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Why does my main breaker box have a shared ground/neutral?

K

KR Williams

Jan 1, 1970
0
I'm thinking of install a 220v 30amp outlet for a welder (small) but my
main service box has the grounds and neutral hooked to the same block.
Take a look

http://members.cox.net/michaelshaffer/p2.jpg

Because the current is supposed to flow in the neutral, and the
ground is there as a *safety*. I.E. *ALWAYS* at ground, no
matter how the current flows. Think of an open neutral somewhere
in your house. If the ground, which is hooked to appliance
cases, were the same as the neutral, these case would suddenly be
at 120V. ...not good.

Ground is your friend (usually). Neutral is there as a return
for electrons. They're tied together at your entrance panel to
keep the peace. ;-)
 
B

Brian

Jan 1, 1970
0
A neutral is only a return in direct current applications.


I'm thinking of install a 220v 30amp outlet for a welder (small) but my
main service box has the grounds and neutral hooked to the same block.
Take a look

http://members.cox.net/michaelshaffer/p2.jpg

Because the current is supposed to flow in the neutral, and the
ground is there as a *safety*. I.E. *ALWAYS* at ground, no
matter how the current flows. Think of an open neutral somewhere
in your house. If the ground, which is hooked to appliance
cases, were the same as the neutral, these case would suddenly be
at 120V. ...not good.

Ground is your friend (usually). Neutral is there as a return
for electrons. They're tied together at your entrance panel to
keep the peace. ;-)
 
G

Gerald Newton

Jan 1, 1970
0
Michael Shaffer said:
I'm thinking of install a 220v 30amp outlet for a welder (small) but my
main service box has the grounds and neutral hooked to the same block.
Take a look

http://members.cox.net/michaelshaffer/p2.jpg

Your picture shows main lugs only. Where is the main service disconnect
and overcurrent protection?
The grounding conductor, grounded conductor, and grounding electrode
conductor are suppose to be bonded at the service disconnect. Your panel
does not look like a service to me.
I have an article on this at:
http://www.electrician.com/electa1/ground100.html
 
D

daestrom

Jan 1, 1970
0
Phil Munro said:
Changing breakers is not difficult. Almost always this would be done
without killing the main feed to the breaker so that other circuits are
not interrupted. Basically, be VERY careful with a screw driver in the
box even if you do kill all the breakers! Hundreds of amps in a screw
driver makes a LOT of HOT sparks, or worse!

Use a screwdriver whose shaft is insulated for this purpose. In a pinch,
spiral wrap the shaft with electrical tape, with 1/2 overlap so each point
has two layers of tape. Just leave the last 1/4 to 1/2 inch of the tip
exposed.

Some boxes, with a lot of stray bare conductors not neatly tucked in can be
very scary places. Especially when you try to push them aside to reach a
breaker :)

daestrom
 
M

Michael Shaffer

Jan 1, 1970
0
That's all there is except for the meter.

Gerald said:
Your picture shows main lugs only. Where is the main service disconnect
and overcurrent protection?
The grounding conductor, grounded conductor, and grounding electrode
conductor are suppose to be bonded at the service disconnect. Your panel
does not look like a service to me.
I have an article on this at:
http://www.electrician.com/electa1/ground100.html
 
G

Gerald Newton

Jan 1, 1970
0
Michael Shaffer said:
It is very unusual to have ready access to the mains when they are only
protected by the primary fuse at the service transformer. That seems to be
you situation.
Before working on this panel hot I would carefully perform a hazard analysis
to determine the risks that you may be taking. The fault current could be
extremely high and you could be placing yourself in harms way by working
this panel hot. I am an electrician with over 40 years experience and I shy
away from working on any hot circuits on the supply side of a service
disconnect. These hot circuits are like working with nitroglycerine.
I would contact the utility company and see if they can pull the meter to
de-energize the panel before working on it. I would also ask for a courtesy
inspection by any authority having jurisdiction including the utility
company. Most utility companies seal any disconnect, box, meter, or panel
that allows direct access to the supply side energized circuits.
 
M

Michael Shaffer

Jan 1, 1970
0
Yup, that's how this one is, there's two mains, one on each side. Then
there's about 2 pole breakers above the mains that can't be turned off.
Unfortunately I have to add one there so I'll have to do it hot.
 
M

Michael Shaffer

Jan 1, 1970
0
Doh, I meant to say there's one main on each side (60 amps) and there
are also about 6 slots above those (2 poles).
 
M

Michael Shaffer

Jan 1, 1970
0
Ok, I just looked and I guess I thought there were more. There are 5
breakers, one emtpy slot.
 
B

Blue Crown

Jan 1, 1970
0
Your picture shows main lugs only. Where is the main service disconnect
and overcurrent protection?
The grounding conductor, grounded conductor, and grounding electrode
conductor are suppose to be bonded at the service disconnect. Your panel
does not look like a service to me.
I have an article on this at:
http://www.electrician.com/electa1/ground100.html
Gerald, don't you remember when it was legal to run unfused service
entrance conductors for long distances without a main overcurrent
protection? You still could not have more than 6 main disconnects at
the panelboard. Most of those panelboards were "split-buss" panels,
where one of the mains was used to feed the lighting and receptacles.
Now, of course, you cannot run the service entrance more than about 5
feet or less without a main breaker. Usually just on the opposite wall
back-to-back with the meter box. Make sense? Later... Blue Crown
 
C

Cougercat

Jan 1, 1970
0
The neutral and ground are usually tied together in the CB panel or fuse
panel of a residence. A #4 copper wire should go from the neutral bar to a
8 foot ground stake that has been pounded into the ground someplace.

Your best bet would be to install a 30 amp single trip/dual circuit breaker
(or 2 circuit breakers with a common trip) and feed your welder off of it.

--jj
 
M

Michael Shaffer

Jan 1, 1970
0
That's for the water heater. I guess I could wait until a thunderstorm
brings a tree down in my neighborhood. It happens often this time of
year. It was off for 3 days last winter.. I just really don't want to
work on it hot. I'm not worried about exceeding 100amps, even though the
oven is 40, air conditioner 60, main lighting 60x2, dryer 30, water
heater 40, etc. We rarely run all of these at the same time. I'm
probably only rarely going to use the 50 amp for the welder/air compressor.
 
M

Michael Shaffer

Jan 1, 1970
0
Bah, I just looked at it more closely, and it's going to take a long
time to hook everything up. I might have to move some other breakers. I
guess I'll have to have the meter pulled.
 
B

Bob Weiss

Jan 1, 1970
0
| The neutral and ground are usually tied together in the CB panel or fuse
| panel of a residence. A #4 copper wire should go from the neutral bar to a
| 8 foot ground stake that has been pounded into the ground someplace.

Two ground stakes are now required.

Unless you can prove 25 ohms or less ground resistance with only one
rod. As a practical matter, you end up driving the second rod...:)

Bob Weiss N2IXK
 
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