Can someone please explain why occupancy sensors and electronic ballasts/CFLs don’t work well together? Switch activates, 120v flows to CFL, and it doesn’t work or doesn’t work correctly. Why? Is it a power quality issue coming off the electronics of the occupancy sensor?
Fluorescent lights and occupancy sensors
- Thread starter MattG0311
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- Tennessee NEC:2017
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- Semi-Retired Electrician
Never had a problem with them. What exactly is not working correctly?
I have twice seen issues with motion sensors paired to electronic ballasts not functioning correctly. Primarily flickering and strobing when the motion sensor is activated, or glowing dimly when it is not. Changing out to incandescents or removing the switch fixes the problem.
I know some occupancy switches or ceiling mounted motion sensors are not rated for use with CFLs, but why aren’t they compatible? Shouldn’t 120v off the switch leg activate any light? All I can think is a lag in current off the switch’s solid state circuitry.
I am still an apprentice and am just diving into AC theory. If anyone else has seen this first hand or can explain what I’m broadly generalizing I would greatly appreciate it.
I know some occupancy switches or ceiling mounted motion sensors are not rated for use with CFLs, but why aren’t they compatible? Shouldn’t 120v off the switch leg activate any light? All I can think is a lag in current off the switch’s solid state circuitry.
I am still an apprentice and am just diving into AC theory. If anyone else has seen this first hand or can explain what I’m broadly generalizing I would greatly appreciate it.
LarryFine
Master Electrician Electric Contractor Richmond VA
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- Henrico County, VA
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- Electrical Contractor
Try an incandescent bulb in parallel, temporarily.
synchro
Senior Member
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- Chicago, IL
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- EE
Although I haven't seen data on it, I suspect that motion sensors which require a connection to neutral should be more tolerant of the type of load because they don't have to rely on the load current to power up some of the internal electronics.
An incandescent bulb such as Larry suggested can draw enough current with a relatively low voltage applied across it to adequately power up the sensor's electronics, but with the filament still not hot enough to cause a visible glow. The is often not the case with LED and CFLs which typically have a very nonlinear current vs. applied voltage, especially at lower applied voltages. These devices can have a visible glow even at very low current levels where the sensor may be operating on a marginal basis.
An incandescent bulb such as Larry suggested can draw enough current with a relatively low voltage applied across it to adequately power up the sensor's electronics, but with the filament still not hot enough to cause a visible glow. The is often not the case with LED and CFLs which typically have a very nonlinear current vs. applied voltage, especially at lower applied voltages. These devices can have a visible glow even at very low current levels where the sensor may be operating on a marginal basis.
Fred B
Senior Member
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- Upstate, NY
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- Electrician
Neither have I, mostly commercial. Residential type just had to be rated for CFL.
Matt, is this a commercial application or residential?
Only issues seen was with the residential type combo sensor/switches, like dimmers they have to be listed as working with CFL or LED, any issues were always fixed, or avoided, by getting the correctly listed product installed. (Not sure any longer given the flood of cheap, poor quality, knock offs on the market lately.) Did have several cheap dimmers that even though listed would cause flicker, 2 out of 4 flickered, changed it, (same brand and type) and flicker went away, HO supplied the switch, get what you pay for, in fact she more than did by time she paid my labor to change them out multiple times. HO Insisted on buying the products herself.
Never had issue with the commercial grade OCC Sensors line connection type. Biggest issue was getting timing and sensor view correct to keep someone on throne too long from being in the dark, lol.
gar
Senior Member
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- Ann Arbor, Michigan
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- EE
211916-1220 EDT
MattG0311:
The problem you and many other electricians have is the you do not study and understand how many devices and circuits work.
Some examples:
Do you know how a tungsten filament light bulb works when a voltage is applied to the bulb? How does current vary vs voltage? What happens under steady state conditions as a 60 Hz applied sine wave goes thru one complete cycle? How does this compare to the starting several cycles after power is applied to the bulb?
How do various phase shift dimmers using a Triac or SCR work? And with different types of loads?
What does the fundamental light generating CFL or LED load look like compared to a tungsten incandescent? How does that affect dimmer operation?
How does a Variac dimmer work vs a Triac dimmer? What is a Variac dimmer?
What does the voltage vs current curve of a fluorescent look like? Or a neon bulb? What is the implication of this characteristic?
How does the short time average current to an electric heater vary as a function of time after application of a constant amplitude sine wave voltage?
If you have a permanent magnet field DC commutator motor what is the approximate starting current from zero speed?
Given a permanent magnet DC motor how is output RPM related to input voltage, and load torque?
.
MattG0311:
The problem you and many other electricians have is the you do not study and understand how many devices and circuits work.
Some examples:
Do you know how a tungsten filament light bulb works when a voltage is applied to the bulb? How does current vary vs voltage? What happens under steady state conditions as a 60 Hz applied sine wave goes thru one complete cycle? How does this compare to the starting several cycles after power is applied to the bulb?
How do various phase shift dimmers using a Triac or SCR work? And with different types of loads?
What does the fundamental light generating CFL or LED load look like compared to a tungsten incandescent? How does that affect dimmer operation?
How does a Variac dimmer work vs a Triac dimmer? What is a Variac dimmer?
What does the voltage vs current curve of a fluorescent look like? Or a neon bulb? What is the implication of this characteristic?
How does the short time average current to an electric heater vary as a function of time after application of a constant amplitude sine wave voltage?
If you have a permanent magnet field DC commutator motor what is the approximate starting current from zero speed?
Given a permanent magnet DC motor how is output RPM related to input voltage, and load torque?
.
Gar,
Thank you for your reply.
I am very interested in the AC theory application as to why this phenomenon occurs. I know it’s likely a triac device that I’m referring to. As I get farther into my studies I’m sure I’ll find out why
Thank you for your reply.
I am very interested in the AC theory application as to why this phenomenon occurs. I know it’s likely a triac device that I’m referring to. As I get farther into my studies I’m sure I’ll find out why
Flicker Index
Senior Member
- Location
- Pac NW
- Occupation
- Lights
Many legacy occupancy sensors use the filament resistance or the resistive components of transformer type ballast to keep the controls energized. This is to avoid the need to have a neutral at the box and/or to cut the installation cost by shaving the time to connect the neutral.
The front end of transistorized ballast used to power LEDs or CFLs don't behave like a resistor and prevents the control circuits from being able to work normally. Some occupancy sensors that do work with semiconductor loads actually use the EGC as return and they don't work with if there is no ground available.
Many legacy occupancy sensors use the filament resistance or the resistive components of transformer type ballast to keep the controls energized. This is to avoid the need to have a neutral at the box and/or to cut the installation cost by shaving the time to connect the neutral.
There’s the answer I was looking for! Much appreciated.
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