Today I had a very close call. I recently bought a Dell PowerEdge 6850, which is a very nice server (computer), and I was hooking it up downstairs. The weird thing about this computer is that it does not run on normal 110-volt power (which is the voltage of any normal outlet). So, I had to hookup a new 220-volt circuit in the basement for it.
Luckily for me, I had already run a double-pole 30 amp circuit for a dryer when I finished the basement last spring. However, the dryer receptacle (outlet) did not match up with the plug for the computer that I had and you can't use regular receptacles since they are only rated for 110 volts. So I went to Codale Electrical and bought a new NEMA 6-20 receptacle and plug so they would match.
Sorry for being so verbose, but these details will help me in the future when I need to do this again. I cut off the end of the plug, trimmed back the casing, stripped the three wires and screwed them into the new 6-20 plug. Then I took off the dryer receptacle and attached the new 6-20 receptacle. This is where things got hairy.
The wires that are rated for 220 volts have four wires in them. The bare wire is the house's ground, the white wire is the neutral, and the red and black wires are both hot (110 volts each). So, in order to get a 220-volt plug you need to combine two hot wires. In other words, you put 110 volts in the left side of the receptacle and 110 volts in the right side of the receptacle.
However, according to the diagram on the box, I was supposed to put the neutral and ground on one side and put both the hots on the other (and break the link between them). This essentially split the receptacle into two 110s rather than having 220 in it. Why would the box say that when it’s a receptacle for “220 volts on 20 amps?” I decided it was best to follow the directions (why would I think otherwise?) and did that, then plugged in the computer and it wouldn't turn on. Dang it! So I got a volt meter from Radio Shack to test the outlet. When I put it into the outlet I was only getting a reading of 110 volts.
When I touched the left prong of the volt meter to the neutral brass on one side and the right prong of the volt meter to either of the hots on the other side it would give me a reading of 110 volts. When I touched it to both hots, I would get a reading of 220 volts. Hmm, what was wrong? So I figured I should touch it to the neutral on one side and both of the hots on the other.
This was my mistake. I leaned over to see the other side of the receptacle and took the metal prong at the end of the volt meter and laid it across both of the hots. With my face about 6 inches away, I heard a really loud pop and a saw a blast of light(ning) that I guess was about 4-8 inches wide. I was so lucky that my face was back just far enough and that the breakers in the service panel (fuse box) tripped. In fact, it was so strong that it tripped the breaker right in the box and then continued all the way to the street and turned off the power to the entire house. My ears were ringing for hours and I saw spots for about 30 minutes. I still feel like I have a few too many electrons floating around in my system. I was so fortunate to have not been any closer or I could have lost an eye or something.
I went back to Codale and they explained to me that I was supposed to ignore the drawing on the box and put the hot cable on each side and only use one of the grounds. Gee, that would have been nice to know before I almost got electrocuted. I wonder why the electrician didn't say anything about that when I was talking to him yesterday. At the time I was buying the parts I didn’t really know any of this stuff so I didn’t know what to ask him or how to ask him these questions. When I went back this time I was speaking their language since I studied up and had seen some physical samples.
I bought a new receptacle, used the bare ground and did nothing with the white neutral, put the black on one side, and the red on the other side. I tested with the volt meter and it was 220 volts! I plugged in the computer and it worked!
Here is what I learned from my experience in the last 24 hours:
1. Each hot wire has 110 volts in it. If you need to put 220 volts into the receptacle, then you put 110 on each side.
2. When you are using two hot wires, it doesn't matter how you order them. Example, the red on the left and the black on the right is exactly the same as the black on the left and the red on the right.
3. The white wire is called the neutral and is the same thing as a ground. The white wire is the power company's ground and the bare wire is the building's ground. Both of them simply take electrons back to the earth. One of them into the rebar sticking into your foundation and the other through the power companies massive ground. For a simple application like this, you just choose one of them and it serves as the ground. Ignore the other one.
4. 100, 110, 120, and 125 volts are all the same thing. It depends on who you are talking to, but for the common man, they should all be considered equal. The diagrams will also say 125 on them. The same thing applies if anyone says 200, 208, 240, and 250 volts. For example, if you are buying a receptacle you need to buy one that is 250 volts, even though the line really only has 220 volts and the server needs 208 volts. It seems really messed up but I learned today that you pretty much just see if it’s 100-something or 200-something and that’s all that really matters.
5. You’re only supposed to plug one appliance (server) into a 220-volt circuit unless you have a PDU (like data centers).
6. The manual says to “work especially carefully because 240 volts is enough to kill an adult.”
Knowing what I know now, I could have had this whole job done in under one hour (assuming I had all of the parts). It was too bad I almost got hurt but I am happy to have had such a good learning experience.