Ground short

Im dealing wit a 3 phase 480 volt breaker that feeds into a lighting system . From tue breaker im getting a ground short reading. What needs to be done fix s ground short

While this isn't a PLC-directed question, I can chime in here...

you need to find the short, somewhere a wire is going to ground on something. Start breaking the circuit up into sections and test each section to ground. As an electrician, I can only say this is something that needs to be done hands on, unless you have some fancy tools like reflectometers (do those even work on non-structured data cables?) you won't find the source of the short easily.

good luck, and don't turn anything on until you know you have got it for sure!

Ditto on Rob's advice. Buy a good insulation tester (megger) and start taking reading to ground. Depending on the ballasts used you might have completely unwire everything because you can read through the coil of ballast transformer and back to ground through the neutral which is tied to ground at the main service panel. Start by spitting the system in half, and just start unwiring things. I've had this exact problem before. I ended up saving myself a lot of time by going to the lighting contactor and megging out the leads to ground right there. Boom!! Dead short on the brown phase. Then I just unwired all the lights connected to the brown phase until I found the short.

My system was 20 street lights, two legs of 480 v to each ballast. It was a complete pain in the *** and took me all day in the freezing cold. One of the many reasons why I am hoping to move my career into HMI and controls.

Is it 277 volt system with a neutral or 480 volt single phase?

LOTO!!

Go to the lighting panel and open all individual lighting circuit breakers. Next, with an ohmmeter check each circuit on the load side of the individual breaker. An Ohmmeter may not detect the ground but if it does then it may be easier than using a megger. Once you locate the circuit that is grounded, leave it off and re-energize the rest of the circuits to find which one is off. Next, go about halfway down the row that is off and disconnect the wire going toward the panel (the "home-run") to see if the short remains. From there you must continue to divide the home run wire until the defective light or short is found.

Edit:
About the same as Post#3 or Post#2. They type faster than me.

Excellent advice jrwb4gbm.

Just remember that if the lighting circuit is 277 volts, all the circuits will have some reading to ground through the circuit to the neutral conductor back to the ground at the main service panel. But the phase with the lowest ohm reading will be the circuit with the ground short.

What im working on is about 60 cells in a prison. The lighfs will intermittently come on at times but will flicker and then go back off. Right now im at the end of the run so I should work my way back down the run until I find the shory. What will the reading b for a short

First of all, consider consulting a qualified electrician for this task. Lighting circuits, especially with several lights on them can be VERY dangerous if you are not sure what you are doing, meaning that they carry enough of a load to KILL you.

In order to tackle this problem we need some more information.

Is this a 480V main breaker that feeds the rest of the breakers in this panel? I think so, but it is important and we should know before we proceed.

One trick you can use to find the bad light is to have someone turn on the breaker while you watch by section and see if any lights spark/flicker/don't turn on. These lights are good starting places to check.

To answer your question: a short to ground will read zero ohms. Make sure you only use your Ohm meter on a dead circuit. Remember to read 480V phase-to-phase.

Be very wary of using a megger on lighting. Don't exceed the 500V setting or you will start burning out ballasts.

If the lights are flickering on at times that tells me it's not tripping the breaker. Correct? If so, that's not a short, it's an intermittent open, i.e. a loose connection or broken wire. If so, it will be at the fixture where the problem starts happening or the one before it. That should be pretty easy to find, but be careful. If it's a loose neutral wire it can have a load on it from other circuits and be very dangerous.

Yes it is not kicking breaker. So I need to start opening up light fixture and trying to locate a loose neutral wire. And your saying if hit breaker we will b able to see where the lughts are flickering and it got s bad neutral connection there or the light before the one that flickering

Not necessarily a neutral. It could be a hot. But it's definitely a loose connection, or a broken wire.

It is 480 main breaker

In a light fixture, or could it b a under swicth

In a lght fixture

It sounds like you better call an electrician. You don't sound like you're qualified to be fooling with 480. You'll get yourself killed.

Thank u ill take ur advice and call contractors.