What is the DANGER, if any, of connecting the white neutral line of the dishwasher, to to black hot line at the power source--- and of course similarly connecting the black hot line of the dishwasher, to the white neutral line at the power source. Now I would not do this, but a fellow at the store said it would not make any difference. In either case the copper wire would go to the green ground screw. I seem to remember from somewhere that if the wiring were to be reversed as mentioned above, that a person touching both the dishwasher and maybe a sink or ground of some sort, that they could possibly get a big jolt of electricity.
* (swapping the hot and grounded/neutral wires) presents no danger to the equipment on an AC circuit. In terms of electrical properties, the conductors are the same. The current switches direction 50 or 60 times each second, and the equipment simply cannot tell the difference between the two conductors. Here's an interesting article in the Electrical Engineering Times about neutral wire myths.
Safety to humans is a different matter. In most of the world, common household current is single phase power, with a “hot” conductor carrying line current, and a grounded “neutral” conductor carrying the return current (120V in North America, 230V in Europe, 100V in Japan, etc.). In North America, the single phase is actually 240V split into two 120V legs, and there is no neutral if you use 240V, but let’s sort of ignore that for now.
The hot/line conductor is dangerous if you touch it, while the grounded neutral is normally safe.
If a device or appliance uses a single-pole on/off switch, so it only breaks one conductor, then it’s dangerous to switch the neutral. If you switch the hot conductor, it de-energizes all the wiring in the appliance. However; if you switch the neutral, it leaves all of the wiring in the appliance energized. If you touch it, or if there’s a fault and you touch the appliance housing, you could be electrocuted even if the appliance's power switch is off.
If an appliance has a two-pole on/off switch, then it will break both conductors at the same time. Consequently, no matter which order you connect the wires in, throwing the switch off will completely de-energize the appliance.
* Polarity: this term is not terribly accurate. It's "polarity" in the sense that the hot conductor on a hot/neutral circuit is connected to one pole or the other of the smaller coil in the transformer outside (the neutral is connected to the center of the coil, not to either pole). But there's no such thing as a correct direction for current to flow on an AC circuit, since AC current changes direction constantly. So this is not like the positive/negative polarity of DC current from a battery.
Electrical appliances usually switch only the hot wire when turning on and off. So if the wires were swapped then if the appliance was off then a fault may cause the chassis of the machine to become hot if improperly grounded. If it was properly grounded it would result in a higher current to the ground wire.
That really depends and I am assuming you are in the USA, but most of it holds for elsewhere too.
In order to obtain 230V, you have 3 wires + ground, 2 are 'hot', 1 is neutral.
You can switch the two hots around if you have a 230V dryer, not a problem.
You cannot switch ground to a non-ground or neutral to a non-neutral. Neutral is generally connected (bridged) to your ground in the breaker panel(s).
If you 'switch' neutral and a hot, your devices will still work but the 'hot' line will continue to be present in your device even after you shut it off. Eg. an exposed heating element or a light bulb socket would have it's "hot" on the wire even after you turn the device off. If you or someone else completes the path between your new 'hot' and the ground, that could have a potentially lethal interaction.
Some very cheap, home made/repaired or very old devices may also connect ground and neutral together at the device (many people make that mistake since it is bonded in the breaker box, they think it can be bonded anywhere). If you miswire your outlet, you may connect hot to ground (short circuit) when connecting said device.
Swapping the hot and neutral wires on an appliance creates a risk for a "switched neutral". Typically, appliances switch the hot conductor to turn the appliance on and off. With the neutral switched, motors, elements, and other parts of the appliance may be energized from the hot wire. The external chassis of the appliance should be connected to the ground rather than the hot, so what you're really looking at are the electrical components within the appliance. And if you complete the circuit from from any of these parts of the appliance to the ground, it will short out or electrocute you.
The highest risk that comes to mind in a dishwasher is the exposed heating element in the bottom, especially with water and a nearby sink involved. If a path can be formed, through your body, from the heating element to a ground like the copper pipes in the sink, you will be shocked.
Note, this entirely depends on the internal wiring of the dishwasher, it's possible they switched both the hot and neutral on exposed parts like this. And with AC current, the wire color indicates hot and neutral, rather than the polarity which many think of with DC power.