Problem: I am getting shocks on the aluminum siding of my garage.
Background: I have a single 12/2 romex wire running from from my house feeding my garage. In the garage, it goes into a junction box, where the lights for the garage are connected. The feed into the junction box is only 2 wires, there is no ground. I consulted an electrician (relative) and he suggested to run a copper wire (6 wire?) from the junction box to a grounding rod, and sink the rod into the ground. I did this, and am still getting shocks. I checked where the feed enters the garage, thinking maybe the wire is nicked, but it is not. Any other suggestions, before I replace the feed wire (underground)?
The first thing you do is make sure the shocks are coming from this source. Kill the power to the wire from the house and see if you're still getting the shocks. If you are, then suspect a buried service that you don't know about.
I am not sure if putting in a separate ground rod is up to code. I suspect it is not, but others can tell you better.
Since you say the feed comes underground, I assume that this is a detached garage, entirely separate from the main house. And when you say "12/2 romex", I assume you mean direct burial UF cable, typically gray, with heavy rubber insulation, right?
You probably have a short somewhere in your garage, not in the feed itself. I would shut off the power to the circuit at the main panel, then poke around with a multimeter. You should be able to see continuity from the hot or neutral to the AL siding in your junction box. From there, start disconnecting wires and try to pin down which leg of the circuit has the short.
Could be someone put a nail through the siding and into the romex in the walls. Or you got some wear or nics where a wire goes through the siding on the way to an exterior light, or something.
Check your grounds and neutrals connections back at the main box. also continuity of your 12/2 neutral wire. A burned or dirty connection there or bad neutral could cause power to seek the path of least resistance back to ground, your metal siding. Let us know what you find. Dave
Does your relative have a vested interest in your death? (life insurance for example) Consider discussing electrical issues with some one else in the future. What is described is a ground loop which is expressly prohibited by the NEC. I will not labor the point of "supplemental grounding" because you do not have a ground conductor.
Some one else suggested that the sheath of the romex may have been pentertated buy a fastener for the siding. This is a good clue and may end up leading you to the exact cause. A VOM or continuity tester on a dead circuit may help you discover the area of the problem. Your going to have to open secitons of the wiring until you find the problem.
Basic electrical theory 101. You already confirmed that when you kill the feed, the problem goes away. So now move to the next step. Shut the power and at the junction box disconnect the wiring where the feed is connected to your lights, so you isolate the problem. Turn the power back on to see if you still get shocks. If no, skip to step 2 at the bottom. Otherwise shut the power and remove the feed from the junction box. It could be shorting on the romex clamp. If you still get a shock, it's something underground.
Step 2: check your lighting circuits to see if anything is shorted. Disconnect all the wiring and connect 1 light at a time to see where the problem is coming from.
What I suspect you have is a neutral to ground fault in the wiring in the garage. Is this a detached garage or is it part of your house? Much of what follows is for a detached garage.
Sleeve the cable; whether existing or new; with rigid nonmetallic conduit from the bottom of the trench to were it enters the garage all the way to the first box to protect it from future physical damage. Check all the metal boxes in the garage until you find the one that has a fault between one of the current carrying conductors and the box itself inside of it. The most likely culprits are boxes that are set in or on the siding to mount outdoor lights on. Once you clear the fault between the current carrying conductors and the metal box the sneak current path to the siding will be broken. After you find and clear the fault you should install a ground fault circuit interrupter in the first box in the garage and feed all of the garage loads from it. This will protect you and your family from a possibly deadly hot to ground fault occurring later. This is the minimum you would need to do to solve the problem.
Be advised that some wiremen intentionally attached the neutral to metal boxes when working with nonmetallic cable before it was manufactured with an Equipment Grounding Conductor in the cable. It was a misguided attempt to provide a fault clearing path that has the unwanted side effect of placing stray neutral currents on any metallic object that is in contact with the metal boxes. If the neutrals in the garage wiring are deliberately bonded to the metallic boxes you will need to rewire the garage in order to clear the faults.
If you do have to rewire the garage and you are not replacing the outside branch circuit to the garage then replace all of the boxes with plastic boxes. Once you do that the garage wiring will be double insulated. The insulation of the conductors and the devices provide one layer of insulation and the plastic boxes together with the plastic cable jacket will provide the second insulating layer. This will markedly lower the likelihood of another fault occurring later.
Even if you decide to run a new outside branch circuit or feeder to supply the garage you will still have to locate and clear the fault between the current carrying conductor; either the hot or the neutral; and one or more of the metallic boxes inside the garage.
If you do replace the outside branch circuit you should consider whether you will need more power in the garage later. If the garage is sound enough to support a second story or there is room for a ground level addition then consider the possibility of a future auxiliary apartment, shop, hot tub, swimming pool, and so forth. Once you dig a trench the additional cost of installing conduit is very small. In order to have a range of options you would install a two inch conduit so that a feeder up to two hundred amperes could be installed in the future without additional excavation.
If you actually anticipate a separate dwelling unit at the garage location you might even want to run a three inch schedule eighty plastic conduit so that the utility could run a service lateral to supply a separate meter at a later date. Installing a one inch raceway for future communications wiring would be a smart move also. If you anticipate a future need for water or sewer to the garage then run the piping now. Since that takes a deeper trench you could use the deeper trench to install a better grounding electrode system.
One last thing to think about when doing trenching is that it is a good time to improve the system grounding. If you install a feeder to the garage then the garage will need to have it's own Grounding Electrode System. The easiest one to install would consist of two driven rods placed at least six feet apart. If instead of that minimum you installed the rods by driving them into the bottom of the trench they will then be deeper then if they were driven from the surface. The further apart the two rods are the better they will dissipate stray energy such as surges, spikes, and lightning. Running bare number two copper Grounding Electrode Conductor (GEC) for at least twenty feet in the bottom of the trench will also improve the grounding electrode system. If the rods strike hard bottom when being driven you are allowed to lay them in a trench if it is at least thirty inches deep but deeper is better. If there is a metal well casing or other underground metallic piping somewhere between the house and the garage then you would route the trench past that piping so you could bond the GEC to the underground metal piping so the pipe can serve as an additional grounding electrode. A metal well casing of any appreciable depth makes a great grounding electrode.
I hope that this is helpful. Let us know what you decide and how it works out.
If his neutral connection was so bad that going through siding and him was the best path, then he would certainly notice that the lights were not very bright!
You have some good tips on locating the source of your short. I would like to point out that every electrical circuit should have a "GROUND". In fact, if it's a detached garage, I don't believe an under ground feed is within code, unless it supplies a sub panel with a legitimate grounding rod buried
It clearly was not the best path: he's still alive to ask questions.
Equally clearly, there was an alternative path; otherwise, none of the lights would have worked at all unless someone was standing there touching the siding.
It doesn't have to be the *best* path to get a shock off of it. It just has to be *a* path.
-- 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?
When non metallic cable was first manufactured it did no have a ground wire in the cable assembly. That includes both underground feeder, type UF, and Nonmetallic Sheathed Cable, type NM.
If a structure is supplied by a single branch circuit no Grounding Electrode System is required. There is also no requirement to have a panel in a residential garage. A detached garage on non residential property would have to have a building disconnecting means and one way to provide that is to install a panel that is suitable for use as service equipment and has a main breaker or contains six or fewer breakers.
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