Hi All,
As our interim measure while we are process of performing an Arc flash analysis study for our facility we have decided to use the NFPA 70E tables (2012 version) to guide PPE requirements for different types of work/tasks being done on the MCC/ Switchgear. However, the tables are accompanied by parameters which state values such as the available short circuit current, FCT etc. Our gear at the 480V and >1kV level for example, may not necessarily follow these parameters. An example of this is at our 480V level, our FCT for our protective devices are greater than those stated in the parameters. Would it be wise to use these tables given that the parameters do not match ours?

Another issue we have is around the use of the term "exposed energised conductors or circuit parts" in the parameters. If you are familiar with the Freedom 2100 Cutler Hammer MCCs, when the cubicle door is open, there are shutters which guard the bus. Can we say there are "exposed" parts in this case?

Appreciate any kind of dialogue on this!!!

Hi Aleesha,

I believe your scenario is somewhat similiar to my original question below. Have a read on that thread and think again.

http://www.arcflashforum.com/threads/1783/#post-8672

We have decided as a company to move forward with classifying the starter the same category as the MCC bus. This is mainly due to insufficient information provided by supplier, mainly the MCCB manufacturer as nobody will gurantee you it is not consider exposed.

Cheers,
Brandon

If the shutters cover the bus in a way that it is insulated, isolated, or even just guarded, then it is NOT exposed. SHOCK hazards do not apply. An arc flash hazard may still be present...you evaluate this a different way.

The key phrase when it comes to exposed is INADVERTENT contact. It can be insulated, isolated, or guarded. For instance recessed bolts common on the lugs of current model circuit breakers are guarded even though I can stick a meter probe (or a screw driver) down the screw slot and contact live voltage. BUT if the installer strips much more of the insulation jacket off the wire while installing and leaves a significant area of the wire going into that lug exposed and I'm working within the restricted approach boundary of that conductor, then it becomes exposed. Inside of some of the reduced height MCC cubicles you may have to make a judgement call at times just because of the equipment arrangement...if there is stuff in the way that prevents accidental contact such as working on the wiring on the right hand side where both the starter lineup and the right hand edge of the breaker block potential accidental contact with the breaker primary lugs, you may want to consider whether or not this acceptable guarding and
ignore the 7" restricted approach boundary which is a "clear space" rule.

Within the limited approach boundary but outside the restricted approach boundary, if nonqualified personnel are restricted from access, then the hazard to qualified personnel is minimal. In overhead line work if there is a possibility of accidentally getting into the restricted approach boundary, they use cover up (line hose, blankets, etc.), and this is equally applicable at lower voltages. This would be adequate justification for performing work within that area...since there is minimal hazard, the hazard is no greater than working while de-energized.