Wiring outbuilding

Recently I had a breaker box installed in an outbuilding (Homeline, 70 amps max, with 2 20 amp breakers). Power is supplied via an underground cable from the main fusebox in the basement of my house. The distance is around

100 ft and the cable is 12-2 w/ground. I wired the buidling myself (four circuits, 2 per breaker). The circuits supply 1 light and 1 receptacle in one room and 1 light and 1 receptacle in the other. However, as there was no ground bar, I tied all the grounds with the neutrals on the neutral bar. A bonding screw was included but not used. My questions:

  1. Does the NEC permit this? Is it safe? (I know that tieing neutral and ground together on a subpanel in the same structure is a no-no.)

  2. Should the building have its own ground rod? There are no connections between house and building except for the underground feed.
Reply to
B. Adams
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You need to add a "grounding electrode." (probably 2 ground rods if you really want to get picky.) If I understand what you said correctly, you should add the bonding screw in order to ground the metal panel box.

What kind of breaker do you have in the house to protect this circuit?

Best regards, Bob

Reply to
zxcvbob

Obviously what you have done is wrong. I am not sure if the grounding rod is an acceptable fix or not.

However, a 100' 12/2 line is pretty long. As long as you just have 100w lights and clocks on it you should be okay, but a significant load will exceed your voltage drop allowance real fast.

If you are not familiar with it, the link below should be helpful.

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Reply to
toller

I think 12/2 is a bit small for a 100' subpanel feed to an outbuilding. I would have suggested 10/3 as the cable of choice for a light load such as yours.

It is a code violation and a potential safety hazard to have the grounds and the neutrals connected together in a subpanel. Buy an appropriate ground bar for your panel and install in the subpanel and relocate all of your ground wires to it.

You do need to install at least one ground rod for your outbuilding and connect it using at least a #6 wire to the ground bar in your sub panel.

John Grabowski

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Reply to
John Grabowski

No the US NEC does not permit that. Since there is an Equipment Grounding (bonding) Conductor (EGC) in the cable you must use it to ground all non current carrying parts of the electrical installation back to the Service Equipment in the house. You need to install an add on EGC buss bar in the Garage's panel. These are available wherever SquareD equipment is sold. You then put all the EGCs on the add on buss bar and keep all of the neutrals on the built in buss bar. The reason for not running the neutrals and EGCs on the same buss bar is that in the event of an open neutral between the garage and the utility's transformer the voltage on all exposed metallic parts of the garage's electric system will go dangerously high if the EGCs are not separate from the neutrals.

The separate building does need it's own grounding electrode system. The minimum is a driven rod, eight feet or more in length, which measures less than 25 ohms resistance to earth after installation. The code requires that a second rod be added unless the first measures < than 25 ohms. Once you install a second rod the code is satisfied so most electricians install two rods to be done with it. The two rods must be at least six feet apart but more is better. Best practice would be to have driven the two rods through the bottom of the wire trench at ten and twenty feet from the building respectively and connect them back to the panel with bare number 2 AWG run in the bottom of the trench. Since it sounds like the trench is long back filled it is too late for that. Just drive the two rods at least six feet apart and connect them back to the garage panel with bare number four copper wire. Using an acorn clamp on each rod run the wire from the furthest rod back to the nearest rod through it's acorn clamp and back to the add on buss bar in the garage panel. That bare copper wire is called the Grounding Electrode Conductor (GEC). It must be protected by conduit if it is exposed to severe physical damage such as from lawn mowers or power trimmers.

-- Tom Horne

Reply to
HorneTD

HorneTD wrote in news:qgxhe.2232$ snipped-for-privacy@newsread3.news.atl.earthlink.net:

As I wrote in my original post, a bonding screw came with the breaker box but was not used. The instructions read: "When it is required to bond box to neutral plate, use long screw enclosed. Insert through hole in neutral plate and thread into hole in box." Does the NEC require it, in addition to adding a ground buss?

Reply to
B. Adams

You *don't* need to install another buss. (I'm assuming you are running a 240V feeder to the garage, and you are using the white wire for one of the hot legs.) In this application, your little panel is considered "service equipment", and it can have a common ground and neutral buss. But the metal box has to be grounded, and that's what the bonding screw accomplishes. If you are running 120V to the panel in the garage, and the white wire is neutral, then you should install a ground buss in the panel and leave out the bonding screw -- but I don't know why your would go to the expense of using a breaker panel in the outbuilding if you just ran a 12/2 120V circuit.

I don't know that the equipment grounding conductor in a 12/2wg cable is sufficient for a grounded neutral wire. You really should have used bigger cable. But maybe it's OK. Your whole installation doesn't make a lot of sense to me.

Best regards, Bob

Reply to
zxcvbob

Inserting that screw is the same as connecting your grounds and neutrals together. NO. Do not insert the green bonding screw in the neutral bar and screw it into the threaded hole for your subpanel. This is only done in your main panel. I'm beginning to wonder if you should be doing this type of work. From what you have posted so far it seems as though you have shortcomings in your knowledge concerning basic wiring.

John Grabowski

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Reply to
John Grabowski

zxcvbob wrote in news: snipped-for-privacy@individual.net:

Thanks for your input. It's 120V, not 220, and it's to a small utility buidling. Also, the load is generally very light, just a couple of 100w bulbs. Occasionally a space heater, which pulls 11 amps.

Are you suggesting that the breaker box was not necessary? The guy who did the work was not a licensed electrician, btw, just a neighborhood handyman who had done work for me before. I hired him to replace the old cable after the building lost power. It turned out the old underground cable had been spliced with pvc tape and had burned in two! There was already an old rusty fuse box in the building and he replaced that with the new breaker box. Who did the original work I do not know, but it sure was a hell of a mess.

Reply to
B. Adams

Do you know what kind of cable he used? It should have been UF cable (underground feeder). It looks like regular NM-B cable, but it has a tough PVC jacket that is weather-proof and sunlight resistant. UF costs a lot more than NM, and it's very difficult to work with.

I think all you *really* needed was a deep double-gang switch box for your light switches. You also need to use GFCI outlets. A ground rod woulda still been a good idea but I don't think necessary.

You have a 120V service box with multiple circuits; you need to install a ground rod.

Bob

Reply to
zxcvbob

No the US NEC Does not require or permit the installation of the bonding screw in this case. To install it would be a violation of 250.24 (A) (5) vis..

250.24 Grounding Service-Supplied Alternating-Current Systems. (A) System Grounding Connections. A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A)(1) through (A)(5). (5) Load-Side Grounding Connections. A grounding connection shall not be made to any grounded circuit conductor on the load side of the service disconnecting means except as otherwise permitted in this article.

-- Tom Horne

Reply to
HorneTD

I'm not going to suggest it I'm going to state it as fact. By installing that circuit as a feeder that supplies overcurrent protective devices he has made work for you with no benefit. If he had simply installed a multi wire branch circuit to the out building he would have doubled the available power without triggering the requirement for a grounding electrode system. Let me suggest that you install a two pole switch assembly in place of the breakers now in use and add a ground bar. This will turn the underground wire into a branch circuit and relieve you of the requirement to install a grounding electrode system.

-- Tom Horne

Reply to
HorneTD

HorneTD wrote in news:x7Che.3242$ snipped-for-privacy@newsread3.news.atl.earthlink.net:

UF was indeed used and GFCI receptacles.

Reply to
B. Adams

NO. In a subpanel, the NEC requires that the neutral NOT be bonded. Bonding is

*only* for service entrances.

-- Regards, Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?

Reply to
Doug Miller

While installing a ground rod(s) is not required if you use the ground (bare) wire from the house, I'd highly suggest you install at least one rod. The main reason is that if lightning hits near that shed, the force will have to travel back to your main panel in the house, and do damage in there. It's not that hard or costly to drive a ground rod and connect it. You could save your computer and other stuff in the house if lightning hits near the shed.

You should NOT be using the neutral for grounding. But the ground bar for your box, or considering that you probably have 5 at most bare wires, you could just wirenut them together including the one from the house. But if you use a gound rod, that #6 wire would be hard to wirenut into the bundle. Ground bars are only a few $$.

Why did you use a 12-2 wire for FOUR 20A circuits. If you have not yet buried the cable, I'd replace it with at least 10-2, or preferably

10-3, which would give you 220 availablity. Otherwise, you are running a 20A circuit to four 20A breakers. Rather pointless. You may as well have just relied on the house breaker and skipped the breaker box in the shed.

Mark

Reply to
maradcliff

The 12-2 may not be very good if you add any power tools. Most table saws should be on a 20S by themselves and not with lights.

Reply to
Edwin Pawlowski

"Edwin Pawlowski" wrote in news:krNhe.168$ snipped-for-privacy@newssvr19.news.prodigy.com:

Thanks for the advice, everybody. I gather that there was really no need to install a breaker box in the outbuilding. I was wondering about that since the main panel in the house would offer circuit protection. So when exactly would you need to install a subpanel or additional box in a separate structure?

Reply to
B. Adams

You put a subpanel (service panel) in the outbuilding when you *really* want more than one circuit out there. A building can only have one electric circuit coming in (with a few very specific and odd exceptions.) So you run a *big* circuit into the building and then use the panel to split it up into multiple small circuits.

In your case, maybe you would run 10/3 cable with a 2-pole (240v) 30A breaker in the panel at the house, then have several 15A or 20A breakers in the garage panel, and have the capability of later adding a 20A 240V breaker for an air compressor or 3500W electric heater without needing to add any new wire from the house. Another good thing about that is, if you overload a circuit, the smaller breaker in the outbuilding usually trips rather than the big one in the house.

Best regards, Bob

Reply to
zxcvbob

Let me suggest that you install a two pole

Had the CB box been properly installed as a branch circuit with neutral and ground separate would the additional ground rods be necessary?

Reply to
John Gilmer

NO, at least not if the circuit from the house was not suppling Over Current Protective Devices. The exception that allows you to avoid installing a grounding electrode system in a separate building applies to buildings supplied by a single branch circuit with an Equipment Grounding (Bonding) Conductor run with the circuit conductors. The US NEC specifically says that a multiwire branch circuit is a single branch circuit for purposes of that exception. The definition of branch circuit is "the circuit conductors between the final overcurrent device protecting the circuit and the outlet(s)." By using the twelve gage underground conductors to supply over current protective devices the local handyman has turned it into a feeder vis.. "Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device." The quoted materials is copyright

2002 National Fire Protection Association.

-- Tom Horne

Reply to
HorneTD

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