Occupancy Sensors: Choosing the Correct Sequence of Operation

There are 4 primary sequences of operation when designing a room with occupancy sensors:

  1. Auto-On / Auto-Off
  2. Auto-On / Manual or Auto-Off
  3. Manual-On / Manual or Auto-Off (Vacancy Mode)
  4. Last Switch State

You need to decide how you want the room to operate ahead of time so you can depict the correct control devices in your design documents. Let’s review each of the above sequences in detail.

 

1. Auto-On / Auto-Off

Occupancy Sensor - Auto-On, Auto-Off Operation Wiring Diagram

Sequence: When occupancy sensor detects motion of a person entering the space, it automatically signals switch pack to turn lighting on. If lighting is left on when room is vacated, occupancy sensor will turn lights off automatically after pre-determined timeout period. There is no manual override switch.

Description: This mode offers 100% automated operation and is great in locations such as corridors, bathrooms and stairwells when you want lights to turn on immediately when people enter the space but you don’t want individuals to be able to turn the lights off for safety and security reasons.

Design Step: Simply show the occupancy sensors and optionally a switch pack for each circuit controlled via symbols on your lighting drawings. Describe the desired functionality and sensor timeout (typically 10-15 minutes) in your Lighting Control Narrative.

Budget Cost: Ceiling sensors run $80-$90 each and switch packs $25-$30 each.

 

2. Auto-On / Manual or Auto-Off

Occupancy Sensor - Auto-On, Manual or Auto-Off Operation Wiring Diagram

Sequence: When occupancy sensor detects motion of a person entering the space, it automatically signals switch pack to turn lighting on. Occupant can manually turn lighting off via low voltage momentary contact switch wired to input lead on switch pack (sometimes wired directly to occupancy sensor). If lighting is left on when room is vacated, occupancy sensor will turn lights off automatically after pre-determined timeout period.

Description: This sequence is used in spaces such as private offices, conference rooms, classrooms, training rooms, and anywhere else you want the convenience of the lights coming on automatically, but also wish to allow the occupants to have override control of the lighting. This may be needed during presentations given in the space, or simply to allow the individual to choose to turn lights off, such as when exiting the room, for greater energy savings.

The reason low voltage switches are used specifically is because certain models of occupancy sensors or switch packs have low voltage inputs allowing you to trigger them to toggle the state of the line voltage relay, turning the lights off or back on again if desired. If line voltage switches are used to interrupt the circuit to the load, they introduce a second switch leg after the power pack. If this second switch is turned off when someone leaves the room it will not allow the lights to be Auto-On by sensor, so your sequence of operation is not consistent – a scenario discussed in sequence number 4 called ‘Last State’.

A few questions may come to your mind about Auto-On / Manual or Auto-Off operation:

1) During a presentation, how do I prevent the lights from coming back on when the occupancy sensor detects motion since individuals are still present?

2) When the room finally does become vacant, how does the sensor revert back to the original Auto-On / Manual or Auto-Off operation?

These are very logical questions. Thankfully, most manufacturers have solved this scenario by using the motion detection in reverse. After the lights are turned off manually (by low voltage switch), the occupancy sensor continues to detect motion in the space, though it does not turn the lights on. Instead it waits until it stops seeing motion for the predetermined time-out period set in the sensor. At that point it considers the room vacant and will revert to Auto-On mode where the very next motion seen does in fact turn the lights on.

Design Step: On your lighting drawings, show the occupancy sensors in the ceiling and optionally a switch pack for each circuit controlled, as well as low voltage switches via symbols from your symbol sheet. Describe the desired functionality and sensor timeout (typically 10-15 minutes) in your Lighting Control Narrative.

Budget Cost: Ceiling sensors run $80-$90 each, switch packs $25-$30 each and low voltage switches $30 each.

 

3. Manual-On / Manual or Auto-Off (Vacancy Mode)

Occupancy Sensor - Auto-On, Manual or Auto-Off Operation Wiring Diagram

Sequence: An individual entering the space must turn lighting on manually via low voltage momentary contact switch wired to input lead on switch pack (sometimes wired directly to occupancy sensor). Lighting will not turn on automatically. Occupant can manually turn lighting off via low voltage momentary contact switch. If lighting is left on when room is vacated, occupancy sensor will turn lights off automatically after pre-determined timeout period.

Description: This sequence of operation is also known in the industry as ‘Vacancy Mode’. Note that the wiring diagram is identical to the “Auto-On / Manual or Auto-Off” sequence, as the difference in operation will be a function of either the settings of the sensor or the specific wire used to connect to the switch pack that makes the components operate in “Manual-On” mode. While this may sound like less helpful functionality than Auto-On operation, it can actually have some big advantages:

  1. There are many scenarios when lighting may not actually be needed in a space. For example, if there are windows that allow sufficient daylight into a room, giving someone enough light to work comfortably without artificial lighting. Or perhaps when an individual enters an office to retrieve something from their desk only to immediately leave again, causing the lights to come on for the full sensor time-out period. By making the occupant choose to turn the lights on only when actually needed, you are saving additional energy and reducing fixture maintenance in scenarios where the lighting may not be needed.
  2. The second issue with Auto-On operation are complaints of false tripping. Occupancy sensors are not perfect and may sometimes ‘see’ movement in adjacent spaces it was not intended to control. If set to Auto-On, this causes wasted energy and undesirable effects for the owner. If occupants are instead required to turn the lights on as they enter a room, it means that only the lighting that needs to be on actually is.

It may seem inconvenient to force people to turn on the lights, but most people are used to doing this in their homes, so it is a minor inconvenience that is quickly overcome and rarely even noticed after a building becomes occupied. It is for these reasons that energy codes such as ASHRAE 90.1 2010 and IECC 2015 now require Vacancy Mode operation. Remember that the true intent of an occupancy sensor is to turn lights off to save energy. Turning lights on automatically is simply a convenient by-product.

Design Step: On your lighting drawings, show the occupancy sensors in the ceiling and optionally a switch pack for each circuit controlled, as well as low voltage switches via symbols from your symbol sheet. Describe the desired functionality and sensor timeout (typically 10-15 minutes) in your Lighting Control Narrative.

Budget Cost: Ceiling sensors run $80-$90 each, switch packs $25-$30 each and low voltage switches $30 each.

 

4. Last Switch State

Occupancy Sensor - Last Switch State Operation Wiring Diagram

Sequence: Lighting will operate as Auto-On or Manual-On depending on the “last state” of the line voltage switch. If switch is in ON position when person enters room, occupancy sensor will signal switch pack to turn lights on automatically. If switch is in OFF position when person enters room, the individual must manually turn lights on via switch. If line voltage switch is left on when room is vacated, occupancy sensor will turn lights off automatically after pre-determined timeout period. Occupancy sensor must be configured for Auto-On mode for this sequence to work. If set to Manual-On (Vacancy Mode), the switch is unable to signal the occupancy sensors to turn on.

Description: Sometimes simply called ‘Last State’ operation, this mode is neither Auto-On or Manual-On consistently – it will entirely depend on where the line voltage switch was left each time the room is vacated. Because of the apparent inconsistency, this outcome does not always make owners happy. It can usually be resolved after some brief training on the matter, though there will always be that difference in operation throughout the building depending on how many people were taught by their mother to turn the lights off when they leave a room vs those that do not.

This happens to be the least expensive way to implement occupancy sensors with manual override control and I see many low-budget jobs designed this way. It can make for an OK compromise if you have many different rooms and are looking for places to trim costs.

One of the challenges I run into on a regular basis is the lighting control narrative calling for Vacancy Mode in a particular room, but the lighting plans depict a ceiling occupancy sensor, power pack and wall box dimmer in the space. Because nearly all wall box dimmers currently on the market are maintained switches on the line voltage side, they act just like a toggle switch and you are back to having ‘Last State’, not true vacancy mode. With LED lighting now mainstream, more and more rooms are getting designed with dimmers in them to take advantage 0-10v dimming built into the LED driver. Combined with energy codes requiring vacancy mode in many municipalities and this presents a problem.

If you need to ensure the room operates the exact same way every time, you will want to be careful to design around one of the other modes. When dimming is required, there are only a few solutions I know of at this time:

  1. Instead of a wall box dimmer, specify a more advanced control device such as the EATON Room Controller or the Wattstopper DLM in the room that can provide full integration of components and the proper logic in order to achieve both Vacancy Mode and allow for dimming control. Be aware this can double the cost of the lighting controls in a small room.
  2. Leviton EMCA has a power pack (OPP20-0D2 and OPP20-RD4) that is now capable of detecting either a momentary or maintained contact closure on it’s low voltage switch input and can be wired to a line voltage switch at a result. Since many 0-10v dimmers do not require line voltage in order to operate, only the low voltage leads are required to be run down the wall to the dimmer.
  3. TachTouch offers a 0-10v wall box dimmer that intercepts the signal from the occupancy sensor and cna be set for either Auto-On or Manual-On operation. An added bonus is the devices are capable of 3-way switching and dimming from multiple locations using low voltage wire to network the units, and the cost of the units are very reasonable, only slightly more than a standard dimmer.

I have personally contacted several manufacturers to request that they produce a 0-10v dimmer with a momentary instead of maintained switch, but as of this writing I am not aware of any manufacturers producing such a device.

Design Step: On your lighting drawings, show the occupancy sensors in the ceiling and optionally a switch pack for each circuit controlled via symbols from your symbol sheet. Use line-voltage switch or wall box dimmer symbols as required. Describe the desired functionality and sensor timeout (typically 10-15 minutes) in your Lighting Control Narrative.

Budget Cost: Ceiling sensors run $80-$90 each, switch packs $25-$30 each. Last State typically cost as little as Auto-On / Auto-Off due to the use of line voltage switching which is only $2-$4 per switch.

 

Conclusion

No matter which sequence of operation you choose, it’s important that you are intentional with your selection as well as your design narrative so you can make your intent crystal clear to everyone down the line and achieve the outcome you are expecting. If you have comments or feel I left anything out, I would love to know! You can post in the comments section below.

 


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