What is a Manual Transfer Switch?

A Manual Transfer Switch (MTS) can be part of power backup systems using a permanent or portable generator (or in some cases an inverter connected to a battery bank). A MTS can be installed to switch between the main utility grid to backup power or between one back-up power source to another back-up power source (usually a fixed back-up generator to a portable back-up generator). In either case, a MTS allows users to manually perform a safe and quick transfer of electrical power, ensuring that your facility can continue operating smoothly during outages.

A Transfer Switch is not just about convenience; it’s also about safety. Without a Transfer Switch, in some cases connecting a generator directly to an electrical panel can result in dangerous backfeeding, which poses risks to both the property and workers. A transfer switch eliminates these hazards, ensuring that power transfer is both safe and compliant with electrical codes.

Manual Transfer Switches may also be known by the acronym MTS, or as Non-Automatic Transfer Switches or as Double Throw Safety Switches.

Automatic Transfer Switches (ATS) are an alternative to MTS panels. An ATS automatically detects a power outage and switches to generator power without human intervention. Automatic Transfer Switches are useful in situations where there is no human present to switch power over, or for critical operations which, for cost or safety reasons, cannot allow any downtime.

Roam offers a line of Manual Transfer Switches with integrated Cam-Lock connectors. Models are available at 200 Amps and 400 Amps, in both Single-Phase and Three-Phase versions, and in panels supporting up to 240 VAC, up to 480 VAC, and up to 600 VAC. All of Roam’s MTS panels are UL 1008 listed, NEMA 3R rated, and use Cooper Crouse-Hinds Cam-Lok brand E1016 (J-Series/16 Series) Male Cam-Lock connectors.

Why do Roam’s Manual Transfer Switches Include Cam-Lock Connectors?

Cam-Lock connectors provide a secure and easy-to-connect connection between a generator and a transfer switch. Roam’s Manual Transfer Switch (MTS) panels combine a Generator Connection Box and a Transfer Switch, providing a single-panel solution for exterior connection and switching of emergency power. These Manual Transfer Switches accept male Cam-Lock plug terminated cables from the back-up power source (usually a generator). Making these Cam-Lock connections requires only a simple insert, push, and half-twist to establish connectivity.

Our Manual Transfer Switch Cam-Lock connectors (and spring cap covers), plugs, and labeling are all color-coded, helping to clearly distinguish between Ground, Neutral, and the separate legs of the power connections.

Roam manufactures MTS panels that support multiple back-up power system configurations: single-phase and three-phase; fixed Neutral, switched Neutral, or no Neutral; and standard power connector color coding (Black-Red-Blue), 480//277VAC connector color-coding (Brown-Orange-Yellow), or Canadian standard power connector color-coding (Red-Black-Blue).

What Should You Look for in a Manual Transfer Switch?

Critical features of a MTS include:

On-Off-On Switching

Roam’s MTS/Cam-Lock panels all use Open (Open Transition) transfer switches, with On-Off-On corresponding to Utility-Off-Generator positions (or to Fixed Generator-Off-Portable Generator positions).

On-Off-On switching avoids the risk of crossing power feeds, and creating a synchronization mismatch between utility and backup power that can damage equipment and risk injury to people working on or near the backup power system.

While Closed Transition transfer switches (also known as on-on, utility-generator, or make-before-break) do exist, they are normally used in rare cases where even short losses of power can cause damage or endanger lives. Such systems always require an Automatic Transfer Switch, as well as equipment to avoid a synchronization mismatch, ensuring that the utility and backup power sources are closely matched in voltage, frequency, and phase angle, and have an overlap time of less than 100 milliseconds.

UL 1008 Listed

Look for Transfer Switches that are listed to the UL 1008. This listing means that these panels have been designed, built, and tested according to UL’s 1008 Transfer Switch Equipment standard. Many local electrical codes will require UL 1008 listed Manual Transfer Switches. UL also provides testing for panels’ adherence to NEMA standards (see below).

You may find some Manual Transfer Switches listed to UL 98 (Enclosed and Dead-Front Switches) on the market. However, UL 1008 standards are significantly more stringent in regards to short-circuit current, temperature rise, number of transfer cycles tested, and current and voltage overload.

NEMA 3R Rated

NEMA 3R means that the panel (in this case a Roam MTS/Cam-Lock panel) meets the National Electrical Manufacturers Association (NEMA) 3R standard for either indoor or outdoor use. NEMA defines 3R as enclosures that “provide a degree of protection to personnel against access to hazardous parts; to provide a degree of protection of the equipment inside the enclosure against ingress of solid foreign objects (falling dirt); to provide a degree of protection with respect to harmful effects on the equipment due to the ingress of water (rain, sleet, snow); and that will be undamaged by the external formation of ice on the enclosure.”

Beyond meeting NEMA 3R, Roam’s MTS/Cam-Lock panels are also extremely rust resistant. They are built of powder-coated Aluminum, with Tin-plated Copper bus bars, and stainless steel nuts, bolts, and washers

Safety Cable-Access Restriction Features

Roam’s MTS/Cam-Lock panels incorporate a cable access restriction features that include sturdy GPO3 plastic safety fingers, and a flap/flange on the bottom of the door that allows the cables to be connected and the door locked. These features prevent accidental or deliberate disconnection of cables once the generator is connected, and the panel door is closed and locked. Roam’s cable access restriction design also minimizes risks of power loss due to vandalism or cable theft—or liability from unauthorized, untrained people accessing high-voltage power connections—while still providing quick access for authorized users.

What Are Some Optional Features You Might Need in a Manual Transfer Switch?

Common optional features of a MTS include:

Service Entry Rated

Service Entry rated means that an MTS/Cam-Lock panel is suitable for use as a service disconnect (service equipment). A service disconnect is simply the first disconnect between the external power source (utility or generator) and the building’s main circuits. Note that Roam’s Service Entry-rated MTS/Cam-Lock panels are available with a standard UL listing (USA), but not with a cUL (Canadian) listing. Most electrical codes require short circuit protection ahead of a UL 1008 listed Service Entry-rated MTS panel, unless that panel incorporates line-side (utility) short circuit protection. Roam’s SE-rated MTS panels do not include internal short circuit protection.

Switched Neutral

Normally, MTS panels are built with the Neutral connection not running through the Transfer Switch (frequently referred to as a “solid” Neutral). However, some electrical designs will require a Switched Neutral, where the Neutral connection is switched through the Transfer Switch (i.e., an additional pole runs through the Transfer Switch) along with the power phases.

Switch Neutral panels are typically used when the generator is grounded as a separately derived system at the site. It is important to be aware that Switched Neutral panels can not also be Service Entry rated under UL 1008. We advise that before selecting a Switch Neutral option, you should consult a qualified electrical designer who is familiar with your site and local electrical codes.

No Neutral

Conversely, some electrical installations will not require a Neutral pole at all. Leaving out the Neutral connection entirely saves money and can be safe and appropriate in some circumstances. But before choosing a No Neutral option, you should consult a qualified electrical designer who is familiar with your site and local electrical codes.