and examples of what is sold in europe
Rationale is that for a bar of length 1.5 * l ,the first 0.5*l doesnt't
account for much since it has a resistivity much higher than the deeper
part (for a soil with homogen resistivity, furthermore, it's likely to be
drier). Approximate formula is R = r' *(ln(4l/r))/4*pi*l. Sorry, this
stupid html is a pain in the ass for formulas > ================================
> Note: All of my responses will be for the USA, Nec 2005..........
>
> At least one Supplemental ground rod is required, at least 5/8" x 8' driven into the earth in
> addition to the main incoming domestic water service line. Providing it is metallic. By the way
> homes have had copper water lines since 50s. Most Power Utility Companies require two Supplemental
> ground rods to be driven for grounding electrodes in addition to the incoming domestic water line.
> A grounding electrode conductor is run from an approved grounding water pipe clamp, connected to
> the incoming water line. And the other end is terminated on the neutral/ground bar of the main
> electrical service panel. A second grounding electrode conductor has one end terminated on the
> neutral/ground bar and the other end connects to one of the supplemental ground rods, with an
> approved ground clamp, the grounding electrode conductor must be continuous, unbroken, and
> connected to the second ground rod with an approved ground clamp.
> Back at the main service panel as you know is where the incoming service entrance neutral is
> bonded to ground. And also as you know all branch circuit equipment grounding conductors will
> terminate on the neutral/ground bar. A star ground.
> ==============================================
> >"A max of 25 ohms is allowed. If greater, a second rod shall be used with conditions"
> >>>>>>>>>>
> NEC requires the same. Where is your 25 ohm reference taken from?
you use 2 measurement rods. One is set 40m from the rod under test, you
inject an AC current once at 43Hz, once at 67Hz. You measure the voltage
with a third rod in the middle of the 2 other (so 20 m from the rod under
test). The measure involves a synchronized detector with a gain of 1 at the
frequency of measurement, and a gain going to zero (for long measurements)
for other frequencies. Measurement time is 1 minute for each frequency. Then
you take the mean, and cry if the 2 measurement are more than a few
percents apart. (these 2 frequencies were chosen to get rid of 50Hz
industrial telluric currents from railways)
> ==================================
> >"The rationale in non using the water pipes is (1) to avoid losing workers' life
> in case of a direct lightning stroke onto a house without a earthing rod.
> If the soil is very resistive (rock or dry sand), the stroke can run on
> long distances and kill remote workers."
> >>>>>>>>>>
> I have never heard of that happening here in the U.S.
Neither me here... But you know, when talking about security, ppl like
officials take actions before an accident happen. and i don't know whether
such an accident happened or not.
The argument of cathodic protection equipment and good separartion of
liabilities (after all, water companies have nothing to do with electric
distribution ones, why should the former worry about the later's concerns?)
Or for ppl who use their own extraction well.
> ======================
> >"Also, problem of liability: you installed lightning protection
> in your main box, got a direct lightning stroke but got all your cherished
> audiophile equipment cooked black smoky.
> Who's liable for the insurance? You (you should unplug your valuable assets in
> case of a storm), the protector manufacturer,Also, problem of liability: you installed lightning protection
> in your main box, got a direct lightning stroke but got all your cherished
> audiophile equipment cooked black smoky.
> Who's liable for the insurance? You (you should unplug your valuable assets in
> case of a storm), the protector manufacturer, the water company who bared
> the pipes in the street for fixing a leak _this_morning, the cherished
> equiment manufacturer (you ;-), God? Not easy to unscrumble"
> >>>>>
> "the pipes in the street for fixing a leak _this_morning, the cherished
> equiment manufacturer (you ;-), God? Not easy to unscrumble"
> >>>>>>>>>>>>>>
> As per NEC an under ground water pipe 20ft in length is considered a grounding electrode.
> Also do not forget the minimum supplemental ground rod.
Really, I wonder about that. Because, since the water pipe and the supplemental
earth rod are not at the same place, imagine a lightning strike close of
the supplemental rod, and farther from the water pipe. Its several tens of
kiloamps would give a huge current in the wire connecting the supplemental
rod and the water pipe (easy calculation to do knowing the impedance of the
rod and water pipe for a 2/20µS edge) . This current is ready to induce in
any nearby conductor. I don't understand why there is such interconnected
separate earth systems.
Since I'm sure they wrote it because it's safe, I'm sure I'm missing
something. But what, no idea
> ============================================================
>
> >"At the customer mains box, there is NO connection between the neutral and
> his/her earth (rod as explained above). Both mains, hot and neutral, stay
> floating as seen by any equipment connected to them. Very diffrent from the
> american way.
> advantages and drawbacks of the european vs american solution :
> EU: as the mains shall be floating, it's easy to check out: just
> disconnect the mains breaker, and check with an ohmmeter you got kiloohms
> between any AC wire and earth."
> >>>>>>>>>>>>>
> We use this type of a floating system here in the U.S. in Hospital surgery rooms
> , Cath Lab rooms, and in some Xray rooms. NEC requires ground leakage detection
> where as it must have a light and audible alarm system. The panel must have a light
> and alarm on it, and the room in which the branch cicuits are installed in must have
> remote light and alarm unit. If any leakage of an ungrounded conductor above 5ma
> to ground is detected, the light comes on and the alarm sounds.
> How do you check for leakage to ground? Say in a kitchen and that grounded sink?...
We use 3 kinds of residual current breakers.
At the mains entrance, a gross protection that triggers the main breaker
above a 300mA leak (this one is not provided for people protection, but for
fire protection). It is set just downstream the primary lightning arrester.
Then, risky zones _any room with plugs AND (water pipes OR faucets OR
earthed metallic surfaces OR outside)_, are protected by a residual current breaker
set at 30mA. The picture on this page is the RCB and breaker of my lab and
audio gear equipment. It's somehow dirty, sorry, I just noticed it when I
opened the box for the pic ;-)
Then high risk plugs have individual residual current breakers set at 5mA.
For example, electric shave or any plug set at less than one meter from
sinks and the like. Also plugs for life sustaining equipment in homes (like
diaresys machines); Or all plugs in hospitals and the like
Obviously, ppl follow or not the code (but for the main RCB and for the
primary arrester, which are installed by the distrib. company). However, to
sell the house or gto hire it for the first time, you need to have an audit signed,
and to pass it, you must comply with the code, so, it's somewhat incentive (same
with albestos, you just cannot sell any house with albestos in it, and you need an audit.
Much more expensive to get rid of it that to comply with the electrical code,
but that's another topic...
> =======================================
> Audio ground loops, I have never experienced the problem My audio branch circuits are
> as per NEC, but not minimum as per NEC.
Your wiring is well done, as most ppl's.
But some ppl have intermixed neutrals and earths. Confusing somewhere in the house
neutral and earth is easy if your electrician don't do or know his job very well. I fixed by
myself such a problem a dozen years ago in NY state (in a place receiving
children) when visiting a friend managing the place... and saw more than
one guy having this problem on the audio forums.
Your electrician was just a good one ;-)
Thanks for all these infos!
