[quote=spdrun]
As far as grounding, the power company equipment doesn’t care whether it’s putting 10A through a load or an additional 50mA through a human body. The grounding is there so the latter situation is less likely to arise. If a hot wire shorts to the case, breaker will trip vs making the case hot. If breaker doesn’t trip, the case will still be grounded. GFCI makes the latter situation EVEN less likely to arise.[/quote]
Explain double insulation… ie. products without the third wire; like todays drills etc.
[quote=spdrun]H->LOAD->N->human->ground — the neutral/grounded side would be connected to hot through the load, but not tied to ground (0V). Since the load generally has a lower impedance than the human body, you’d have close to 120V across any grounded human that is unfortunate enough to touch the casing.[/quote]
Please explain why you receive a shock when you just touch the hot wire on a single phase 120v supply, even if you are wearing rubber soled shoes and are not connected to any ground or neutral? Do you know what the internal resistance of the human body is? Did you measure with needles or on dry skin? The human body is highly conductive, the skin isn’t.
[quote=spdrun]Separating neutral and ground at the main breaker box is done for LIFE SAFETY, not for the power company’s safety.[/quote]Not completely accurate. The neutral and ground are REDUNDANT paths. Neutral is the return path(of sorts) and ground is the safety path. Take a look at power lines (high voltage transmission lines). Identify the ‘neutral’ or ‘ground’ wire. You will find that there are none. So where is the ground wire? On a two or three phase supply, it is effectively the ‘center-tap’ and it is also tied to a copper rod driven into the ground (up to 25 feet sometimes). When setting up a house, it is important to ‘balance’ current draw or load between the two phases on a house supply, else you will have a ‘noisy’ or poor ground. If you have a chance to see the wires coming in through the meter, you will see two ‘bus’ bars. These are not supply and ground. They are BOTH hot. They differ by phase (they are 180 degrees out of phase). This is how it is possible to get the 240 volts for electric ranges, ovens and dryers. The power is taken by going across the phases instead of to ‘neutral’. Home breakers are ALWAYS placed on the ‘hot’ side. That is because almost full power can be sunk straight to ground (partially explained by the answer to one of my questions above).
If you have one of the older houses supplied by power from wires mounted above ground, you will generally see 2 black wires wrapped around a silver bare wire. The black wires are the two 120v phases, the silver wire is the ground or neutral ‘tie’ that will join the ground/neutral of the house to the neutral that is sunk with the transformer. You will generally see two wires tied to insulators on top, not 3 (because there is no ‘return’ neutral wire back to the power plant). When a house power service is installed, a copper rod is sunk (driven) into the ground near the breaker box. On old houses, you could find often find it. With newer houses, it is harder to find – but it is there just the same. The neutral and ground that you have in the house are tied to the same point near the breaker box. The required wire gauges are different though. In general, ‘ground’ is intended to divert ‘static’ electricity generated by rapidly moving insulators, air moving across isolated conductors, or similar static sources (triboelectric effect).
GFCIs work by comparing the current between the ‘hot’ wire and neutral (they don’t look at ground wires). The currents have to be the same. If they aren’t, then current is ‘leaking’ from the correct path and a GFCI will trip. GFCIs don’t care about the total current going through them.
Standard breakers sit ONLY on the hot wire, and measure current coming from the mains and going to… wherever it is going. They don’t care where the current is being sunk. They care only about the total current and are there to protect the wiring (sized to the gauge of the wire being used on that circuit).
NOTE: GFCIs and Breakers DON’T have the same function.
