How to Override a 0-10V Dimmed Fixture with an Integral EM Battery

May 18, 2021
Tech Tuesday

This Tech Tuesday is one of our first customer-submitted suggestions for an application. It involves using a Functional Devices ESR device to override a 0-10Vdc signal on a fixture with an integral EM battery. Thanks to Michael Merchut from Graybar Phoenix for the idea!

In most UL924 applications, the building has two circuits involved. One circuit is Normal Power being supplied from the Utility feed, and the other is the Emergency Power being supplied by either a generator or inverter. During normal operation, both circuits draw power from the Utility feed, allowing lights on both circuits to be controlled as the user sees fit. When Normal Power drops, an Automatic Transfer Switch upstream directs power from the emergency source to only the Emergency Power circuit, and an ESR device bypasses any switch in the circuit to force the emergency lights on.

As batteries increase their storage capacity and light fixtures become more efficient, it has become more and more popular to include an internal battery in the fixture as the emergency source of power. This typically eliminates the need for emergency circuits, inverters, generators, and transfer switches altogether. This method works great as a simple solution for on/off fixtures, but it gets a bit more complicated the moment dimming gets involved.

Most 0-10Vdc dimming drivers supply a constant current to a separate dimming switch or rheostat, which acts as a variable resistor. As the user adjusts the resistance, the voltage changes with it, giving the driver the signal it needs. The problem with this is that the driver will supply the constant current to the dimmer switches as long as it is receiving power, which includes when it is drawing from the EM battery. Unless the dimming signal line is broken, the light will remain at the brightness set by the user before a loss of power, and not full brightness. In other words, even with an integral EM battery in your fixture, a UL924 ESR device is still needed to force your emergency lights full brightness upon loss of power and comply with code. 

Luckily, the setup is very simple and similar to just about any UL924 application despite the difference in Emergency Power source. Here’s the diagram:

Like in most ESR applications, the ESR monitors the incoming Normal Power. When power drops out, the ESR’s N/O contact opens up, breaking the 0-10Vdc dimming signal. A great device for this application would be either the ESR2401B for 120Vac or ESR2402B for 208-277Vac. As always, if you have any questions about the setup or anything else ESR-related, be sure to give us a call or email at Tech Support.


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About the Author

Tym Moore is an Electrical Engineer who hails from the best state of Colorado.
He graduated from Colorado State University in 2017 and moved to Indiana shortly afterward to marry his now wife. Outside of work, Tym spends most of his time driving back home, and complaining about how flat Indiana is.

Be sure to give Tym a call for tech support. He will always do his best to find a solution for you.