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

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.
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http://members.cox.net/michaelshaffer/p2.jpg
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On Mon, 10 May 2004 03:03:30 -0400, Michael Shaffer put forth the notion that...

It's supposed to. Just make sure you keep them separate at the other end when you run your outlet.
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snipped-for-privacy@cox.net says...

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. ;-)
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A neutral is only a return in direct current applications.
says...

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. ;-)
-- Keith
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| A neutral is only a return in direct current applications.
In Edison 3-wire DC, one line was + and the other line was - so the neutral was technically not always a return. What is really meant is as if each hot line was sending out power, regardless of polarity. And that's the same in DC or AC.
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wrote:
| 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.
The neutral is grounded so it is a reference voltage. The neutral used to be the grounding conductor, too. But it didn't serve that purpose very well when unbalanced currents (or worse, fault currents) were present. By having a separate ground wire that is not supposed to take current back to the source, then it can be held an true ground potential, thus avoiding shock when a human touches equipment chassis properly grounded.
Because both wires do go to ground, they have to join somewhere, and that is defined to be the point where power first enters the building. Beyond that, the neutral and grounding wires are not to be connected, or else the unbalanced or fault currents the neutral might be carrying would also be carried by the grounding wire, defeating the purpose of its existance.
What type of plug does your welder unit have? What is the NEMA code for it? Does it have a 6-30P, 10-30P, or 14-30P (with maybe an L suffix)?
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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
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That's all there is except for the meter.
Gerald Newton wrote:

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It's a Pushmatic box and breakers. I have one of those, too, but with a single run of breakers. Mine has a MAIN breaker which kills everything below it, plus several breakers above the main breaker which are NOT killed by the main breaker. It is hard to tell from his picture just what his box has, but it is probably similar. HE needs to know how to kill power in HIS box! --Phil
Michael Shaffer wrote:

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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.
Phil Munro wrote:

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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).
Michael Shaffer wrote:

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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! Secondly, you can replace a breaker in one of two ways. 1) Put the wire on the breaker before you put the breaker into the slot. Try to have the breaker in the OFF position when inserting it. Or 2) Put the breaker into the box, turn it off, and then put the wire on the screw. I prefer this second method since the screw can be tightened more firmly and easily. Remember that the individual breakers above the main should be rated at a higher than normal max interrupt current (I think it is called something like that) since you do not have a main breaker to give you extra short circuit protection. Also, consider rearranging breaker positions so that the ones above the main are circuits that make sense being there, 20 A circuits like furnace, basement, etc., that would be ones you might want on when killing the main breaker, or perhaps dedicated circuits with fewer items being fed. This is not any professional advice you are getting, so you are on your own with what you do. I am a DIYer with electrical education, but I am not an electrician. --Phil
Michael Shaffer wrote:

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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
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wrote:
| That's all there is except for the meter.
To totally disconnect all power, how many breakers and/or switches do you have to operate into the off position to get it all off? The NEC code allows for no more than 6.
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Ok, I just looked and I guess I thought there were more. There are 5 breakers, one emtpy slot.
snipped-for-privacy@ipal.net wrote:

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http://members.cox.net/michaelshaffer/p2.jpg
Michael Shaffer wrote:

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wrote:

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.
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| wrote: |> >> |> >> | That's all there is except for the meter. |> >> |> >> To totally disconnect all power, how many breakers and/or switches do |> >> you have to operate into the off position to get it all off? The NEC |> >> code allows for no more than 6. |> >> | 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.
IANAE, but if this were me, I'd definitely NOT work on a panel hot, and especially NOT the one I see in that picture. I especially don't like the placement of the neutral and ground bars relative to the main lugs.
This is most definitely a case to have the power company come out and pull the meter for the day, at the very least.
IMHO, you should hold off on adding a circuit and take a look at doing a complete changeout to a new panel with more space and a real main breaker. Or at least add a separate enclosure for a main breaker by itself and run the service through that first.
Do you have children living in the house?
Also, you need to consider the added load this is putting on the service entrance. Since there is no main breaker, you have to add up all the lower section submains, plus the breakers above them (which should total no more than 6), and make sure the service wiring can handle that amperage. What I see doesn't look like it will do more than 100 amps, but there could easily be over 100 amps of unchecked load with an added 2 pole breaker.
What is that disconnect box on the left?
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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.
snipped-for-privacy@ipal.net wrote:

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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. Michael Shaffer wrote:

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