By Randy K. Logsdon
First Quiz Question: The electrical equipment in your work area suddenly quits. Nothing seems to be working right today. You make the trek over to the motor control center and discover that the circuit breaker for the equipment has tripped. What is your next course of action?
There are a number of right answers; and some that are clearly wrong. The immediate solution (and we’ve all done this) is to reset the circuit breaker. If it stays reset – problem solved. But that course of action does not answer the underlying question: Why did it trip?
We know that circuit breakers are designed to trip when an overcurrent (overload) occurs. It’s a safety feature designed to protect the equipment, prevent fires, and safeguard personnel who might be in harm’s way. Any number of mechanical or electrical defects could be the root of the problem. Reading flags, performing tests and a thorough physical inspection of the equipment is likely to reveal the problem. Something may be jammed. A bearing may be defective. Something could just be in a bind. Neglecting the investigation will likely result in the circuit breaker tripping out again and again. It could also result in significant damage or even injury.
Second Quiz Question: You are changing a tire on a service truck. It’s not a routine job, but one you’ve done dozens (perhaps hundreds) of times. You’ve planned the work and gathered the necessary tools you will require. The truck is blocked. The keys are in your pocket. You’ve jacked the vehicle up, blocked the frame, and you’ve removed the lug nuts. The tire is deflated. You find that the wheel is frozen to the hub. You tug but it won’t come off. What is your next course of action?
Before you answer, consider the similarities to the first question. An unexpected variance has developed in both scenarios. With the electrical circuit, it was the tripped circuit breaker. With the truck, it’s the frozen wheel. In both cases, experience tells us that there is a speedy remedy: reset the circuit breaker; apply force to the elevated wheel. Such force could damage the rim or other vehicle components. It could affect the stability of the jack. Parts could go flying.
Isn’t an investigation in order? What are the forces that are preventing the release of the wheel? Yes, it may just be rust and dirt, and confirming that may lead you to your original remedy. But what if there is a different cause? Taking a few moments to investigate – to double check – will give you a better understanding of the problem and an opportunity to plan a safe solution. You can deliberately address the problem rather than simply react.
Rarely does every job or project go entirely according to plan. We try to anticipate – to predict – those variances but invariably, we’re caught by surprise. Regardless of the setting, your safety just may be dependent on whether you deliberately act or unconsciously react.
Circuit Breakers
The three common types of circuit breakers are:
• Magnetic Type Circuit Breakers use a type of electromagnetism to interrupt a circuit. Some designs incorporate the use of a solenoid. As current increases, so does the pulling strength. When excessive current passes through magnetic breakers, the electromagnetic energy increases as well. As the load reaches a tipping point, the magnetic force becomes strong enough to flip a switch, moving a contact plate.
• Thermal Type Circuit Breakers use heat to interrupt a circuit. Many electrical distribution boards use thermal circuit breakers. Thermal breakers use a bimetallic strip in series with a circuit. The heat produced by the current at the time of an overload deforms the bimetallic strip and flips the breaker.
• Hybrid Type Circuit Breakers use both electromagnetism as well as heat for protection. These types of breakers have an electromagnet that guards against abrupt surges in the electrical circuit and a bimetallic strip that shields against extended electrical load and overheating. Other types of circuit breakers include: medium-voltage circuit breakers, high-voltage circuit breakers and sulfur-hexafluoride, high-voltage circuit breakers.
Source: RG Industries.
Randy K. Logsdon, CMSP, is manager of safety for Intrepid Potash New Mexico operations. He has practiced safety on both the coal and metal/non-metal side of mining for more than 30 years. Randy is a Certified Mine Safety Professional. He can be reached at [email protected].