How can you tell if a breaker is good or not? What you don't want to do is "test by tripping." That method merely proves the breaker can be opened — it does not prove that the breaker will automatically open or will do so at the correct setting. Doing this with loads on the breaker is extremely unsafe once you get beyond the small branch circuit breakers. Before opening a breaker, remove the loads by opening all downstream breakers (using lockout/tagout).
The process of verifying if a breaker is good consists of many tasks. The first task is to remove the loads and take it out of service. Using your DMM, verify that this breaker is de-energized. Now you're ready for the next step, which is a visual and mechanical inspection. We'll look at this in our next issue.
||Get a grip on accuracy.
The Fluke 62 Mini non-contact thermometer is the perfect introduction to infrared (IR) thermometers for the professional. With the best accuracy in its class, the Fluke 62 Mini offers quick and reliable surface temperature readings. Rugged enough for industrial environments with its protective rubber "boot, the 62 Mini also comes with a handy nylon holster.
Last year, insulation resistance test trending showed that several cables needed replacing. While scoping out the job, you determined it required two crews working two shifts to complete the work. Why would it take so much time to perform this type of work?
For starters, there was barely enough working room. Adjacent switchgear had to be de-energized, which required coordination with a second production department. Further difficulty arose due to the size of the cables combined with the distance from outside access points, plus limited room for staging the pull. Three production machines had to be disconnected and temporarily located out of the way.
Recently, two of those same cables have actually faulted. What might be wrong now?
Visit EC&M's website to see the answer.
Don't let a cable pull go tragically wrong. The key to safe cable pulling is respect for the rope. Climbers have long known this, and cable pullers need to know it, too. The rules are a bit different for each group. Cable pulling crews need to observe these rules when selecting a rope:
- Choose one specifically for a given pull rather than just grabbing the nearest rope.
- Use one that's strong enough. Look up the "average breaking strength" of a rope you're considering. It needs to be at least four times the rated capacity of your puller.
- Pick one that's made of low-stretch material. When high-stretch ropes break, the release of their stored energy dramatically increases the danger.
Rely on the motto, "if in doubt, throw it out."
- Don't pull ropes over sharp edges. If there's a sharp edge in the pull path, cover it with something that can be securely fastened over it.
- Don't drag ropes over the ground (especially if it's a rough surface) or through puddles.
- Don’t walk on ropes, and never stand in front of the rope's "snap path."
- Don't use ropes that are old, frayed, dirty, or in any kind of questionable condition.
- Never use a rope with splices, kinks, or loose fibers.
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Why can't you use the 90°C column of the ampacity tables in Chapter 3? Well, you can but only if every component (including connectors) is rated for a 90°C application [110.14(C)]. This generally means you can't use that column because connectors aren't typically rated for 90°C use, and your connectors and your cables are typically in the same ambient temperature space.
To get a connector of adequate ampacity, you must use the larger conductors in the 60°C column. If you use a connector that fits the conductor in the 90°C column, the connector will be too small to handle the current thus imposed upon it.
To read more on this story, visit EC&M's website.
If you're on a big project where you're using cleaners and epoxies, can you stow these in the gangbox? No, you need to store them in special containers designed for flammables storage.
The rags you use when working with solvents become flammable vapor sources and kindling. These require special containers for storage/disposal. The typical flammables container is unbreakable, with a flame arrester and a spring loaded cover. It's also color coded; that's why kerosene cans are blue and gasoline cans are red. Use the right kind of container for the flammable you're storing; read the MSDS to determine what that is.
In addition, don't store flammables near corrosives or oxidizers (see MSDS of each chemical). Nearby corrosives might eat the container from the outside while oxidizers might cause it to erupt in flame. For example, don't store solvents in a battery room. Escaping fumes can travel along the ground to ignition sources hundreds of feet away. Close container lids tightly, and provide ventilation per the information in the MSDS.