There are many frequently asked questions about performing an arc flash study (risk assessment) and understanding electrical safety requirements. A careful read of standards such as NPFA 70E or IEEE 1584 can answer some questions. Yet, other questions can be more complex, gray areas can lead to confusion, second-guessing and wondering how everyone else does it. Continue reading →
Question: What are you guys recommending to reduce incident energy levels on fire pump controllers fed directly from the secondary side of utility transformers?
Answer: Can’t be done. This is a common practice but is very illegal in most cases. NEC is very specific in that overload protection (ie, overload relay) is eliminated and short circuit protection only remains. I have no idea why and I’ve had multiple fire marshals actually try to tell me that fire pumps get ZERO protection which is utterly false. In most cases the short circuit protection on the primary side is NOT sufficient to protect the branch circuit on the secondary side. And that’s the answer to your problem…short circuit protection (e.g. a MCP aka magnetic-only circuit breaker or simply a fuse) with the instantaneous trip point set below the arcing current fixes the problem and is 100% legal, and in most cases such as what you describe where it’s a huge Code violation, it also fixes that issue. READ MORE.
I believe it to physically impossible to sustain an arc flash at 120 V but can someone point me to the proof? Can someone indicate where a code specifically states no arc flash PPE is required at 120 VAC? READ MORE.
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NFPA 70E requires that an Arc Flash Risk Assessment be updated when a major modification or renovation takes place. It shall be reviewed periodically, at intervals not to exceed 5 years, to account for changes in the electrical distribution system that could affect the results of the arc flash risk assessment. Countries outside of the US that do not use NFPA 70E may have a similar label review/updating requirement.
NFPA 70E further states that where the review of the arc flash hazard risk assessment identifies a change that renders the label inaccurate, the label shall be updated.
What is the maximum number of times you have updated any arc flash label since first applied? -Still have original labels -Updated once -Updated twice -Updated more than twice -No labels yet -I don’t do labeling
1910.269 requires arc flash protection for hands with exceptions when wearing leather protectors over rubber gloves, and when wearing heavy duty work gloves. The workers state that sticks should be used bare handed, and that work gloves will contaminate the stick. Any advice on this topic? Leather gloves aren’t going to contaminate a hot stick unless for instance they get saturated in creosote or other materials. Granted there are tons of nasty, sticky materials in the utility work site and if the gloves get soaked with the more flammable ones, their “fire retardant” properties disappear.
It has been shown that up to 12 cal/cm2, leather gloves are sufficient.
You can’t use gloves realistically at high voltage and above (as per IEEE 516) because the voltage across the gloves might exceed their ratings. Since it is so hard to find class 3 or 4 gloves I kind of disagree with the current version of IEEE 516 cutting off the “no gloves” limit at 40 kV and I think it is more realistic to do this above 15 kV.
Finally with the hot stick method the intent is that some current flows through the worker’s body. Wearing gloves with hot sticks interferes with this. You are basically mixing work methods, the insulated tool method and the rubber glove method. READ MORE
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