Vacancy vs. Occupancy switch

[ultramegabob]

What is the advantage of a vacancy switch (manual push on, auto off when room is empty) over an occupancy switch (auto on when you enter, auto off when you leave). Also does anyone know if they make these that do not require a neutral in the switch box?

 

[Bigrig]

The advantage? Energy savings. An example would be in an office supply room where people pop in and out of all day to grab one item. With a vacancy sensor most people will not bother turning the lights on as long as there is sufficient light from the corridor or window. It is also my understanding that they are also required in California by code. Many wall-mounted occupancy sensors do not require a neutral, as they "bootleg" off of the ground wire.

 

[steve66]

The advantage? Energy savings. An example would be in an office supply room where people pop in and out of all day to grab one item. With a vacancy sensor most people will not bother turning the lights on as long as there is sufficient light from the corridor or window. It is also my understanding that they are also required in California by code. Many wall-mounted occupancy sensors do not require a neutral, as they "bootleg" off of the ground wire.

Minor difference, but I think they actually "bootleg" by drawing a small current run through the connected ballasts (or light bulbs for incandescent fixtures).

 

[Bigrig]

Minor difference, but I think they actually "bootleg" by drawing a small current run through the connected ballasts (or light bulbs for incandescent fixtures).

Depends upon the manufacturer/model. A quick search of the forum will show earlier discussions about using the EGC as a neutral for some manufacturers. I try not to specify models that do this. It is probable not dangerous (they are UL listed). However, with the increased use of GFCI and AFCI breakers I wonder if there may be issues with tripping of breakers.

 

[Sharpie]

Same sort of scenario: If you want to go into the bathroom or kitchen in the middle of the night and don't want all the lights coming on just to blind you.

 

[hillbilly1]

Sensor Switch has models with built in photocells that if the room has sufficent light, will not turn the lights on. Has adjustable setpoints. They have some models that do draw an extremely low current off the ground to power the sensor.

 

[ultramegabob]

this is a commercial project and the customer is specifying vacancy switches, and I will install whatever they want, I just think vacancy switches are an odd choice for breakrooms, bathrooms, offices etc.... I can understand a vacancy switch in a bedroom, where you want to turn the lights on manually, then get ready for bed and when you lay down the lights turn off, then if you move around in your sleep or get up to get a drink you dont turn the lights on unless you go over and press the switch manually again.

 

[ultramegabob]

Depends upon the manufacturer/model. A quick search of the forum will show earlier discussions about using the EGC as a neutral for some manufacturers. I try not to specify models that do this. It is probable not dangerous (they are UL listed). However, with the increased use of GFCI and AFCI breakers I wonder if there may be issues with tripping of breakers.

I believe most of the switches in this building do not have neutrals in the switch boxes. and since it is a commercial job, I dont think GFCIs or AFCIs will be an issue, worst case would be in a bathroom or the break counter, and if it should become an issue, it would be easier to pull an new circuit to those locations than re-wire every switch location for a neutral.

 

[hillbilly1]

this is a commercial project and the customer is specifying vacancy switches, and I will install whatever they want, I just think vacancy switches are an odd choice for breakrooms, bathrooms, offices etc.... I can understand a vacancy switch in a bedroom, where you want to turn the lights on manually, then get ready for bed and when you lay down the lights turn off, then if you move around in your sleep or get up to get a drink you dont turn the lights on unless you go over and press the switch manually again.

The customer probally had a bad experience with improperly installed sensors that tripped on when somebody just walked by an office.