In my basement, the main service panel is on one side of the house and they had to run about 25 ft through the joists to tie the ground into a copper water line. I need to add a couple of circuits in the basement. Is it acceptable to run the romex through the same holes as the copper ground? The holes are plenty big. It would save me drilling about 20 new holes.
Thanks,
Why not? It would make your house less weakened by not drilling new holes. As long as you don't run the romex thru the pipe there should be no problems. Double-check your local code guy. Adding circuits in the basement means you will have to GFCI the outlets or at the box.
Nothing down there is on a GFI at the moment.
New code requires it in most cases. You might as well cover the existing ones while you are at it. Theoretically you do not but the inspector could decide he thinks you are making changes and have to bring it all up to date. If you are having it inspected or not. Home inspector could ding you on resale as well. If they are on their own circuit then changing to a gfci breaker in the box will do it.
GFCI is required for receptacles in an "unfinished basement". Once it is "finished", you can use regular receptacles. Of course "finished" is subject to interpretation.
Cheers, Wayne
Is the idea that a finished basement is less likely to get flooded and thus is less likely to be a hazard????
The instructor at my code classes says "unfinished" means an uncovered concrete floor. Concrete is a conductor so there is a greater possibility of someone getting shocked.
AHA!
Dry concrete is a very poor electrical conductor, probably as poor as dry wood. Damp concrete is another story, along with damp wood.
Then why does the U.S. electrical code consider concrete, brick or tile walls as grounded when considering working clearance requirements in front of panels? See Table 110.26(A)(1) Why is a Ufer (concrete encased electrode) ground such a good ground for lightning protection?
I don't know anything about the electrical code, but I do know facts. Go get your ohm meter and measure the resistance between a dry concrete floor and ground. If you can't get a reading, put a few drops of water on the concrete. Still if the slab is dry, there will be a very high resistance.
Actually I do remember part of the code, but it may just be for FL? The rebar in the footing is all electrically tied together and serves as the ground instead of the ground rods. That isn't too bad since the footer is on ground that will normally be damp. But up a foot, on top of a layer of stone, the concrete floor normally stays dry, if it's done properly anyway.
If you are so confident about this assessment, then grab a 12 gauge conductor (wire) that is long enough to reach from one of the input terminals of a power meter and touch it to the nearest concrete slab while having it wrap around your arm from elbow to wrist (insulated wire is okay).
or
If the meter is above a concrete slab, touch that terminal while having bare feet.
You might find the results shocking. :)
That test would require an expensive specialized tester. The U.S. code says one is supposed to drive a ground rod, test it, and drive a second if the first one doesn't show 25 ohms or less to the earth. The instructor asked how many electricians had one of those testers. No one out of fifty or so did. He gets similar responses where ever he goes. People just drive two ground rods and are done according to code.
Herbert Ufer developed this during WWII in Arizona. The Army needed a better way to ground for the bomb bunkers. I guess ground rods would have been impractical in meeting the Army's requirements in the Arizona soil. . Using rebar in concrete solved the problem. Resistance to earth was under 5 ohms even years later. There is some info here about halfway down the page:
Dry or damp, my experience is that concrete is often worse than wood. I have seen plenty of concrete acting electrically as if it was damp while wood that has been on top of the same concrete in the same spot of the same basement for years behaved as dry wood.
I would consider concrete baked to be *known* to be dry about as good as wood that is "merely looking good and dry".
I would be more concerned about what the resistance is once the contact area gets to be that of a human hand or a human foot. An ohmmeter probe has contact area smaller than that of human hands and feet by about
3 orders of magnitude. And perspiration is a lot more conductive than most tap water.One more thing, slightly important: Getting less than 100 or 50 mA conducting through your body does not mean that you will certainly survive the shock. Many sources say that 100-1000 milliamps is a deadly range due to causing ventricular fibrillation, and some say that range goes down to
50 mA. But I would not consider 40 mA safer than a few amps. I have heard of the rare failure to survive getting shocked by 30 mA neon sign transformers, and I don't think that survived full-current shocks by those frightening things are all that common either.Now, for an even more important thing: Shocks of a few milliamps can be bad, even if you feel safe betting your life on lack of electrocution by a few milliamps: The shock can still jolt you into contacting a source of a worse shock, or more likely can jolt you into falling and/or throwing/hitting/bumping-into things and breaking things including your body. A 1 milliamp shock can startle a few people. A 3 milliamp shock probably startle many people. 5 milliamps can cause involuntary muscle contractions, and 10 milliamps usually does and also usually produces a startling amount of outright major pain.
What kind of "expensive specialized tester" are you talking about? An ohm meter? Also where exactly do you test it, from the ground rod to where? To the neutral?
So is that national code now or just code in FL?
Yes it is, but with perspiration the concrete wouldn't be dry like I said. I think it's mostly the salt in perspiration that makes it more conductive.
Well I don't know the mA of the hundreds of shocks I've received, and I'm not saying any of this is safe, but at least 5 times I got the 35KV from a large color monitor. Enough for it to have arced about an inch before it got me. And a few times accidentally touched the horizontal output transistor with one hand and the other hand to ground. I forget the voltage there, over 1000v and high frequency. The high frequency really gives it a bite! I had a customer call me to repair their pinball machine in their basement. The complaint was they were getting shocks. This model from the 60's is among the few that used line voltage for the coin switches. I got there and a kid with bare feet was playing it. I pulled the plug and got him out of there. Then the mother came down and told me it only happens when they come in from the pool soaking wet! Holy shit! I found and repaired the short from line voltage to the metal door, to the hinge, and to other brackets where they were getting shocked. Then I replaced the lamp cord and plug (not polarized) with a grounded cord. Ran a ground wire all over the machine to almost every place a dangerous situation may develop. And before leaving told the whole family to never touch it unless they are dry and wearing shoes.
I would have no problem at all taking a 12 gauge hot wire with no breaker and touching it to a dry concrete floor. If I can find an easy spot on the garage floor that isn't epoxy coated maybe I'll video it for you.
What is the point of having insulated wire wrapped around my arm? What is that supposed to do?
Yes I may indeed! But only a fraction of the shock having one hand grounded and accidentally touching a hot terminal with the other hand.
Reminded me of a cabin we would go to as kids. Had to plug in the refrigerator when we got there. Then it was a 50/50 chance if it would give us shocks when barefoot, if it did then we would turn the cord to switch the polarity.
I've never seen one and don't know much about them. They're called ground resistance testers. Prices on a quick search ran from about $700 to over $5000. The test is from the ground rod or electrode to the earth. I ran across this while looking:
National, I think. It was one of several alternative for a long time. There was a push to get the concrete guys to put them in in all new construction. Electricians are supposed to use everything that's available. I work on irrigation systems which are probably more prone to lightning than say houses. We've been using the ufer ground for some time. Besides, it's easier to stick an extra rebar in concrete than drive a rod.
I asked because I tried using an ohm meter on my newer service. I could't get accurate readings with any of my VOM's. My guess was that there was some slight chemical reaction between the rod and the earth making a sort of battery. Switching polarity of the ohm meter gave different strange readings. Basically it looked like I had over 30k ohms! I don't suggest others do this, but I disconected the ground wire from the rods. Then I took an extra 30 amp breaker and ran the hot outside. Turned on the breaker. Measured 120VAC from hot wire to ground. Touched hot to ground rods and got a spark and the breaker blew. I didn't need to do the math, it's well under 25 ohms! When testing the ground in a home, I normally use a 100 watt light bulb from hot to ground. If it's not full brightness I say it's bad. I don't think those handy little outlet testers put enough load to really test the ground. Maybe they do now, but back 30 years when I first bought one I realized it's ground test was useless.
Wouldn't the electrician need to come out before the pour and bond all the rebar together, then run one rebar out for the service? I was told it all had to be connected, or at least real connectors all the way around the perimeter of the footer and to the wire mesh, the little "twist ties" the concrete guys use are not enough. Copper wire and brass/bronze clamps in a big loop.
You can't determine ground resistance with a single measurement on a single VOM. Here's why:
"Ground" is the potential of the earth in bulk. When you want to connect to "ground", you use a grounding electrode (e.g. a ground rod), but since you aren't connecting to all of the earth, you have a resistance between your grounding electrode and "ground". This is the resistance of the earth in the near vicinity of your grounding electrode.
[For the case of a ground rod, think of the earth around the rod as divided into concentric cylindrical shells of fixed thickness and increasing diameter. Then the resistance of the individual shells goes to zero as the diameter gets large. When you hit zero (or close enough), you've hit "ground". The sum of the resistances of the shells is the resistance of your grounding electrode.]So how do you measure the ground restistance of a grounding electrode? You can hook one lead of an ohmeter to the grounding electrode, but where does the other one go? The only place you could possibly put it is in the ground, but in doing so, you've created a second grounding electrode, and you are measuring the resistance of the two in series. [If the second electrode is just a little voltmeter lead, it will be a very poor grounding electrode, and the resistance will be quite high.] That is why measuring ground resistance is tricky.
[Don't quote me on this, but I think with three grounding electrodes sufficiently far apart and a digital voltmeter you could determine the ground resistance of each one as follows. Measure the resistance of each pair of electrodes to get the sum of their two ground resistances. Then solve the simple system of three linear equations in three unknowns for the individual resistances.]Unless you have disconnected the grounding electrode conductor connecting your ground rods to the main panel, you aren't checking the resistance of the ground path. It would be very unusual for the ground path to have low enough resistance to trip a breaker at 120V. For end use voltages (120V-480V), the ground path is never relied on to trip breakers.
Cheers, Wayne
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