Over 40 cal/cm^2 equipment entry

The Dude

Member
Location
Santa Clarita, CA
Occupation
Electrician
How does one open a panel that is over 40 cals? I have read that the appropriate PPE has to be worn to test for absence of voltage. We have a panel that is rated at 169 cal/cm^2 (from a recent arc flash study) that we need to get into. Since there is no PPE for that amount of incident energy (and the company put a 40 cal limit anyway), How do we get into it to replace a breaker? Any clarification is appreciated.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Basically, you shut it down and test for absence of voltage upstream, then consider installing closed-cover voltage checking hardware.
Are you sure there is only one source of energy to the panel?
 

The Dude

Member
Location
Santa Clarita, CA
Occupation
Electrician
Basically, you shut it down and test for absence of voltage upstream, then consider installing closed-cover voltage checking hardware.
Are you sure there is only one source of energy to the panel?
Yes, it is by a transformer that is fed by 12kv. The 12kv switch is over 40 cals as well.
 

xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
Occupation
Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
How does one open a panel that is over 40 cals? I have read that the appropriate PPE has to be worn to test for absence of voltage. We have a panel that is rated at 169 cal/cm^2 (from a recent arc flash study) that we need to get into. Since there is no PPE for that amount of incident energy (and the company put a 40 cal limit anyway), How do we get into it to replace a breaker? Any clarification is appreciated.

You never work it hot, but you treat it as such until you establish an ESWC.

They do make arc flash gear rated over 40-cal/cm^2.

The system might benefit from arc energy reduction (NEC sections 240.67 or 240.87) or other arc-flash hazard mitigation solutions.

The arc flash study could also be over conservative if default/generic bus gap, enclosure dimensions, electrode configuration, and working distance were used in the calculation. Field verification of study inputs is always recommended.

Note 40 cal/cm^2 is an arbitrary limit. There really is no basis for this cut-off as you can get seriously injured even far below this incident energy exposure.
 

Besoeker3

Senior Member
Location
UK
Occupation
Electrical Engineer
How does one open a panel that is over 40 cals? I have read that the appropriate PPE has to be worn to test for absence of voltage. We have a panel that is rated at 169 cal/cm^2 (from a recent arc flash study) that we need to get into. Since there is no PPE for that amount of incident energy (and the company put a 40 cal limit anyway), How do we get into it to replace a breaker? Any clarification is appreciated.
Interesting measure of units.
 

The Dude

Member
Location
Santa Clarita, CA
Occupation
Electrician
You never work it hot, but you treat it as such until you establish an ESWC.

They do make arc flash gear rated over 40-cal/cm^2.

The system might benefit from arc energy reduction (NEC sections 240.67 or 240.87) or other arc-flash hazard mitigation solutions.

The arc flash study could also be over conservative if default/generic bus gap, enclosure dimensions, electrode configuration, and working distance were used in the calculation. Field verification of study inputs is always recommended.

Note 40 cal/cm^2 is an arbitrary limit. There really is no basis for this cut-off as you can get seriously injured even far below this incident energy exposure.
We don't work panels hot, but we still need a way to enter the section to install a closed cover test station and upgrade the main breaker.

We are limited by our EHS to 40 cal suits. They are going by the NFPA and OSHA recommendations.

We have recommendations from Schneider that were made during the arc flash study, but we still need to enter the panel at least once before the new equipment can be installed and the hazard can be mitigated.

The study has been field verified.

This is a sticky gray area that we're trying to work out. Thanks for the input.
Interesting measure of units.
Interesting measure of units.
This is from the arc flash study. Is there a different measure for incident energy?
 

Besoeker3

Senior Member
Location
UK
Occupation
Electrical Engineer
I'm familiar. I don't see any other way to state incident energy. I overstated it. 168 cal/cm2 not 169.
Yes. The cal/cm^2. Not a problem with that. But the units are interesting.
Most USA units are in feet, pounds, yards etc.........
But the units are interesting. You and other engineers are using cgs units. The centigram, gram, seconds. which is different.
The British and the rest of the world use SI.
:)
 

xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
Occupation
Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
That works for opening the switch but not entering the panel to test for absence of voltage.
If this is radially fed, confirmation of visual separation of the blades at the MV switch is reason enough to open the MV switch cover/door to use a tic-tracer at the end of a hot-stick. Live-Dead-Live check the load side of the MV disconnect, transformer, load-side of the LV breaker. Done.

If it's a double-ended substation, repeat the above on the other side.

We don't work panels hot, but we still need a way to enter the section to install a closed cover test station and upgrade the main breaker.
The above is sufficient.

They are going by the NFPA and OSHA recommendations.
What recommendations are those?

The study has been field verified.
They used actual bus gap, enclosure dimensions, electrode configuration, and working distance? That's pretty rare.
 
Last edited:

The Dude

Member
Location
Santa Clarita, CA
Occupation
Electrician
Yes. The cal/cm^2. Not a problem with that. But the units are interesting.
Most USA units are in feet, pounds, yards etc.........
But the units are interesting. You and other engineers are using cgs units. The centigram, gram, seconds. which is different.
The British and the rest of the world use SI.
:)
I'm just glad we use those units. We should have gone metric 40 years ago.
 

The Dude

Member
Location
Santa Clarita, CA
Occupation
Electrician
If this is radially fed, confirmation of visual separation of the blades at the MV switch is reason enough to open the MV switch cover/door to use a tic-tracer at the end of a hot-stick. Live-Dead-Live check the load side of the MV disconnect, transformer, load-side of the LV breaker. Done.

If it's a double-ended substation, repeat the above on the other side.


The above is sufficient.


What recommendations are those?


They used actual bus gap, enclosure dimensions, electrode configuration, and working distance? That's pretty rare.
Good advise. I was just trying to find a way of opening the individual panel without having to shut down the whole building. We may have to anyway. It is a radial feed.

EHS went by the CALOSHA and NFPA recommendation that work on anything over 40 calories of incident energy is too risky. It may also be an insurance consideration as well.
 

xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
Occupation
Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
EHS went by the CALOSHA and NFPA recommendation that work on anything over 40 calories of incident energy is too risky. It may also be an insurance consideration as well.
NFPA 70E suggests working on just about anything live is too risky. Table 130.5(G) suggests the cut-off is >12-cal/cm^2. The 40-cal/cm^2 thing is an outdated and unsubstantiated limit that is no longer valid.
 
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