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#151178 - 07/28/06 03:20 PM What exactly is that PPE protecting against?
SteveFehr Offline

Registered: 03/19/05
Posts: 1192
Loc: Chesapeake, VA
This is not a question PPE, but about potential failures in LV switchgear. I know we're to wear PPE where shock is a risk- no question there. But it's also standard to wear PPE during events where no live components are exposed, but there exists potential for arc faults or exploding breakers, etc. What exactly happens when a breaker fails that would cause injury to an unprotected person? What does an arc fault in 480V switchboard look like? I've not talked to anyone who's actually seen a breaker explode, but everyone seems to have heard about some accident 2nd-hand or 3rd-hand with little detail, and are afraid to manually throw a high current breaker without protection.

[This message has been edited by SteveFehr (edited 07-28-2006).]

Arc Flash PPE Clothing, LOTO & Insulated Tools
#151179 - 07/28/06 05:45 PM Re: What exactly is that PPE protecting against?
renosteinke Offline
Cat Servant

Registered: 01/22/05
Posts: 5305
Loc: Blue Collar Country
Cooper-Bussman have an extensive research facility near St. Louis, and they have produced a number of videos on this subject. The videos are available through your Bussman rep.

Bussman, under lab conditions, deliberately creates arc flashes and arc blasts.

The "flash" is mainly exposure to light, when an arc occurs. Besides the visible light, large amounts of UV rays are made... think "welding arc," rather than "flash bulb." These rays will cause burns, and damage eyes. Raw potatoes at bed time, anyone?

A "blast" has the appearance of an explosion. There is a shock wave, fully capable of moving you to a new zip code. In addition, metal components become vaporised into a plasma, and are quite capable of doing to you what a HEAT round does to a tank.

The PPE has two primary functions. The first is to shield you from the rays; the other is to not make things worse, by igniting, melting, or otherwise interfering with your second career as a model....

#151180 - 07/29/06 02:49 AM Re: What exactly is that PPE protecting against?
SteveFehr Offline

Registered: 03/19/05
Posts: 1192
Loc: Chesapeake, VA
Ah, I see! I figured as much for the arc- I was envisioning it like an welding arc x 2 orders of magnitude. I found video of both at this link:

#151181 - 07/31/06 12:20 AM Re: What exactly is that PPE protecting against?
Trumpy Offline


Registered: 07/05/02
Posts: 8532
Loc: SI,New Zealand
One thing you have to remember about an Arc Welder, is it uses a relatively low current to fuse 2 pieces of metal together.
My Welder here has a highest output setting of 400A (for the BIG stuff).
Short-circuit current is usually in the order of thousands of amperes, depending upon how close the short-circuit is to the supplying transformer(s).
The closer, the higher the current.
I've witnessed a 400V 200A breaker explode while livening it with a hot-stick.
An internal fault caused the short.
Big huge blue flash and a humungous bang, molten copper everywhere.
All I can say is thank God for tinted safety glasses.
I was at the time wearing a Fire Service helmet with a visor and a Nomex jacket.
Both have to this day, bits of copper imbedded in them.
I'm glad it wasn't my skin.
Let's face it, these days if you're not young, you're old - Red Green grin

#151182 - 08/28/06 12:09 PM Re: What exactly is that PPE protecting against?
ruggedscotty Offline

Registered: 06/09/05
Posts: 17
Loc: Edinburgh Scotland
What is PPE protecting against ?

two things -

first off its protecting you

second its protecting the company from having to recruit another person, and its protecting against any lawsuits that may arise due to injury and such. If you were not wearing the correct PPE then the company can justify doing a blame proportioning exercise....

So it is always worth wearing what PPE you have availiable.

Four occassions I have seen or been in the locale of a major electrical incident and on each occassion if PPE had not been worn then there would have been some major injuries involved. Complacency breeds contempt and that is something that you have to be aware of. It would be all to easy just to go about without any PPE and you would probably get away with it - but that one time and that is all it takes - that one time it would bite ya and that would be it - horrific burns blindness never work again that is if you survived !

Electrical faults in industrial locations can be horrific. Even at your service board being in close proximity to a short there you would know all about it.


#151183 - 08/28/06 04:10 PM Re: What exactly is that PPE protecting against?
BKey Offline

Registered: 12/07/05
Posts: 10
Loc: Kissimmee, Florida
Arc flash/blast

Arc- phase to phase or phase to ground

Heat- 35,000 degrees

Intense light- from arc

Copper turns to vapor, expanding 67,000 times

Schrapnel- breakers, parts of the panel/ switchgear

Molten metal

Pressure waves- 200 lbs per Sq ft

Sound waves- think of Thunder, only closer,
all of this happens faster than you blink.

These are the things PPE is protecting from, FR PPE protects from secondary injuries, will you get injured in an arc blast while wearing PPE? Probally, just not as severe as you would without.

Check out this video, very good training tool
The link for the video is at the bottom of the page

[This message has been edited by BKey (edited 08-28-2006).]
Bryan L. Key
Safety Inspector/Trainer
Terry's Electric Inc.
An Xcelecom Company
600 N. Thacker Ave., Suite A
Kissimmee, Florida 34741

#151184 - 08/29/06 07:50 AM Re: What exactly is that PPE protecting against?
gfretwell Offline


Registered: 07/20/04
Posts: 9026
Loc: Estero,Fl,usa
In my infamous mishap with the 3p tape drive connector fire was shooting out of that metal plug about 3-5 feet for several seconds until I could beat the molten metal out. It was certainly as intense as a $15 "fountain" you buy in a fireworks stand. I would certainly not have been healthy if that was shooting at me. That was just 208v and maybe only a 120v fault although I believe all 3 phases were involved..
Greg Fretwell

#151185 - 08/30/06 03:13 PM Re: What exactly is that PPE protecting against?
Scott35 Offline

Broom Pusher and

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
I have seen a few Arc Faults - none which would qualify as "Large", but were "Large enough for me!"
Also saw the results of a large and bolted fault, and a few failed devices.

The Arc Faults were mostly on 480 VAC equipment, however I had witnessed two separate events on lower voltages - one was at 208 volts, the other was at 120 volts.

First the 480 Volt mishaps:

2 from mis-rated fusible disconnect switches, failing during a fault on the load side.
The equipment fed from the switches had large Induction Motors, driving very heavy dynamic inertia loads.

Someone dropped a steel beam across the load side conduits to these machines, resulting in a 3PH bolted fault.

The fuses in the switches opened first - but the switches were rated for 240 volts, and were very undersized for the conditions! (not only rated for 240V and using fuses rated for 240V, but general purpose types too!)

Currents simply Arc'd over the opened 240V fuses, which must have evolved into L-L-L Arc faulting within the first few minutes.
Soon afterwards, the switch enclosure's front covers were blown open, and finally the branch circuit's OCPD tripped (likely from a solid ground or line to line fault).

We were quite a distance away, but it really made an impact! Loud and scarry!

The other one was in a section of Switchgear, which had failing terminations across the bus kit.
That one turned into an L-L-L Arc Fault first, then branched over with L-G Arc Faults - of which, activated the GFPE Trip on the Main Service Disconnect.

We were sent to service an "intermittant loss of power" problem, and had this take place while we were opening the suspected gear section (another reason to always wear PPE!!!).

As to the lower voltage arc faults, saw one on a 3PH. 208 VAC Heat Pump Branch Circuit, which was run across the roof, and tripped over by nearly every person ever walking by it! (the EMT resembled the symbol for a Resistor!)

Since the EMT was not bonded with an EGC, any L-G fault would leave the conduit hot - and resulted in a "kind of" corner grounded system (not a real one, but in the same way an ungrounded system will somewhat become corner grounded if one line gets faulted to metallic equipment).

We were repairing the HVAC Branch Circuitry - and the roof equipment was also being upgraded by others at the same time.

Some poor guy tripped over an EMT run for its last time.
That thing went nuts! Fittings were being blasted apart everywhere; Arcs were forming between conduit ends - and as they moved further apart, the Arcs turned into large Plasma flames.

Previous EC must have been from Kaos, Inc.

Lastly, saw a Photocell turn into a red flare from an internal Arc Fault. This was a 120 VAC circuit.
That was really bizzare!

As to component failure, I have seen a few Breakers which ended up having the contacts fried closed.

Saw one frame which may have been damaged from an explosive fault condition.

Saw a size 2 Motor Starter explode from a combination of mistaken circuitry and a bolted L-L-L fault condition.
Luckilly, I was a distance away when the guy whom wired it went for a smoke test.
Will never forget that one!

The worst accident ever (so far), was due to some clown(s) attempting to steal the Main Service Disconnect (Circuit Breaker) from our switchgear's service sections.
They got away with the first one, but when they returned a few days later to get another one, the PoCo enegized the Transformers (which were not energized during the prior theft).

This particular gear section was no more than 50 linear conductor feet from the Transformer.
Transformer was a 500 KVA, 5.0% Z pad mount, and the Gear was fed with Paralleled 750 MCM al. It was a 1200 amp section & breaker, so there must have been 3 sets of 750's feeding to the UGPS's lug landings.

The thief created a bolted L-L fault, which even though it's only 87% of the available L-L-L value, still had one hell of a punch!

There was splattered aluminum all over the place - similar to a textured wall!
Huge blast / flame marks scorching the enclosures and the "proposed ill-gotten booty" 1200 Amp breaker - rendering it useless.
Bus bars feeding the breaker were completely destroyed.
Oh, and the bandit(s) left their tools when they fled.


edited to fix spelling blunders!

[This message has been edited by Scott35 (edited 08-30-2006).]
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#151186 - 09/20/06 10:12 AM Re: What exactly is that PPE protecting against?
Trumpy Offline


Registered: 07/05/02
Posts: 8532
Loc: SI,New Zealand
Thanks for your post Scott,
In my time as a Line Mechanic/Faultsman, I saw a few things that were rather worrying as far as Arc Faults go:
  • One night out on a patrol to find a fault on a 3-phase 11kV distribution line, some nut-job had a chain draped over the lines waiting for me to reset the fuses.
    I'd already been past where the chain was placed, there was no chain there when I passed the first time.
    I reset the fuses and got the first in and hit the second, there was a huge bang and a lot of light.
  • We had a bad batch of Air-Break Switches, the likes of which are below:

    These ABS's if broken or closed under load would blast out molten silver and copper.
    They were supposed to be rated for full contact voltage and current.
    A bad batch so I am told, but it goes without saying, when I last reset one of these things, it rained fire!.
  • I was always taught (as we all were) about the effects of Fault currents, especially the Electro-Mechanical effects of it.
    I had a 22kV transformer torn off of a pole once, when the transformer internally shorted.
    The mounts were good, it sheared all the bolts off.

That's my 2c
Let's face it, these days if you're not young, you're old - Red Green grin

#151187 - 10/07/06 09:01 PM Re: What exactly is that PPE protecting against?
tajoch Offline

Registered: 02/09/01
Posts: 53
Loc: Quinlan texas, usa
The closest I ever been to an arc flash, was when we did a PM on a switchboard, and someone left a 12" adjustable wrench laying across the bus's, we turned power back on, and power went right back out.
when we re-openned the switchboard we found the former chrome wrench, it was still chrome, but now a really nice shade of blue..
Oh and it was no longer adjustable.........


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