OK the gripe about electricity--my question

The ground wire is there to protect you & others & be a safety deal, just in case something goes wrong.

Both of them bleed off electricity to the same bonding point at your main disconnect.

However, if you bond them at any other places, then you defeat the purpose of the grounding wire, & potentually electrify every metal bare thing on your place. _not_ a good thing.

For an example, many cities get their water from the river; and they return their sewage water back to the river.

So, will you loop your water pipes together in your house, so the fresh water & sewer pipes are connected at several points, to share waterflow? After all, they start & end at the same basic place..... ..

--->Paul

Not quite. Power currents are never deliberately allowed to flow into or out of the physical earth. First, earth is too lossy, and second, you'd have a real problem with corrosion.

In a residential installation, the actual return path is via the feeders back to the pole transformer. Your loop analogy is good, when you consider the loop starts at the pole transformer, flows through the wiring into whatever you've got plugged in, and then flows back to the transformer. On the primary side of the transformer, the return path is via the second wire on the pole back to the transformers in the local substation. Similar paths exist all the way back to the generating station.

In the U.S., the power distribution system is referenced to physical earth for two reasons. First, to provide a path for lightning currents, and second, to minimize shock hazards which would exist if the system floated above ground. Our power distribution system would work just fine without ever being connected to earth, but there would be a lot more instances of people getting zapped.

As point of interest, you're doing really well to get the resistance between a single ground rod & the physical earth down to 10 ohms, & then only under ideal soil conditions. I know this because I've measured a number of them installing large communications systems. 10 ohms is fine for establishing a discharge path for lightning, and does provide some modicum of a voltage reference for safety purposes as long as there isn't any significant current flowing through this resistance. This resistance is also why multiple grounds at a single location must all be connected together to minimize voltage differentials in the event of a high-current fault.

One other thing to keep in mind, circuit breakers are intended only for fire protection. They don't respond fast enough or at low enough currents to protect against shocks.

Keith

The reason for having a separate "grounding" conductor is to provide a path for fault currents which do not flow back through the neutral (the "grounded" conductor. For example, lets say the transformer in a microwave overheats & develops a short between the primary winding & the transformer core. The core is then connected to the microwave chassis.

This particular fault will not blow the breaker, because the unit isn"t drawing any more current than normal, however, the cabinet is at some voltage above ground because of the connection between the transformer primary and the case. Now, if I happen to touch the microwavce case & something grounded, such as a faucet, I get zapped. A fatal shock requires much less current than that required to trip a breaker.

In this case, the third wire ground would provide protection against a shock hazard by keeping the microwave case at ground protential and, depending on how far up the winding the fault occurred, possibly drawing enough current to trip the breaker.

Ground fault interrupters provide another layer of protection against this type of fault, where there are paths for fatal currents that do not trip a breaker. The GFI works by monitoring the monitoring the current in the hot & neutral leads & tripping if there"s ever a difference. Such a difference indicates that there is a fault path somewhere.

Neutral and ground are connected together at ONE point ONLY, usually in the breaker panel. If you connect neutral and ground together at more than one point, then there will be currents flowing in the safety ground wire all the time, and it will no longer provide the fault protection path.

Electrical codes are there for a reason. The codes are based on good engineering practices and have been reviewied by numerous professionals, and represent a good compromise between safety and cost. The fact that you don"t understand the rationale behind the code doesn"t mean the code is invalid...

Be safe!!

Keith

PS - I"m an electrical engineer, and once had a position that required me to design power distribution system for large communications facility installations, so I do know of whence I speak.

Reading this again, I realized you might think the "because you don't understand it" was directed at you. Not so. Just seems like every time this comes up, there's a bunch of people jump in with "I do it this way because...", most of which is wrong.

Sorry for the confusion.

Keith

if there is a short and the water lines or gas lines do not provide adequate ground, the path of least resistance is through whoever is touching the conductor. always install a ground rod.

The way I see it, there is no real Neutral in this type of setup, only line and 'ground'. It works ok, but is not at todays spec, where the ground is a real ground to pick up any 'stray' voltages/amps and send them to a safer place.

I have put in new style plugs throughout, and just did not use the ground on the plug, and if I did run a new wire I connected the ground on the plug end but did not connect at the panel end (it will make life easier when the line entrance to the house is upgraded to new type, if ever...).

The way I see it, there is no real Neutral in this type of setup, only line and 'ground'. It works ok, but is not at todays spec, where the ground is a real ground to pick up any 'stray' voltages/amps and send them to a safer place."

You have a neutral which is held to ground/earth potential. Not line and ground wires.

• neutral/ground

Of course, my eyeballs could be right, but then that'd make the ground more positive than the clouds. Chuckle.

Mark

I've heard folks that have been struck by lightning say that they started tingling before it happened. Yep, that would be a flow of current moving from the ground on its way up to the sky on its way to turn them into a human lightbulb in a very bad way.

Mark

If the neutral and ground were jumpered togther at an outlet, as you suggest, and the neutral failed, any exposed metal on whatever was plugged into the outlet would then be at 120 Volt potential, and likely KILL someone.

Areo