Emergency lighting is a critical component of building safety, ensuring illumination remains available during power outages. When integrating emergency lighting controls, reliability and compliance with UL 924 standards are essential.
Functional Devices offers UL 924 Emergency Lighting Relays listed for controlling lights on an emergency lighting circuit. The Automatic Load Control Relay (ALCR) versions are very popular(see the ESRN device). However, what if a simpler UL 924 device could be used to shunt or bypass a local electrical switch for emergency lighting control? For such applications, we offer the slimmed-down, 20A contact rated ESR2401B or ESR2402B as a good starting point.
SHUNT/BYPASS APPLICATION
When Normal Power is present, the ESR Bypass/Shunt relay coil is activated (Contacts N/O), and the emergency panel is fed from Normal Power. The lighting load can be switched on/off using an individual wall switch. When normal power drops out, the ESR coil is deactivated and N/C contact falls closed.
If there is already a local wall switch or other means of controlling power to an Emergency light, then the ESR2401B could be used to force the light on if Normal power drops out. The ESR2401B is for a feed of 120Vac Normal power. If there is a feed of 277Vac Normal power, use the ESR2402B model.
Now, what about applications where there is 0-10Vdc dimming and the light needs to be forced to full brightness if Normal power drops? The ESR2401B or ESR2402B may still be used and wiring it up would look like the diagram below.
DIMMING OVERRIDE LOW VOLTAGE APPLICATION
When Normal Power is present, the ESR coil is activated and the N/O contacts are closed, allowing for the 0-10 Vdc to control the dimming of the load. When Normal Power is lost, the N/O contacts open, breaking the 0-10 Vdc dimming control, bringing the light load to full brightness.
We also offer double-pole, double-throw (DPDT) versions in both 10A contact rating and 20A contact rating. Please see those options in the table below:
| MODEL | NORMAL/UTILITY VOLTAGE INPUT | CONTACT RATING |
| ESR2401D | 120Vac | 10A |
| ESR2402D | 208-277Vac | 10A |
| ESR01P | 120Vac | 20A |
| ESR02P | 208-277Vac | 20A |
When it comes to UL 924 applications of controlling Emergency lighting, you may not need a full ALCR device. Using the shunt/bypass options detailed in this blog may be wise, as the installation will be simpler and more cost effective. The results are savings in time and money. Be sure, though, that a UL 924 device for shunt/bypass is appropriate for your application.
Do you have any technical questions? Give us a call and ask for Tech Support or send in a support email - we're happy to help!
About Functional Devices, Inc.
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At Functional Devices, Inc., we have been designing and manufacturing high-quality electronic components in the USA since 1969. Our mission is simple: to enhance lives in buildings and beyond by delivering reliable, innovative solutions for the building automation industry. Our product lineup includes RIB® relays, current sensors, power controls, power supplies, transformers, lighting controls, and more—each designed to meet the highest industry standards.
We test 100% of our assembled products, ensuring an exceptionally low failure rate—less than 1 in 16,000 in the field. This commitment to excellence means you get products that perform reliably, reducing downtime and increasing efficiency. With every Functional Devices product, you receive more than just a component—you gain confidence and peace of mind knowing your systems are built on trusted, field-proven technology.