Multiple Lighting Control Zones on single Electrical Circuit


New member
I have been an Buildings Electrical Design Engineer for about a year and a half now and theres something thats always bugged me about lighting controls that I was hoping to get some input on. My company has an independent lighting department that I am not a part of so my experience on this is a bit limited.

I've seen many scenarios where we've generally provided power circuiting of lighting fixtures that is somewhat independent of the controls zones. While we try not to break up a single control zone onto multiple power circuits, we tend to put multiple controls zones on a single power circuit. These zones consist of a variety of different controls types. For example we may put a room with 2 fixtures controlled by a wall timer switch, a room with 5 fixtures controlled by an occupancy sensor and manual override switch, and a room with 4 fixtures controlled by (2) 3-way switches all on the same electrical circuit since the load is well within the NEC 80% loading rule. Each of these rooms would be controlled separately by the controls method specified.

This is probably a rudimentary but I'm having trouble visualizing that this wouldn't cause an issue. If the rooms are on the same electrical circuit, wouldn't the controls of one room affect all of the lighting on the same circuit? I've had individuals tell me that its all about how you wire it but I can't really imagine how you could wire it that they could all be controlled independently.

If this is generally not an issue, are there any particular instances that would cause a problem? I know that some dimming applications need to be on dedicated circuits unless the dimming controls module allows for multiple independent dimming control zones. Are there other controls devices that would generally require a dedicated circuit?

I know this is a bit of a broad question but any input you can provide on the subjust would be helpful.
Thank you.


Staff member
1. You can have multiple series circuits (a load in series with a switch) wired in parallel downstream of another switch without interference. Basic electricity.
2. You can also have one control affecting multiple branch circuits IF that control has multiple contact poles or communicates with multiple downstream devices.
3. Some control systems are more like data communication networks than simple interconnected switches and relays. For those you need to make sure that they can communicate without interference.



Senior Member
As long as the controls are wired parallel with each other and so work independently and each set of lights that a control device switches are only in series with that switch, should be fine.

Pretty common install.


Senior Member
140426-2306 EDT


Consider a single voltage source. This means an energy source with approximately constant voltage output independent of load current. Any number of loads can be connected in parallel across this source with little change in voltage. Any one or more of these loads can be connected in parallel and switched with a single switch. Such a parallel electrical distribution system was conceived by Edison based on the logical functionality of gas lighting.

Various different switching devices can be used to control one or a group of loads.

A simple SPST toggle switch could switch a group of X bulbs.

Or a single relay could switch the said group. But in turn any complexity of combinatorial logic switches could control the relay.

Consider two separate voltage source. These don't even need a common connection. You desire to simultaneously control a bank of X bulbs on one supply with a bank of Y bulbs on the other supply. A two pole relay with isolated contacts or even a DPST toggle switch can perform this control function.

Next suppose you want to use a system to control the loads via a communication signal sent over the power wires. This type of system has to use some sort of coding scheme to determine what control signal goes to what switching or control device. There are many ways to do this.



Norman, OK, USA
Another way to think about it is this:

The control zones you speak of are analogous to the multiple circuits in a panel board.

Likewise, the single power circuit you speak of is analogous to a panel feeder.

Each circuit is "controlled" by its respective breaker, but all of the circuits are powered by the same panel feeder.