OSHA’s Electrical Safety related Work Practice Standards 29 CFR 1910.331-335 specifically 333a1 states that “Live parts to which an employee may be exposed shall be deenergized before the employee works on or near them”.
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9910This is essentially the same verbiage as NFPA 70E Article 130.1
The key words are, on or near them. When an electrical enclosure is opened whereby exposing live parts then that requires PPE until the circuit is deenergized, locked and tagged out, and verified for “absence of voltage” with test equipment. Only when this has been completed can the PPE be removed.
Somehow all that got watered down to simply working live, and with a very nebulous definition of same and even more vagueness of the required PPE required. A look at the NFPA 70E hazard risk category classification tables require PPE for both burn and electrocution protection whenever any enclosure dead front cover is removed to expose energized electrical parts.
The level of burn protection required is NOT dependent upon voltage but rather the available level of fault current. In short the magnitude of the arc blast/arc flash is energy related not voltage related. Factors which dictate the available level of fault current are the separately derived system/transformer size, feeder/circuit/conductor impedances between the transformer and the point of potential exposure. It is true as mentioned in another post that the fault current levels are generally greatest at 480v. The closer you are working to the transformer and the larger the transformer the higher the available energy and the greater the level of PPE. I have a simple saying I use in the classroom. The bigger the equipment the greater the hazard (and consequently the higher level of PPE required). IEEE 1584 is OK for engineers but unless you are a EE don’t even look at that standard, it will make your hair fall out and eyes cross. The tables in 70E are much better guide. They don’t include every conceivable task but you can find a task listed in the tables close to what you are doing and have a decent PPE guide.
Cycling equipment with covers on the electrical enclosures poses essentially no electrical hazard exposure although the cycling of high energy/current equipment by say flipping a 200a breaker on and off where a breaker could blow apart for various reasons (breaker failure, improper short circuit rating etc.) it would be wise to at least have on FR coveralls, leather glove, safety glasses equivalent to a hazard risk category one in the 70E tables. Additionally the cycling of equipment where a mechanical hazard exposure exists because a barrier guard is missing or non existent would require lock out under another standard for protection of the mechanical exposures although this should have already been addressed through machine and machinery guarding including belts, pulleys, gears, sprockets, moving machinery, points of operation etc. This is not an electrical hazard exposure issue but a machine guarding and machinery lock out issue as was also mentioned in another post. There is another OSHA Lockout/Tagout standard for these exposures. 29CFR 1910.147
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9804Finally, I’d like to mention that I have conducted many fatality investigations. One investigation was where someone was working in a 480v disconnect switch, in the off position with only the line terminals energized, additionally a barrier guard over the line terminals and the person was burned to death in an arc blast. Was it switch failure, uninsulated tool or hardware dropped across the energized terminals? Well never know for sure. The indisputable facts of the case are these: There were energized/live parts inside the disconnect switch (not deenergized and locked out), the disconnect cover was open, the electrician was doing something inside the switch, tools were being used to some extent, none of the electricians tools were rated (insulated), the electrician was wearing synthetic blend clothing, this was in a power plant, and the deceased victim had a wife and several children.
80% of the fatalities among qualified electrical workers are due to arc blast/arc flash. Please be careful out there!
