Confirm UL approval on gensets

Generator sets should be Underwriters Laboratories (UL) 2200 listed. Confirmation of this approval before installation and commissioning is crucial.


A misting rain is simulated with UL-specified spray heads while the genset under test is running under no load for a minimum of 4 hours. The no load condition gives maximum airflow into the enclosure while the light rain allows the most water droplets to be picked up and deposited inside the enclosure and genset under test. Courtesy: Baldor Electric Co. When you see an Underwriters Laboratories (UL) 2200 mark on a completed genset system, is it fact or fiction? The natural response would be, well yes, it’s UL 2200—right? After all the time spent in researching and specifying the genset, mounting location, features and accessories, well yes, we specified UL 2200. Don’t be too sure.

UL 2200, the Standard for Safety of Stationary Engine Generator Assemblies, was first introduced in 1998 and since then has been adopted by many genset manufacturers and specified by many more genset owners and operators. Genset owners and operators recognize the UL listing as a sign the genset system has been evaluated and approved by an internationally recognized product safety organization. A genset manufacturer receives approval to apply the UL listing to its genset only after a rigorous review and identification of all the genset components, which is conducted through in-use performance evaluation of the various components and verification testing of the complete genset system. Only then is the original equipment manufacturer allowed to apply the UL listing label.

The UL review includes extensive evaluation of all the various genset components for safety and installation. These components would include genset and engine controllers, voltage regulators, battery chargers and cabling, engine block heaters, onboard load banks, terminals and terminal blocks, circuit breakers and transfer switches, fuses and fuse blocks, power disconnects, control switches, lighting and convenience power outlets, control and power cable routings, acoustic insulation, exhaust heat wraps, air filters, fuel hoses, and exhaust silencers. If any of the components are already UL recognized or UL listed, then in-use testing and evaluation may only be required by the UL genset inspection and evaluation process. Any genset components purchased from others, which have not already been scrutinized by UL at the point of original manufacture, will undergo additional evaluation during the genset listing process.

Some genset components, such as alternators, are specifically reviewed to ensure genset operation at rated load will not exceed 125 C temperature rise of the internal electrical insulation. Other components, including power wiring and terminals, are required to be specified to ensure lower operating temperatures, typically below 90 C. Circuit breakers also will be selected and limited to not exceed 125% of the genset output. All of these items are designed to allow the genset system to run cooler and provide more safety margin than gensets produced without regard to the UL 2200 standard. This additional margin of safety typically results in some oversizing of the components as compared to older genset designs. All of the various electrical components will be recorded by part number and manufacturer in the UL file for traceability. Traceability of components is a critical tool in any failure analysis by insuring companies, if a catastrophic event should ever occur.

A multitude of temperature probes and thermocouples are located on or near various genset components and airflow locations inside the genset enclosure to monitor critical temperatures during a UL2200 test. The probe wiring is secured and routed outside the unit under test for monitoring and logging of the various temperatures and their locations by the lab technician. Courtesy: Baldor Electric Co. A UL inspector also will visit the genset manufacturer on a quarterly basis to review the manufacturing process and ensure proper components, assembly methods, and system testing, as identified in the UL listing file, are still being carried out by the genset manufacturer. Any components that are not identified in the UL listing file are not acceptable for use on a genset system carrying the UL listing label. The process to change any listed genset component can take a couple of weeks in the case of swapping one UL listed component for another UL listed component, or it may trigger a complete system evaluation as in the case of modifying any major component of the genset system such as the engine, alternator, or genset enclosure.

Genset enclosures

The genset enclosure is often one of the most overlooked genset system components selected by the owners and operators when UL 2200 is specified. A genset is allowed to carry the UL listing label in a variety of configurations as identified in the genset manufacturer’s UL listing file. When a genset manufacturer applies the UL 2200 listing to an enclosed genset, additional testing is required by the UL 2200 standard that is not specified for open genset designs, such as a rain test and blocked air inlet test. Because modern genset enclosures are designed for minimal footprint and outdoor use to protect the genset from the forces of Mother Nature, additional consideration is given in the UL 2200 standard to ensure the expected margin of safety is part of the genset system design.

When a genset enclosure is designed by a genset manufacturer to meet UL 2200, the enclosure is tested with a fully functional and fully operating genset inside the enclosure during the tests. A rain test is performed that simulates a heavy rain using specific water nozzles, water pressure, flow rates, and direction of spray onto the genset enclosure while the genset is operating at maximum airflow through the enclosure. After the water is sprayed onto the genset enclosure for 1 hour per side, the genset is shut down, and any amount of water accumulation inside the genset is evaluated for potential electrical hazards. The alternator is also hipot tested to ensure the electrical windings have not been damaged and to check for other electrical shorting by any ingress of moisture.

Heat run testing

Areas and surfaces deemed likely touch points by human hands are thoroughly scrutinized during the UL testing. Here, the engine dip stick handle is monitored to ensure a safe touch temperature if the engine oil were to be checked right after engine shutdown. Courtesy: Baldor Electric Co. The most dramatic enclosure tests performed to meet UL 2200 are the heat run tests. The genset manufacturer is required to run the genset at full load while monitoring a number of temperature probes located on or near any heat producing components of the genset system. All system components are required to stay within acceptable temperature limits during the [several hours of run time necessary for the genset to become temperature stabilized. The time required to reach a stable temperature will vary from a few hours to as much as 12 hours, depending on the enclosure design, internal airflow characteristics, and thermal time constants of the various genset components such as engines, alternators, and other heat-generating components. After the <s>this</s> initial test to confirm normal operation will not cause abnormal heating of any of the components, the genset is wrapped in a combustible cheesecloth and run in an overload condition to verify that no sparking of any components or localized heating will cause the cheesecloth to catch on fire.

Gas-fueled engines, found in <s>on</s> natural gas or liquid propane-fueled,gensets, are also subjected to a forced backfire test to verify an engine backfire will not cause any external damage to the engine that would ignite a fire. This is a particularly expensive UL 2200 test, as in many cases the genset engine is damaged or destroyed during the backfire test. Most reputable genset manufactures would not ship a backfire-tested engine to an unsuspecting customer disguised as a normal production item. Instead, the manufacturer would use a prototype genset for this test and would only ship the genset to a customer as an engineering sample, if at all.

The final heat run to meet UL 2200 is a test that blocks the cooling air inlet into the enclosure while the genset is running at full load. After the genset is run for several hours to heat soak the genset components, 100% of the enclosure air inlet area is blocked off while the genset continues to run at full load. The test will continue until a steady operating temperature is obtained or until the engine or genset controller shuts down the genset due to fault condition. Typically the fault condition will be a high engine coolant or engine oil fault. After reaching steady-state temperature or if a fault occurs, the genset enclosure is opened and the genset is inspected to ensure that running at elevated temperatures will do no significant damage to any of the genset components, connections, or wiring. Any damaged system components would cause further design evaluation and additional testing.

Confirming UL approval

The areas immediately around genset components are monitored to confirm the ambient temperatures surrounding critical control items will not exceed the manufacturer’s specifications. Any items nearing or exceeding the ratings may be redesigned or relocated to give a better margin of operating safety. Courtesy: Baldor Electric Co. The UL 2200 label on a genset actually means that a significant amount of planning, testing, and independent review for safety have been done in order to provide the genset owner with a product that meets the UL design standards. Some may claim or imply the complete genset system is UL 2200 approved by running an enclosure rain test or applying a UL label to a basic open genset that is then modified by a second party with additional components or protective housings before it reaches the final customer. A quick check on the UL website will give insight as to which supplier can actually provide a UL 2200 labeled genset.

If the genset is modified in any way after shipment from the genset manufacturer that applied the UL 2200 label, the genset is probably no longer a UL listed piece of equipment. Even modifications made at a manufacturer’s dealer, which is not shown in the UL follow-up file as an alternate manufacturing location of the original manufacturer, will not be allowed to claim a UL 2200 listing. The potential owner or purchaser of a new UL 2200 genset would be wise to specify that a statement of all modifications, made beyond the original UL 2200 genset manufacturer, must be supplied to the purchaser and approved by the purchaser before final acceptance of the genset installation will be given. The purchaser can then proceed with acceptance of the commissioned product with full knowledge of fact or fiction for its new genset. After all, you specified UL 2200 on your new genset.

Yates is generator product manager at Baldor Electric Co. He has more than 25 years of experience in industrial product management, ranging from electric motors and motor controls to power generation.

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