I am replacing the wiring of an old house( partially burned),some of the 220v appliances such the stove and the clothes dryer have only 3 wires( black, red and white), I think (not sure) the house is grounded through the water copper pipes( the white wire-the neutral- is connected to the ground bar in the panel) . My first question is : do I need to run a dedicated ground wire for each appliance or I can leave the old wire connected as they are( keeping the neutral connected to the ground)?My second question is: do I need to install a grounding rod to supplement the existing grounding which I assume is connected to the water pipes ? Thank you
Grounding of an old house
grounding
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The grounding electrode can be connected at the service drop. It's kind of unconventional, but it is fine.
Here is an excellent graphic from Mike Holt. Keep in mind, most areas now disallow connection inside a meter can.
©Mike Holt
The grounding is accomplished through the metal pipe, not through the water.
Pure water is an effective electrical insulator. It's only conductive when there are dissolved salts in it (not just NaCl, but any metal salts creating free ions floating around in the water). In that case, water can become a very good conductor. But it isn't really the water doing the conducting.
That PVC pipe is not creating a suitable path to ground.
You need to drive at least one grounding rod (probably an 8' copper or galvanized steel solid rod, which you can buy at your local home improvement warehouse), and run a #6 copper wire from that rod to your main service panel, where you'll bond it to the grounding bus. You also need to leave all of your copper and/or iron pipes bonded to the grounding bus in your main panel.
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Best Answer
If you are replacing the wiring (after a fire, I guess you mean by "partially burned"), I believe the normal standard is to meet the current codes at the time of replacement, not the code at the time of the building construction.
As such, you will need 4-wire service (hot, hot, neutral, ground) to 240V appliances that use the neutral. 240V appliances that don't use the neutral only need hot, hot, and ground.
You will also need to bring the grounding system up to current applicable code.
My sense from your question is that you might want to self-educate a bit more, or consult with an electrician in the planning stages, rather than have to re-do stuff later from improper planning now.