Incident Prevention Magazine

Dave Johnson, CUSP, and Mack Turner, CUSP

7 Electrical Theory and Circuitry Myths – Busted

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In the electric utility business, we have highly trained employees who are proud that they have learned the skills to be able to safely work around high voltage. However, a phrase we hear too often is “Hey, it’s only secondary,” which implies that secondary is not as hazardous as primary, lightning or fault current. We’re not going to debate that in this article, but we are going to discuss – and bust – some common myths about working with 120-volt circuitry and equipment, as well as myths regarding lightning and fault current exposure.

Myth 1: Circuit breakers are better than fuses.
If you utter this statement and are merely talking about convenience, you may have a cogent argument, but convenience does not outweigh safety. If you are merely talking about cost, you may again have a cogent argument, but the cost argument doesn’t win when it comes to safety because how do you put a price on a human life?

So, why might a fuse be better than a circuit breaker? All fuse manufacturer representatives will assure you that fuses in general operate faster than breakers. They may operate in less than a quarter of a cycle compared to three to four cycles for many circuit breakers. If you are in series or parallel with fault current flow, you literally are being cooked from the inside out. Reducing the amount of time the circuit is allowed to operate is a better protection strategy than allowing current flow to go on longer. Additionally, fuses typically are better at interrupting an avalanche of fault current from an incoming service. Breakers and fuses have maximum amp interruption capacity ratings, meaning if a breaker or fuse is installed on a circuit with a higher fault current capability than the breaker, the breaker or fuse can simply melt or arc across and fail to operate. The least-protective fuse interrupts 10,000 amperes of incoming energy, while a typical branch circuit breaker interrupts 5,000 amperes.

Myth 2: If you turn on a light switch with wet hands, you will get electrocuted.
While there is a possibility you might get electrocuted, you probably will not. That’s not to say you won’t get shocked; you must understand the difference between shock and electrocution. A shock occurs anytime current flows through your body, via any path, for any duration and at any magnitude. Electrocution is a shock that kills you by interfering with bodily processes. It only takes as little as 50 milliamps to send an adult heart into ventricular fibrillation; death is imminent within four to six minutes of ventricular fibrillation.

Another definition also is useful here: Fault current is current flowing anywhere you don’t want it to flow, especially through you. Fault current can flow in parallel or in series with normal current flow, or with the load. You don’t want to be in the path of fault current. Fortunately, the likelihood of being in a fault current path while operating a modern plastic switch, even with wet hands, is very low. Even lower is the likelihood of electrocution from the event.

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