# Harmonics: At what point will electronic ballasts anhilate eachother?



## theForce (Mar 21, 2013)

Hello. I lack experience with harmonic distortion and so a job I'm on has me baffled. An office building built in 2001 has numerous dead flouresent ballasts. They are 120V T8 32W Electronic Instant Start Ballasts, high power factor, THD rating <20%. I have not checked to find out if total lights were divided amongst one or more circuits. I notice that I can't check for output voltage at the ends of a working/energized/shining bulb. My meter screen just fritzes out. Ok, using a wiggy to check line in voltage my status lights indicate 120V but they pulsate at a regular rhythm. I don't have a power quality meter but plan to use an averaging ammeter and true rms ammeter to find a ratio as a test for distortion. What I am hoping to learn from this post is if there is somone here who knows what it is really like to have enough harmonic distortion to loose lights. Has anyone detected damaging harmonic distortion on a lighting circuit? Is fixing it as easy as running a new circuit using MC (flex). Thanks.


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## JW Splicer (Mar 15, 2014)

Are you checking voltage at the tombstones? Those ballasts should output around 700V right?

Also how many ballasts are out compared to total # of lights? How many circuits feed the lights, and are the lights that are out on the same circuit? Neutrals are all good?


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## fargowires (Aug 26, 2010)

I really like the thread's title.


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## Bad Electrician (May 20, 2014)

I have been doing harmonic studies for maybe 25-30 years (I'll me 63 this year and 45 years in the trade forgive me if I get forgetful):laughing:


I have seen harmonic issues BUT NEVER with lighting panels loaded with nothing but lighting supplied bu all types of ballast, at 480/277 and/or 208/120.


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## JW Splicer (Mar 15, 2014)

I don't thinks it's a harmonics issue.


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## theForce (Mar 21, 2013)

Thank you all. It's been several days since I started this thread so I appologize if anyone were wondering what happened. I replaced all the bad ballasts first, over the last few days. Then today I looked over the circuit and checked for current. I have also studied the schematics for electronic ballasts and from the job I'm on I took an electronic ballast apart. I agree with you all that this is not a situation where the lights were knocked out by harmonics. I will explain the readings and distribution of the lights. But first may I ask what else could have fried 6 of 12 lights on one circuit and 4 of 6 lights on a different circuit -- with several of those having been replaced at one time already? The ballast I took apart had a blown fuse on the circuit board where input power is. Also, the rest of the ballasts that were replaced had indications of a blown fuse: working bulbs were in each fixture and had 120V on the line but current draw on the line was zero. So, maybe something killed the fuses. What problems can blow a ballasts internal fuse? Furthermore, the ballast I took apart contained high frequency NPN switching transistors; I don't know if they were damaged. But, what problems are transistors in an electronic ballast succeptible to? Can line swells and sags kill electronic ballasts? Should I ask for the rental of a power quality meter? I have a book that walks one through use of such a meter. Below is the things I discovered today, just number circuits, lights, current at the light at each end, current on the neutral for the circuit at the panel (both true rms and average current).


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Ballast label shows 120v, 4 T8 lamps, 32 watts, and 0.98 A.

Circuit A 7 lights
Circuit B 12 lights

Neutral shared for Circuit A & B. Average current on neutral (distribution panel) 10.2 A. True RMS current 9.8 A.

On circuit A, at a light on the end of the circuit with the first junction box from the distribution panel, average current on line is 0.92 A and RMS is 0.91 A. For a light on this circuit at the end with the furthest (last) junction box, average current is 0.87 A and RMS is 0.89.


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