Problem Solved:
Putting Terminal Blocks to the Test
By Alan Sappe, Product Marketing Lead Specialist—CLIPLINE
Phoenix Contact

When faced with demanding specifications for solar and navigation systems for offshore India, Automatic Power chose Phoenix Contact to provide durable, high-performance terminal blocks that could comply with customer requirements.

In 1985, Engineers India Limited (EIL) contracted Automatic Power to supply lighting, foghorns, and solar power systems to an Offshore Natural Gas Commission (ONGC) platform in the Bombay high field offshore India. Having little experience with Phoenix Contact, Alan Trojanowski, chief of engineering, selected Universal Screw Connection (UK) terminal blocks, as they met the required UL and CSA standards. Phoenix Contact catalog sheets supplied the testing standards that had to be met and their engineers supplied some independent testing results that satisfied EIL and ONGC.

“There have been no failures since I’ve designed in Phoenix Contact, which is huge. No failures in 24 years is unheard of,” said Trojanowski.

Due to his limited experience with Phoenix Contact, Alan also decided to do some testing of his own. “I was worried the terminals were going to corrode, so I placed rail assemblies with three different brands of terminal blocks on my bay boat,” said Alan. He checked them after nine years, and found the Phoenix Contact terminals unscrewed with no problem—unlike the competing terminals.

Tough conditions require a tough terminal block
High temperatures. Humidity. Dust. Chemicals. Saltwater. These are just a few of the harsh conditions common in industrial environments such as those found in wastewater, petrochemical, and food and beverage plants. Vibration is also a threat to a secure connection in many applications.

Terminal blocks connect or terminate discrete conductors or wires. The quality of terminal blocks has a major impact on the reliability of the overall system. Terminal blocks that corrode or rust in mission-critical applications, or loosen under constant vibration, could lead to a full system failure. Depending on the application, this can cost hundreds of thousands of dollars to repair.

The right material for the job
Withstanding environmental challenges is a true test of a terminal block’s mettle—and its metal. A terminal block’s conductor body must have excellent conductivity capability, but corrosion resistance is equally important. Copper alloy provides the most reliable choice for this. Nickel or tin plating are commonly used.

A nickel-plated copper alloy is often the best choice for the terminal block’s conductor body. It offers three main advantages:

1. It ensures electrical conductivity. This allows low resistance with minimal temperature rise. As a result, low voltage and low current signals remain accurate.

2. The alloy reduces thermal expansion caused by changes in temperature between the conductor and the clamping body. This eliminates the loosening of screws and or wires. Because the wire and metal body are both made of copper, they expand and contract at the same temperature.

3. Last but not least, it eliminates electrolytic and environmental corrosion. Electrolytic corrosion results from action between the copper conductor and a non-copper terminal block. Environmental corrosion results from moisture and corrosive gas in the atmosphere, elements that react negatively with a non-nickel-plated copper alloy metal body. No matter what the source, corrosion will eventually lead to an unreliable connection.

Safe and secure: reducing the effects of vibration
A variety of connection technologies are used in terminal blocks, and each has its advantages, depending on the application. However, screw terminal blocks have the highest clamp-down force—up to 300 Newtons—which ultimately can provide the most secure connection in high-vibration conditions.

Screw terminal blocks meet very high demands. Many are designed to provide multiple conductor connections, which makes them ideal for use in a small space. They are the most commonly used terminal blocks and are accepted worldwide.

Terminal blocks with a rising cage clamp keep constant force on the screw, preventing loosening or backing out. This screw-locking technique greatly eliminates or reduces potential problems in applications with high vibration or extreme temperature variations.

The technique is simple: As the screw is tightened, the pressure plate moves upward toward the conductor to be clamped, while the conductor stays stationary. Once the pressure plate contacts the conductor, it exerts increasing pressure, resulting in an equivalent upward counter force on the threaded bar.

The angled extrusion edges of the threaded bar press against the upper edges of the rectangular slots in the metal body walls. This causes the walls to press against the peaks of the screw thread. The screw is locked in place and will not vibrate loose.

This method provides a gas-tight, stable connection that not only withstands the impact of vibration and other forces, but also provides further corrosion protection, as it keeps out potentially damaging corrosive gases and liquids.

While the environmental influences on an electrical system vary among different industries, a terminal block that can withstand corrosion and vibration can ensure reliable operations for many years.

With more than 15 years experience in technical sales and marketing, Alan Sappe has supported contract manufacturers, distributors, system integrators, and OEMs across a wide range of industries. Currently, Sappe is responsible for marketing DIN rail-mounted terminal blocks and related products for Phoenix Contact USA. He can be reached at 717.944.1300, ext. 3386 or asappe@phoenixcon.com.