Changing Breaker Box - Looking for Different Perspective
Bookmark this page:
 Yahoo!
 Google
 Windows Live
 del.icio.us
 digg
 Netscape
|
|
|||||||||||||
|
Posted by emilio_estevez on May 5, 2008, 2:21 pm
Please log in for more thread options his Federal Pacific breaker box to a newer, safer one. My background is in industrial controls and I don't normally deal with power at the service level. I only have about two years experience so as I am now trying to learn more on my own, I'm finding a lot of things that don't add up. I started by doing some research to see what it would take to change out a breaker panel in a house without turning off the service power. It seems to me that it would not be any different getting shocked by one of the mains than it would be to get shocked by the 120V at an outlet. Each incoming line is 120V to ground (the same as the power at a receptacle) and my body's resistance to ground would be roughly the same. And according to Ohm's Law, the current that would go through my body would be the same. I don't understand the difference. Now obviously I don't plan on attempting this if the risk is actually as serious as i've read, and I do realize that even very low voltages can kill you if the current is high enough (would normally have to break through the skin and into the blood stream where resistance is very low), but the question still remains. Am I missing something? I've read that if you touch either incoming service line that you will most certainly die. Is that just to scare people that don't know enough about what they're doing into hiring someone? Lastly, I would like to point out that I work on a regular basis around 480V / 240V and am quite frankly, scared of being shocked, and I take every precaution available (which normally entails shutting off the power at its source) before working around any live circuits. I also understand that even 120V can definately be deadly, even at a receptacle. I only used that as an example because I know people will often change them without killing power. I'd like to leave this topic as purely hypothetical. Simply an example to learn from. Thanks. | |||||||||||||
|
Posted by Tim Wescott on May 5, 2008, 3:06 pm
Please log in for more thread options _I_ turn the power off when I'm working around 120V. It won't always kill you when you touch it, but I hate that tight feeling in my chest for the hour or so after the 'event'. Consider that when you're changing that 120V socket you're playing with 120V and ground on wires no bigger than 12 gauge, in a fairly well controlled environment. With the breaker box change, you're wrestling with 4 or 2 or 0 gauge wires, the pair of which have 240V between them, which have to be threaded out of one box, threaded into another, possibly trimmed and certainly bent to new shapes. And what if they're six inches too short and you need to run new ones? Add to that the fact that these wires are fused for 100A or more, so even if you don't electrocute yourself you run the risk of one hell of an arc if you short them together. Me? I'll wimp out and call the power company to have the mains turned off. And when they tell me they won't turn things back on without an inspection I'll think of my homeowner's insurance and say 'yea verily and thank you'. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" gives you just what it says. See details at http://www.wescottdesign.com/actfes/actfes.html | |||||||||||||
|
Posted by bud-- on May 6, 2008, 3:54 pm
Please log in for more thread options emilio_estevez wrote:
> My question came up when a friend of mine asked if I could change out
> his Federal Pacific breaker box to a newer, safer one. My background > is in industrial controls and I don't normally deal with power at the > service level. I only have about two years experience so as I am now > trying to learn more on my own, I'm finding a lot of things that don't > add up. > > I started by doing some research to see what it would take to change > out a breaker panel in a house without turning off the service power. > It seems to me that it would not be any different getting shocked by > one of the mains than it would be to get shocked by the 120V at an > outlet. Each incoming line is 120V to ground (the same as the power > at a receptacle) and my body's resistance to ground would be roughly > the same. And according to Ohm's Law, the current that would go > through my body would be the same. I don't understand the difference. > > Now obviously I don't plan on attempting this if the risk is actually > as serious as i've read, and I do realize that even very low voltages > can kill you if the current is high enough (would normally have to > break through the skin and into the blood stream where resistance is > very low), but the question still remains. Am I missing something? > I've read that if you touch either incoming service line that you will > most certainly die. Is that just to scare people that don't know > enough about what they're doing into hiring someone? > > Lastly, I would like to point out that I work on a regular basis > around 480V / 240V and am quite frankly, scared of being shocked, and > I take every precaution available (which normally entails shutting off > the power at its source) before working around any live circuits. I > also understand that even 120V can definately be deadly, even at a > receptacle. I only used that as an example because I know people will > often change them without killing power. > > I'd like to leave this topic as purely hypothetical. Simply an > example to learn from. The hazard is not just shock. If you short the hot wire to hot, neutral, or ground you will get a current of maybe 2,000A up to 10,000A. That makes things like screwdrivers evaporate. Worse, they evaporate onto your face. Added to the fun is that the transformer protection may allow the fault current for an extended time. You -really- don't want to change the panel with the wires 'hot'. If you work around 480 you should have some familiarity with 'arc flash'. An electrician might pull the meter. If you do, you have to be able to be sure that kills the power. The utility company may take a real dim view of cutting their seal on the meter. You better plan on telling them, in advance. And service panels have some unique features, like N-G bonding and grounding electrodes. Also maybe aluminum wire. Another problem is what you do if the wires are too short for the new panel as Tim wrote. I have read (but do not know) that Cuttler Hammer has replacement 'guts' for FPE panels. -- bud-- | |||||||||||||
|
Posted by Dave on May 8, 2008, 3:04 pm
Please log in for more thread options
> My question came up when a friend of mine asked if I could change out
Dude, don't go there. Have you ever heard of anyone changing out their own
> his Federal Pacific breaker box to a newer, safer one. My background > is in industrial controls and I don't normally deal with power at the > service level. I only have about two years experience so as I am now > trying to learn more on my own, I'm finding a lot of things that don't > add up. > breaker panel, much less doing it live? No? Huh, wonder why that is? The power that'll slam into you through 0 or 2 ga wire is HUGE and UNFUSED... thousands of amps. The transformer on the pole has overload protection, but it won't kick in until WAY after you're dead. What you are considering is RIDICULOUSLY DANGEROUS. Trained professionals don't do it. | |||||||||||||
|
Posted by Paul E. Schoen on May 9, 2008, 3:52 am
Please log in for more thread options
>
>> My question came up when a friend of mine asked if I could change out
>> his Federal Pacific breaker box to a newer, safer one. My background >> is in industrial controls and I don't normally deal with power at the >> service level. I only have about two years experience so as I am now >> trying to learn more on my own, I'm finding a lot of things that don't >> add up. >> > Dude, don't go there. Have you ever heard of anyone changing out their
> own breaker panel, much less doing it live? No? Huh, wonder why that > is? > > The power that'll slam into you through 0 or 2 ga wire is HUGE and > UNFUSED... thousands of amps. The transformer on the pole has overload > protection, but it won't kick in until WAY after you're dead. > > What you are considering is RIDICULOUSLY DANGEROUS. Trained > professionals don't do it. You are right about that. The transformer is only fused at the primary to protect it from overloads and malfunction, and many of these "pole pigs" are 50 kVA or more. This means that a 120 VAC line to neutral or earth current of 500 amperes would just start to make the fuse notice, and the instantaneous current could be as high as 5000 amps (half a MegaWatt) for a few cycles. Certainly enough to create a huge fireball and hurl globs of molten copper and steel at the unfortunate amateur electrician who just happened to let a scredriver slip across the mains. A friend was working with another experienced test technician, doing routine breaker testing in a large facility. Most of the switchgear was disconnected, but the other test technician had to do some work in the main fuse box, which I think was a 480 VAC feeder with heavy bus bar, probably rated at 2000 amps or more. I think he had to tighten a bolt, and normally he would have used a wrench that was mostly insulated with rubber tape, but he was probably tired and in a hurry, and somehow the wrench slipped and landed across the live bus. My friend saw it happen, and turned to the side just as the fireball erupted, and it burned much of his face and body. The technician who was responsible was badly burned, and soon died from his injuries. Here is a website with some images and movies of actual electrical arc blasts so you can see the "potential" for danger: http://205.243.100.155/frames/longarc.htm. Note that one of them is "only" 480 VAC. Actually, I changed out the old breaker box in the house where I now live, but I was completely remodeling it, and I had the utility company come out and pull the meter. I had a separate feeder from my other house next door, so I could provide temporary power. I actually located the new box on the other side of the wall, next to the meter, inside an enclosed porch, and I routed the 100 amp service cable into the new box while it was totally dead. Even so, I treated it with respect, and I taped the exposed conductors while I relocated them, and removed the tape only when I could safely connect them to the main 100 amp breaker. It was several years later that I was able to finish the bulk of the work, and I was able to have BGE come out and replace the meter. I had tested the installation beforehand by patching the other supply onto the mains, and I checked carefully for any loose strands of the incoming service cable. Even so, I was a bit nervous when the meter was reinstalled, but at least I had a main breaker directly on the incoming line. The old breaker box did not have a main breaker. More information and videos: http://www.lanl.gov/safety/electrical/ Paul | |||||||||||||
> his Federal Pacific breaker box to a newer, safer one. My background
> is in industrial controls and I don't normally deal with power at the
> service level. I only have about two years experience so as I am now
> trying to learn more on my own, I'm finding a lot of things that don't
> add up.
>
> I started by doing some research to see what it would take to change
> out a breaker panel in a house without turning off the service power.
> It seems to me that it would not be any different getting shocked by
> one of the mains than it would be to get shocked by the 120V at an
> outlet. Each incoming line is 120V to ground (the same as the power
> at a receptacle) and my body's resistance to ground would be roughly
> the same. And according to Ohm's Law, the current that would go
> through my body would be the same. I don't understand the difference.
>
> Now obviously I don't plan on attempting this if the risk is actually
> as serious as i've read, and I do realize that even very low voltages
> can kill you if the current is high enough (would normally have to
> break through the skin and into the blood stream where resistance is
> very low), but the question still remains. Am I missing something?
> I've read that if you touch either incoming service line that you will
> most certainly die. Is that just to scare people that don't know
> enough about what they're doing into hiring someone?
>
> Lastly, I would like to point out that I work on a regular basis
> around 480V / 240V and am quite frankly, scared of being shocked, and
> I take every precaution available (which normally entails shutting off
> the power at its source) before working around any live circuits. I
> also understand that even 120V can definately be deadly, even at a
> receptacle. I only used that as an example because I know people will
> often change them without killing power.
>
> I'd like to leave this topic as purely hypothetical. Simply an
> example to learn from.