Changing breaker live

[Rockyd]

How about landing wires on the load side of a disco with the line hot?

Why challenge fate? On top of that, you bring the whole industry standard down. You do it for some guy in the office, he thinks it's standard practice;completely unaware of the risk YOU decided to take.

It only takes one really good slip to be into an ICU unit. How much pain, anguish, and money is that worth, or saved?

 

[daleuger]

Why challenge fate? On top of that, you bring the whole industry standard down. You do it for some guy in the office, he thinks it's standard practice;completely unaware of the risk YOU decided to take.

It only takes one really good slip to be into an ICU unit. How much pain, anguish, and money is that worth, or saved?

Just asked the question. I don't agree with it either but I've seen it done. Of course that statement can go for a lot of things.

 

[cycotcskir]

If we aren't going to work anything hot, then why do we have all that ultra-cool Cat 4 PPE? We need to use it to justify buying it, sheesh!

Actually, I once got layed off for not working something hot. I'm still here to talk about it, though

From Websters:

Main Entry: im?prac?ti?ca?ble
Pronunciation: \(ˌ)im-ˈprak-ti-kə-bəl\
Function: adjective
Date: 1653
1 : impassable <an impracticable road>
2 : not practicable : incapable of being performed or accomplished by the means employed or at command <an impracticable proposal>

Main Entry: prac?ti?ca?ble
Pronunciation: \ˈprak-ti-kə-bəl\
Function: adjective
Date: 1648
1 : capable of being put into practice or of being done or accomplished : feasible <a practicable plan>
2 : capable of being used : usable <a practicable weapon>

Main Entry: im?prac?ti?cal
Pronunciation: \(ˌ)im-ˈprak-ti-kəl\
Function: adjective
Date: 1865
: not practical: as a: not wise to put into or keep in practice or effect b: incapable of dealing sensibly or prudently with practical matters c: impracticable d: idealistic

Main Entry: prac?ti?cal
Pronunciation: \ˈprak-ti-kəl\
Function: adjective
Etymology: Middle English, from Late Latin practicus, from Greek praktikos, from prassein to pass over, fare, do; akin to Greek peran to pass through — more at fare
Date: 15th century

 

[220/221]

Being a 400A Breaker has nothing at all to do with it,

I think it does.


I will still screw or clip a small breaker on to a live bus. It's a less dangerous installation.

 

[jim dungar]

I think it does.


I will still screw or clip a small breaker on to a live bus. It's a less dangerous installation.

The danger is the same - injury or death.

The hazard is in the arc flash that occurs, which is a function of the available short circuit current not the size of the breaker.

Maybe you meant the risk is less because the tools being used for a small breaker are more easily controlled, and therefore less likely to cause an arc, than the ones used for a large breaker.

 

[zog]

I think it does.


I will still screw or clip a small breaker on to a live bus. It's a less dangerous installation.

No it does not, what makes you think it would? The frame size rating of the breaker has nothing to do with the Ei at that point.

 

[zog]

How about landing wires on the load side of a disco with the line hot?

How about reading the NFPA 70E? It dosent matter, same rules apply.

 

[busman]

No it does not, what makes you think it would? The frame size rating of the breaker has nothing to do with the Ei at that point.

Not directly, but there is much less incident energy available in a 150A residential panel that is fed by a 200 foot feed of 1/0 wire from a 50kVA transformer on a pole versus a 1200A panelboard that might accommodate a 400A breaker fed 50 feet from a pad mounted 400 kVA transformer.

There's a big difference. I've personally experienced the explosion of a residential meter can at 240 volts 200A 100ft from a pad mounted transformer. It was a big boom and dangerous, but there is a difference. I've still got the meter can. I'll try to post a photo later.

 

[iwire]

Not directly, but there is much less incident energy available in a 150A residential panel that is fed by a 200 foot feed of 1/0 wire from a 50kVA transformer on a pole versus a 1200A panelboard that might accommodate a 400A breaker fed 50 feet from a pad mounted 400 kVA transformer.

That is exactly what I was pointing out but I figured the heck with it, zog has no gray area.

 

[busman]

I should add that if you need real world experience to see this in action, think of the small flash you get at the end of a 100 ft run of #14 wire in an outlet box. I'm sure we've all sparked one a few times in our lives.

Mark

 

[daleuger]

I should add that if you need real world experience to see this in action, think of the small flash you get at the end of a 100 ft run of #14 wire in an outlet box. I'm sure we've all sparked one a few times in our lives.

Mark

Not Zog. He cut the main first

 

[mivey]

I'm sure we've all sparked one a few times in our lives.

Who's we? You got a mouse in your pocket?

 

[220/221]

No it does not, what makes you think it would? The frame size rating of the breaker has nothing to do with the Ei at that point.

There is more involved than Ei

Like Jim pointed out, tools for example.

And risk...danger...potayto potaughto

 

[zog]

There is more involved than Ei

Like Jim pointed out, tools for example.

And risk...danger...potayto potaughto

Huh? Ei is a numerical value of the danger, the risk. I dont think you understand what I am talking about.

 

[jim dungar]

And risk...danger...potayto potaughto

'Risk and danger' are closer to 'cause and effect' than they are to each other.

 

[zog]

Not directly, but there is much less incident energy available in a 150A residential panel that is fed by a 200 foot feed of 1/0 wire from a 50kVA transformer on a pole versus a 1200A panelboard that might accommodate a 400A breaker fed 50 feet from a pad mounted 400 kVA transformer.

There's a big difference. I've personally experienced the explosion of a residential meter can at 240 volts 200A 100ft from a pad mounted transformer. It was a big boom and dangerous, but there is a difference. I've still got the meter can. I'll try to post a photo later.

I understand what you are trying to say, and yes the available fault current is higher in your 400kVA transformer than it is in the 50kVA transformer example you presented, but what about clearing times??? Clearing time is the key here, Ei is a directly proportional to the product of Available Isc and clearing times. You can have higher Ei's on systems with lower Isc.

My point is, (and thanks for proving my point about the common misconceptions most people have about arc flash) that with out knowing all the info you cant make any assumptions and say that a 150A breaker will have a lower arc flash hazard than a 400A breaker. That is a dangerous assumption.

I consult engineers at plants daily that are shocked by the results of thier arc flash study, they dont understand how certian things came up with such high values, it is my job to find a solution to reduce the hazard down to workable levels or better yet, to a level where no PPE is required.

 

[zog]

That is exactly what I was pointing out but I figured the heck with it, zog has no gray area.

Bob you are misunderstanding me, in fact I am the one saying there is a grey area here. I am saying you cant make any assumptions about what equipment has low or high arc flash levels based on only one or two pieces of the equation.

 

[zog]

I should add that if you need real world experience to see this in action, think of the small flash you get at the end of a 100 ft run of #14 wire in an outlet box. I'm sure we've all sparked one a few times in our lives.

Mark

Real world experience about arc flash is doing hundreds of arc flash studies, covering thousands of peices of equipment. Real world experience is doing arc flash testing at KEMA labs in a controlled environment with monitors measuring arc duration, fault current, and heat levels produced.

Blowing something up or sparking something is not real world experience.

I saw a fireworks show last 4th of july, saw the pretty explosions with my own eyes, does that experience make me an explosives expert and qualifiy me to give others advice on handling explosives??

 

[chris1971]

Shut down the power. You can do it after hours and charge the customer after hour rates.

 

[ceb58]

I consider myself to be pretty safe, but maybe I'm wrong about this. We have to change a breaker (HKD65K 400A 3-Pole). I was going to shut down the breaker we are changing, and change it. My boss says I'm crazy to change that breaker with the panel live and that we shoud shut down the main feeing the bldg to kill our panel, then change the breaker.

Sounds like the boss is the smart one in the crowd. From his stand point if he allowed you to change it hot, and it did flash on you. Then where would you be? In the hospital or the morgue. Where would he be? Up the creek with out a paddle.