Steve A wrote:
>As a plumber, I have run into about 4 cases of the water bond having
>enough voltage to give me a good tingle when it was disconnected. We
>have learned to use automotive jumper cables to jumper ground wire to
>water service while bond clamp is being reconnected.
Without going into great detail:
You have to remember that wire - ALL wire - has resistance. So when you
disconnect one, then current will take the path of least resistance to
ground. If that happens to be through you... Anywhere you are in the
circuit may just be a shorter path. More complications follow;
Your house ground is connected in your panel to the big block where the
return, or neutral, wire is connected. This wire is a current carrier,
and if you disconnect house ground, you are creating a *floating ground*
in your whole house system. This makes the "ground" a part of the live
current-carrying circuit, even if there are no direct problems with the
circuit otherwise. This is a *potentially* very dangerous condition,
especially because you don't yet know if there *is* any other problem.
The potential for disaster in this case is probably fairly low in *most*
houses, but in others, well, how do you know? Why play russian roulette?
I would highly recommend turning the main breaker off while working to
reconnect the ground. Being careful doesn't take any more time or effort
than being stupid, but you'll get bitten less.
When working on the electrical system of the house there can be problems
due to faulty wiring, poor design (and you would be pretty surprised to
find how many houses are wired really poorly), and grounds having
resistance due to corrosion, dirt, etc. Also, due to electrical wiring
having resistance, and more resistance over distance, you may find even
*de-energized* circuits carrying current through you if you aren't
careful (this is *usually* an example of poor design - not separating
multiple circuits adequately - sharing neutrals/grounds, etc. and is
very, very common in house wiring. Remember, I didn't say it was right,
I said it was common).
A case in point; I was recently working in a house replacing some
switches and outlets. In one switch box, after de-energizing the
appropriate breaker, I was pulling the white (neutral) wire out and my
hand brushed up against the grounded wall box. I received a small, but
quite noticeable electrical shock that made me run down to the basement
to verify the right breaker was turned off and again check the circuit
in the switch box with a meter. And sure enough, there was still a
significant voltage present between the hot and neutral. In this case
the circuit had the neutral tied into (shared) another circuit down the
line, and that circuit had a light on - i.e.: the circuit was carrying
current through the neutral. Due to resistance over distance (i.e.:
resistance increases over distance in the wire), the distance between
the open neutral I held - through me - to the grounded box, was shorter.
This was of course something that we repaired. Since that time I double
check every circuit I work on with a meter, and always look for
inappropriate tie-ins in every box I open. BTW, while doing that, you
would be surprised to find how many wire nuts aren't screwed on, and how
many wires are just barely hanging on - a potential fire hazard.