PPE for Arc Flash Scenario 5

[nightfox1925]

We had a 480VAC MCC with a calculated bolted fault at the bus at 11kA sym.,and the calculated Arc Flash is around 40cal/cm^2. Our contractor is suppose to plug in a new motor starter to this existing MCC (which is enegized) but because he does not have his PPE rated for the Arc Flash, the work was stopped.

My question is, if the MCC main and vertical bus is enclosed in a separate compartment within the MCC which does not expose our contractor to live parts, is he supposed to wear a PPE rated for >40cal/cm^2.

What about if the work only calls for example opening of a de-energized MCCs spare starter for visual inspection, are we suppose to be wearing >40cal/cm^2 PPE rating?

I am still in the process of familiarizing myself with the Arc Flash standard.

 

[REM76]

Thedroid,

1- If you have higher than 40 cal/cm2, you will need to shutdown the power and do the work de-energized. Arc Flash PPE is only recommended for up to 40 cal/cm2. Above forty, there will be other hazards (i.e. blast pressure) associated with the arc other than the thermal hazard, which is the PPE is good for. For example, someone could wear 100 cal/cm2 suit, but if there was a 100 cal event, the PPE will only portect the skin and everything inside will be jello.

2- Look at the settings at the upstream breaker that feeds the MCC. You may want to adjust the settings to lower the incident energy at the MCC to below 8 cal/cm2. This may cause some mis-coordiantion...but safety should take precendence over coordaintion. After you put the starter in, you could re-adjust the settings to where they where. New trip unit have a switch that allows the owner to lower the settings during the maintenance period.

see the following web site for details.

http://www.arcflashsafetysolutions.com/productduration.html

 

[unclebob]

May be need for an ''Arc Proof MCC''

 

[nightfox1925]

Good news! We were able to get a shutdown on the MCC. based from what I learned in this forum, we initially made a proposal to adjust the instantaneous setting of the MCC upstream LV circuit breaker from "Hi" to "Lo" and it reduces the arc flash to a low level. Once the work is done, the circuit breaker will be set back to its original setpoint to maintain coordination.

Thank you for all the tips and more power.

 

[Zogzog]

QT=Quick Trip , AC PRO's arc flash reduction (maintenance) switch

http://www.utilityrelay.com/QUICK-TRIP_Page.html

 

[Thedroid]

I glanced at an AC PRO this morning but did not see a Quick Trip Setting. Maybe it's within a menu. I didn't have a chance to open up a manual. If they are QT capable would I enable this feature anytime I working on something within the MCC?

Cement Plant Electrician and
Instrumentation Technician

 

[dpc]

The Quick Trip is an option that has to be added on. If you're working on a MCC, you'd want the Quick Trip on the breaker upstream from the MCC. It has to be manually enabled and disabled. While enabled, there is a serious sacrifice of selective coordination in order to reduce the clearing time.

 

[Zogzog]

Thats why the switch is padlockable, to control when it is used, but if an arc flash occurs, and the reduced hazard keeps me out of a burn center, I dont care about selective coord, I dont think anyone would.

The Droid, it is not a setting but if your programmers say "with quick trip" on the front, the option can be added easily, if not you would need to upgrade, but you can get a large credit for your old units.

 

[Thedroid]

I'm going to look at some tommorow. We have at least 40-50 AK breakers with the AC PRO's. It would be nice to have that option. The 4160 goes through the magne blast to the transformer and after the transformer there is a what i think is called a main secondary which is an AK breaker, 1200A i think, then there are 4-5 smaller AK's each feeding an MCC. . What are these last breakers called?

Cement Plant Electrician and
Instrumentation Technician

 

[Zogzog]

They are usually just called "feeders"

The quicktrip will be an easy solution for you either way, I can get you a kit to do the upgrade in house, only takes about an hour (Or less) per cell and is very inexpensive.

Scott

http://www.cbsnuclear.com