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Temporary Connections for Generators and Load Banks

 
Small and mid-size businesses need access to backup power at reasonable cost. Facilities with mission-critical loads need a second generator when they take their sole generator offline for service. Some facilities need to comply with requirements for periodic testing without overinvesting in load test equipment. This brief explains how connections for temporary critical power equipment can help meet these needs.

Simple Access to Backup Power

For some small and midsize facilities, a permanent generator system for backup power may be too costly. However, these facilities can access backup power at lower capital cost by installing a Manual Transfer Switch (MTS) and a Quick-Connect Panel (QCP). These panels utilize standard cam lock receptacles (Figure 2) that enable rapid connection to a temporary generator when needed, one that can be transported to a site when utility outages occur. Figure 1 shows such an arrangement.
 
Note that each application uses multiple Cam Lock connectors. For single-phase power, there are two phase wires, a neutral, and a ground. For three-phase power, connection would include one for each phase wire, one neutral and one ground.
 
Applications for this type of arrangement are many. For example, this arrangement can make power available to a small business such as a gasoline station, which would then be able to supply gasoline during outages that follow storm or disaster events. A business that relies on refrigeration to preserve fresh goods could haul a rented trailer-mounted generator to a site, which could provide backup power shortly after outages occur. Residential healthcare facilities can supplement backup power to include not only life safety loads, but also cooling loads during outages. Each of these facilities gain access to power to continue serving their communities without the cost of installing and maintaining an engine-generator set. Further evaluation of backup power solutions for small and mid-size facilities can be found in ASCO’s white paper entitled California Power Outages.

Integrated QCP Applications

Integrating a quick connect panel into a transfer switch can offer additional benefits. First, it can require less space than two separate devices. Second, using an integrated unit streamlines both procurement and installation, speeding deployment. These also can be obtained with integrated service entrance equipment, further increasing the value of the solution. An example of an MTS with an Integrated QCP is shown in Figure 3.
 

A “Backup for the Backup”

Article 700.3(F) of the 2020 National Electrical Code®(NEC®) applies to regulated facilities with a single generator. It requires a means to connect a supplemental power source when the primary unit is taken offline for service, as follows:

700.3(F) Temporary Source of Power for Maintenance or Repair of the Alternate Source of Power.
If the emergency system relies on a single alternate source of power, which will be disabled for maintenance or repair, the emergency system shall include permanent switching means to connect a portable or temporary alternate source of power, which shall be available for the duration of the maintenance or repair.

The Article goes on to allow for the use of an MTS for this purpose. This type of arrangement is shown in Figure 4.

 
Arrangements like the one in Figure 4 enable full compliance with the NEC requirement using a temporary generator, such as a truck-mounted or trailer-mounted unit. This arrangement can benefit organizations with multiple facilities, such as a healthcare provider with multiple hospitals in a metro area. Using a single trailer-mounted generator, scheduled service can be performed sequentially at different facilities. Where site layout requires location flexibility, separate transfer switch and connection equipment can be used. The ASCO video entitled ASCO SERIES 300 Manual Transfer Switch Solutions reviews the applications and benefits of this and other arrangements.

Connecting Supplemental Load

Not only do facilities need to connect temporary power sources, they sometimes need to connect supplemental temporary load. The most common reason is to ensure that periodic testing of backup power systems is completed with load levels that exceed requirements set forth by industry codes. For example, NFPA 110 - Standard for Emergency and Standby Power Systems and other standards require that monthly tests be completed at loads of 30 percent or more of genset nameplate rating. Temporarily connecting load banks can be used to supplement building load to ensure compliant test results. As with power sources, quick connect panels can be integrated into transfer switches or be installed as stan-alone units. An integrated solution is shown in Figure 5. For more information on using load banks for compliant backup power testing, review ASCO’s document entitled Testing Hospital Backup Power Sources.
 
For load bank applications, quick connections generally include four connectors, one connector for each phase plus one for ground. Commonly, load banks are delta-wired, so there is no neutral. If the load bank is wired in a wye configuration, the neutral is left floating.

Summary

Quick connect panels and manual transfer switches can be used to quickly add power source and load equipment to backup power systems. The panels can be installed alone or integrated into manual transfer switches, allowing deployment in arrangements that best suit site features. Depending on application, these solutions can provide backup power and load at lower capital cost than permanent installations, but require that generators be brought to sites while someone connects the equipment and operates the switch.

For mission-critical facilities, quick connect panels enable continued backup power capability when primary generators require service. This promotes compliance with Article 700.3(F) of the NEC and allows for seamless transition to backup power even if outages occur during service events.

Quick connect panels are also available for adding supplemental load. As with generators, this can allow facilities use load banks to meet minimum loading requirements without purchasing and installing permanent equipment.

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