Our main breaker is grounded by a wire attached to the main copper water pipe.
[This is the only grounding our system has, i.e. there is no ground rod]
I need to disconnect this wire from the water pipe, then re-route it to go through
Ceiling joist, then reconnect.

Question: Is there any danger in this if I shut the main breaker power?

There could be, have you ever noticed that when working on underground water pipes the workers install a jumper wire across any section they need to break before they do it? This is because the water pipes can carry current. If they were to break it and touch both sides they could be dead. What I'm saying is that it is possible for there to be current traveling through your ground back to your panel and then to the service. This happens if someone else's neutral is not properly connected between their panel and the transformer leaving no other path but through your service. Turning off your main breaker will not disconnect the neutral so the danger could still be there. I'm not saying this is always the case, just that the potential for danger exists.

If you really need to reroute it then install the new grounding electrode conductor before disconnecting the old.

I'm sorry but I'm a little behind the curve on this one.

Exactly what conductor are you planning on moving?

If you are talking about one (usually bare) of the three service drop conductors then you are talking major danger and turning off the panel will not help you at all. The bare conductor that comes in on the service drop is the "Grounded Conductor". It is a live current carrying conductor that can only be powered off by the power company as it is their equipment.

There is a Grounding Electrode that runs from the main panel to the metallic water pipe this can also run to an additional ground rod.
Neither of these conductors should be touched without making sure that there is no current or voltage in the circuit.

If you are talking about the Neutral Point Conductor from the Power Company's transformer, you must call the power company.

Quote:

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Originally Posted by Tev

This is because the water pipes can carry current. If they were to break it and touch both sides they could be dead.

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How about when I disconnect the ground wire from the water pipe, I first measure the
Voltage from the ground wire to the water pipe. If there is any voltage,
I can cover the tip of the wire, and reroute the wire carefully. This ground wire looks
Like a #2 thhn wire, i.e. it has a black color insulation on it. Of course like you said,
The copper pipe coming into the basement from the outside, could have current on it too.

Thank you all for your response.

I gave you the safest way to do it in my first post. I don't think a DIY'er should be doing it any other way.

Quote:

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Originally Posted by abcsalem

How about when I disconnect the ground wire from the water pipe, I first measure the voltage from the ground wire to the water pipe. If there is any voltage, I can cover the tip of the wire, and reroute the wire carefully.<snip>

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NO, DON'T DO THAT! There is no voltage on a ground wire, only current. You can kill yourself because you (falsely) will think you are safe because it measures 0 volts. And just the act of removing it, if there is any amount of current on it, will expose you to that current. It is current that kills you, not voltage. Do as Tev said, install a grounding stake and the new ground wire and make certain that it is SECURELY fastened before tinkering with the old one.

I had to move the ground wire in my house, at one point, but I made damn certain that I had another fully operational ground before I touched the old one. There was over 5 amps on it at the time.

If you want some more explanation on the whys of all this, look up a post I made a month or so ago on this topic.

EPM

PS:

Make sure the main breaker is OFF two when doing it.

YOU MUST RUN A PARALLEL WORKING GROUND BEFORE DISCONNECTING THE OLD ONE!

"I need to disconnect this wire from the water pipe, then re-route it to go thru
ceiling joist, then reconnect."

Again, Why are you rerouting this conductor? Did you move your main panel to an upstairs location? This conductor is supposed to be connected to the Grounding Bus in the main panel and from there to the water pipe within 5' of the pipe's entry into the home. It should not have to go through a ceiling joist unless it was installed that way originally. So again I say, why are you even thinking of moving the Grounding Electrode Conductor?

According to the NEC, the "Primary" conductor is the attached to the metallic water pipe within 5 feet of entering the home. That metallic water pipe must extended at least 10 ft. from the home and you must have a bonded jumper around the water meter.

Are all the water pipes in your home still metallic?

What has changed that makes it necessary to move or even touch this conductor?

Help me out here, please?

This work is now complete. I followed the suggestions and made the safe re-routing.
To answer dconf questions: All water pipes in our house is copper.
The re-routing of this wire was necessary due to it's
Original installation was over the studs wall where I was going to install drywall (I am
Finishing the unfinished basement). The main is in the basement, and the copper
Pipe coming into the basement is about 10 feet away. The work that I needed to do was
To drill 5/8" holes in about 5-6 joists (considering joists safety and it's limits where
It can or cannot be drilled), then remove the wire off the wall and pass it
Through the new holes in joists. i.e. the two end point connections (main and water pipe)
Remaines the same and in the same location, the wire now goes through joists rather
Than being stapled to the wall. Since I went through all these trouble, I replaced the
Builder's cheap water pipe connector with solid brass ones.

Back in late 70's, I worked as a test technician for a electrical factory
Manufacturing transformers. I used to test and evaluate 200-3000+ Amps current
Transformers. Their practice was to work on live circuits without any safety gear, and
I was way way too young to say otherwise. I remember getting shocked once with pretty
High current. It's amazging how much abuse human heart can take.

I have to tell you my worst story and I was probably in high school.

bare feet, no shirt. Insulation damage on a flat extension cord. I was doing body work on my car and no one was home. No GFCI's back then.

I caught the extension cord between my toes and could not let go because I was mechanically stuck. I consciously decided to scream, That was enough to allow be to remove myself from the cord.

Needless to say I respect:

The HV in color TV's; about 40 KV
Tube RF transmitters at 1000 W
100 KV at 0.1 Amp DC X-ray power supplies
15 KV at 1 Amp DC power supplies

when fixing these.

Microwave capacitor left a mark on me once.