I have seen 3 ohms stated as a typical ground resistance for an urban metal water distribution system. The NEC considers 25 ohms ground resistance acceptable for a single ground rod, or you can use more than
2 rods and it doesn't matter. Would seem like a water pipe is a better grounding electrode.bud-
In any installation governed by the US National Electric Code you must use the underground metallic water piping as a grounding electrode. Not using it is not a choice you would have.
-- Tom Horne
Then what pray tell are you grounding to? The grounding impedance of two driven rods is often over fifty ohms. The grounding impedance of underground metal water pipes that are part of a community water system is usually less than ten ohms. Changing what we say does not reverse those figures. It is the underground metal water piping that provides the low impedance connection to earth. The driven rods are strictly a back up in case the piping is replaced with non conductive piping.
-- Tom Horne
Are you sure? I don't have a copy of NEC here, but what I remember was verbage more like this:
"If ten feet of metal underground water pipe is available, it must be used as a grounding electrode; however, it must always be supplemented by an additional electrode."
--- from:
Water line MUST be unified to electrical ground, and a jumper MUST be placed across the water meter so that ground is still good if the meter is removed and elmnates meter rubber washer interfying with a good connection
And city code here requires electrical isolation from the water system. Meters, installed at the street, have about 10 feet of plastic pipe before they make connection with the copper pipes going to the house.
Actually it is + 60 times a second and - 60 times a second. Sixty hertz is "60 cycles per second" and each cycle has both + and - alternations. Reversed power wiring often is caused by people who are more familiar with automotive or electronic wiring than with AC power conventions. It obviously works but creates totally unnecessary and possibly severe hazards.
Don Young
I have no idea what "get electricity OFF the pipes" means.
You are right about 10' - in the post of Rich256 the water pipe (plastic) is not a grounding electrode.
Of the electrodes normally available in a house, the best by far is 10' or more of underground water pipe (doesn't have to buried 20') and if such pipe exists it MUST be part of the grounding electrode system. This was the only required grounding electrode until recently.
The ONLY reason a suplementary electrode is necessary is that the metal water pipe may in the future be replaced by plastic (as Tom Horne said). Note the term "supplementary". If the water pipe is metal the supplementary electrode adds little or nothing.
Of the "supplementary" electrodes that can be used, probably the worst is a ground rod because of high ground resistance. Unfortunately it is the easiest to provide. Far better. with a long term tested ground resistance of 5 ohms, is a concrete-encased electrode (Ufer ground). These are easy to include in new construction. Next best is probably a ground ring - also easy to provide in new construction.
bud--
probably negative-ground DC. where the - (ground) wire is often black.
If you're using that 60Hz AC to power an incandescent light, the light output is 120Hz (since either polarity lights it). It wouldn't be easy to get 30Hz from it.
According to Bud-- :
Recent electrical code revisions appear to be prefering grounding plates over rods. These plates are approx 12" square by 1/4" thick.
More surface area than a rod. Somewhat trickier to install - undisturbed dirt contact, not just flung in the backfill.
I believe that this is the activity of making sure that the water coming out of your shower is the same electrically as your ground.
That way, you do not get shocked just because you left hand is in the water while your right hand is holding the shaver with a case ground.
AC mean that 30 time a second that one wire is +, the other 30 times a second it is -.
Now, that timing needs to be the same as your water supply. That way, when your water is +, so is everything else.
No current flow possible.
If it is +, when everything else is -, then you get shocked.
You may be right. I would have to get access to an oscilloscope to be sure.
Either way, it switched way to often and fast for me to try to keep track of it so I just try to make sure that all my plugs are the same.
The thing that amazes me is how few people actually know or understand this fact (AC switches + & - on the same wire).
I have even had people that worked with the electric company who's profession was to work on the high lines that constantly clamed that I was wrong.
He kept saying that an AC current was traveling down the line, but could not comprehend what that actually meant.
Swore that the + wire was always +, but with an AC signal going down it.
No. 60 times a second one wire is + and 60 times a second that same wire is negative. The other is always at ground potential. The hot wire actually gets to about 170 volts positive and 170 volts negative during those swings. The RMS voltage being 120 volts.
Or about 162 volts peak if we refer to it as 115 volts AC.
A quick look shows there are quite a few web sites that describe this:
Now if you have 240 volt service one of the hots gets 170 volts positive and at the same time the other line is 170 volts negative. They both cross the 0 volts at the same time. So if you are looking at them relative to each other the one line gets to be 340 volts different than the other.
In Europe with 230 volt service one line is grounded and the other gets to 325 volts at 50 cycles (Hz). Or about 310 volts peak if you refer to it as 220 volts.
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