PPE for 480V and 4160V and above?

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
As someone that works for a utility I have to ask why?
why are these racked out hot? Why can’t you have the utility de energize the facility?

I have one plant that is scheduled like clockwork. We kill the entire facility’s higher voltages for 3 or 4 days every Fourth of July for them to do maintenance on their breakers and MDPs.
YEARS ago they put in some 120/240 single phase lighting circuits and outlets just for this maintenance purpose.
 

powerpete69

Senior Member
Location
Northeast, Ohio
Occupation
XXX
As someone that works for a utility I have to ask why?
why are these racked out hot? Why can’t you have the utility de energize the facility?

I have one plant that is scheduled like clockwork. We kill the entire facility’s higher voltages for 3 or 4 days every Fourth of July for them to do maintenance on their breakers and MDPs.
YEARS ago they put in some 120/240 single phase lighting circuits and outlets just for this maintenance purpose.
This is certainly a great suggestion, but it would only work if we wanted to knock the entire 4160V switchgear fed by the utility transformer.
If we are turning off the main breaker on the 4160V switchgear to look at whole bus and all 10 feeder breakers, then yes, we will have the utility company turn off that transformer.

Incidentally, our 4160V gear has those large, tall "suitcase" looking breakers that roll out completely. These get tripped with the doors closed but the electrician still wears the full suit. The 480V substations have the draw out breakers. These breakers get operated more often to be able to service the MCC"s that they energize.
 

wtucker

Senior Member
Location
Connecticut
It's my understanding that NFPA 70E is not quite this strict, but most of these guys operating these switches have families and just aren't willing to risk it which makes perfect sense to me. Lot of arc flash videos out there with massive explosions.
What about downstream MCC's with non pullout breakers? What are electrical guys wearing when they operate those breakers?
Our guys suit up to operate CB's 480V or more for the first time, out of fear that it's going to blow up (although none of the guys I've spoken with know anyone it's ever happened to). One of 'em even turns his back on the gear and operates with CB with his non-dominant hand.
 

wtucker

Senior Member
Location
Connecticut
A normal condition to most is a breaker in excellent or new condition. However, when they are 50 years old, we don't know what condition they are in. Have they been serviced? Have they been lubricated? Are they full of dust? In there a mouse lying across the terminals? Etc.
Anybody ever seen a 50-year-old CB that's had documented service (or even exercise) every three years? Me neither.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
This is certainly a great suggestion, but it would only work if we wanted to knock the entire 4160V switchgear fed by the utility transformer.
If we are turning off the main breaker on the 4160V switchgear to look at whole bus and all 10 feeder breakers, then yes, we will have the utility company turn off that transformer.

Incidentally, our 4160V gear has those large, tall "suitcase" looking breakers that roll out completely. These get tripped with the doors closed but the electrician still wears the full suit. The 480V substations have the draw out breakers. These breakers get operated more often to be able to service the MCC"s that they energize.
I’ve worked around those old rack out breakers, I understand the nerves. The Westinghouse spring loaded gets me every time. still not used to the sound it makes.

had one the knifes didn't line up correctly when it closed.. there’s about 8 grand gone
 

powerpete69

Senior Member
Location
Northeast, Ohio
Occupation
XXX
Anybody ever seen a 50-year-old CB that's had documented service (or even exercise) every three years?
Yes, we service ours and document them every 3 years. The relays are updated to the AC PROS, etc. They are in excellent condition and some even say they prefer them over the newer units.
 

jeffmackinnon

Member
Location
Nova Scotia
Occupation
Electrical Engineer
Sure you can get suits above 40 cal, but it’s just the difference between an open casket and a closed casket. The concussion blast would most likely kill you at that point.
This is a common mis-understanding. Arc Flash incident energy and Arc Blast intensity don't properly correlate.

Arc Blast is wholly dependent on current and where in the sine wave the arc is initiated.

Arc Flash energy is dependent on current and the time that it exists.

There are a lot of videos where you will see someone fly backwards wearing their PPE, in a lot of these cases it is an automatic motor response, not the concussive force of the arc.

There has been a lot of great papers published on this in recent years at the IAS Electrical Safety Workshop.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
This is a common mis-understanding. Arc Flash incident energy and Arc Blast intensity don't properly correlate.

Arc Blast is wholly dependent on current and where in the sine wave the arc is initiated.

Arc Flash energy is dependent on current and the time that it exists.

There are a lot of videos where you will see someone fly backwards wearing their PPE, in a lot of these cases it is an automatic motor response, not the concussive force of the arc.

There has been a lot of great papers published on this in recent years at the IAS Electrical Safety Workshop.
I know of a lawsuit where the lawyer and one of the posters on here made the argument the concussive force injured an electrician, he had virtually no burns and was not wearing ppe. They won the case, but I believe he actually had a stroke from how it happened, but I digress.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Engineer
There are a lot of videos where you will see someone fly backwards wearing their PPE...
It takes a lot less blast to move a person than it does to kill them.
I have no doubt you could get injured from a blast, I argue with the training that >40cal/cm² rated PPE is nothing more than a body bag.
 

jeffmackinnon

Member
Location
Nova Scotia
Occupation
Electrical Engineer
Anybody ever seen a 50-year-old CB that's had documented service (or even exercise) every three years? Me neither.
I have, but they are few and far between. While they may not have a complete history, the ones that I've seen (I'm thinking of one client in particular) started consistently doing the checks 10 years ago AFTER we handed in our Arc Flash Analysis report with the large assumption that this was completed.

Since then they have tested and conditioned their SWGR breakers on a regular maintenance cycle along with the regular maintenance of the rest of their major equipment.
 

jeffmackinnon

Member
Location
Nova Scotia
Occupation
Electrical Engineer
I argue with the training that >40cal/cm² rated PPE is nothing more than a body bag.
emphasis mine

I don't agree with this, while energized work should always be kept to the extreme minimum, if there is an incident energy level of 80cal, but this is from a 1MVA transformer that has long tripping on the primary AND that can't be changed, the potential blast is minimized by the maximum current that this relatively small transformer can let through.

As for the heat energy transmitted, that long blast will ensure that the entire person is engulfed and that the heat within the suit will raise significantly. If they are in the suit for an extended period the sweat will cause worse burning than a pure radiant burn; but it is still very survivable.

PPE must always be the last line.

If you would like to continue this discussion offline please PM me.

Regards,

JM
 

jeffmackinnon

Member
Location
Nova Scotia
Occupation
Electrical Engineer
I know of a lawsuit where the lawyer and one of the posters on here made the argument the concussive force injured an electrician, he had virtually no burns and was not wearing ppe. They won the case, but I believe he actually had a stroke from how it happened, but I digress.
The concussive force CAN kill. I would have to go back to some ESW papers that I read last year, but there can be enough force in a arc flash event in a system with a lot of capacitive stored energy to collapse lungs and blow out eardrums; but that doesn't mean they will also have a lot of heat energy; which is all the incident energy calculations in IEEE 1584 account for.
 

jeffmackinnon

Member
Location
Nova Scotia
Occupation
Electrical Engineer
In a lot of cases the arc blast is not significant. I recommend reviewing this paper - https://ieeexplore.ieee.org/document/7565738
They went up to 16kA at 480V.

The theory that copper vaporization is a substantial component of the initial arc blast pressure is not supported by these experiments. - From the conclusion.
From what I've read, it takes ~15psi of blast over pressure to cause injury. The maximum pressure measured in this experiment was 12.5psi with copper electrodes in a closed box.
 

mayanees

Senior Member
Location
Westminster, MD
I would also be careful with taking arc flash stickers as gospel law.
……...
Here's an example. If you see a 1 calorie sticker on the secondary of a 4160V to 480V, 2000 KVA transformer, a bell should ring in your head that something might not be right. I would expect that to be more around 40 calories give or take 25% or so.
To your example Pete, I was just at a CON-ED powered facility in Brooklyn, NY standing in front of switchgear that was powered from a network-connected 480V distribution system. I knew that right across the wall from the switchgear sat (5) 2500 kVA transformers paralleled on their secondaries…. the arc flash label indicated an incident energy level of 0.84 calories!!!!!

I was able to see the Power Study that was responsible for the calculation, and discovered the problem. The software was SKM, and the arc flash report indicated that at 200kA available, the IEEE 1584 calculation was not applicable, so the software chose the Lee equations, and reported that it was only applicable in open air and this is not open air. So some action was required.

When I ran it in my SKM model, the software suggested using the Doughty-Neal Paper, which resulted in a calc of 160 calories.

I say it all the time, that anybody can buy a software package, enter the data, and press go. Interpretation of the results is the responsibility of the user.
 

powerpete69

Senior Member
Location
Northeast, Ohio
Occupation
XXX
Here's another example on the secondary of a 1500 KVA 12.47KV to 480/277V transformer.
The arc flash for the line side of the main breaker is as expected at 67 calories at 24".
The load side of the breaker shows up at 3.8 calories at 24" which is all good.
The instantaneous of that main breaker holds that at all settings until it gets above 16,000 amps. Basically going from setting 10 to setting 12.
When you get to setting 12 (19,200 amps) on the instantaneous on the square D "PA" breaker with micrologix 3.0H trip unit, the arc flash jumps to 63.6 calories at 24" !!!!!

The short circuit current must run just left of the instantaneous portion of the graph as it takes 1.89 seconds to trip, hence the massive energy. You can see the trip curve just go to the left around 1.9 seconds.

Any setting less than this and the device trips in roughly .126 seconds.

The point is, be careful out there and take any arc flash sticker with a grain of salt. Just one wrong click by the operator can be the difference between 3.8 calories and 63.6 calories!!!

This also shows that there is always a fight between short circuit protection for keeping your factory online....... vs personnel protection.
 
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