Testing for proper ground?

[djjsr]

I have a couple of sub panels that are connected from the main (about 60 ft away) with large pvc conduit. All of the circuits that the panels supply are in metal conduit and test good for ground using one of those 3 light testers, but I can't see where these panels are grounded. There are no ground stakes and there doesn't appear to be any main cable on the ground bar or in the pvc back to the main. How do I test for proper ground of the panel?

Btw, I started wondering about this because of radio static from lights, chargers and power tools, if that means anything.

Thanks

 

[banzaitoyota]

I would call in a qualified electrician to address your concerns.

 

[Teken]

Is it static or is it a hum? One can be induced EMI, the other is over the air RFI

 

[sberry]

You might need some help, this can be complicated to explain. If there was conduit I would pull a 4th wire, if these subs are fed 3 wire the bond screw must be installed in the panel. 3 wire may be legal provided there are no other interconnecting metal pathways (metal gas lines, phones etc) between the buildings. In all separate buildings there should be ground stake.

 

[dugger10]

How many wire come from the main panel to the subs? Should be three,, 2 hots and one neutral. Code probably states you need four, the extra one is for the ground wire. The reality is you don't need the fourth on but its a good ideal for safety purpose's. Static from floursant lights, chargers and power tools is quite common. If everything is working OK then I would make sure my lights were on a seperate circuit, away from any plugs use for power tools and chargers. Concerning the sub panels, if connected by metal conduit someone may be using the conduit as the neutral, not a good ideal at but will work. If this is the case I would run another wire to each panel and us it for the neutral. This could be very dangerous and pose's a fire danger to your build and shock hazard to anyone else.

 

[oleguy]

never use a conduit for a neutral.not code.run 2 hots one neutral and a ground to each sub panel.ground and neutral are not connected together in sub panels.neutral needs to be isolated from the panel.ground is bonded to panel.

 

[djjsr]

The conduit is not being used as a neutral, it's being used as a ground. All of the wiring was done by the previous owner of the building and he was an electrical contractor. Everything seems to be done properly and I haven't had any problems, BUT I just can't figure out if the subpanels are properly grounded. If they are, I just can't figure out how he did it. I'll take another look to see if I'm missing something.

 

[sberry]

If the conduit is metal its probably the ground but,,, in this case there needs to be a separate ground bar in the panel and the bond screw removed,, you have pictures?

 

[oleguy]

my comment was directed to dugger10.just his comment that conduit was not a good idea but would work.bad statment.

 

[GeorgiaHybrid]

I'm getting confused.... looking at your original post, the conduit is PVC. When did that start being conductive and allowed to be used as a ground???

 

[dugger10]

Oleguy, if you'll read my statement it clearly states using the conduict as a ground is not good. Fact is it will work, just not a good ideal. Thirty years in the business has taught me a lot of things will work, but some are just not good to use.
djjsr if you don't have the 3rd wire running from the main panel to the sub panels and all your electrical stuff is working right then your return current is finding an alternative path back to the main pannel. This could be causing some of your noisy. My advice would be to run an additional wire no more than one size smaller than the hot leggs from the main panel to the sub panels to act as the neutral. Returning paths of neutrals or grounds for that fact can cause noisy on things like radio's. It also can cause some interesting problems with your equipment. Conduit acting as neutrals will go bad at some point. The couplins used to connect the conduit will fail, not design to carry current(amps). Good luck with your issues.

 

[walrus]

I'm getting confused.... looking at your original post, the conduit is PVC. When did that start being conductive and allowed to be used as a ground???

I don't understand plastic as a ground either, maybe its magic plastic?

 

[GeorgiaHybrid]

After an education from Charles, from my understanding, you should have four wires from your main panel to your sub panels. 2 hot legs, a neutral and a ground. Once they leave the main panel, the ground and neutral should be kept separate. At the main panel, the ground and neutral are bonded together.

At your subpanel, you should have a neutral bar and the panel itself should not be bonded to the box. The only way this can happen is by using 4 wires if you are running them in PVC conduit.

On the runs from the sub panel to the outlets, you have metal conduit if I am reading your original post right. You can run 3 wires thru metal conduit (2 hot legs and a neutral) for 220 or you can run 2 wires (1 hot and a neutral) and use the metal conduit for a ground for 110.

I have seen some run 2 wires for 220 (2 hot legs) and use the conduit for neutral but that gets back to keeping the ground and neutral separate after the main panel. It can be done but I don't think it's right. You really need one of the electron gods to answer this question though instead of us non-pros.

 

[djjsr]

Sorry, I didn't explain it very well about the pvc. The big conduit (1 1/2" or 2") that contains the main supply lines feeding the sub panels is pvc. All of the circuits coming out of the sub panels are in metal conduit and that metal conduit is used as the ground.

 

[GeorgiaHybrid]

It sounds like the bonding screw is still in your subpanel and the conduit is grounding thru the panel

Edit: How many wires do you have coming from the main panel to the subpanel?

 

[Gary S]

There are two different ways I check for a proper ground.
1. With power off, use a multimeter in resistance (ohms) setting. Check across your conduit in question to a known good ground (water pipe or ground rod). Reading should be very low, near 0 ohms.
1. With power on, use the voltmeter in AC volts setting. Check across the same points as in #1. Any voltage reading more than a few millivolts would indicate a bad ground.

DIsclaimer: I'm not an electrician. I've spent the last 40 years as an electronic technician maintaining and repairing all kinds of electronic equipment. All this equipment is powered by AC, 120, 240, 480, or whatever, so I'm always chasing electrical problems as well as the electronic ones.

 

[djjsr]

It sounds like the bonding screw is still in your subpanel and the conduit is grounding thru the panel

I think you're right. Is it acceptable to put a ground stake near the subpanel and simply wire it to the ground bar?

 

[GeorgiaHybrid]

I think you're right. Is it acceptable to put a ground stake near the subpanel and simply wire it to the ground bar?

A year ago I would have said yes. I have been educated a lot by the electricians on this board however and understand that you should have a ground run back to the main panel. This is a safety issue that needs to be corrected.

Once the ground has been run and tied into the sub panel, remove the bonding screw and you will be OK.

Edit: The reason it is a safety issue is that if the neutral becomes disconnected, YOU will become the ground... If a hot leg is disconnected you just don't have any juice. The ground is there as a safety fallback to prevent you becoming grounded. The separate lines makes it very unlikely that both will fail. If you are using the neutral as a ground and not running all of the way back to your main panel, you are unprotected downstream of the main.

 

[walrus]

Is the building attached or detached, Codes have changed in recent years 3 wires could be ok to a detached building assumed no metallic paths(water lines copper, telephone lines, cable lines) between where the main panel is and the sub panel is. No to just driving a ground rod unless you have 4 wires between main and sub panel

 

[Furious D]

I totally agree with GeorgiaHybrid. I'm not a residental electrician,more of an industrial one so I cant quote you on exact code but I can tell you that an ungrounded panel could cost you your life.

I have seen more than a few times a motor have a phase become shorted and have a direct path to the housing. Even though the conduit is grounded over the years because of rust and exposure to the elements the conduit becomes a poor path for grounding. Then you come by an touch it and now your the new path to ground, Not good.

I'd probably just add the wire from your main just for peace of mind, I doubt an electrician would charge that much to pull a single wire thru conduit. Plus if you ever want to sell your house they will probably catch it upon inspection and make you fix it anyway.

 

[sberry]

Edit: The reason it is a safety issue is that if the neutral becomes disconnected, YOU will become the ground... If a hot leg is disconnected you just don't have any juice. The ground is there as a safety fallback to prevent you becoming grounded. The separate lines makes it very unlikely that both will fail. If you are using the neutral as a ground and not running all of the way back to your main panel, you are unprotected downstream of the main.

The reason for the 4th wire is to allow for insulated neutral and eliminate alternate pathways for neutral currents which are current carrying conductors and part of the working system. Keeping these separate, all the grounds tied together also keeps the potential of all the metal equipment the same, the rod helps with this as it keeps the ground you are standing on at the same potential as equipment you may come in contact with, the rod is NOT a short (fault) return pathway.

 

[Falcon67]

Mine is separate and done to "old code" I'd guess you'd say - three #4s to the panel from the meter on the house, 6' ground rod under the slab, neutral bonded to the cabinet. There are no other metal connections between the buildings. The slabs abut with the patio but there is no shared rebar. If I ran something like a network/cable/phone out there, I'd want to pull a 4th wire and remove the bonding screw.

 

[djjsr]

Well, I've decided to get some professional help.

I took another look inside one of the subpanels. There is no ground bar or ground wiring. All of the circuits going out are in metal conduit.

There are 4 wires coming from the main panel through pvc conduit. Looks like 2 hots, a neutral and a 4th "mystery wire" that isn't even connected to anything, just taped up. I'm guessing it's about a 4 gauge, maybe bigger, but it's the smallest of the 4.

So I go back to the main panel, about 60 ft away in the same building. Upon opening the panel door, I immediately decided to call a pro. Even though this building is just a workshop/hobbyshop for me, it has 3 phase wiring that I find intimidating.

That mystery wire is connected to a lug with another giant wire and I ain't messin' with it. There's also some pretty big fuses, about 6" long and 1 1/2" in diameter. Looks like this isn't a breaker box but a main disconnect.

Thanks for the help anyway, but this ain't a DIY job for me.

 

[Torque1st]

Thanks for the help anyway, but this ain't a DIY job for me.

Sometimes discretion is the better part of valor.

 

[Thedroid]

Good call on hiring someone. For further reference a good way to check your grounds is to splice a long wire to an old lead and hook it to you meter. Attach the other end to known good ground,preferably at the main panel. Set your meter to read resistance and go poking around your outlets checking the grounds. You can also check the outside of your panels, and any appliances that aren't double insulated. Check the resistance of your test lead before you start, and subtract that from you readings. Your looking for an ohm or less. Always remember that in the event of a fault, the current has to travel all the way through the utilities transformer, and back to your circuit breaker with enough current to trip the breaker.