Closing a CB for the first time

wtucker

Senior Member
When our guys close a 480V (or sometimes more) CB or switch for the first time, they always gear up in arc-rated PPE. It got me wondering: How often do they flash the first time they're operated, and why? Our guys say they've heard of it happening, but I don't know anyone with direct knowledge of it. Manufacturer's defects seen unlikely, given the testing these things undergo before they're put under load. A couple of the guys suggested they blow up because tools and debris might have been left in them during installation. Thoughts?
 

ptonsparky

Senior Member
Operator error, someone goofed up on installing load conductors would be my first thought. I have had factory internally miswired items fail.
IMO, they are doing it correctly, for whatever the reason.
 

Sahib

Senior Member
You may need to refer to electrical accidents statistics for a calculation of risk of arc flash involved in operating the breaker for the first time.
 

Strathead

Senior Member
If all covers are in place, there should be no requirement for PPE and no more risk than that of getting struck by lightning on a sunny day. The only caveat would be a true bolted fault on a breaker who's AIC rating was calculated so incorrectly that the hedge factors in everything are overcome.
 

MAC702

Senior Member
Never in my career have I seen a brand new circuit breaker in the box in the closed position. Except that one time... :ashamed:

And this wasn't bought from a big store where people just manhandle things and put them back on the shelf. This was in a pallet of goods shipped overseas to a project I was working on in Colombia. Thank goodness it was only a 3-phase 208V panel, in the electrical room of a 5-story residential complex (90 rooms plus multi-purpose rooms on the bottom).

So it was already near the end of the day (may have been the last breaker) and I took it out of the box and pushed it onto the bus. My three fingers were on the three screws, and it lit me up. My hand was numb for three days. :dunce:
 

tkb

Senior Member
Why? Do you know of anyone who's had one blow up? Or just being cautious?
I had a motor starter blow up when I turned on the power.
The cover blew off and dented the duct about 8’ away.
If I were standing in front of it, I would have taken the hit and flash.
 

Coppersmith

Senior Member
Even for residential panels I always stand off to the side and use the door as a shield when flipping on a breaker. I avoid turning on a breaker with the cover off if I can. I carry level 1 arc flash gear in the truck and put it on when pulling and replacing meters.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
When the load wiring is new (service change, new circuit, etc.), I routinely use my solenoid tester between a line-side hot and each load terminal to make sure that no load conductor is grounded before energizing.
 

Jraef

Moderator
Staff member
The only time I've been exposed to a serious arc flash event was when someone closed a breaker for the first time. I was working on a panel with a 600HP soft starter in it and I finished, so I told the guy in the other room that I was done and I started to close the doors of the panel. Just as the local disconnect handle interlock engaged with the door, he closed the breaker in the switchgear feeding the soft starter. The local disconnect was open, but they had nicked a LINE SIDE conductor in the conduit and it vaporized, blowing a fireball out at me. Because the doors were almost closed and the interlock held, the blast was deflected mostly up and down so it torched my boots and singed my eyebrows and hair where the safety glasses didn't cover. I did NOT, by some miracle, wet myself... Ever since then I always stand to one side rather than directly in front of anything.

In the investigation as to how that nicked conductor was allowed to be there, turned out they meggered everything, then pulled the conductors BACK into the conduit in order to remove and re-install the back panel for the soft starter. But they failed to re-megger the conductors again, ASSuming they were OK after being pulled back into the conduits.
 

zog

Senior Member
If all covers are in place, there should be no requirement for PPE and no more risk than that of getting struck by lightning on a sunny day. The only caveat would be a true bolted fault on a breaker who's AIC rating was calculated so incorrectly that the hedge factors in everything are overcome.
That is a false statement unless the enclosure is arc rated
 

kwired

Electron manager
I suppose there may be some increased chances of a fault from miswiring or bad equipment that "first time", though there is still risk anytime you turn it on. Even after there has been some kind of repairs done that risk may be a little higher the first time afterward. Testing for faults before turning on "the first time" should lower the chances, if you find and fix any faults indicated in the testing.

Even on low incident energy applications (maybe typical dwelling or small commercial project) how often do you find something is faulted the first time you energize a circuit? Maybe not all that many times for most of us, but sometimes the fault isn't something we did but rather a defect in something and we never noticed until energizing it.
 

romex jockey

Senior Member
Seems the tenured sparks aways have their anecdotals.

Myself i was blind for what was the worst 5 minutes of my life....:eek:..so far...

None of this is necessarily our own neglect , miswiring, whatever....

You guys all know the 'ol bold electrician addage .....:happyyes:

~RJ~
 

Fulthrotl

~~Please excuse the mess. Sig under construction~~
Can you quote a source that requires PPE when all covers are in place?
yeah. me.

i closed a main breaker on a residential panel, with all the
covers properly in place. the arc came crawling out between
the cutout hole, and the edge of the breakers, burnt the skin
off the back of the middle two fingers on my right hand..

you need to wear PPE. you can quote me if you need to.
 

kwired

Electron manager
yeah. me.

i closed a main breaker on a residential panel, with all the
covers properly in place. the arc came crawling out between
the cutout hole, and the edge of the breakers, burnt the skin
off the back of the middle two fingers on my right hand..

you need to wear PPE. you can quote me if you need to.
Yet we are required by code make these things readily accessible, which is also readily accessible to the unqualified, makes a lot of sense right?

But OSHA is only for the employed, so what if others are in any danger I guess. Now comes the manager at an office building or other employee in similar situation that doesn't ordinarily do any electrical work tasks that tries to reset a tripped breaker in their office building - I guess we should at least be putting big warning signs on this equipment that only qualified individuals can even open the dead front cover and operate any devices inside, though I anticipate even that will get ignored most the time.

Typical dwelling, the available incident energy isn't that high all that often to be able to do that, but sometimes it is.
 

Jraef

Moderator
Staff member
If all covers are in place, there should be no requirement for PPE and no more risk than that of getting struck by lightning on a sunny day. The only caveat would be a true bolted fault on a breaker who's AIC rating was calculated so incorrectly that the hedge factors in everything are overcome.
Can you quote a source that requires PPE when all covers are in place?
In Table 130.7(C)15(A)(a) where they provide the list of appropriate PPE for tasks, it says the following under the task of operating a circuit breaker:
Under the column heading "Equipment Condition", no additional PPE is required only if;
All of the following:

The equipment is properly installed
The equipment is properly maintained
All equipment doors are closed and secured
All equipment covers are in place and secured
There is no evidence of impending failure
But, under the following conditions, yes, PPE IS REQUIRED if:
One or more of the following:

The equipment is not properly installed
The equipment is not properly maintained
Equipment doors are open or not secured
Equipment covers are off or not secured
There is evidence of impending failure

Should there be an injury and a door WAS closed, an OSHA inspector is going to demand DETAILED RECORDS of whether the equipment was properly installed and maintained. The reality is, almost NOBODY has records like that.


And BEFORE that, they provide this "Informational Note"
Informational Note No. 2: The collective experience of
the NFPA 70E Technical Committee is that, in most cases,
closed doors do not provide enough protection to eliminate
the need for PPE in situations in which the state of the
equipment is known to readily change (e.g., doors open or
closed, rack in or rack out).
 

jaggedben

Senior Member
One guy I worked with told a friend of his died after he left a wrench against the busbars in a residential panel and turned on the breaker. This was in the context of replacing a 200A main breaker on a resi panel and the guy stood to the side and used a broom stick to turn on the replacement. Just in case.

It's not the breaker that will blow up, most times.
 
Top