I am installing a 100A subpanel to a detached workshop and would like 220V. I naively followed the advice from the electrician working in the local Home Depot when buying the wire. I purchased 2/2/4 aluminum direct bury but now believe I should have purchased 2/2/2/4 in order to have 220V. The cable has been buried and I would really prefer not to bury a forth cable. The work will not be inspected but I desire to install the subpanel properly. I live in Norfolk, Virginia. I do not expect to need 100A so I can drop down to 70A if necessary. I suppose this would require me to ground off each panel, which I don't believe is a good idea. Please let me know if I have any options other than running 110V. Thank you.

Hey Dmcjr1976...

Sounds like you are fine to me...

220 volts to an appliance isn't obtained by running 220 volts to the panel as much as it attained by installing a DOUBLE POLE BREAKER in the 100A panel for each 220 volt appliance you wish to run.

For example, If you wanted to install a 220-240 volt electric water heater you would need to install a 30 amp double pole breaker. At this double pole breaker you would be running one 110 volt line from each breaker to the heater which would give a total of 220-240 volts (I believe you would run a 10-2 indoor wire for this setup).

Check out the picture below... hopefully it makes sense.

I am not a licensed electrician so please wait to speak to one of our electricians here... but I think you'll be fine!

Good luck here...

MARK


PS... Please reconsider getting this inspected as today, if found to not have pulled permit and fire burns garage down your insurance company will NOT cover replacement! Just an FYI... ;)
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What you have is a "3-wire" feeder with no equipment ground run. This is legal under certain circumstances. The two main ones being: 1) If you are not yet under the 2008 NEC; and 2) There are no other metallic paths between buildings such as CATV, phone or copper water piping.

You always need a grounding electrode (ground rod) at a detached structure served by a feeder. This is NOT your safety ground that goes to your receptacles. It serves a totally different and unrelated purpose.

In the case of a 3-wire feeder the panel in the shop would be treated the same as a main panel, meaning the neutral is bonded to the panel box and the grounds and neutrals share the same bars.

Again, this is not a legal option under the 2008 NEC.

Hey neighbor, I'm in Va. Beach

Some disputes to the above answer.

The key is "Detached". This redefines just about all of the above.

1) Get a permit and have the work inspected. It will protect you if there is a fire. If the work has been inspected and approved, it is covered by your home owners insurance. You are dealing with 240 VAC not 220.

2) If you direct buried the cable from the main panel to the sub panel, it should be at a depth of 18" to 24" below grade. Also, after you start to back-fill the trench, you should place a tape label warning that there are electrical wires below the tape. This warning should cover the length of the trench and be at least 12" below grade. Then you can back fill the trench. If you choose to use conduit to protect the cable, then the depth is 18".

4) All outlets in the shop should be on GFCI protected circuits or protected receptacles. I personally suggest that you use 12 AWG and 20 Amp breakers for these outlets. Also, while you can use 15 amp receptacles, I would again suggest that you use 20 amp receptacles so that any one using these outlets knows that they are 20 amp listed.

3) On the sub panel or "B" panel in the shop you attach the ground bus and from the ground bus via an ECG (Equipment Grounding Conductor) to a ground rod. You do not bond the second panel. In fact the neutral bus on the panel must be electrically insulated from ground. See NEC 250.32. If you are only going to have one (1) branch circuit at the second building then you do not need the ground rod.

There are numerous cites in the NEC that apply to this type of installation. Unfortunately, I only have a copy of the 2008 version of the NEC. Norfolk may well be using the 2005 version. I know that Virginia Beach just went to the 2005 version this year.

Quote:

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Originally Posted by stanfortyman

and 2) There are no other metallic paths between buildings such as CATV, phone or copper water piping.

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I failed to mention the trench includes 1. direct bury 2/2/4 2. direct bury 3-way #12 3. electrical conduit w/ CAT5/phone/cable 4. copper city water 5. cpvc well water. Does this preclude me from not running ground? Thank you.

Quote:

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Originally Posted by dmcjr1976

I failed to mention the trench includes 1. direct bury 2/2/4 2. direct bury 3-way #12 3. electrical conduit w/ CAT5/phone/cable 4. copper city water 5. cpvc well water. Does this preclude me from not running ground?

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NO, I'm sorry it doesn't.
That installation MUST have an EGC run.


And I forgot to say earlier. The dude at Home Depot was NOT an electrician. He was just the dude that works at Home Depot in the electrical dept.

First of all, thank you very much for your time. I'm new to these forums and very grateful.

OK, I redug the trench to install the additional cable (that was fun). However, the guy at Home Depot maintains his position that a common ground is not necessary because there are two separate grounding fields due to the distance (100' from house main to workshop main). He went further to say that a common ground would present a hazard because of the 2 separate grounding fields. Therefore, my grounding rod at the workshop main breaker panel s/b my only ground. Any thoughts? Also, where can I determine if this is in the code? I'm reconsidering having this inspected but I've been told that as the homeowner, I would not have liability assuming everything is to code. Thanks again for your time.

The guy at HD is clueless. There is no "grounding field". If you run a feeder to a detached structure (which is exaclty what you did) you MUST have a grounding electrode system (a ground rod) installed. This is quite clear in the 2005 NEC 250.32.
250.32(B)(1) describes a 4-wire feeder and 250.32(B)(2) describes a 3-wire feeder.

250.32(B)(2) was removed in the 2008 NEC.


I definitely would have this job inspected.

The reason you do not have a ground supplied from the main panel is that there could be a difference between each end of the ground wire from the main panel.

This difference of potential can easily be enough to cause a current between points A and B. You will have all manner of electrical problems if there is a ground current.

To stop that, you run a separate grounding system at the detached shop. You tie the ground bus from the sub panel to a ground rod at the detached shop. All bare grounds in the shop would attach to the grounding bus at the shop. Since the shop is grounded directly to earth, no ground loop will occur between the main panel and the shop's sub panel.

That leaves you with 2 ungrounded conductors from the main panel and one grounded (Neutral) conductor.

The electrical path from the Neutral conductor back to the main panel and via the EGC to the main panels ground.

If the main and sub-panel were in the same building, then it would be fine to use a 4 wire feeder between the panels.

But not when you go outside to a different building.

Do you need code-cites? Better yet, ask the guy from Home Depot what code references he is using to base his answers to you.

Quote:

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Originally Posted by donf

To stop that, you run a separate grounding system at the detached shop. You tie the ground bus from the sub panel to a ground rod at the detached shop. All bare grounds in the shop would attach to the grounding bus at the shop. Since the shop is grounded directly to earth, no ground loop will occur between the main panel and the shop's sub panel.

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3 wires is OK or are you saying that I need 4-wires but the ground rod will prevent the loop?:confused:

Quote:

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Originally Posted by donf

If the main and sub-panel were in the same building, then it would be fine to use a 4 wire feeder between the panels..

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I'm confused as to whether you are agreeing that I need four wires (w/ common ground) or if 3 wires is ideal with a detached structure.

Quote:

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Originally Posted by donf

Better yet, ask the guy from Home Depot what code references he is using to base his answers to you.

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Not being an electrician, I don't want to come across like I know what I'm talking about to him. I presume he's working under the old code since Norfolk is not on NEC 2008, but earlier posts lead me to believe that 3-wire feeder under the 2006 code would be prohibited due to the other metallic paths.
A code cite would be great if you happen to have one, neighbor ;) Stan gave me the cite for NEC 2008, but I don't think that is code for Norfolk at this time.

Thanks again (to all) for your time and sage advise. David

Don, your whole last post has me confused. :confused:

DMC, you seem to be not sure.

This is the correct answer:

Quote:

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Originally Posted by stanfortyman

The guy at HD is clueless. There is no "grounding field". If you run a feeder to a detached structure (which is exaclty what you did) you MUST have a grounding electrode system (a ground rod) installed. This is quite clear in the 2005 NEC 250.32.
250.32(B)(1) describes a 4-wire feeder and 250.32(B)(2) describes a 3-wire feeder.

250.32(B)(2) was removed in the 2008 NEC.


I definitely would have this job inspected.

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I think this is very clear.

Also, in the remote panel, the neutral bar remains isolated, does not get Main Bonding Jumper installed, (green screw or small strap that connects bar to panel box).

The equipment ground bar gets bolted directly to the panel box using machine screws, and connects all green and bare ground wires, including the #6 that will connect to at least one ground rod. Also connect a #6 to any metal water line in the building, if served by underground, keep as close to entrance no father that five feet in.

Always check with local codes for changes, but inspectors don't usually delete grounding for their code, they usually add,sometimes in error.

Dmcjr1976,

Pardon the slap at the Home Depot rep. Just curious were you using the Home Depot on Military Highway near North Hampton Blvd?

I was saying that three wire will be just fine since you are setting up a grounding system at the shop's sub panel.

The goal is to avoid and "un-desireable current" between the ground lines connected to both panels.

Setting a ground rod and using an EGC to connect the metal parts of the sub panel to ground at the sub panel creates a "Path of least resistance" right at the panel.

Quote:

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Originally Posted by donf

Setting a ground rod and using an EGC to connect the metal parts of the sub panel to ground at the sub panel creates a "Path of least resistance" right at the panel.

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Just so we are clear. A ground rod is NOTHING to do with the EGC or clearing faults.
Your fault clearing "ground" comes either from a dedicated equipment ground conductor , or a neutral to ground bond such as found in a main panel.

DMC,

Stan has given you the correct information.

Don, under the 2008 National Electric Code, this is not allowed any longer:

Quote:

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Originally Posted by donf

Dmcjr1976,
I was saying that three wire will be just fine since you are setting up a grounding system at the shop's sub panel.

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I don't even know what this means:

Quote:

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Originally Posted by donf

The goal is to avoid and "un-desireable current" between the ground lines connected to both panels.
Setting a ground rod and using an EGC to connect the metal parts of the sub panel to ground at the sub panel creates a "Path of least resistance" right at the panel.

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Do you realize that grounding is only for the purpose of insuring that the Neutral, equipment grounding, and exposed metal of systems are all at zero or "earth" potential" ?


You may be getting confused with equipotential and ground fault path.

Different parts of a grounding and grounded system have different purposes.

And regarding advice from retail clerks, never take their advice unless that person can produce a license or certificate for the trade they are advising.

Try asking for advice at a wholesaler counter. You will not get any advice.

TK - Stan,

Please educate me. I was referring to 2008; 250.32 (B) and (C) when I wrote my responses.

Did I misread the section? Also, I have a 2008 Study Guide that diagrams the sub-panel with a ground rod and EGC tied to the Ground Bus of the sub-panel. It also shows the Neutral conductor electrically connected to an isolated Neutral on the Neutral bus.

Has there been an errata page or modification to the 250.32 section?

Yes, 250.32 was changed to no longer allow a "3-wire" feeder to a detached structure.

My comment was that a ground rod has nothing to do with the equipment grounding conductor.

Thank you all. Your time is much appreciated. I'll be installing the 4th wire :)

Quote:

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Originally Posted by donf

TK - Stan,

Please educate me. I was referring to 2008; 250.32 (B) and (C) when I wrote my responses.

Did I misread the section? Also, I have a 2008 Study Guide that diagrams the sub-panel with a ground rod and EGC tied to the Ground Bus of the sub-panel. It also shows the Neutral conductor electrically connected to an isolated Neutral on the Neutral bus.

Has there been an errata page or modification to the 250.32 section?

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Why are you asking TK and Stan "only" . You have more than two qualified persons on this site. Just don't ask me, I'm new to all this!!








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