Electrician Talk banner
1 - 10 of 10 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter · #1 · (Edited)
As I am currently in school I'm trying to do some research on Phase Bucking.

Some of my classmates and I were doing some test wiring. We were wiring 4 sets of fluorescent lights (4 T8 bulbs each) and some receptacles. The power is coming from a three phase panel, using two breakers (one for lights, one for receptacles [one on the A phase and one on the C phase]). When we turned on the breaker the lights came on, even though the light switch was off, and when the switch was turned on we heard the wires in the conduit vibrating and then the breaker tripped. The guy that wired the switch said he hooked up the neutral (we only pulled one neutral because the two circuits were on different phases) and one of the power wires.

Do you have any knowledge on this type of problem or can you direct me to some resources where i can find out more information? Any help will be greatly appreciated.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #6 · (Edited)
First as apprentices you should be using proper terminology

You either have a phase to neutral short
Or a phase to phase short.

Where was your instructor in all this? When I taught classes I checked and tested everything prior to energizing.
I did ohm the circuits out and didn't find any shorts before we energized them. Also, I am trying to do research to learn what the proper terms are and trying to understand what happen. I do not think that he hooked the neutral wire up to the light switch but i believe that he hooked both hot wires up to the switch. If you know where I might learn more about phase to neutral shorts and phase to phase shorts I would greatly appreciate it.

In addition, there were no sparks just hearing the wires vibrate then the breaker tripped.

As far as my teacher, lets just say that I wish he had better teaching skills too.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #8 ·
There must be a dead short. Maybe he hooked the hot to the neutral? A short is the only way the breaker will trip that fast It's not an overload. That would take time for the thermal part to heat up. The hot could be hitting the emt and going to ground.
Thats what he said he did, but why did it not show when I ohm'd it out (there was no continuity from either hot to ground)? Also, why would it not have tripped the breaker as soon as I flipped the breaker on (dead short)? Instead it didn't trip until the light switch was turned on (after the lights were turned on it to a few seconds for the breaker to trip and we heard a lot of vibrating noise coming from the conduit).
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #13 ·
I may be a phase to phase short across the switch. One of the phases is on the load of the switch. When you closed the switch, it went across to the other phase.
Or your wiring is really messed up.

I agree that is probably what happened. What I am really trying to understand more is the what, how, and why ,phase to phase, and phase to neutral short, works...I get very little info when I google them.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #27 ·
If it was just a switch leg you probably sent the neutral down to the switch. Or you shorted the phases when you completed the circuit with the switch. Did you teacher say a neutral is needed at all switches for now on?
No he didn't say we needed it. The guy who hooked up the switch said he remembers hooking up the neutral wire (which we know to be wrong). Really I am trying to understand what happened because of it. The wires vibrated in the conduit for 3-5 seconds after the switch was turned on and before the breaker blew.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #28 ·
And this was explained by several posters somewhere in your set up there was a wiring error, somehow in your testing the circuit you over looked this wiring error.
Yes we know that there were errors made, in my testing of the circuit and in wiring of the switch (which we can fix for future events), what I am trying to understand if what happen because of it. What made the wires vibrate and why did it take so long for the breaker to trip. Just trying to increase my knowledge and so if I trouble shoot something in my future career I have a proper understanding of the events.
 

·
Registered
Joined
·
10 Posts
Discussion Starter · #32 ·
When you have a instantaneous high current occurrence in a circuit and the conductors are not tightly bound such as in NM or MC there is a strong magnetic field and the two conductors move away from each other very fast and this results in the conductors slapping the side of the conduit.

This will happen when energizing motor, transformers or any high current loads especially a fault.

I can post a video of this next week when I get into the office, if you like.
That would be great!!! Thank you very much.
 
1 - 10 of 10 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top