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Selecting the Proper Inverter for Emergency Lighting Systems
October 18, 2017
In the event of a building-wide power outage, electrical engineers and contractors have several options when it comes to powering emergency lighting systems mandated by the NFPA and International Building Code (IBC).
The first is to install dedicated lighting fixtures that provide temporary power from built-in battery packs; the other is to utilize centrally located inverters tied to back-up batteries that can provide utility-grade power to both existing architectural and dedicated emergency lighting.
For many electrical engineers, given the simplified design and installation requirements of a new generation of “smart” inverters, a more centralized approach has increasing appeal due to significant savings on installation and long-term maintenance costs.
In addition, more advanced automated reporting and self-testing of these web-connected inverters also simplifies NFPA mandated testing, provides alarms and decreases the potential liability for building owners.
“Today’s inverters provide a number of advantages when used for emergency lighting,” says Ron Doyle, vice president of specialty electrical distributor Wiedenbach Brown. “Not only can an inverter power many lights from a central location – including new and existing architectural fixtures – but it can also supply power in “pure sine wave” output consistent with that from the utility, making it much more effective in working with LEDs.”
For those choosing to use inverters, calculating the size of inverter needed in terms of AC load requirements is usually a relatively simple matter. However, there are multiple factors that should also be considered in making a final inverter selection that best suits the application.
These include selecting inverters that provide pure sine wave AC power; are designed to operate at their designated rating so over-sized, de-rated units are not required at additional cost; are modular by design to simplify repairs; and that have foolproof instructions to ensure correct and fast installation.
Given the increasing use of LEDs in architectural lighting, it is important to select an inverter that incorporates pure sine wave technology.
Pure sine wave inverters provide cleaner, utility grade power than modified sine wave models and work better with LED drivers. In addition, pure sine wave models have a high surge capacity which means they are able to exceed their rated wattage for a limited time to meet the high inrush currents of LED’s.
“When utility power is lost and the influx of current from LED fixtures is drawn from an inverter, most standard inverters are incapable of handling the inrush although they are rated for the total rated load,” says Doyle.
In order to accommodate retrofit installations of inverters into battery-powered emergency systems, the inverters are bi-directional.
Capable of switched or dimmed output load, the Isolite inverters allow building owners to use the existing lighting fixtures for emergency purposes, which often reduces overall system costs.
The smaller units have wiring schemes that allow for two independently controlled circuits with breakers, with larger units allowing for more.
“These pure sine inverters are highly efficient and can handle a high percentage of the rated load to support the number of emergency lighting fixtures on it,” says Doyle. “So, you don’t have to de-rate the Isolite inverter as you would with like manufacturers, and then unnecessarily up-size at additional cost.”
Long term maintenance savings
Another key advantage of a centralized inverter design is the ease of serviceability when batteries eventually need to be replaced.
To meet the emergency lighting requirements along the path of egress, many commercial lighting fixtures come with small inverters and dedicated batteries attached. Because the batteries are not always replaceable, this often means that the fixture itself must be replaced every 5-10 years.
“When it comes to servicing the batteries, even if fixtures have high-quality NiCad batteries, every 7-8 years you are going to have to replace them,” says Doyle. “That means going up into the ceiling areas and changing out the entire fixture.”
For the building owner/lessor, inverters are easily maintained with all the batteries located in one cabinet. As a result, there are inherent, long term maintenance savings with centralized inverters.
If there is a knock on centralized inverters, it is often related to incorrect installation – not performance of the unit itself.
For electrical contractors that are less experienced in this type of equipment, the relative ease – or lack thereof – of installation can cost time, lead to potential call-backs and affect overall system functionality.
“The contractor really is the person that is going to make or break the success of an installation,” says Doyle.
For this reason, companies like Isolite go to extreme measures to make inverters as contractor-friendly as possible. This can come down to small details such as small instructional tags and warning signs that ensure the unit is wired properly or access to batteries from the front. Responsive technical support from the manufacturer can also be invaluable.
To prevent start up failures, Isolite builds in diagnostics that identify wiring errors. Similarly, error codes indicate specific fault conditions that can often be resolved over the phone.
“With the start-up diagnostics, the system will literally not start if it is wired incorrectly,” says Doyle.
The inverters are also designed to simplify maintenance and repair in the field. Isolite’s modular inverter design allows installers and other technicians to remove a full module and replace it if an upgrade or repair is needed. This modular capability also greatly improves MTTR (mean time to repair).
Automating critical requirements
One of the most important capabilities of advanced inverters for emergency lighting is the ability to automate testing and reporting functions.
NFPA code requires that emergency lighting systems are tested for 10 minutes every 30 days, and to be discharged for 90 minutes once annually. Records must be kept for review by Fire Marshalls or other officials that make periodic inspections of emergency lighting systems.
If testing and reporting is performed manually, there is a good chance that it can be overlooked or the results lost in the shuffle.
“The more advanced inverter systems keep record of all of that information,” Doyle explains. “A Fire Marshall can simply review the logs and see the testing was automatically performed as scheduled and see any alarms.
The inverters can also be controlled through a unique web interface that allows a facility manager to monitor multiple inverters at the same time as well as set alarms and automatic notifications. The system also conducts and records data related to the regular monthly tests required by code.
Records within the inverter can be accessed through the front panel or a web browser with proper login authentication. Information is stored securely in cloud-based storage.
For more information, contact Isolite at 31 Waterloo Avenue, Berwyn, PA 19312; call 800-888-5483; or visit them on the web at www.isolite.com