 |
Search Sci.Electronics.Basics |
|
|
|
|
|
|
 |
|
|
Sci.Electronics.Basics -> Changing Breaker Box - Looking for Different Perspective
There are 13 messages in this thread.
You are currently looking at messages 1 to 13.
|
Author: emilio_estevezDate: 14:21 05-05-08
|
|
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.
Thanks.
|
|
|
|
Author: Tim WescottDate: 15:06 05-05-08
|
|
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.
_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
|
|
|
|
Author: bud--Date: 15:54 06-05-08
|
|
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--
|
|
|
|
Author: DaveDate: 15:04 08-05-08
|
|
"emilio_estevez" <poguen@gmail.com> wrote in message
news:34803565-2327-4a43-9b90-d7d7369139a1@e53g2000hsa.googlegroups.com...
> 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.
|
|
|
|
Author: Paul E. SchoenDate: 03:52 09-05-08
|
|
"Dave" <dspear99ca@yahoo.com> wrote in message
news:u9IUj.1150$Yp.150@edtnps92...
>
> "emilio_estevez" <poguen@gmail.com> wrote in message
> news:34803565-2327-4a43-9b90-d7d7369139a1@e53g2000hsa.googlegroups.com...
>> 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
|
|
|
|
Author: Michael A. TerrellDate: 14:24 09-05-08
|
|
Dave wrote:
>
> "emilio_estevez" <poguen@gmail.com> wrote in message
> news:34803565-2327-4a43-9b90-d7d7369139a1@e53g2000hsa.googlegroups.com...
> > 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.
I had to do one live in the '70s. The utility company said they
wouldn't reinstall the meter for at least three working days after they
were notified that the work was done, unless I used their 'authorized
electrician' who wanted about $1200 to install the new box I had. That
would have been at least 24 hours.
I pulled the main fuse cartridge, and removed the tops of the old
fashioned clamshell clamps, then wrapped each wire in electrical tape,
followed by friction tape. I didn't want to do it hot, but it was the
middle of August, and the fuse box was _very_ overloaded. We would have
lost a freezer and refrigerator full of food if I let the
'authorized electrician' do the work. There was no way I was going to
pay $1200, and lose over $300 worth of food for an hour's work.
I had someone right there with an insulated rod, in case something
went wrong. I removed the neutral and ground connections first, and
connected them last in the new box. That way if I slipped and either
side of the line touched the box, it wouldn't arc. I agree that it
shouldn't be done, but then I have worked on the HV power supplies on TV
transmitters, reconnected pole mounted CATV power supplies to the
secondaries (240 VAC lines run between power poles) after a repair, and
other dangerous things because it was part of my job.
All it takes is one careless move, and you die.
--
http://improve-usenet.org/index.html
Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM
If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm
|
|
|
|
Author: DaveDate: 15:09 09-05-08
|
|
"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:TIednQoOGrhwC7nVnZ2dnUVZ_tninZ2d@earthlink.com...
>
There was no way I was going to
> pay $1200, and lose over $300 worth of food for an hour's work.
>
Would your wife and kids agree that $1,500 is WAY more than your life is
worth? Or not...
Life is full of unavoidable risks, why tempt fate when the odds are against
you? I doubt the OP was even cognizant of the risk factor prior to his
post, he is the WRONG person to attempt this... it would be beyond
"dangerous", it would be reckless and stupid.
>
> All it takes is one careless move, and you die.
>
Edzackery.
> --
> http://improve-usenet.org/index.html
>
>
> Use any search engine other than Google till they stop polluting USENET
> with porn and junk commercial SPAM
>
> If you have broadband, your ISP may have a NNTP news server included in
> your account: http://www.usenettools.net/ISP.htm
|
|
|
|
Author: Michael A. TerrellDate: 16:37 09-05-08
|
|
Dave wrote:
>
> "Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
> news:TIednQoOGrhwC7nVnZ2dnUVZ_tninZ2d@earthlink.com...
> >
> There was no way I was going to
> > pay $1200, and lose over $300 worth of food for an hour's work.
> >
>
> Would your wife and kids agree that $1,500 is WAY more than your life is
> worth? Or not...
I wasn't married, and I didn't have the $1500. I also did industrial
electrical work.
> Life is full of unavoidable risks, why tempt fate when the odds are against
> you? I doubt the OP was even cognizant of the risk factor prior to his
> post, he is the WRONG person to attempt this... it would be beyond
> "dangerous", it would be reckless and stupid.
>
> >
> > All it takes is one careless move, and you die.
> >
>
> Edzackery.
I also replaced the service entrance cable on a friend's house. The
insulation was so bad that you could see the two line conductors inside
the spiraled neutral. A fiberglass ladder, a hacksaw, and I worked on
one conductor at a time. After hacksawing them off from the drop, they
were taped up. Then the old cable & meter socket were removed. The cable
to the breaker box was replaced, the new meter box was mounted, then the
new service cable was spliced to the drop with new split bolts and
No-ox, then properly insulated. The city inspected it an hour later,
passed it, and resealed the meter.
--
http://improve-usenet.org/index.html
Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM
If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm
|
|
|
|
Author: emilio_estevezDate: 12:38 12-05-08
|
|
Well, I've already gotten a hold of the Electic Company to come out
and pull the meter. And there have been several things brought up
that could go wrong that I didn't think of. But... the answer to my
main question hasn't been answered. I have decided that it is not
worth doing it live because of several of the possible accidents
mentioned above. I realize that, because there is basically no
circuit protection, an accidental short could create thousands of amps
resulting in an enormous arc flash.
But, what I still don't understand is when Dave said that, "The power
that'll slam into you through 0 or 2 ga wire is HUGE". I know that
size of wire is capable of delivering extremely high currents -- but
that's what it's capable of doing. Not what it would actually do. If
someone gets shocked by the 120V at an outlet or switch in their home,
that wire is capable of delivering 20 amps before the breaker trips.
But if you get shocked by it, the breaker doesn't trip because the
resistance of your body keeps the current low. If you're body doesn't
even trip out a 15A breaker, I don't see how the fact that because you
use bigger wire, the current that flows with 120V potential, through
your body (high resistance), to ground is any different.
Sure there's plenty of reasons not to change a breaker box hot, but i
still don't see how any of them have to do with the fact that getting
shocked by the incoming feed is any deadlier than the 120V anywhere
else. I really believe that it's just a misconception, and that the
only true danger is the possibility of an arc flash because of an
accidental short.
|
|
|
|
Author: Michael A. TerrellDate: 15:48 12-05-08
|
|
emilio_estevez wrote:
>
> Well, I've already gotten a hold of the Electic Company to come out
> and pull the meter. And there have been several things brought up
> that could go wrong that I didn't think of. But... the answer to my
> main question hasn't been answered. I have decided that it is not
> worth doing it live because of several of the possible accidents
> mentioned above. I realize that, because there is basically no
> circuit protection, an accidental short could create thousands of amps
> resulting in an enormous arc flash.
>
> But, what I still don't understand is when Dave said that, "The power
> that'll slam into you through 0 or 2 ga wire is HUGE". I know that
> size of wire is capable of delivering extremely high currents -- but
> that's what it's capable of doing. Not what it would actually do. If
> someone gets shocked by the 120V at an outlet or switch in their home,
> that wire is capable of delivering 20 amps before the breaker trips.
> But if you get shocked by it, the breaker doesn't trip because the
> resistance of your body keeps the current low. If you're body doesn't
> even trip out a 15A breaker, I don't see how the fact that because you
> use bigger wire, the current that flows with 120V potential, through
> your body (high resistance), to ground is any different.
>
> Sure there's plenty of reasons not to change a breaker box hot, but i
> still don't see how any of them have to do with the fact that getting
> shocked by the incoming feed is any deadlier than the 120V anywhere
> else. I really believe that it's just a misconception, and that the
> only true danger is the possibility of an arc flash because of an
> accidental short.
He means there is less resistance to limit the current, so any
accident can be _much_ worse. A single strand of fine wire can vaporize
and create plasma that will continue to arc, because you have a much
higher fault current available.
--
http://improve-usenet.org/index.html
Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM
If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm
|
|
|
|
Author: bud--Date: 12:20 14-05-08
|
|
emilio_estevez wrote:
>
> Sure there's plenty of reasons not to change a breaker box hot, but i
> still don't see how any of them have to do with the fact that getting
> shocked by the incoming feed is any deadlier than the 120V anywhere
> else. I really believe that it's just a misconception, and that the
> only true danger is the possibility of an arc flash because of an
> accidental short.
An additional hazard is in most panels there is a lot of exposed metal
that is hot. It is real easy to make accidental contact. And easy to
make contact with larger skin area which means lower resistance. You can
also get across 240V.
--
bud--
|
|
|
|
Author: Rich GriseDate: 17:42 14-05-08
|
|
On Mon, 12 May 2008 09:38:23 -0700, emilio_estevez wrote:
...
> Sure there's plenty of reasons not to change a breaker box hot, but i
> still don't see how any of them have to do with the fact that getting
> shocked by the incoming feed is any deadlier than the 120V anywhere
> else. I really believe that it's just a misconception, and that the
> only true danger is the possibility of an arc flash because of an
> accidental short.
It's not about getting electrocuted - it's about the explosion of
copper vapor that happens when you feel the tickle, react, and
short one of the hots to ground. =:-O
Be Safe! :-)
Rich
|
|
|
|
Author: sparkyDate: 21:55 15-05-08
|
|
On May 14, 5:42=A0pm, Rich Grise <r...@example.net> wrote:
> On Mon, 12 May 2008 09:38:23 -0700, emilio_estevez wrote:
>
> ...
>
> > Sure there's plenty of reasons not to change a breaker box hot, but i
> > still don't see how any of them have to do with the fact that getting
> > shocked by the incoming feed is any deadlier than the 120V anywhere
> > else. =A0I really believe that it's just a misconception, and that the
> > only true danger is the possibility of an arc flash because of an
> > accidental short.
>
> It's not about getting electrocuted - it's about the explosion of
> copper vapor that happens when you feel the tickle, react, and
> short one of the hots to ground. =3D:-O
>
> Be Safe! :-)
> Rich
About 30 years ago I was employed by a mining company for maintaining
electric hoisting motors. One of the motors was an 8000 Hp DC motor
operating from an SCR bank at 1000 VDC. The armature breaker was
installed in a room about 10 feet square. The door was interlocked so
the motor could not be energised if the door was open. One day the
breaker
failed. The entire room looked like it had been painted with
copper. The
breaker contacts had vaporized and the copper condensed on the walls
of the room.
Thank God for interlocks!
|
|
|
|
1 |
|
|
|
|
Contact | Electronic Portal
|
|
|
