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Joined: May 2007
Posts: 55
Up2code Offline OP
Hello all. Hope all is well out there! Supply house is currently bidding fixtures on a lighting upgrade project which will require replacing 333-400W High-Bay Metal Halides(assuming Probe Start) with 333-6 lamp T8 Fluorescent(instant start) High-Bay fixtures. Going from roughly 450W to 224W a fixture. My concern is harmonic currents introduced to factory power system with upgrade. Motors on machines are 480V 3Ph. No specs on number of VFD or what kind if any. Lights are all 277V. Would harmonics increase or decrease in this possible situation? Half of these fixtures burn 24/7. Harmonic currents are not my specialty, by any means, but issue should be addressed before I bid labor on this project.

Joined: Apr 2002
Posts: 7,333
Likes: 7
OK, 72 views and no 'takers' on this one.

IMHO, harmonice are much more involved than can be addressed verbally, plus much more data is required. Are you using the existing lighting circuits/wiring?

Ballast data from the replacement fixtures is required, (THD), as well as any/all data regarding the other loads within the structure. Most, if not all available ballasts (OEM) are within industry minimum-maximum values. Info on the lighting circuits, number of conductors, AWG of hots & neutrals, etc. As you mentioned VFD's and motors, are you concerned about the service? Feeders?

Are you concerned for liability issues? Is there a design professional (engineer or architect) that specified the fixtures? Or, is this just a 'swap out' one-for-one job with energy efficiency the driving force?

Joined: Mar 2004
Posts: 947
twh Offline

Joined: Jul 2004
Posts: 9,788
Likes: 14
Scott is our engineering guy. I suspect everyone was waiting for him. I would just say upsize the neutral 2 sizes and cross my fingers.
Any time you have 3P wye and any kind of non-linear load you have a likelihood of triplin harmonics.

Greg Fretwell
Joined: Oct 2000
Posts: 2,722
Broom Pusher and

If you utilize the same Circuits that were used to run the original 400W MH Fixtures, you should not have any issues from "possible Triplen Harmonic Currents" in the Common Grounded Conductor of 4 Wire Multiwire Circuits.

Since the new Fixtures will draw apx. 40% less Volt-Amps than the original Metal Halide Fixtures, the Circuitry will also be reduced apx. 40% of the original Amperes.

Most - if not all, of the commonly used "Brand-Name" Electronic Ballasts, have a THD of 10% maximum.
That's about the same as an HID's Constant Wattage Autotransformer (CWA), High Reactance-High Power Factor (HX-HPF) or Regulated Lag (Reg. Lag) Ballast.

*** Installation Note - per 4 Wire Multiwire Circuitry & Triplen Harmonics ***

If the L-N Loads are kept to a "Design Limit" of 10 Amps, even with a THD of 33.333%, the absolute maximum Current that could possibly flow on the Common Grounded Conductor of a 4 Wire Circuit would be 30 Amps.

In reality, the Harmonic stories have been grossly exaggerated.

It is true that Harmonic Currents will exist and flow in ANY AC System which drives Reactive Loads.
These Currents "Reflect" back from the load, and "against" the Transformer feeding that load.

Harmonics exist in 2 Wire Circuits and 3 Phase 3 Wire Circuits, where Reactive Loads are driven; however, there is no "Triplen" scenario involved.

Harmonics also exist in Single Phase 3 Wire Systems, where Reactive Loads are driven; however, as with the 2 wire Circuits and the 3 Phase 3 Wire Circuits above, there is no "Triplen" scenario to deal with.

3 Phase 4 Wire Wye Systems have the "Triple-N" (Triplen) scenario, which is the relevant issue of design - and what you're concerns are pertaining towards.

Don (Resqcapt) made a very good statement:
"If the manufacturers of a certain piece of Equipment design it to be extremely noisy (reflect THD >30%), then that manufacturer should be responsible for "cleaning" the AC input outside of the Load's input"

Simply this means that the THD on the Line input of a piece of Equipment should not be higher than 10% at any Harmonic point(s).
Even 10% seems somewhat excessive to me, as there are methods of reducing the Distortion (noise) being reflected back from a given Load, to a level lower than 10%.

If you believe there may be an excessive THD issue, see if you could obtain the listed THD of the Ballast used.

Typical "Electronic" Instant Start Ballasts, for 6 F32T8 Lamps (265ma Lamps), will be listed as <10% THD.
Refer to the Fixture catalog for THD quoted values, or request the THD value(s) from whomever is quoting the Lighting Package.

Good luck with your project.

Feel free to post again if you have further questions, or any information towards the possible THD listed on the proposed new Ballasts.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Jul 2002
Posts: 8,432
Likes: 3
Go for T-5's.
You can hang them like a high-bay fitting and with less harmonics and more light output.

Joined: Oct 2000
Posts: 2,722
Broom Pusher and

I have uploaded some drawings, which briefly cover Circuitry of Lighting Systems and the Harmonic Currents + Volt-Amps added to the Fundamental Currents + Volt-Amps.

Refer to the following links to the Technical Reference Section:

THD Examples #1 of 2: F32T8

THD Examples #2 of 2: T5HO

*** NOTE ***
Click on the underlined text above, to view that linked page.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Dec 2002
Posts: 330

Thanks for the information you posted in the Technical Reference Section. I realize how much time this took and thank you for the effort. I do not see where you can come up with the time.

Thanks again,


Joined: Oct 2000
Posts: 2,722
Broom Pusher and

Thank you for the positive comments! thanks thumbs cheers

Receiving positive feedback like this makes it all worthwhile.


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Joined: Jun 2004
Posts: 1,273
I second Trumpy: go with HO T-5...

Siemens developed this along with Phillips...

T-8 is so yesterday.


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