Blowing stuff up in lab

[OS]

I'm taking a power systems/engineering lab and I swear every thursday I am half scared to death to go to lab. Most EE labs aren't a big danger because no one cares if you melt a chip or smoke some electronics. Not so for power systems. Basically we run high current, high voltage electrical systems every lab. We're either pulling current straight off the wall socket, or even worse, we use 3 phase power.

Just as a primer, wall sockets put out single phase power, so you can think of three phase power as using three separate wall sockets at once, except that each socket has a different phase, 0, 120 and 240 degrees. Because of this phase difference, it creates a 208 volt line to line voltage. Let's make it super easy, think of 3 phase power labs as just wiring random stuff up to three separate, out of phase wall sockets. :Q

Now, no one in the lab ever knows WTF they are doing, the prof talks for 5 minutes and walks out. So that leaves us students to try to decipher from bad photocopies what exactly we're supposed to do. Fuses and equipment are blown left and right, for example we recently did a lab on coils and we had iron core coils start pulsing/vibrating and giving off a burning smell. Sometimes we have to improvise wiring and there are floating 208 volt conductors laying around. Again, let's make that easy, basically if you accidentally touch any of those exposed leads, you'll get electrocuted. :Q

Finally, the entire lab is controlled by a central console with a giant laser red 'power on' indicator, constantly reminding us that we are one bad connection away from a catastrophe. I'm surprised that no one has been electrocuted, no one has started an electrical fire, nor has anything exploded. Yet. But every week, I walk into this lab and think, I hope there are no fires, electrocutions, or explosions today. . .

 

[Mookow]

you worry too much. Go try something that is really dangerous. I recommend something along the lines of dating mike tyson.

 

[rgwalt]

No one lives forever my friend.

Ryan

 

[QTPie]

Don't worry about it. It's amazing that no one has ever got killed, hehehe... I used to have a lab course like that, too. It's scary but fun.

 

[rgwalt]

Reminds me of the time we were doing an experiment with falling masses in physics I lab in college. We would hang a mass and then release it. Current would arc between two electrode plates across the mass and through a piece of paper at constant intervals so we could track the rate of decent and work with newton's laws and other equations. Anyway, the cool part was that a buddy of mine was scared to hang the mass for fear of getting electrocuted. So, when he went to hang the mass, I came up behind him, grabbed his sides, shook him, and made an electrocution noise akin to "SSsssssZzzzzzzzzz!!!!". I think he almost pissed his pants. It was truly classic.

Ryan

 

[bacillus]

Don't worry about it. It's amazing that no one has ever got killed, hehehe

hmm, do you know that for a fact??

 

[joohang]

Those damn labs.

It would help a lot if the prof or the T.A. cared a bit more and actually explain a little on WTF is going on.

Any ways, good luck.

 

[Mookow]

Originally posted by: rgwalt
No one lives forever my friend.

Ryan

Exactly.

I was going to write about what I did about 2 weeks ago, but decided to keep my mouth shut just in case it was reported to the police. PM me if you want the details.

Basically, the gist of the story was: go out and do something. Bleed a little. Get some scars. Get laid (actually not in the story, but the moral of the story encompasses this too). Take some risks. Do you really want to die without having used those adrenal glands? Everyone expects people in college to act stupid. You've already got a good excuse as to why you did it if you're asked about it later: "I was in college at the time."

 

[Jerboy]

Originally posted by: OuterSquare
I'm taking a power systems/engineering lab and I swear every thursday I am half scared to death to go to lab. Most EE labs aren't a big danger because no one cares if you melt a chip or smoke some electronics. Not so for power systems. Basically we run high current, high voltage electrical systems every lab. We're either pulling current straight off the wall socket, or even worse, we use 3 phase power.

Sweet I wanna play in there for a while .

Just as a primer, wall sockets put out single phase power, so you can think of three phase power as using three separate wall sockets at once, except that each socket has a different phase, 0, 120 and 240 degrees.

Three phase online has three wires all together. Some have four, but you don't use neutral when you have a three phase load.

Because of this phase difference, it creates a 208 volt line to line voltage. Let's make it super easy, think of 3 phase power labs as just wiring random stuff up to three separate, out of phase wall sockets. :Q

What you have is a 208Y/120V system. Between any two phases, you have 208V. Between a phase and neutral, you have 120V. This kind of circuit is designed for predominantly 120V load. Not many devices use 208V. 208V is usually just a by product and the number comes from 120 x sqrt 3=208. Three phase power is basically for the advantage of power company. Motors and large switchmode power supplies run better on three phase though.

In a large building like university, there is another set of three phase power. This is 480Y/277V(Y denotes wye connection). 480V loads are usually large motors. 480V is often used for large motors like elevators, air conditioners, fan, air compressor and such. 277V(phase to neutral) is used almost exclusively for lighting.

Now, no one in the lab ever knows WTF they are doing, the prof talks for 5 minutes and walks out. So that leaves us students to try to decipher from bad photocopies what exactly we're supposed to do. Fuses and equipment are blown left and right, for example we recently did a lab on coils and we had iron core coils start pulsing/vibrating and giving off a burning smell. Sometimes we have to improvise wiring and there are floating 208 volt conductors laying around.

That's why you should look in schematic thoroughly. I take it you're running motors on the bench? Having all three-phases at the outlet is useless except for motors. If we have three phase power at home, refrigerator and air conditioner can actually benefit from it. Everything else, you don't see difference.

Again, let's make that easy, basically if you accidentally touch any of those exposed leads, you'll get electrocuted. :Q

Not quite. 208V can kill but it's not really that high of voltage. Even though current capacity is high on 208V line, your body's resistance won't allow that much current. Have you ever worked with fluorescent lighting? Ballast can easily put out about 620V .

Finally, the entire lab is controlled by a central console with a giant laser red 'power on' indicator, constantly reminding us that we are one bad connection away from a catastrophe. I'm surprised that no one has been electrocuted, no one has started an electrical fire, nor has anything exploded.

Doesn't each bench have a separate switch? In case of a short circuit the circuit breaker for your circuit will trip, so you're pretty much safe.

By the way, three phase power is an every big-time woodworker's dream, because almost all high power commercial grade power tools(which big time wood working hobbyist likes to use) has a three-phase motor.

 

[etech]

Jerboy

Not quite. 208V can kill but it's not really that high of voltage. Even though current capacity is high on 208V line, your body's resistance won't allow that much current. Have you ever worked with fluorescent lighting? Ballast can easily put out about 620V

I consider that wrong and misleading information. 208V will kill. It's not something to take lightly. Anything over 48v is considered a hazordous voltage. I've worked on radars with 30Kv. That doesn't mean that 208 is any safer or something to not take caution with.

Doesn't each bench have a separate switch? In case of a short circuit the circuit breaker for your circuit will trip, so you're pretty much safe.

Wrong. A circuit breaker is there to protect equipment. It will not protect a person especially at the currents this lab is running. A GFI will limit the current so you will not get electrocuted.

I know of an electrician that was planning some work in a 480v breaker box. The day before he and his helper opened it up to check inside. The electrician while holding a screwdriver by the blade pointed at one of the breakers inside. The voltage jumped to the screwdriver. The funeral was three days later.