lrb91849, The person posting that "got zapped" because he was working with a shared neutral circuit. Someone who previously wired the circuit didn't use a double pole breaker, like a 240 breaker, that would have cut off the remaining circuit. Double pole breakers in a panel are not always 240 circuits. When a shared neutral is used you use a double pole breaker that trips both circuits when there is failure. It is wired with a 3 wire cable, red, black and white. That goes from the panel to a junction box so two 120 circuits can be run off of it at the junction box using one white, shared neutral. Look at the size of your wire and you can tell if it is 240 circuit or a 120 split circuit. Split circuits usually have a #14, #12 or #10 size wire. A 120 circuit gets a 2 wire cable/one breaker unless it is shared. A 240 gets 2 wire cable/double breaker with no neutral. A 240/120 gets three wire cable/double breaker and it of course has the white neutral. Hope this helps somewhat.

The best way to check is to measure the voltage between the two hots on the multiwire circuit. If you measure 240V, you are OK. Your's should be alright, but would be confusing to someone not familiar with multiwires.

lrb91849 "ÂIn the post labeled "Got Zapped Today" there is a lot of talk about Multi-Line Circuits.

In the post there are things like .....
They should be on different legs
They should be staggered
They should have 240v between themÂ"

The PoCo delivers electrical power to your home via three wires; the neutral wire that is connected to the center tap of the PoCoÂs transformerÂs secondary winding, and two other wires (Line1 and Line2) that connect to the end taps of the transformer. A voltmeter connected to Line1 and Line2 will read 240vac. A voltmeter connected to Line1 or Line2 and the neutral wire will read 120vac and, when measured with a visualizing device such as an oscilloscope, it will be observed that the voltage waveforms are 180degres out of phase.

To rephrase:
When measured with reference to the neutral conductor Line1 and Line 2 are 180 degrees out of phase.
The voltage measured between Line1 and Line2 is 240 volts.
The voltage measured between either Line and the neutral is 120vac.

The fact that the neutral conductor is grounded is irrelevant to circuit function.
The safety grounding wire or the lack thereof is irrelevant to circuit function.

If I connect Line1 and Line2 to a lamp, the current will flow through Line1, through the lamp, then through line2.

If I connect Line1 and Line2 to two lamps in series, the current will flow through Line1, through lamp1, through lamp2 and then through line2.

If I connect Line1 and Line2 to two lamps sharing a common connection (neutral wire) the current will flow through Line1, through lamp1 then through the neutral wire. Also, current will flow through line2, through lamp2 and then through the neutral wire. An electron leaving the common connection via Line2 negates an electron that enters the common connection via Line1.

The preceding paragraph describes the Multi-line circuit or shared neutral circuit. Since Line1 and Line 2 are out of phase, the currents through the neutral conductor will subtract from each other. If lamp1 and lamp 2 are identical, the neutral current will be 0amperes. If the lamps are different wattages, the neutral current will be proportional to the difference resistance but always less than the current in Line1 or Line2.

If Line1 and Line 2 were not out of phase, the neutral currents would be additive and equal to the sum of the currents in Line1 and Line2. It is possible the current may exceed the capacity of the neutral wire and, since it is not protected by a circuit breaker, heat it beyond the ignition temperature of its surroundings.

Thus it is extremely important that the shared circuit connects to Line1/Line2, not Line1/line1 and not Line2/Line2! The best way to achieve this is to use a two-pole, single throw breaker and the best way to verify it is to measure 240vac between the Line1 and Line2. If 0vac is measured, turn the breaker off until corrected.

What a great explanation!