Designing a Safe Reefer Connection: Part 2

Designing a Safe Reefer Connection

Increasing safety

While little has changed in the construction of the receptacles themselves over the years, ESL is constantly challenged to find new solutions that meet unique customer safety and operational requirements. Usually terminal operators have limited or no control over the maintenance and standards associated with male plugs on reefer container cables, the quality of which varies considerably. A male plug with water and salt ingress can “flash” outwards into the operator when the interlock actuator is engaged. In order to energize a receptacle from a safe distance, ESL designed a rear-actuated receptacle that removes this safety risk by requiring the operator to engage the actuator rod from behind the assembly enclosure, out of the way in case of a flashover. Since the development of our rear-actuated receptacle, ESL has installed systems at terminals in Philadelphia, Nairobi and Vancouver. In Philadelphia, ESL added LED lights on the rear of the enclosures so operators can see they have energized the correct receptacle.

Damage control

Properly treated and maintained, a safety-interlocked reefer receptacle is designed to last many years. The reality, however, is that equipment is often damaged through misuse. In our experience, the number one cause of receptacle damage is “drive-offs”, where the reefer is moved without first being disconnected. This will destroy a nylon or plastic ROA, but not a stainless steel one. Stainless steel ROA’s can be repaired by just replacing the receptacle or swapping out a safety-interlocked outlet from another ROA. In North America, the incidence of drive-offs is such that stainless steel ROAs should be considered as an industry standard. ESL also offers microswitches in the receptacle that signals whether a container is connected, regardless of whether the reefer is energized or not. This information could be sent to the terminal operating system (TOS) and an instruction to move a reefer could be blocked if it is still connected.

If you missed part  of our series  focusing on operating reefers at terminals efficiently click here.

Designing a Safe Reefer Connection: Part 1

Safe reefer operations require a receptacle system that exceeds minimum standards in electrical codes.

Designing a safe connection - part 1

Safely connecting and disconnecting reefer containers operating on 3 Phase 440-480v power represents one of the largest safety risks from an electrical hazard at the majority of container terminals. Reefer receptacles are designed and listed to electrical safety standards of UL and CE self-certification, but these only “certify” that the receptacle can carry the required electrical load. Other standards, such as IEC 60309-1 and 60309-2 cover configurations of the plug and receptacle and ensure compatibility. It is widely accepted that dealing with 480v, 32A supply presents a safety (and liability) risk and that the standard is to have interlocked connections. A safety interlock is a mechanical or electrical device that prevents a receptacle from being energized unless the male plug is properly engaged and disconnects the power supply automatically as the plug is removed. Although the safety interlock design prevents operators from “making” or “breaking” under load, it is not required under electrical codes and in some cases, terminal construction contractors look to install non-interlocked receptacles, which pose a higher safety risk to operators, but offer cost savings. Some situations arise where contractors facing strict budgets try to install non-interlocked receptacles. The objective is to make sure interlocked receptacles rather than “complying” receptacles are specified when projects are tendered. As far as the design of the interlock is concerned, there are several options. ESL’s standard system detects the ground pin of the male plug before allowing the unit to be energized, whereas other designs interlock off the key on the side of the plug. ESL believes the ground pin is the safer option. Additionally, in some markets, plug keys are frequently “shaved off” to allow a 32A plug to mate with a 30A (non-interlocking) receptacle, meaning the 32A male plug must be replaced elsewhere in the supply chain in order to safely connect to a receptacle that interlocks at the key.

Operating Efficiently

Another important aspect of reefer power supply is designing the receptacle system so the terminal can perform reefer operations efficiently. In considering the layout of the reefer area(s), terminal management has to weigh the initial costs of installing more reefer outlet assemblies (ROAs) against the labor costs of managing cabling from fewer centralized ROAs. A reefer rack structure is typically six or seven containers wide and some operators opt for an ROA with six or seven receptacles mounted centrally. This configuration is more prone to tangled reefer cables, which present tripping hazards and the chance of disconnecting the wrong cable. Terminals with wider reefer racks may even require extension cables to reach the outer containers. Installing more receptacles per ROA is ultimately a cheaper solution, but a trend towards two and three-gang ROAs due to operational efficiencies is growing. Demand is also increasing for two LED lights, one to indicate line power is available to the ROA and a second to show that the receptacle is energized and power is flowing. If the first LED is not showing, the operator will know immediately that there is an upstream power supply problem. An available option is the incorporation of an equipment ground fault protection (GFP) device on an outlet module to isolate the effect of a phase to ground short. ESL has frequently been asked to incorporate a simple ground fault protection device that can isolate a fault at the receptacle and prevent upstream switch gear from being tripped by a short. Terminal design engineers need to take into account that reefers generate ground currents during the defrost cycle, so the GFP devices should be selected and set at a value above the defrost cycle ground currents to avoid nuisance tripping.

Read part 2 of our series  focusing on reefer receptacle safety and damage control.

Intro to Company Switches for Temporary Show Power


Company Switches – Questions to Ask…

When making specifying and purchasing decisions regarding electrical equipment for entertainment venues there are many factors to consider. When challenged with choosing between company switches and standard disconnect switches, the top of the priority list should always be safety. While disconnect switches may often be the more affordable option, the value added into a company switch becomes apparent once all factors are considered.

What is a Company Switch?

A company switch is a power tap box that portable lighting, sound, automation, motors, and power distribution boxes can be plugged into. Often located backstage or in hidden areas of theaters and arenas, standard company switches are rated 100 – 400 amps. Company switches usually consist of a main circuit breaker and connection chamber; a common configuration is 208/120VAC 3-Phase 5 Wire. Equipment connections in the U.S. are typically made via female cam-style connectors. Color-coding for 208/120 is most often Red-Phase A, Black-Phase B, Blue-Phase C, White-Neutral, Green-Ground. However, additional options and configurations are available per customer requirements.

What Should I Consider When Selecting a Company Switch?

Safety is the primary concern in any production, especially when dealing with live power. A safety-interlock preventing access to live connections is critical. The door of a company switch should be safety-interlocked to only allow access to the connection chamber. Access to the deadfront-protected circuit breaker compartment should only be permitted after the main circuit breaker is physically turned to the off position. Further safety recommendations include indicator lights that show when power is being fed to the unit and also when upstream power has been cut to the unit, signaling that it is safe to perform maintenance or repairs.

Verifying that the assembly has passed a series of performance and safety tests and is specifically designed for the intended application is critical. Company switches that are third party certified undergo rigorous tests to ensure the safety of the units. Underwriters Laboratories (UL) is a widely recognized, independent safety and certification organization. In order to receive UL certification, company switches must pass temperature, short circuit and environmental tests. The use of Company Switches that are not UL Listed can result in less than desirable performance, but more importantly, might be unsafe.

In order to restrict operation to authorized personnel, Company Switch assemblies should be equipped with a padlockable main access door allowing access to the connection chamber only. It is also beneficial for the interlocked circuit breaker handle to be padlockable so the circuit breaker can be locked in the off position, thereby preventing unauthorized use.

Since Company Switches are typically installed close to the stage for accessibility, it is important to ensure the unit remains hidden from the concert-goers’ view. Some Company Switch manufacturers provide options such as a wrinkle black finish and other custom colors to match the surroundings. Enclosures can also be furnished with a flush front and recessed circuit breaker handle, or a surface mount design that can be positioned unobtrusively in the background and prevent anything from catching on the handle.


Various facilities may have power requirements that cannot be met with an off-the-shelf solution. This is often true with large scale venues that have tailored designs to suit particular needs, such as:
• Flush Mount/In Wall Design
• Custom Finishes and Colors
• 100% Rated Breakers
• Bare Wire connectors behind interlocked doors
• Isolated Ground
• Dual Neutrals
• Reverse connectors (Male for N+G) to ensure that phase connections cannot be mistakenly connected to the neutral or ground
• Posi-Lok or Pin & Sleeve connectors
• Auxiliary GFCI power outlets
• Meters & Indicator Lights
• Custom Modular Units for larger power needs

Download Company Switch Specifications for Engineers here.

As a manufacturer of safety-interlocked power distribution equipment since 1991, ESL specializes in engineering safe solutions for custom Company Switches. ESL has had the opportunity to provide standard and custom Company Switch assemblies to venues such as Madison Square Garden, Rose Bowl, UCLA Pauley Pavilion, L.A. Live, Los Angeles Stadium, Las Vegas Stadium, and Kannapolis Ballpark to name a few. Visit to learn more about ESL’s Company Switch product line.


Introducing the New Q: ESL’s Latest Innovation

Safety, Value, Quality, and Innovation have played a key role in making ESL a worldwide industry leader in the design and manufacturing of safety-interlocked power outlets for refrigerated ISO containers. With this continuing mission in mind, ESL’s new Q module provides unparalleled safety and incorporates additional advances such as high visibility indicating light and extensive cycle testing for increased product reliability.

Watch ESL’s Q Module demo video to learn how we continuously stay ahead of product safety innovations.