Five stars for the detailed photos and concise text which provide foolproof guidance. But this book is typical of electrical DIY books in that it provides a confusing version of the underlying science, IMHO. So I will use my review to provide my own. Hopefully some will find it useful.
There are three wires entering the home. They originate from the top, middle and bottom of a coil inside the utility pole transformer. This coil is immersed in a 60 Hertz oscillating electromagnetic field created by a surrounding coil attached to the power company wires. The voltage between the top and middle wires is 120 V; that between the middle and bottom wires is also 120 V so connecting top to bottom gives 240 V. The middle wire is called "neutral" and the top and bottom wires "hot". Houses are wired so each hot wire supplies about half the overall household power. Interestingly, this minimizes current (thus heating) in this neutral wire, as the AC phases from each hot wire cancel each other out.
To protect against dangerously high voltages entering the home, such as from nearby lightning strikes, the neutral wire is connected to the earth via the home plumbing or a rod driven into the soil. Thus the neutral wire is "grounded". (Since the three wires are connected inside the transformer, any of them could be used for grounding, although neutral is the best choice since it limits "ground faults" to 120 V. See below.) So neutral means that you have split the voltage available at the transformer in half; and ground means that your wiring is attached to the earth to protect against an electromagnetic pulse from lightning.
But connecting the neutral wire to your plumbing/soil creates a new hazard: ground faults, which could produce a 120 V shock should one accidentally contact either hot wire while also in contact with a faucet or concrete floor and thus with neutral. This would happen, for instance, if a hot wire inside a damaged power cord touched the metal exterior of a washing machine or power tool. To guard against this, manufacturers originally attached these surfaces to the neutral wire, inside the appliance, out of sight, so an errant hot wire would have an alternative parallel path to neutral which would cause a short circuit and shut off power at the circuit breaker. This scheme depended on plugging the appliance into the receptacle in a particular way, matching plug neutral to receptacle neutral, so a polarized wide-slot/narrow-slot convention was adopted.
Unfortunately, this approach could still fail if the receptacle were accidentally wired backward, with hot and neutral reversed, causing our appliance exterior to be permanently hot instead of permanently neutral, an accident waiting to happen. To solve this problem, a three-prong receptacle was introduced. Now protection was provided by connecting the appliance exterior to a new round pin on the plug, which connected to a second neutral wire in the receptacle, bare copper to avoid confusion, which connected to the original neutral wire only at the electrical panel (before it is contaminated by connections to hot wires indirectly through appliances, which tends to make it slightly less neutral), thus reducing the chances of wiring errors. This new wire normally carries no current, that is, is never attached to the hot wire through an appliance; that function continues to be performed by the original neutral wire. Its sole purpose is to lie in wait for some hot wire to come in contact with the conductive surface to which it is attached. As with the original current-carrying neutral wire, should this happen, it will overheat and trip the circuit breaker, shutting off power.
Although this is referred to as "equipment grounding", in fact, as mentioned, it protects against shocks by introducing a parallel circuit which connects an errant hot wire directly to neutral, effectively bypassing the path to neutral which includes you and the ground you're standing on. It is similar to grounding, in that it provides a parallel circuit which protects inhabitants, but unlike it because the protective circuit works by bypassing ground, not including it.
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Top reviews from other countries
Tim Hoeppner
Excellent reference guide the do-it-yourselfer
Reviewed in Canada on September 16, 2013