Relay Test Switches

There are new relay test switch designs on the market that are safer to operate and pose significantly less risk to the technicians who will be required to operate them. These test switches comply with ANSI/IEC 60529 and have an IP20 rating.

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New designs enhance safety, comply with ANSI/IEC 60529

By Steve Lytle

In this time of the Industrial Internet of Things (IIoT), the electric power industry is focused on smart meters, smart grids, IEC 61850, NERC CIP, FERC, and more. Governmental requirements for reliability are driving investment in predictive technology rather than preventive technology. Equipment is getting “smarter” to minimize downtime and reroute power on and off the grid. Distributed energy resources are influencing generation load requirements, and that’s just on the inside of the substation or control room. Outside, there’s another batch of security requirements such as cameras, motion detectors, lighting controls, fences, and walls that must be considered.

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The North American Electric Reliability Corporation (NERC) requires that components in transformer stations be tested every six years.

In the midst of all of this, it’s no wonder that engineers and technicians are resistant to change when it comes to panel equipment. One example is the test switch for safety relays. For several decades, the knife-blade design of the test switch has been accepted as the norm. However, there are new designs on the market that are safer to operate and pose significantly less risk to the technicians who will be required to operate them. These test switches comply with ANSI/IEC 60529 and have an IP20 rating.

North American Electric Reliability Corporation (NERC) regulations dictate that relays must be tested for proper operation every six years. Sounds pretty simple, right? For the most part, it is. But, it’s also potentially deadly if done improperly.

Testing Basics

Control transformers are used to measure the currents (CTs) and voltages (PTs or VTs) produced and distributed throughout the substations and electrical grid. CT installations are permanent; they cannot be removed while current is flowing. To do so would pose considerable risk to both life and property. The act of removing (or lifting) one of the two wires that connects the CT to the safety relay while current is flowing will result in immediate, infinite rise in voltage and the potential for an arc, which will cause major damage. This circumstance is referred to as “opening a CT” (see Fig. 1).

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Fig. 1. Typical three-phase test switch wiring diagram.

Test switches have been implemented for this reason. All of the test switches on the market have the ability (when properly configured) to short the primary and secondary of the CT, and also isolate them from the control instrumentation, such as safety relays, which makes it safe to perform necessary testing and maintenance tasks.

It is during commissioning that test technicians have the most interaction with the test switches as the safety relays are extensively tested. Some of the concerns raised by these technicians are:

• Adequate labeling of terminals

• Reliability of the switch itself

• Ability to see that CTs are in a safe mode prior to testing

• Opening of a CT

Of these, opening of a CT is the single biggest concern of technicians and engineers. To this end, seminars and training classes have been developed to increase the safety and well-being of the individuals who interface with safety relays and test equipment. One example of such an event is Reliability First’s Protection System Workshop for Technical Personnel.1

Relay technicians have developed several techniques to ensure that they are safe when working on or in relay panels. Some of these solutions are:

• Installing magnetically mounted curtains to ensure that they do not access the wrong CT

• Writing on the relay panel with dry-erase ink during testing

• Hanging tags on wires for proper identification

There are two primary reasons that technicians perform testing: NERC requirements (every six years, minimum) and component maintenance.

When performing the NERC-mandated testing, typically a test paddle is used. This paddle is wired to a tester that runs various scenarios and checks the response of the relay. During this testing, the CTs and PTs are typically isolated from the relay by opening the contacts via the test paddle insertion.

Traditional test paddles are usually custom-configured and specific to each test switch and tester combination. When performing component testing, the test paddle may or may not be used. Technicians can test countless scenarios, such as CT saturation, relay response to an injected current, individual voltage, or current readings.

There are typically two types of electrical tests performed on relays: voltage reading and current reading.

A Safer Way to Disconnect

New test disconnect systems, designed specifically for the North American electric power market, address technicians’ concerns (see Fig. 2).

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Fig. 2. The new FAME 3 test disconnect system simplifies the regular testing of power switchgear.

With the new testing system, these tests can be performed through the test plug and tester. They can also be performed with individual test probes.

To take a voltage measurement, insert the meter leads into the appropriate test ports and record the voltage (see Fig. 3).

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Fig. 3. Test plug for isolating and testing safety relays.

To take a current reading, the ammeter leads must be properly inserted into the test plug or test probe prior to insertion into the test switch. The multiple contacts achieve the “make-before-break” function as the probe is inserted, and the current is redirected through the ammeter (looped in).

Many technicians are accustomed to using alligator clips to take readings. By inserting a bridge into the test probe, the same function can be achieved in a way that poses less risk of accidental contact with the wrong terminal. The bridge would connect terminals 3 and 4 (see Fig. 4), thus overriding the “break” function at full insertion of the probe.

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Fig. 4. Test probe for individual component test measurements.

There are instances when a technician may wish to isolate a CT and perform saturation tests. To do this, the technician can insert a two-pole test probe that will safely short the CT and isolate it from the relay. (To achieve isolation without shorting the CT, the bridge would need to be removed prior to insertion of the test probe. CAUTION: Doing this improperly can result in opening the CT.)

The same thing can be achieved using the test handle. This test system also offers the added benefit of the opportunity for redundancy. CT shorting can be accomplished in both the test socket and the test probe (or handle). This feature also allows the user to customize either the handle or the socket, based on personal or company preference. It also allows for standardization of test equipment.

Another benefit of the new technology is the flexible configuration. Bridges can be removed or relocated to accommodate the configuration of a new tester. The associated wiring can then be adjusted accordingly on the back of the switch, and then marked “adjusted” on both the front and back of the switch. Then, the test system is available for use. This flexibility eliminates the absolute need to configure before purchasing, and makes field changes possible when needed. As an example, the position of CTs can be changed, or the function of the poles can be redesignated from CT to PT or PT to CT as needed. This eliminates the need to purchase a new custom-configured test switch every time the relay tester is updated.

To address marking concerns, each terminal has marking areas on both front and back (as shown in the photo). This can reduce confusion when performing repetitive tests, especially during commissioning. It’s not uncommon for technicians to attach test equipment to the wrong relay sets because of having to walk around racks to get from front to back. Not only are there markers for each pole, but there are additional markers available to include other information such as relay identification, drawing number, etc.

Once the switches are wired, covers can add security. There are two different styles for the back of the switch, as well as a see-through cover with tamper-seal capability, and a dust cover with marking and tamper-seal capability.

In addition to the test probes, there are also isolation probes in one- or two-pole styles, and available in red and green. All probes can be marked to add to the understanding of how each is applied, or which pole to apply it to.


The electric power industry is changing rapidly, and utility workers need to adapt to new technology and regulations at a very fast pace, but safety needs to remain the top priority. With the new test disconnect system, technicians can perform manual testing operations more quickly and flexibly, without sacrificing personal safety.

The Author: Steve Lytle is Phoenix Contact’s manager of global market development for the electric power industry. He has more than 20 years of experience in product management, with a focus on transmission and distribution substations.


1. “Workshops Materials & Webinars,” Reliability First,, accessed Jan. 2, 2019.

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