ARC FLASH Study Understanding

[adityalagudu]

We have 0.48 KV (Main -Tie-Main) switchgear (PCC-21-01)fed from 13.8 KV/0.48 KV transformer. It is a 4000A switchgear.

I am confused while understanding the Arc flash study report. Please help me in understanding the format and which label goes to where. Please see the attached.

How come CB in the switchgear has more Incident energy than the Switchgear? What does Danger mean in the Risk Category level?

 

[petersonra]

We have 0.48 KV (Main -Tie-Main) switchgear (PCC-21-01)fed from 13.8 KV/0.48 KV transformer. It is a 4000A switchgear.

I am confused while understanding the Arc flash study report. Please help me in understanding the format and which label goes to where. Please see the attached.

How come CB in the switchgear has more Incident energy than the Switchgear? What does Danger mean in the Risk Category level?

Danger means there is no level of PPE available that would allow one to work on the equipment while it is energized.

I think they are saying the IE on the line side of the CB is higher than on the load side. That makes sense as the CB could well trip fast enough to reduce the IE downstream.

 

[adityalagudu]

That makes sense. Why the IC-1 CB itself has the more Incident Energy than the Switchgear itself?

 

[mayanees]

Danger means there is no level of PPE available that would allow one to work on the equipment while it is energized.

That is a common misunderstanding in the arc flash world; the RED DANGER tags that say NO SAFE PPE EXISTS when the incident energy level exceeds 40 calories.

I've seen 125 calorie PPE suits advertised, and I'd expect you can find even higher.

It came about because the software manufacturers provided label templates, and still do, that print out RED DANGER when 40 calories is exceeded. That's in violation of the ANSI label standard Z535 that defines DANGER as being an imminent hazard, and arc flash is not that. I'm sure they chose 40 calories because that's where the 70E table stops for PPE 4. And also because there used to be an Informative Note that referenced using additional precautions above 40 calories, but that's been removed.

We got into trouble with the DANGER tags when the USACE folks refused to open disconnects because of the label. Now they have 65 calorie suits and can get into everything if necessary. We now only issue ORANGE WARNING arc flash labels. Of course a client can choose to keep the 40-calorie cutoff and prohibit access as part of their electrical safety program.

John M

 

[adityalagudu]

As of now, we have 40 Cal suit with us. So unless until if we don't have 130 Cal suit, it is not safe to work on I/C-1,2 CB while the bus energized. Is this correct?

So even one of the Transformer is shut down and tiebreaker closed, still we can't work on the I/C as the tie is energized.

So the safe way is, to kill all the loads in any of the Bus so that work can be performed at the I/C CB. This is always not feasible, killing the loads.

So what is the right solution? Getting the 130 CAL suit?? And our study report says above 50 CAL is Danger.

 

[mayanees]

As of now, we have 40 Cal suit with us. So unless until if we don't have 130 Cal suit, it is not safe to work on I/C-1,2 CB while the bus energized. Is this correct?

So even one of the Transformer is shut down and tiebreaker closed, still we can't work on the I/C as the tie is energized.

So the safe way is, to kill all the loads in any of the Bus so that work can be performed at the I/C CB. This is always not feasible, killing the loads.

So what is the right solution? Getting the 130 CAL suit?? And our study report says above 50 CAL is Danger.

You will probably never be able to justify with an EEWP doing "hot" work on that 130 calorie bus, but you may still need to verify the absence of voltage if you can't do in in some alternate fashion. But yes, in order to access that bus at the 18-24" working distance, you need a 130 calorie suit.
You could also use your 40 calorie suit and increase the working distance by some means (hot stick maybe) to perform the voltage check. Stay at a working distance that reduces the exposure to 40 calories, which is likely around 4-5 feet.