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.
NEC 240.87 has addressed a potentially hazardous situation beginning with the 2011 edition. When selective coordination is critical, e.g., minimizing the extent of an outage, a common design practice is to use a main circuit breaker without an instantaneous tripping function and feeder breakers with one. Without an instantaneous, the main can time delay up to 30 cycles or 0.5 seconds greatly increasing the arc flash hazard. Continue reading
The NEC defines a “Hazardous Location” as a location “where fire or explosion hazards may exist due to flammable gases or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings.” There are 13 articles and 68 pages in the NEC regarding hazardous locations, installation practices and equipment requirements. Understanding what makes a location “hazardous” is the first step in providing a safer electrical system.
Materials that can cause a location to be classified as hazardous range from hydrogen, to grains, coal dust, petroleum products and many others.
Jim Phillips, P.E. – October 2005 – NEC Digest
Download Article: NEC Digest Hazardous Locations
The next time you are near the bulletin board at work, look for the poster that has the words “It’s the Law” and “OSHA” on it. It has probably been hanging there for a very long time but most people never really notice it or seem to read it. Further down on the poster is the statement “each employer shall furnish to each of his employees employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to employees. This statement is known as OSHA’s General Duty Clause and is at the heart of linking many of the other standards to OSHA.
Jim Phillips, P.E. – February 2005 – NEC Digest
Download Article: OSHA NEC NFPA