Do I need ground rod at subpanel?

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Old 05-07-14, 02:02 PM
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Do I need ground rod at subpanel?

Noticed no ground rod at detached garage. Existing installation.

#8, 3 wire feeder in rigid conduit protected by 40A breaker in main. No water pipe between building, no separate egc run, conduit is egc. The neutral bus bar is not bonded to subpanel enclosure. Subpanel serves 2, 20A circuits.

Do I need to drive a ground rod and install a grounding bar to subpanel?

Suggestions welcomed.
 
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Old 05-07-14, 02:10 PM
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Do I need to drive a ground rod and install a grounding bar to subpanel?
Yes. ALL sub-panels in detached buildings require at least one, and sometimes two, grounding electrodes, aka ground rods. Whether or not you need two depends upon the soil conditions and the LOCAL code requirements.
 
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Old 05-07-14, 02:21 PM
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When did this become a requirement? Wondering if it was mandatory at the time of installation which might have been 10 or 20 years ago.

Also, as the panel stands now, with the neutral buss NOT bonded to the enclosure, that is incorrect as well, right?
 
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Old 05-07-14, 03:53 PM
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Also, as the panel stands now, with the neutral buss NOT bonded to the enclosure, that is incorrect as well, right?
Neutral bus under modern code is not bonded and there is a separate bonded ground bar. If this is grandfathered and there is no ground bar then the neutral bar would be bonded. Is this a 3 or 4 wire service?
 
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Old 05-07-14, 04:55 PM
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With the neutral buss not bonded in the installation I described in the first post, that means the intended EGC (the conduit) is not grounded at all... is that correct?
 
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Old 05-07-14, 05:07 PM
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The rod is for things like a lightning strike.

The egc is to trip the breaker. Entirely different purpose. The conduit should be grounded by its connection to the first panel.
 
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Old 05-07-14, 07:31 PM
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All answers are assuming the interconnecting conduit is continuous between panels and is either IMC (intermediate) or RMC (rigid) conduit. Grounding locknuts on the conduit if it enters holes without concentric knockouts or else grounding bushings with a green or bare conductor of the appropriate size for the circuit breaker connecting the bushing to the equipment grounding bus in each panel.
 
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Old 05-08-14, 04:41 AM
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The rod is for things like a lightning strike.

The egc is to trip the breaker. Entirely different purpose. The conduit should be grounded by its connection to the first panel.
Yes I know what the function of a GEC and EGC are... my question is why is having the neutral floating without a ground bar improper??

And I could get away without a ground rod or ground bar if there is only one circuit in the garage. I assume I can use the existing enclosure as a junction box. If so, does having a single breaker or a disconnect switch require the GEC again?

Also does anyone know when a separate GEC for detached garage became a requirement?
 
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Old 05-08-14, 05:47 AM
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The neutral is not floating, it is held at earth potential by the neutral-earth (ground) bond in the service panel. There is no connection between the neutral and the equipment ground beyond the service panel because doing so would make a parallel path along the equipment grounding conductor for return currents on the neutral conductor. This parallel path could under certain circumstances impress a voltage above ground potential on any metallic object that was bonded to the equipment ground.

The requirement for a grounding electrode, and grounding electrode conductor, on buildings separate from the service has been in place for decades.
 
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Old 05-08-14, 06:02 AM
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Maybe its too early, haven't had my coffee.

I will ask again though, the neural buss bar is not bonded in my subpanel.

Why was this allowed at some point? Why is it wrong now?


If this is grandfathered and there is no ground bar then the neutral bar would be bonded
No ground bar, but neutral bar is not bonded. Why is this wrong?
 
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Old 05-08-14, 06:27 AM
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Bonding of the neutral bus to the enclosure of sub-panels was common prior to the requirement of equipment grounding conductors. This practice was continued for far too long (in my opinion) until some smart cookie realized the potential hazard of the practice. I think it was the 2008 NEC that finally disallowed the practice of neutral-equipment ground bonding in sub-panels although the practice had only been allowed when there were no other metallic connections, including a water pipe or a telephone cable, between the buildings for several years prior.

I will admit that I honestly don't know if the metallic conduit would have counted as a "metallic path" but I think it would and if so the neutral-equipment ground bond in the sub-panel would have been prohibited several years prior to the 2008 code.

No ground bar, but neutral bar is not bonded. Why is this wrong?
As previously stated, bonding the equipment ground and the neutral would create a potentially hazardous parallel path for return currents that should ONLY be carried by the neutral conductor. If you have no equipment ground bus and your equipment ground wires are connected to the isolated neutral bus then that is definitely wrong.
 
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Old 05-08-14, 06:39 AM
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There are two 20A circuits in the subpanel. I have a 40A breaker and 3 #8 feeders going to the garage in rigid conduit.

How can I make this one circuit, use the subpanel as a junction and avoid having to drive a ground rod? Can I do this without having to pull new conductors?

If you have no equipment ground bus and your equipment ground wires are connected to the isolated neutral bus then that is definitely wrong.
No ground buss. EGC is the EMT. Neutral buss is not bonded. Then I assume from your responses that is correct (although I still need a ground rod) in that case I would add a ground buss. Keep the neutral buss unbonded and run the GEC from Rod to ground buss.

Or just turn it into one circuit....
 
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Old 05-08-14, 07:12 AM
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At the very least you need to install an equipment grounding bus in the panel. That is a fairly easy job, and then move any equipment grounding conductors (bare copper wires in the downstream wiring) from the neutral bus to the equipment ground bus. If the steel conduit is connected to the enclosure through an eccentric knockout or a knockout that has any concentric rings remove it is probably okay but ideally it would have a grounding locknut. A grounding locknut is one that has a pointed screw that when driven in makes a secure (electrical) connection to the enclosure.

Or, you could use a grounding bushing which has a terminal screwed to the side of the bushing and a green or bare bonding conductor to the equipment ground bus. For a feeder circuit breaker of 60 amperes or less this conductor needs to only a #10 copper conductor.

No ground buss. EGC is the EMT.
Are you now telling me the conduit is EMT, also known as thinwall? EMT is not to be used underground because it will rust away in a few years, only intermediate or rigid conduit is to be used underground. Is the conduit threaded or does it use adapter fittings that clamp on the conduit and then have screw threads and a locknut to attach to the enclosure?

Rigid or intermediate conduit CAN be used for the equipment grounding conductor in an underground feeder. It may be allowable to also use the conduit instead of a grounding electrode, I simply don't know but I have never heard if that being allowed.

Changing this installation to a single circuit would be a mistake in my opinion. You would have to change the circuit breaker in the service panel to a maximum of 20 amperes thereby cutting the power available in half. Just because you don't want to drive a ground rod. Please tell me why you are so adamantly opposed to driving the rod?

I'm going to bed now, we can pick this up later.
 
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Old 05-08-14, 01:37 PM
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Bottom line, what would someone suggest if I was turning this into a single circuit? And if I do that can it be 240 or maybe a mwbc with a handletie and I can run the GDO off one leg and some lights and an outlet on the other?

FYI- Ground Rod would have to be remote and running #8 from the distance is expensive.
 
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Old 05-08-14, 02:30 PM
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If you don't have a reliable EGC you have an ungrounded circuit and changes can't be made to an ungrounded circuit. If the conduit is EMT it is probably to compromised to be a reliable ground. As Furd wrote:
EMT is not to be used underground because it will rust away in a few years,
and if the wires are #6 or smaller none of them can be redesignated as a ground. However code does permit you to run a separate EGC from the main panel but if your going to dig a trench for that why not just replace the feed.
 
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Old 05-08-14, 02:48 PM
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If you don't have a reliable EGC you have an ungrounded circuit and changes can't be made to an ungrounded circuit. If the conduit is EMT it is probably to compromised to be a reliable ground. As Furd wrote:



EMT is not to be used underground because it will rust away in a few years, and if the wires are #6 or smaller none of them can be redesignated as a ground. However code does permit you to run a separate EGC from the main panel but if your going to dig a trench for that why not just replace the feed.
Ive mentioned it a few times now... I have rigid between the buildings that contains #8 3-wire feeder. Im not digging any trenches... unless you want to come over and do [email protected]!!
 
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Old 05-08-14, 03:23 PM
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But you wrote:
No ground buss. EGC is the EMT.
Didn't say you meant just inside. So drive a ground rod and install a ground bar and your good to go. If you can't drive the ground rod straight down using a " or " hammer drill you can drive it at 45 or bury it horizontally in a trench.
 
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Old 05-09-14, 12:31 AM
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Why are you so chary in giving us the information that we need to help you? More than once you mention having rigid conduit but you have also mentioned having EMT, Electrical Metallic tubing. Which is it? You mention it is expensive running #8 for a grounding electrode conductor but the truth is that for a GEC using #8 requires physical protection and for that reason most GECs are run with #6 copper. You are adamant that you do not want to install a Grounding Electrode (ground rod) but you never explain WHY you don't want to install. You make vague statements that running the GEC and installing the ground rod will entail having the rod at a significant distance from the panel but again, nothing on WHY it has to be so.

Assuming that your outbuilding is sitting on a concrete slab that is considerably bigger than the dimensions of the building you CAN rent a hammer drill along with a 3/4 or 1 inch bit and simply drill a hole through the concrete (if indeed this is what you have) and then drive the rod into the earth through this hole. This can even be inside the structure immediately below the panel and THAT would reduce the amount of wire to maybe five feet or so.

Nor have you told us if the "conduit" from the service panel is installed through a knockout with concentric rings, eccentric rings or no rings at all. You won't tell us if there is a grounding locknut, grounding bushing or just a plain locknut.

I told you how you can make this into a single circuit (multi-wire branch circuit) and why that would cut the available power in half. You never commented on that so I am left wondering if you even read it.

Quite honestly, I am getting tired of having to ask and ask again the details of your installation only to be be ignored or having you get all defensive. If you want my help, or the help of anyone else on this board, you need to freely communicate what you have and what you want. At this point it seems to me that what you REALLY want is for one, or all, of us to sprinkle some holy water on your non-code compliant installation and state it is fine. THAT is not going to happen.
 
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Old 05-09-14, 04:34 AM
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I would insert the "beating the dead horse" emoticon here but I cant find it. So instead :

:repostit:
 

Last edited by Tolyn Ironhand; 05-12-14 at 03:30 PM. Reason: added emoticon ;)
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Old 05-09-14, 06:44 AM
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Furd may be acerbic but his points are valid and your reply a non reply not helpfully responsive. Your question seems to have been answered. Do you have other questions. If so please list them and we'll try to answer them.
 
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Old 05-09-14, 09:09 AM
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Furd may be acerbic but his points are valid and your reply a non reply not helpfully responsive. Your question seems to have been answered. Do you have other questions. If so please list them and we'll try to answer them.
Any questions that remain are in regards to turning this into a single circuit. But I have a feeling you really don't want me asking any more questions.
 
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Old 05-11-14, 07:08 PM
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Any questions that remain are in regards to turning this into a single circuit.
Go back and read post number 13.
 
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Old 05-12-14, 04:34 AM
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Any questions that remain are in regards to turning this into a single circuit.
Go back and read post number 13.
Changing this installation to a single circuit would be a mistake in my opinion. You would have to change the circuit breaker in the service panel to a maximum of 20 amperes thereby cutting the power available in half. Just because you don't want to drive a ground rod. Please tell me why you are so adamantly opposed to driving the rod?
Sorry Furd, but I thought this thread died. But since your telling me to reread #13 I should mention..... I fail to see where any advice was offered about changing this to a single circuit? Im not talking about the part where you assume my electrical needs and advise not to since it cuts power in half.

So pretty much #13 is you asking about the EGC... which I clarified multiple times is sufficient.

Don't get me wrong though Buddy, I appreciate ANY advice I have read on this forum. Have a nice day.
 
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Old 05-12-14, 03:36 PM
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From post number 13:
You would have to change the circuit breaker in the service panel to a maximum of 20 amperes...
I'll elaborate. Using the existing wiring from the service panel (the main panel) to the sub-panel you would first replace the existing 40 ampere double pole circuit breaker with a 20 ampere double pole circuit breaker. The conduit, assuming it is rigid (heavy wall and most likely threaded connections) and continuous between both panels becomes the equipment ground. At the sub-panel you need to install a bonded equipment ground bus, assuming there isn't one now. Move any green or bare equipment ground wires from the neutral bus to the equipment ground bus. You have now changed the previous 40 ampere feeder to a 20 ampere multi-wire branch circuit. No grounding electrode (ground rod) or grounding electrode conductor needed.

The circuit breakers in the sub-panel are now redundant. If this sub-panel has a main circuit bre3aker that circuit breaker becomes the building disconnect. If no main circuit breaker then the panel may not allow for more than six individual circuits and those individual circuit breakers (maximum of six handles) become the building's disconnecting means.

Understand that the integrity of the buried conduit is the determining factor as to whether or not you may convert this to a multi-wire branch circuit. Anything else would technically require pulling the existing wiring out of the conduit and adding a green insulated wire along with a white and a black to make a 120 volt only 20 ampere branch circuit OR adding a fourth wire (any color other than white, grey or green) to make a 240/120 volt multi-wire branch circuit.

While you could theoretically use one of the existing "hot" conductors as an equipment ground the code does not allow for the re-identification (changing the insulation color) of any conductor smaller than #4 gauge.

So again I ask, is the conduit between the two panels RMC, IMC or EMT and is it continuous between both panels?
 
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Old 05-12-14, 04:46 PM
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Thank you Furd, now that is concise and informative and I appreciate it.

The only issue I see after reading your latest greatest post is if I change it to a single circuit, now the wire are #8, very large and probably not a great idea to be splicing #12 directly. There is no main breaker in the sub, just a pair of 20A. As it stands now the outlets are pigtailed to one breaker and the lighting is pigtailed to the other breaker.

So again I ask, is the conduit between the two panels RMC, IMC or EMT and is it continuous between both panels
RMC, continuous. I have continuity at both ends.

again thank you
 
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Old 05-12-14, 05:17 PM
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Picture of the sub-panel without the cover would help but...

The conductors being #8 is not a problem. I assume they are connected to the main lugs of the circuit breaker sub-panel and if so that is fine. Does this sub-panel have room for more than six circuit breakers? If not, then you are fine.

The new two-pole 20 ampere circuit breaker in the service (main, house) panel should accept the #8 conductors without problem. The only thing that needs to be changed at the sub-panel is the addition of an equipment ground bus bar and moving the bare or green wires from the neutral to the new ground bar. Adding a grounding bushing to the RMC at both ends and a green #12 (for 20 amperes) from the lug on the bushing to the neutral bus in the service panel and to the equipment ground bus in the sub-panel would be ideal.

[ATTACH=CONFIG]31590[/ATTACH] (Image courtesy of Global Industrial dot com.)
 
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Old 05-13-14, 04:21 AM
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So essentially all I have to do to avoid a ground rod is swap the 40A with a 20A in the main (consider the two twenties in the sub as disconnects, there are only room for these two breakers)? I do not have to pull a separate EGC technically since I have RMC between the structures)

As for the ground bar. The EGC in the garage is the emt raceways. No wires to add to a ground bar.

Thx
 
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Old 05-13-14, 06:03 AM
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You do not need to add an EGC.
 
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Old 05-13-14, 06:27 PM
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I see the original poster has moved beyond the ground rod install idea, but I was wondering if one can use a ground plate down there....we seem to use them a lot up here...soil is rock around here...depth requirements are less than a rod.

http://www.tnb.com/ps/fulltilt/index.cgi?part=1016TB
 
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Old 05-13-14, 07:14 PM
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I was wondering if one can use a ground plate down there....we seem to use them a lot up here...soil is rock around here...depth requirements are less than a rod.
That particular product doesn't seem to be U.L. Listed for use down here. Do they have something else intended for use here that is U.L. Listed?
 
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Old 05-13-14, 07:26 PM
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For reasons we can only guess at Bigboypete has by omission failed to tell us if he can or can't use a ground rod. I gave him several possibilities and he ignored my post. This thread has run it's course. I am closing it. Bigboypete if you want more help and are willing to help us help you by answering the questions we ask please start a new post.
 
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