2

Basically there's 3 wires running from a 125 amp breaker on the main service. A red(125v) A black(125v) and a white wire(neutral on ground/neutral bar) in main, all running to an older building with a 125 amp subpanel.

At the subpanel the bar that connects the neutral and ground has been removed. All the grounds are on one bar, all the neutrals are on another. The 2 hots are hooked correctly with awg #2. The neutral bar is connected to the neutral wire also #2 running back to the main.

The ground bar is connected to a AWG #2 wire to a grounding rod. So in this particular case wouldn't the bar that runs from neutral to ground in the subpanel need to be connected or something else?

The 3 wires are all #2 and are buried in pvc. not an electrician. but I do understand the basics. Don't need code talk, just regular speak please. Thanks in advance for your help. p.s. There's no water, gas or anything else metal underground near the shop.

  • What size is the PVC conduit? – ThreePhaseEel Oct 11 '16 at 23:29
  • 2 inch plastic pvc pipe – hank9999 Oct 12 '16 at 1:03
0

Since you have a 2" PVC (assuming schedule 80) conduit here, providing 742 mm2 of room for wire fill, and your 3 2AWG wires (assuming THHN/THWN or XHHW here) only take up 66*3 = 198 mm2 of that space, you have plenty of room to stuff a bare wire down the conduit to bond the subpanel and main panel grounding bars together. A 6AWG bare copper wire will do the job, and should be fishable through the conduit with the power to the main panel turned off. Connect it to the ground bar in the main and sub panels, turn the main panel back on, and you're in business. (Of course, if you don't want to play "fishtape wrestler" for a day, you can pay the nearest friendly electrician for that service instead.)

P.S. no, you do not need to remove the ground rod once you install the bonding wire between the two buildings -- in fact, current Code requires outbuildings to have their own earth ground, in addition to the bond back to the main panel's ground. (This is done to keep all the wires to the outbuilding from soaring to some crazy-high voltage in case lightning strikes near the circuit conductors.)

  • Update after further inspection there is a bare copper wire inside the wire casing it was just snipped and hidden from view. so, once i connect the two ends to the breaker & subpanel I'm golden. I will kill the power beforehand. Thanks my friend. Just hard to believe some dummy messed that up to begin with. What would make someone cut that to begin with is leaving me stunned. – hank9999 Oct 12 '16 at 2:32
  • Can you figure out what size it is? It might be too small to be a proper bond between the two panels...that's the only sane reason I can think of that it'd be cut. – ThreePhaseEel Oct 12 '16 at 2:39
  • Looks like a 6 maybe even a 4. This guy is just plain old dumb. who knows? But it appears as though I'm good now. Really appreciate the assistance tho good buddy. Thanks much. – hank9999 Oct 12 '16 at 2:47
1

First part is answered here: sub panel bonding. But in short, sub panels are not allowed to have their neutral bonded to ground. That only happens in the main panel.

Now to answer your grounding question: Yes, your sub panel is not properly grounded. Any fault current would have to travel through the earth back to the main ground rod or whatever grounded metal object is in the path first. The resistance of the earth varies and corrosion can also add resistance. This can create a high resistance enabling a ground fault (short to ground) to energize the garages ground circuit with a potentially fatal current without tripping a circuit breaker. In plain English: a short to ground could make every grounded metal object in that building live with respect to the main ground rod. A separate ground conductor must be ran from the main panel ground bar to the sub panel ground bar. That ground wire must also be in the same conduit as the other three feeder conductors and appropriately sized to the hot conductors.

  • the shop is about 120 feet from the pole. the pipe is buried about 2 feet. I have no idea how i will run another wire through the pipe. if the wire was solid copper and not stranded it could in theory be smaller than the hot wires. right? could i run a solid copper wire thru the same pipe and bolt it to the ground side in the subpanel without removing the wire going to the grounding rod? the building is old. the sub panel looks more recent. – hank9999 Oct 12 '16 at 1:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.