ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Recent Posts
Swimming pool pump
by gfretwell - 04/01/23 02:57 PM
Using THWN on automotive circuits
by BigB - 03/23/23 11:19 AM
Continuous load
by HotLine1 - 03/08/23 02:11 PM
How's all our Non-US folks doing?
by dsk - 03/08/23 11:56 AM
Old Computers?
by Bill Addiss - 03/04/23 05:06 PM
New in the Gallery:
Burger King crown sillyness
Burger King crown sillyness
by wa2ise, December 11
240/208 to a house
240/208 to a house
by wa2ise, October 9
Who's Online Now
0 members (), 14 guests, and 51 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Joined: Aug 2006
Posts: 7
Yeknom Offline OP
New Member

Within about 5 minutes of one or more HVAC fans being activated on a floor all 9 compact fluorescent light fixtures on that floor dim. Opening of doors that separate mechanincal room with HVAC equip from hallway where dimming fixtures is located dramatically hastens onset of the dimming and causes dimming to be considerably more extreme, but dimming still occurs with doors shut. Voltage at fixtures remains constant.

Mfg: GE
Compact Fluorescent Biax T/E
4 pins Base: GX24q-3
26 watts

mfg: Universal Lighting Technologies
Triad C2642UNVBES

Emergency Ballast
Mfg: Iota Engineering

Mfg: Edison Price Lighting
Model: Triples -H 126/6-EM at 4 corners of hallway area
Model: Triples -V26/6-EM at 5 other locations

Light fixtures are on 14 floors of a residential high rise building with 2 or 4 apt units on each floor
Light fixtures are recessed in dropped ceiling, which is not a plenum for air conditioning.
Fixtures are wired with emergency ballasts, one for each fixture.
Lights and HVAC equipment are located interior to building with ambient temp about 70 def F.

Dimming takes place only when one or more fan motors of HVAC( 3 ph, 208v) air handler on the same floor is operating
(without heating or cooling being activated)
Dimming occurs over a period of about 6-10 minutes, slow enough not to be perceived as you are looking at the lamp
Only fixtures on the same floor as the air handler become dim
All 9 fixtures on the floor become dim, equivalently dim, even though 4 are on one circuit & 5 on another circuit, in the same panel located in the basement or on the uppermost floor.
Two large doors (interior one metal, exterior one wood) separate HVAC equipment on the floor from the hallway where
the lights are located
Opening of these doors dramatically hastens onset of the dimming and causes dimming to be considerably more
extreme, but dimming still occurs with doors shut
Subsequent closing of the doors causes the lights to become brighter.
Blocking fan intake with plastic sheet, in effort to duplicate increased load on motor caused by doors being shut, has little effect on phenomena.
Single fixture disconnected from bldg power and separately powered by battery/inverter source does not dim when other
fixtures on same floor dim
HVAC units are powered via circuits on apartment panels located on each floor. Hallway lighting is powered from PL&P
panels located in bldg basement or bldg penthouse.
Although most fan motors have Variable Freq Drives, same phenomena is observed with units without VFD
Incandescent lamp inserted on same circuit as fluorescent fixtures does not dim when fluorescents dim
No voltage drop is observed on lighting circuits when lights dim
No noticeable change is observed on neutrals of lighting circuits when lamps dim
Phenomena continues to occur:
when emergency ballast is removed from a single fixture
when existing ballast is replaced with new from a different manufacturer
when a single fixture is disconnected from usual power and powered from one phase of HVAC power on that floor
when a neutral of a single fixture is replaced with neutral of HVAC power on that floor, or if neutral of fixture is grounded on nearby water pipe.

Joined: Jul 2007
Posts: 1,335
Are the ballasts that you are using a dimmible ballast?

"Live Awesome!" - Kevin Carosa
Joined: Mar 2004
Posts: 947
twh Offline
When all else fails, consider harmonics.

Joined: Jul 2007
Posts: 1,335
That would been my next guess

Last edited by sparkyinak; 04/13/08 06:56 PM.

"Live Awesome!" - Kevin Carosa
Joined: Aug 2006
Posts: 7
Yeknom Offline OP
New Member
Ballst used is not a dimable ballast. Harmonics is also what I thought. However, why would
1) the harmonics only be affecting fixtures on the same floor as the active HVAC fan?
2) the harmonics be affected by opening the door between the HVAC mechanical room and the hallway with the dimming light fixtures?

Joined: Jul 2007
Posts: 1,335
As the air is restricted or unrestricted, it loads and unloads the motor in the HVAC altering the THD which can effect the ballasts. Is the power supplies for HVAC and lights in the same panel? If the lights do not have a dimmible ballasts, how (or by what) are they controlled?

"Live Awesome!" - Kevin Carosa
Joined: Mar 2004
Posts: 947
twh Offline
You're probably right about harmonics.

The time delay between turning on the fan and the lights dimming sounds like a temperature problem, but you've eliminated everything related.

All I can offer is wild guesses.

Is there any vibration?

Are the neutrals in the apartment panels isolated from the grounds. I've seen unexpected currents on wires when a system is grounded twice.

Good luck!

Link Copied to Clipboard

Tools for Electricians
Tools for Electricians

* * * * * * *
2023 National Electrical Code (NEC)
2023 NEC Now Available!
* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman


Member Spotlight
Posts: 28
Joined: February 2011
Top Posters(30 Days)
jt7 3
BigB 3
Popular Topics(Views)
305,310 Are you busy
233,642 Re: Forum
218,288 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.5