Ppe needed

[bure961]

when working on a mcc the main circuit breaker of a motor controls Center the ppe needed is listed at a4. the bucket
next to the main circuit breaker is listed as a 1. what level of ppe is needed to work in the bucked.?

 

[petersonra]

is this a test question?

 

[bure961]

Just a question. It seems to me if i am working next to a main breaker in a mcc with say a 165 in. af boundary with the ppe listed as 4 on the label that i may have the the wrong ppe on even if the label on the bucket i would work on is listed as a 1 for the ppe .
The main circuit breaker in the mcc has a different level label then the buckets in this mcc.

 

[petersonra]

Just a question. It seems to me if i am working next to a main breaker in a mcc with say a 165 in. af boundary with the ppe listed as 4 on the label that i may have the the wrong ppe on even if the label on the bucket i would work on is listed as a 1 for the ppe .
The main circuit breaker in the mcc has a different level label then the buckets in this mcc.

Does the AF boundary prohibit people from walking within 165" of the main breaker if the main breaker compartment is closed?

How is there a hazard just by being in the space when you are working on a bucket versus just walking by?

 

[jim dungar]

You need to have a good understanding of the zones that the labels actually cover.
Unfortunately it is not uncommon that the person doing the study also does not understand them.

For this discussion:
Zone 1 = the line side of the MCC main breaker. The Arc Flash Incident Energy (AFIE) is dependent to the performance of the protective device feeding the MCC.
Zone 2 = the load side of the MCC main breaker, this includes the internals of the MCC (e.g. the interior bussing). The AFIE is dependent on the MCC main breaker.
Zone 3 = the load side of the individual starter buckets. The AFIE is dependent on the protective device in each bucket.

Some common mistakes.
1) On many MCCs there is little to no difference between Zone 1 and Zone 2 because there are almost no internal barriers which would prevent a fault on the internal bussing from engulfing, or overrunning, the MB. (it seems this is most common on 1200A and smaller).
2) The most dangerous mistake is assuming that the inside of each bucket is in Zone 3 when they are realistically in Zone 2. Again there is rarely internal barriers that will contain the fault and keep it from involving the internal bussing.

 

[bure961]

BOB, I can not answer either of your questions .

Jim , thanks for the very informed answers it does help a great deal to get some serious information, I really appreciate your time and help here.