Mystery 2 me

[silverromex]

This has remained a mystery to after 3 years. I use to work for a company 3 years ago that would send me on service calls even though I was unlicensed and had only 1 year of experience. This 1 call I was sent on involved maybe 12 H.I.D. lights in a wharehouse that were tripping a 3 pole, 20A, 120/208V breaker. The breaker fed 3 rows of lights with phases A-B down row 1, A-C down row 2, and B-C down row 3. I think the amp readings per phase were close to 25 amps, whatever they were I remember the breaker would trip after about 5 minutes. What my boss had me do to fix the problem was run a 3rd wire down each row from the phase that wasn't being used in that particular row of lights , so the row using phase A-B now had a C phase wire installed but it wasn't connected to anything. This did correct the problem because when I finished installing the 3rd wire down each row of lights the breaker finally held and the amps dropped down to something like 15 per phase. My question is was this installation code compliant and what caused this to lower the amps just by adding the 3rd wire that didn't connect to anything, something to do with inductance or magnetism? Thanks.

 

[bphgravity]

Re: Mystery 2 me

Based on your decription, I do not see how the third phase conductor would make any change to the circuits by being installed but not connected to anything. Magnetic inductance would only play a role if the third conductor was carrying current.

 

[voltamp]

Re: Mystery 2 me

Did all three phases share a neutral? If so, it wasn't installed properly. Could be harmonics, did the lighting have electronic ballasts? JMO

 

[hbiss]

Re: Mystery 2 me

I can see why this is a mystery to you because if you are relating this correctly it's impossible for the third wire to do anything.

If these were existing fixtures they were obviously in operation previously with no problems. At some point excess current began to be drawn. Perhaps the lamps were reaching the end of their life or there were ballast problems?

My theory is that you were sent to pull the third wire and another person was to come along later and use it to redistribute the loads, though I can't see what that would do unless additional breakers and circuits were added for each row.

Possibly by switching the fixtures off for a period of time they cooled down and drew less current until they became hot again. Perhaps you "jumped the gun" in assuming you fixed the problem because you didn't wait long enough.

-Hal

 

[silverromex]

Re: Mystery 2 me

Originally posted by voltamp:
Did all three phases share a neutral? If so, it wasn't installed properly. Could be harmonics, did the lighting have electronic ballasts? JMO

I don't remember a neutral wire in the conduit and I dont know if the ballasts were electronic or not. I know this question was difficult to answer with the little bit of information I supplied. I just remember my boss at time saying "just add the 3rd wire, don't tie it to anything, and don't ask any questions." He said the wire would balance the 3 loads out which it did and to this day I have never encountered anything like this situation and still am baffled as to why that 3rd wire in each row of lights made a difference. Oh well, guess I will forget about it.

 

[voltamp]

Re: Mystery 2 me

I reread your original post and just now see you stated they were 120/208v lighting as well as stating two phases each row was fed from (208v).Thats the reason you didn't see a neutral.
I understood originally 277/480v, sorry for the confusion.

[ August 29, 2004, 11:14 PM: Message edited by: voltamp ]

 

[steve66]

Re: Mystery 2 me

I think I agree that someone else came along and tied the third wire to every third light.

Original load = 25A * 208V = 5200Watts.
New load = 15A * 208V * sqrt(3) = 5400 Watts.

Both the above agree pretty close (less than 1 amp would explain the difference).

Maybe your boss had someone else connect the lights since you wern't liscensed.

Steve

 

[charlie b]

Re: Mystery 2 me

Originally posted by silverromex: . . . would send me on service calls even though I was unlicensed and had only 1 year of experience

That is your first clue.

I just remember my boss at time saying "just add the 3rd wire, don't tie it to anything, and don't ask any questions."

That is your second clue.

I infer that the boss wanted to do something that may or may not have been proper, but didn?t want you to know what it was. He had you do the hard part ? pulling the wire. He had someone else ? I am guessing he did this himself ? do the final wiring.

This did correct the problem because when I finished installing the 3rd wire down each row of lights the breaker finally held and the amps dropped down to something like 15 per phase.

Please clear up one issue. The way you wrote this sentence, it sounds like as soon as the wire was in, and before anyone had a chance to connect it to anything, you immediately checked the amps. Is that how it happened? Or did you go home for that night, and come back the next day to measure the amps? Was there time for someone else to have made some connections before you had a chance to measure the amps?

My question is was this installation code compliant . . . ?

Pulling a wire that is not connected to anything is not a code violation, unless, and this is the only ?unless? I can come up with, you end up with more than 40% of the internal area of the conduit filled with wires. However, the real question, the one you cannot answer nor can any of us answer, is, ?Is the completed installation code compliant?? Not knowing who wired it and in what way, there is no answer.

 

[charlie b]

Re: Mystery 2 me

By the way, if you started with a 25 amp, 208 volt, single phase load, then your load is 208 times 25, or about 5200 VA. If you take that and wire it for three phase 120/208 volts, then the current will drop to 14.4 amps. Since you said that you had measured 15 amps, it sounds like that is how someone wired the lights, after you left.

 

[silverromex]

Re: Mystery 2 me

Charlie, I can remember that the problem was corrected by the time I left the plant because my boss had me on his 2-way radio and I was standing by the panel and I can remember taking an amp reading with my Fluke and when I told my boss that the amps had dropped by adding the 3rd wire he said ok , your done. Its only when I asked him ,why adding the 3rd wire into the conduit with the other 2 wires had caused the amps to drop even though It never got landed to anything ,that he said "don't worry about it". When I was TRYING to learn by asking questions to other electricians in the field its like it was all a big secret. Wish I had found this site 3 years ago.

 

[jimwalker]

Re: Mystery 2 me

with him as a boss you shoulda found a differant company 3 years ago.If he wont even try to answer your questions then there is no chance of learning