? on Arc Flash PPE

[Jimland58]

Scenario: 480v MCC bus has incident energy of 68 cal/cm2. Policy is to de-energize the MCC by opening, locking and tagging the remote breaker that feeds this MCC before doing any work on this MCC. Policy is to wear Class 00 gloves when doing the voltage test at the MCC to confirm de-energization before working.

Question: Do you have to wear Arc Flash PPE when doing the voltage test for de-energization? If so, the site has only 40 cal arc flash suits so how would you protect the worker from a potential arc flash at the incident energy of 68 cal/cm2?

 

[wbdvt]

Yes you have the wear the appropriate AR PPE to test for dead. Until it is proven de-energized, you must wear the appropriate AR PPE as well as protect from shock.

I am surprised that the Incident Energy is so high at an MCC. I usually find high IE's like that on the first piece of equipment on the low side of the utility transformer. So I have so questions about the study that the IE is from.

1. Does the upstream breaker have an adjustable instantaneous function?
2. What is the arcing time of the fault at the MCC?
3. Were any recommendations made in the report to reduce the incident energy?
4. Were other distances and IE's provided? For example: is there a way to test using probes on the end of a 3 ft hotstick where the IE is less that 40 cal/cm2.
5. How have you been performing work on the MCC up to this point? For example how do you reset overloads if there is no reset button on the mcc cubicle door? How do you replace a blown control transformer fuse inside the cubicle?

 

[Jimland58]

1. Does the upstream breaker have an adjustable instantaneous function? No, upstream OCPD is a S&C Fuse
2. What is the arcing time of the fault at the MCC? 2 seconds
3. Were any recommendations made in the report to reduce the incident energy? De-energize
4. Were other distances and IE's provided? For example: is there a way to test using probes on the end of a 3 ft hotstick where the IE is less that 40 cal/cm2. No, but this is a good idea. My rough calculations show if I change working distance from 18" to 24" it drops from 68 cal to 39 cal and if I go out to 36" it drops to 17 cal
5. How have you been performing work on the MCC up to this point? For example how do you reset overloads if there is no reset button on the mcc cubicle door? How do you replace a blown control transformer fuse inside the cubicle? OL resets are on the door. Any work with door open was being done de-energized but the issue as I see it is how you protect the worker doing the voltage check.

 

[petersonra]

I wonder how you get the door open and stay outside of the blast zone.