Electrical problems and a concrete question

[mike rawl]

Hi Everyone,

I recently moved into a house that has a small one car garage that I am turning into a workshop. The floor of the garage was poured so that there would be concrete under the car tires but the space in between is dirt. I do not want to have any dirt on the floor of my shop so I am digging out the dirt so that concrete can be poured. I am not sure if I will pour the concrete myself but digging a hole is something I can do well. The question that I have is would digging 4" down and poring the concrete strait on the dirt be ok or should I dig deeper and put down gravel bed to put the concrete on?

The electrical problem I have is a frustrating one. The electricity in the garage is all messed up. I when i try to turn on any electrical device the lights go out. It isn't the equipment because the equipment works fine every where else. I did not realize it when I first moved in but the florescent light fixture is even loading down when turned on. I have isolated or unplugged everything and nothing seems to fix the problem.

I have looked at the breaker box and it seems to be wire ok but I have a question, the neutral and ground are identical in the garage's sub panel. Is it supposed to be this way. I thought that in a sub panel the ground and neutral were supposed to be separated. The home inspector didn't mention anything about it so I guess it is ok. I went to HD today to look at breaker boxes and could not fined one where the ground and the neutral can be isolated from each other. I have also redone every electrical connection in the box to see if the breakers, corrosion, or anything else could be the problem. Nothing I did fixed the issue. The only thing that I have not take apart are the wall outlets

Another thing that is strange is the electricity that is coming in. At the main breaker on side reads 74V ac and the other side reads 170V ac. Is this normal or is it odd? I am not sure how accurate the readings are because I am using a $7 harbor freight multimeter.

Any advice that can be given on either issue would be greatly appreciated.

Thanks,
Mike

[Bill ThompsonNM]

Sounds like you should find an electrician to hire for a half day before you damage some equipment.
I would consider gravel and maybe even some insulation under the concrete.

[Charles Lent]

You have a problem with the Neutral line coming from your house panel if the garage is the only place with this voltage unbalance problem. If your house is also having different voltages between the incoming lines, then the power company is having the problem or it's where the neutral connects to the main panel. Open or poor connections of the main neutral lines will cause all kinds of strange electrical problems like this where the voltage is very low on on 120 volt circuit and very high on the other. You can also experience shortened lamp life and damage to appliances. A failed main ground connection to the house main panel could also be a part of the problem. This is the only place where the main ground and the neutral buss should be connected together. If you aren't experienced in working with high current electrical power circuits, call an electrical contractor to solve this.
This problem is very serious and needs attention immediately.

Charley

[Jerome Stanek]

Put down plastic under the concrete you don't need stone to pour on

[mike rawl]

Thanks for all the info. I did some more looking at my sub panel. I realized that I was checking the power at the main breaker with the lights on which messed up the reading. With the breaker of and no load it reads 120/120 like it should. I did notice something that may explain why it is unbalanced but I am not sure. There is a 3 wire feed from the house, 2 hots and the neutral. The ground attached to a grounding rod at the garage. The neutral and the ground are electrically identical. if I got a new pannel that separates the ground and the neural would that cure my problem or should I try to get a 4 wire feed from the house?

[Nick deMolitor]

Another thing that is strange is the electricity that is coming in. At the main breaker on side reads 74V ac and the other side reads 170V ac. Is this normal or is it odd? I am not sure how accurate the readings are because I am using a $7 harbor freight multimeter.

Thanks for all the info. I did some more looking at my sub panel. I realized that I was checking the power at the main breaker with the lights on which messed up the reading. With the breaker of and no load it reads 120/120 like it should. I did notice something that may explain why it is unbalanced but I am not sure. There is a 3 wire feed from the house, 2 hots and the neutral. The ground attached to a grounding rod at the garage. The neutral and the ground are electrically identical. if I got a new panel that separates the ground and the neural would that cure my problem or should I try to get a 4 wire feed from the house?

Definitely bad neutral connection. Your voltage should always be 120/120 +/- 2 to 5 v Whats happening is when you turn your lights on they are not connected well enough on the neutral. The neutral should carry your unbalanced load, instead it's coming back on the other phase. So it's as if some of your lighting is in series. Same as the plugs when you try a tool, any power for the tool has to travel through the lighting to get to the tool. As an electrician I'd call an electrician.

edit: The one thing you could check is with the power OFF. Try to tighten any connections in case it is just a loose connection.

[Charles Lent]

I agree with Nick. You still have a bad Neutral connection somewhere. It is connected well enough for the 120/120 readings with no load, but does not carry the unbalanced load when any equipment/lights are on. A poor connection will cause this, and it can cause a fire, as the poor connection will get very hot when current is flowing through it. This heat can damage the electrical connection, so it may require more than just tightening. Call in an electrical contractor and have this fixed correctly before you ruin your equipment or burn your house/garage down.

Charley

[Steve Meliza]

For a sub panel the neutral and ground must be separate so you need a 4 wire connection back to your main panel. There are some exceptions to this rule, but I don't believe that any apply here. Since you are aware of the requirements and what is needed I don't see a problem with you doing the work on your own to run new wire to feed the panel and even replacing the panel if needed to get the neutral and ground separated and eliminate any doubts about loose or corroded connections. I believe you can leave the ground rod at the garage connected to the sub panel.

Many panels that you can buy at HD do come with a split ground and neutral and include a green bolt for connecting the neutral to ground in case you are using the panel as a main panel. The problem is you're not seeing two separate bars because some panels require that you buy the ground bar separately for use as a sub panel. For an example sub panel go to HD's website and search for "HOM1224L125VP". This panel has no main breaker (just lugs for connecting the feeder wires), slots for 12 full sized breakers, and comes with two 20A breakers all for about $44. If it is a long distance to the main panel or you want the ability to kill power to the sub panel without walking back to the main panel then search for "HOMVP5" to get a panel with a 100A breaker and room for 20 full sized breakers and five 20A breakers for about $53. Note that with this second panel you have to buy and install a separate ground bar "PK23GTA". The first panel that I mentioned was designed to be a sub panel so it already contains a separate ground bar. I don't know what you have now, but if putting in a new feeder wire I suggest NM-B 6/3 and a feeder breaker in the main panel rated for 60A.

[Ron Natalie]

Where are you putting the other wire from your HF meter?

Is this an attached garage? Actually, in older versions of the code, you were allowed to run only three wires to an accessory building provided there were no other metallic paths (water piping, phone, cable, etc...) to the building. However, something is definitely wrong, so I would definitely have an electrician in to look at it and what you want to do.

[Kevin W Johnson]

My 2009 shop is an accessory building, and only 3 wires running from main panel in the house to the sub-panel in the building. The ground for the sub-panel goes to its own ground rods, per code.

[Jim Andrew]

Pouring concrete on dirt is a problem, as the dirt tends to absorb the moisture out of the concrete faster than is good for the concrete. I poured a driveway once on dirt, and it dried so fast that the concrete cracked as it was drying. I mean cracked every which way.

[Ron Natalie]

Usually it's the other way around. We put a vapor barrier down to keep the moisture from the soil OUT of the concrete. But it ought to work both ways.

[Ron Natalie]

The 3 wire exception was removed in the 2008 NEC. It would depend on what the effective date of the code in your area is.

[Kevin Presutti]

Mike,

First I would check from one existing slab to the other as to how level it is. You will be "cold jointing" the concrete to the two existing slabs, not really optimal choice and I'm sure you would prefer to have the floor somewhat level. How big is the garage, how many square feet, how much of the garage has concrete already there? All very big deciding factors on what to do. Concrete is an investment and generally not easy work, so you really want a good job that will last, most important is good it's not easy to make right once cured. As far as your electric problem is concerned it sounds like you have one circuit into the garage probably 15 amp and the wire is way undersized probably 14 ga. If the garage is detached and is more that 20 or so years old most likely that is the case. If you pm me with answers to some of those questions I asked I would hope I could give you some sound advice.

Kevin

[Brad Schafer]

you don't want multiple ground points, thus the 4 wire "take ground back to the main panel" discussion. it will work as is but if you have a wiring issue (like you apparently have) it's a potentially dangerous situ.

i saw something like this happen years ago when someone had wired into a box assuming that it was just some kind of junction ... when it was a junction for a 3 way switch ... so "connecting black to black and white-to-white" didn't exactly do what was intended. sounds like maybe the lights are involved in such a mess. unless you know what you're doing, i concur with the other guys - get someone who knows their stuff to take a look.

much luck, -b