new range

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Old 09-22-08, 02:04 PM
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new range

My new range should be a four wire connection in my area. My question is in my cable and the way it is wired to the load center. Coming in the load center is two black 6ga. going in to 50 amp 2 pole breaker and a bare 6ga. copper stranded wire attached to the nuetral bar. I also have a separate 10ga. green wire connected to ground bar running to range but it is outside the cable. I am questioning if this is a true 4 wire set up. Why is the nuetral wire bare and since it touches the load center chasis which is earth grounded, is this a old 3 wire set up. Can it be used for a 4 wire set up? I confused about that bare nuetral wire.
 
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Old 09-22-08, 02:18 PM
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this is a 3wire the external ground wire (green) although it works this is not code. you must purchase 6/3 romex which is good for 50amps. the romex will have a bare ground wire in the cable. when you get to the main panel the ground and neutral wires can be on the same bar. sometimes the ground wires will have their own bar but in a main panel both can go to the same.
 
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Old 09-22-08, 02:54 PM
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nuetral and ground question

Thank you jjkjr. One more question. What confuses me about the neutral and earth ground is why they can be connected together in the load center. But when connected together in the load center, can voltage or amp. be carried back to the range through the neutral? I never really understood how that works.
 
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Old 09-22-08, 04:08 PM
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Simply, the neutral is for return of operating current for 120V loads in the appliance, and ground is to safely return any fault current that may reach the chassis.
 
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Old 09-22-08, 04:11 PM
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Grounding accomplishes a few things. The easy one is basic lightning protection, if a surge comes down your line big enough to jump from a hot to the panel shell, the ground gives it a path to earth. Same thing for static charges, it dumps 'em to the earth.

The second function is to ensure that the neutral and the ground are more or less the same voltage. If the neutral isn't grounded anywhere, it can have significant voltage between itself and ground, and then the hots have even higher voltage to ground. Old ungrounded industrial facilities occasionally have wire failures because of this floating neutral problem. On a smaller scale, many electronics are built assuming that ground and neutral are the same voltage, a difference of even a couple volts and stuff gets damaged. This is one of the things that forces people to upgrade old ungrounded house wiring, when it starts destroying their computers.

So because of those issues, the neutral gets grounded at the panel. However, that should be the only place in the system where they are tied together. This is because the neutral carries current while under normal operating conditions. It is the return path back to the transformer. The ground, which is often bare, and usually connected to many of the touchable metal objects in your house, should never have significant current running on it for longer than it takes to throw a breaker or GFCI. If you tie a ground and neutral together someplace in your house, that ground wire now has current running on it all the time. Then merely touching the screw on the cover plate could make you part of the circuit... not safe. Also consider what would happen if someone disconnected the neutral and thought there would be no more current flow, when instead the ground just starts carrying all the return current. This is how people get hurt.
 
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Old 09-22-08, 07:55 PM
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Originally Posted by fullfstop View Post
Thank you jjkjr. One more question. What confuses me about the neutral and earth ground is why they can be connected together in the load center. But when connected together in the load center, can voltage or amp. be carried back to the range through the neutral? I never really understood how that works.
The neutral current will not back flow on the other wires terminated to the neutral bus as the transformer is like a sink and all current flows to it (its the source). Another way to look at it is the transformer is the completion of the circuit loop for all 120 volt branch circuits of your homes wiring. In the case of your range it has both 240 volt requirements and 120 volts requirements and must have a neutral for the 120 volts.

Your also asking about the equipment grounding conductor in your premise wiring (branch circuits). And why it ends up with the neutrals on the neutral bus of your load center. To clarify this only happens when the load center has the main disconnect for your home located in it. In which case it is the service equipment...ie....first means of disconnect that the utility hot conductors land on. In this situation both neutrals and equipment grounds terminate on the same neutral bus. They are not earth grounding conductors though they are bonded to to earth by virtue of the connection to your grounding electrode system which is also connected to the same neutral bar. However they have nothing to do with sending current to earth. The bare wires in you branch circuits are there for one reason.. to carry fault current back to the transformer center tap not to earth. The only way back to the center tap is over the utility service neutral which carries all unbalanced neutral current of your premise wiring back to the transformer center tap. Current seeks its source (transformer) and it will use all paths available to get there including the earth. Nearly all current will seek the lowest impedance path to the transformer center tap. The service neutral by far provides the lowest impedance so nearly all premise neutral current returns on it to the transformer. The key here is unless we can get fault current back to the center tap on a low impedance path other than earth you cannot get a breaker to trip if a ground fault occurs somewhere in your homes wiring. The only low impedance pathway back to the transformer is over the service neutral so we bond all the equipment ground wires of your branch circuits to the service neutral at the main disconnect panel. This allows fault current to utilize the low impedance of the service neutral to get back to the center tap of the serving transformer. All your equipment ground wires bond all metal likely to be energized in a ground fault to the service neutral so that all fault currents will seek the low impedance of the service neutral to the transformer center tap. this will allow enough current to flow to trip a circuit breaker. If fault current tried to go to earth to get back to the transformer center tap then the relatively high impedance of earth would not let enough current through the branch circuit breaker to trip it on fault. All metal in contact with the ground fault would come to line voltage and pose a electrocution issue to any one touching the metal involved in the fault.
This intentional path for bonding metal together with the equipment ground wires is called the "effective fault current path". This provides for low impedance/resistance back to the main panel and then to the center tap of the transformer over the service neutral and protects people from electric shock.

Remember the utility runs only 3 wires to your home 2 hots and the service neutral. The service neutral is the only low impedance path back to the center tap of the transformer for neutral current and fault current. So we bond both white neutral wires in the branch circuits and the equipment grounding wires (green and bare) to the neutral bus where the service neutral is terminated so that both can use the service neutral to get to the electrical source.


A few diagrams to help you understand....



 
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Old 09-22-08, 08:18 PM
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"The only way back to the center tap is over the utility service neutral which carries all unbalanced neutral current of your premise wiring back to the transformer center tap. Current seeks its source (transformer) and it will use all paths available to get there including the earth. Nearly all current will seek the lowest impedance path to the transformer center tap."


Qualify that this is only true if you have a good neutral connection. Many residences have have good low impedance connections through city water pipe ground connections. This forms a web of connections that make their way back to the transformer center tap. E.G. if your neutral were open the path could be through your water pipe to your neighbor and then out their neutral or to several neighbors. There are many sneak paths for current in a dense residential system. Try putting your clamp on ammeter over the water pipe entering a home and you may be surprised! So while the ideal path is the neutral wire to the transformer in some cases this may not be true.
 
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Old 09-22-08, 09:26 PM
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Originally Posted by dsc3507 View Post
"The only way back to the center tap is over the utility service neutral which carries all unbalanced neutral current of your premise wiring back to the transformer center tap. Current seeks its source (transformer) and it will use all paths available to get there including the earth. Nearly all current will seek the lowest impedance path to the transformer center tap."


Qualify that this is only true if you have a good neutral connection. Many residences have have good low impedance connections through city water pipe ground connections. This forms a web of connections that make their way back to the transformer center tap. E.G. if your neutral were open the path could be through your water pipe to your neighbor and then out their neutral or to several neighbors. There are many sneak paths for current in a dense residential system. Try putting your clamp on ammeter over the water pipe entering a home and you may be surprised! So while the ideal path is the neutral wire to the transformer in some cases this may not be true.
Why ask me to qualify anything? If you have something to add post it.

His question was 'why do we bond the neutral and ground at the service equipment'? I saw no reason to open his neutral..... I would be more concerned with objectionable current that is coming into my home over the water pipes...and my neutral not opened.

Are you saying that if the service neutral opened the water pipe bonding would become my neutral return and I would not have any issues going on with my homes wiring?

BTW what do you suppose the statement "current seeks its source and will use all paths to get there" included....

Open a thread and we will discuss this objectionable current on water pipes, there is a lot learn in doing so....

Try putting your clamp on ammeter over the water pipe entering a home and you may be surprised!
How many amps surprised should I be?
 

Last edited by Bruto; 09-22-08 at 10:50 PM.
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