# HRC Ratings



## knowshorts (Jan 9, 2009)

Went to kill a circuit this morning and I noticed they had an engineer place all the arc flash stickers on everything sometime recently.

800 amp 3 phase 480 volt gear with 100 amp breaker feeding a 45kva xfmr. Secondary was feeding a 200 amp 3 phase 480/277 volt panel with a 150 amp main. Tranny was just to obtain the neutral. All equipment was next to each other on the same wall.

HRC rating on the gear was 2, tranny was a 1, and the panel was a 3. 

That doesn't seem right. Engineering mistake?


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## Zog (Apr 15, 2009)

Gear is protected by main breaker which will have slower trip than the feeders so the gear will often have higher HRC than downstream of the feeder, in this case the transformer. So that seems right. 

The secondary side of the transfomer will have long clearing time due to no OCPD on the secondary side, likely they used the 2 second default so having a higher HRC seems right as well. 

All typical stuff and the fact this seems odd to most electricians is exactly why arc flash training is so important.


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## knowshorts (Jan 9, 2009)

I agree it's important, but with the lack of a sticker most will go by the chart. The panel is listed as a 2 on the chart, but someone could be under-protected by 17 cals. 

Without getting all scientific and mathematical, wouldn't one think that testing for 0 voltage would be the safest in the 200 amp panel?

In the same electrical room, there is a large enclosure. Approximately 9' wide by 6' deep. There is 3 removable fronts. No OCP, just ventilated covers. Behind left and center is a 12000 to 480 volt transformer. Behind the right section is the bus taps feeding the transformer from the ATS. There is no dividers. Remove the middle cover and you can reach into the left and the right section. The left and middle sections have the red HRC sticker with absolutely no permissible entry (exceeding HRC-4). The right section has an HRC of 1. Why wouldn't the right section have the same HRC rating when you can enter the 4+++ area from the 1 area?


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## Zog (Apr 15, 2009)

Sounds like it should, but hard to tell without visuals.


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## knowshorts (Jan 9, 2009)

All I know is that piece of equipment makes scares the crap out of me. If I ever have to get in there, it is definitely something I am going to sub out.


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