installed 2 safety switches so that I could easily turn off all the power in my shop. I have one 200 amp panel for the upstairs of my house, and this pic shows the second 200 amp panel in my shop which feeds part of my upstairs and then feeds the two 100 amp subpanels. One subpanel for only CNC related items and one subpanel for the remainder of the shop. Perhaps I got carried away with my electrical system :D
23251

[harryball]

Thanks for the info, I'm moving along the same trail.

I unexpectedly found a good electrician and here is what I learned in my case. What I have is "safe" but not to code. The ONLY reason it is safe is there are no "outlets" or ground fault devices on it but rather equipment is wired direct AND there is no tie to the neutral of the building to interfere with the ground faults there. Any current leaked to ground is tied to earth through the ground in the box.

However, it could be noisy. The neutral can introduce noise onto the ground bus in the subpanel. So, his advice (which confirms what I've heard here and on the phone), add a neutral bus to the subpanel and tie it back to the neutral of the main panel. Ground the chassis of the bot to the ground bus of the sub panel. DO NOT install a separate ground rod for the bot, if anything add another ground rod about 6 feet from the current ground rod and add a #6 wire between them to improve the current earth ground.

He stated he never likes to see multiple ground taps in any single system. But rather improve the single ground by adding more ground rods and increasing the size of wiring to ground.

Makes sense and I'll be making the corrections.