Possible ground loop

[budm]

Re: Possible ground loop

That electrical box is grounded when the face plate is bolted to the box since the outlet GND makes contact with the face plate via the brass strap on the back of the outlet.
https://www.ecmweb.com/qampa/code-qa...-conductor-box

[stj]

Re: Possible ground loop

unshiethed earth wires - yuk.
what's the gray paste-shit on the incoming N wire?

[Spork Schivago]

Re: Possible ground loop

Here's a pic of the two 240VAC receptacles that I installed myself. They run to dual pole breakers installed on opposite sides of the panel.

There's also a pic of one of the boxes with the cover removed, so you guys can see how I did the pigtail. I did this so if one of the supply lines ever came free, God forbid, and touched the metal box, it should trip the breaker, rather than energizing it so if someone touched it, they shouldn't get shocked.

What really surprised me, my neighbor who works for a company that installs junction boxes all the time, never heard of grounding those boxes like that, and doesn't understand why it needs to be grounded.

[Spork Schivago]

Re: Possible ground loop

Here's a pic of the two 240VAC receptacles that I installed myself. They run to dual pole breakers installed on opposite sides of the panel.

There's also a pic of one of the boxes with the cover removed, so you guys can see how I did the pigtail. I did this so if one of the supply lines ever came free, God forbid, and touched the metal box, it should trip the breaker, rather than energizing it so if someone touched it, they shouldn't get shocked.

What really surprised me, my neighbor who works for a company that installs junction boxes all the time, never heard of grounding those boxes like that, and doesn't understand why it needs to be grounded.

[Spork Schivago]

Re: Possible ground loop

Here's some pics of the panel.

Phone took the pics sideways for some reason. The first shows how the Neutral and gnd are hooked up to the panel. Second shows how the electrician ran the earth gnd to another point on the panel. The bare copper that's buried goes into the panel at the top, where the Neutral is hooked. The bare gnd that runs through the basement that everything is bonded to goes to the bottom the gnd buss bar. The gnd and neutral buss bars are connected at the top with a bar. The bar came with the panel. The conduit I ran is the cantex schedule 40 rigid PVC.

[Spork Schivago]

Re: Possible ground loop

Is ground loop causing problem in your setup right now?

No. But I fear if something goes wrong (not because of me), perhaps company's will not warrant my hardware because of it. Do you think I'd be fine if I just left it?

[Spork Schivago]

Re: Possible ground loop

Yes.



Also, yes.
For fun, put an AC ammeter in series with this jumper- you should read no current. Well, maybe a few milliamps from the line-GND Y-caps in any noise filters...



If that's a service panel (not a subpanel), neutrals and grounds can be landed on the same bars. There should be some kind of jumper from both bars, and from the GND bar to the panel enclosure as well. Depending on the particular panel, the "bond" from the neutral bar to enclosure can be a green screw that's turned in completely, engaging threads in the enclosure.. since the GND bar is always tied to the panel, this effects the neutral-GND bond, by way of the neutral bar->bonding screw->enclosure->GND bus.

Sometimes, there's a jumper. Or a little of both; sometimes there's a #6 solid between the two bars in addition to a green screw bonding the can.



Should be, you've got conduit or MC from the panel to each box, with one of those green pigtails jumping up to the receptacles. Or NM with ground to each box instead.

If I may ask, these units do not power any 120V loads? Only 240V loads?

Also, lose the bond to the gas line, unless you have CSST, which is another story.

Iron/steel gas pipes are typically bonded thru the EGC of any electrically-operated device connected to such pipes. Eg- via the EGC of a gas dryer, furnace, range/oven/cooktop, etc...



'Welcome.

Thank you. We do have CSST, but the main supply run is black iron or black pipe, what ever its called. I wanted CSST the hole way, but the installer fibbed a bit and said you couldn't build up a supply with CSST. I want to say his reason was because they didn't make it large enough diameter, but I guess that was wrong. He just really really likes black iron. It's okay though, just a straight run of black pipe, then we branch off that straight run with CSST.

I will send a picture of the panel. It is not a sub panel. There is a green screw, but I believe it's not being used. The bare copper comes in where next to where the Neutral from the pole comes in. Both the gnd and neutral bars are connected.

[budm]

Re: Possible ground loop

Is ground loop causing problem in your setup right now?

[stj]

Re: Possible ground loop

draw a wiring schematic, i cant follow this.

[kaboom]

Re: Possible ground loop

Could you go a bit more in detail about what you mean by outside leg? I believe the answer to your question is yes. Two 120VACs coming in, centre-tapped. Each of the 120VACs are 180 degrees out of phase with the other. Are these the legs you speak of?

Yes.

Are you saying unhook that wire from the rack that goes to that bare stranded wire, and instead run a wire from the rack directly to the ground bar in the panel?

Also, yes.
For fun, put an AC ammeter in series with this jumper- you should read no current. Well, maybe a few milliamps from the line-GND Y-caps in any noise filters...

That (I think it's 8 gauge, but might be larger, like 6) runs to the panel as well and connects to the ground and neutral buss bars. There's one on each side, but the electrician who installed it didn't seem to run the bare copper to one side, the neutrals to the other, like I probably would have done. I can show pics if you'd like.

If that's a service panel (not a subpanel), neutrals and grounds can be landed on the same bars. There should be some kind of jumper from both bars, and from the GND bar to the panel enclosure as well. Depending on the particular panel, the "bond" from the neutral bar to enclosure can be a green screw that's turned in completely, engaging threads in the enclosure.. since the GND bar is always tied to the panel, this effects the neutral-GND bond, by way of the neutral bar->bonding screw->enclosure->GND bus.

Sometimes, there's a jumper. Or a little of both; sometimes there's a #6 solid between the two bars in addition to a green screw bonding the can.

I ran a continuity meter between the receptacles and saw 0 ohm resistance, because they're sharing the same ground. Code enforcer checked everything out and passed us. Could you please elaborate how this EGC should be done with the metal boxes? These boxes had a raised spot, and that's where I installed my pig tail, grounding the receptacles metal boxes. Is that not correct?

Should be, you've got conduit or MC from the panel to each box, with one of those green pigtails jumping up to the receptacles. Or NM with ground to each box instead.

If I may ask, these units do not power any 120V loads? Only 240V loads?

Also, lose the bond to the gas line, unless you have CSST, which is another story.

Iron/steel gas pipes are typically bonded thru the EGC of any electrically-operated device connected to such pipes. Eg- via the EGC of a gas dryer, furnace, range/oven/cooktop, etc...

Thanks!

'Welcome.

[petehall347]

Re: Possible ground loop

sounds like a proper headache with split 240v . its normal here on single phase . although we do have 2 supplies here and when i done a party here we had to split the supplies . told everyone where to plug in lights and audio . they never listened and i had to find what they had done .. lights in audio supply and audio in lights supply caused the problem .

[Spork Schivago]

Re: Possible ground loop

240V as in the two 120V outside legs of a single-phase distribution transformer?

Could you go a bit more in detail about what you mean by outside leg? I believe the answer to your question is yes. Two 120VACs coming in, centre-tapped. Each of the 120VACs are 180 degrees out of phase with the other. Are these the legs you speak of?

If so, and they're straight-240V (not using the neutral or no neutral current) ground on the supply side isn't involved.



They're already bonded to each other in the rack- just run a #6CU bonding jumper from rack to the GND bar in the panel. Don't run the rack jumper to the grounding electrode conductor(s) going to the waterpipe or ground rod(s).

Take the rack back to its source.

We currently have the rack bonded to a wire that runs to the earth electrodes buried in the ground, that the panel also uses, that the splitter uses, the gas line, the water pipes, etc.

Are you saying unhook that wire from the rack that goes to that bare stranded wire, and instead run a wire from the rack directly to the ground bar in the panel? That (I think it's 8 gauge, but might be larger, like 6) runs to the panel as well and connects to the ground and neutral buss bars. There's one on each side, but the electrician who installed it didn't seem to run the bare copper to one side, the neutrals to the other, like I probably would have done. I can show pics if you'd like.

Your metal boxes still need to an EGC per NEC.

I ran a continuity meter between the receptacles and saw 0 ohm resistance, because they're sharing the same ground. Code enforcer checked everything out and passed us. Could you please elaborate how this EGC should be done with the metal boxes? These boxes had a raised spot, and that's where I installed my pig tail, grounding the receptacles metal boxes. Is that not correct?

Thanks!

[kaboom]

Re: Possible ground loop

240V as in the two 120V outside legs of a single-phase distribution transformer?
If so, and they're straight-240V (not using the neutral or no neutral current) ground on the supply side isn't involved.



They're already bonded to each other in the rack- just run a #6CU bonding jumper from rack to the GND bar in the panel. Don't run the rack jumper to the grounding electrode conductor(s) going to the waterpipe or ground rod(s).

Take the rack back to its source.

Your metal boxes still need to an EGC per NEC.

[Spork Schivago]

Re: Possible ground loop

Would I test by plugging on each PDU and running a voltmeter across the two PDUs? Any suggestions on how to keep the two separate receptacles but do away with the ground loop?

**edit:

The two receptacles have a pigtail running from the ground to the metal workmans box. If I used metal conduit to connect to the two metallic boxes together, that should tie to the two grounds together, and prevent the grounding loop, correct? They'd share the same potential voltage difference than.

[petehall347]

Re: Possible ground loop

yes most likely

[Spork Schivago]

I have two seperate PDUs in a rack. I have two seperate 240VAC receptacles running to seperate dual pole breakers. I have the rack attached to the bonding wire that the gas lines, coax spilters, water pipes, etc are bonded to.

By having each PDU on a seperate circuit like I have it, did I create a ground loop?