During the monthly test of your diesel powered generator, you are required to load at least 30% of its nameplate rating to improve its performance. However, if the connected load cannot produce enough engine loading to reach 30% minimum load level, you should connect a portable resistive load bank each year to the generator to meet NFPA 110 requirements.
You can rent a portable load bank from a generator service company to load bank your generator or find a generator quick connect tap box. Mostly, when these load banks are manufactured, they have an incremental switch that allows generators to ramp up without getting damaged by block
NFPA 110 requirements state that each diesel powered EPS installation should meet the 8.4.2 requirements. If a generator has not met this requirement, a monthly EPSS load will be exercised and supplemental loads annually. This is to guarantee that these requirements are met by each diesel generator used.
During a load bank exercise, the procedures should be well thought of to mitigate any problems which might occur due to electric failure during the process. As a precautionary measure, output load cables from the breaker(s) or generators should never be disconnected during a load bank test. This is necessary because if these output cables are disconnected during the test, and an outage occurs, there is no way that the cables could be reconnected for the generator to provide power to required loads within 10 seconds which are required either for life safety or any other critical load. In fact, NFPA 110 rules state that equivalent loads that are used for testing should be replaced automatically with emergency loads in case the primary source fails.
How to perform load banking safely
Here’s a few tips on how to perform load banking safely courtesy of Fox Fab. You can find Generator sales at www.foxfab.com.
For a safe load bank test, the load bank connection should be paralleled to the building load. Therefore, the load bank is either connected to a dedicated bus which is away from overcurrent protection device in a switchboard or to a bus that is located inside the NEMA 3R connection box that is usually mounted outside the generator building. If you don’t have a NEMA 3R connection box, you can find one for sale.
The second alternative for safe load banking is having the circuitry engineered such that the load or portable generator can be connected to the bus. This can be helpful when the permanent generator fails during the test or is disabled to be repaired. This circuitry allows power to be back-fed into the bus during the test. As an insurance during the process, having both the load bank and a portable generator on the site could be better in case the permanent generator fails. Although it is expensive and more enhanced, it is safer. Finding portable generators for sale can be difficult though.
Thirdly, you can add a permanent pad-mounted load bank just outside the generator building. The major benefit of using this method is that the load bank can easily be hard wired into a switchboard for automatic disconnection when electric utility failure occurs. The method is less expensive when compared to adding additional building loads.
Here is the recommended procedure to follow for a load bank test:
• Start and run the diesel generator until the water temperature stabilises
• All manual or automatic transfer switches should be transferred to the emergency source
• Using the load bank, step load the generator until it reaches the desired load
• After the test is complete, remove the load bank first
• Then, all the transfer switches should be switched back to their normal position
• Since load bank test takes at least half an hour, allow the generator to cool down as per manufacturer’s guidelines because it will be too hot
• When through, you can add the building load first to avoid losing power in case of normal power failure
According to NFPA 110 requirements, all diesel generators should be exercised monthly for 30 minutes at an operating temperature and to at least 30% of kW nameplate load every three years for 4 hours.
When carrying out load bank testing, you are required to follow any lockout or tag out procedures for safety. Besides, you should wear personal protective equipment (PPE) as described by NFPA 70 E and OSHA regulations. You can find this for sale at any hardware store. It is also important to understand that load banking is dangerous when carried out wrongly. Hence, most manufacturer’s offer free training to either their rental or sales customer to facilitate safety. You should, therefore, attempt load bank testing if you don’t have any skills or experience in load banking.