Why both a Neutral and ground wire

Since the neutral wire and the Ground wire are both connected together at the Service entrance, why are they both needed? Instead of connecting the
ground wire to the case of appliances, connect the neutral wire to the case and throw the ground wire away. I have never been able to get an answer on this. I've Googled this to death. Can anybody out there clear this up?
Thanks for any insight.
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Earth wire never connect to a neutral, an earth wire should be direct to the ground. Please correct if this is wrong.

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Wrong. In the US, the neutral and ground (earth wire) are bonded at one point in the service panel.
I believe in european terminology that is a TNCS system.
Charles Perry P.E.
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The code states that they must be connected together at the service entrance(breaker box).
mike

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The neutral is a current carrying conductor. The ground wire is only meant to provide a path for fault current long enough for overcurrent protection devices to operate.
Charles Perry P.E.
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Charles, Thanks for your input. I agree with what you say, but I guess what I am saying is that the neutral wire can still be the current carrying conductor AND be the path for current in an anomalous situation that would trigger a breaker.
mike

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wrote:

If you are speaking of the North-American power system, there are many 240 appliances that carry neutral current because they have sub-systems that carry 120 V loads. Some examples would include your dryer and your electric range. The 120V sub-systems may be lights, clocks, dryer motors, timers, etc.
Neutral systems (that carry current) that are shared with Grounding-Earth Conductors (that are not supposed to carry current except for short duration electrical faults) CAN BE dangerous. For years, the US Electrical code permitted 3 wire plug and outlets (Hot - Hot - and a shared Neutral - Ground) . The assumption was that this would be safe as long as the neutral was never disconnected.
Note that this is no longer permitted in new work. Electric Dryers and Ranges are now required to have 4 wire plug and outlets (Hot - Hot - Neutral - and a safety protective Ground/Earth wire)
Presumably, you understand the importance of a safety earth/ground connector. Is the correct?
Both the US and Euro systems have neutrals that have grounded earth connections. The Euro systems usually have voltages of 220-240 to ground. The maximum nominal voltage for a US system is 120 volts to ground.
Another example: The overhead light in your basement or hallway.
Proper wiring practice means installing a switch in the hot lead and not the neutral lead. If you get it reversed, some unknowing person who changes the light bulb might turn off the switch thinking the power to the socket has been cut off. Then they might accidently touch the the center pin of the socket (or if things are really mis-wired, the shell connector of the socket). Either way, if they make contact with the hot and say, the conductive ladder on a damp floor or a water pipe or some grounded air vent ductwork, they will get a shock and possibly be injured or killed. Cases like this have been documented throughout the last 100 years or so.
If the light socket and the switch are wired properly, the person might only accidently touch the neutral, in which case they are likely to stay alive.
Case 3 - Grounded systems provide additional protection from lightning and rare cases where, for instance, the primary conductors falls on and makes contact with a secondary feeding a residence. This is why utilities are so concerned about bonding and grounding.
Beachcomber
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Beachcomber,
In your first example, with the 220V, you make the statement "The assumption was that this would be safe as long as the neutral was never disconnected". I agree, since the current would go through me to ground (if I were grounded). This would happen when you just turn the Dryer on normally or if the hot wire was inadvertently touching the metal of the Dryer. I'm assuming that both the Neutral and ground wires were connected to the Dryer metal. The same situation would occur on a 120V system. I guess I could make the statement for a currently legal 120V system: "The assumption is that it will be safe as long as the Ground wire is not disconnected AND the hot wire never touches the metal case". Maybe I talked myself into it here. In the legal case, (where the ground wire was disconnected) the problem ONLY occurs if there is a malfunction in the appliance or fixture (hot wire touching the metal), but in the illegal case, the problem is there anytime you turn it on. This may not be the real explanation, but for me, I guess it would justify having both wires.
mike

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| Since the neutral wire and the Ground wire are both connected together at | the Service entrance, why are they both needed? Instead of connecting the | ground wire to the case of appliances, connect the neutral wire to the case | and throw the ground wire away. I have never been able to get an answer on | this. I've Googled this to death. Can anybody out there clear this up?
The neutral wire carries current. There will thus be some voltage present at locations away from the ground bonding. The further away, the higher the voltage. The higher the current, the higher the voltage. The smaller the wire, the higher the voltage.
The EGC (Equipment Grounding Conductor) is different. It does not carry current (except during times of a fault connecting to it). Therefore it will not have the voltage on it that a neutral could have at times under normal usage.
The 240 volt circuits (known as "two-twenty") are different. Both of the electrical conductors are always "hot" or "live". Neither is a neutral. In these cases there is no choice; an EGC needs to be there to provide a ground reference. You could have a neutral wire not carrying any current, but that would effectively be the same thing if it goes to the service entrance panel (not so if it goes to a subpanel). The typical appliances using this type of circuit are heavy duty air conditioners, central electrical heating, and electric water heaters.
The dual voltage 120/240 circuit is the most complex in a home. It has 3 current carrying conductors. It is the 240 volt circuit with a neutral added. It also poses a greater risk since that neutral could become disconnected and cause the voltage on the frame of the appliance to be elevated to a rather high level. This danger is real because a broken neutral connection would not normally be detected as a fault and so the appliance would still have power and probably operate (maybe operate just fine or maybe operate erratically). Add the EGC and connect it to the frame instead of the neutral, and now you have the safety. The typical appliances using this type of circuit are kitchen ranges and laundry room clothes dryers. These do so because some components of these appliances (lights, clocks, and motors compatible with low power gas versions) are designed for 120 volts rather than 240 volts.
The very rare instance of three phase power in a home in the USA is not any different with respect to the EGC. The numbers may work out a little different, but essentially it is the same, except that you may see as many as 5 wires in some places (3 hots, neutral, and EGC) whereas you would only see as many as 4 wires with single phase.
Note that the NEC requires subpanels to _not_ bond the neutral to EGC. One of the reasons for this is that the neutral conductor at the subpanel can have a voltage due to current flowing on the feeder neutral that will be present on every branch circuit of the subpanel. Additionally, this voltage could be substantial if there is a neutral connection problem, while such a condition would typically not cause breakers to trip nor be seen as an electrical outage that needs to be fixed. Connecting the EGC and neutral together at the subpanel, along with proper grounding via a grounding electrode, could lessen the issue, but it will create other more complex issues (such as cross feeding significant current over other kinds of wiring like telephone or cable TV).
Many homes still don't have any EGC wiring, or have it only in limited cases, and yet have not burned down or electrocuted anyone. That does not mean a lack of EGC is perfectly safe. These things are a matter of degree. The NFPA (National Fire Protection Association) Electrical Code Making Panel (CMP) has studied the issue for years based on input from fire departments, emergency rescuers, and medical personnel, for decades and has concluded that the numbers warrant having this extra protection in all new and rebuilt installations. We have a very safe electrical system these days (particularly compared to what was 100 years ago). Still, older wiring is substantially riskier in comparison, for many reasons, with the lack of EGC as one of them. An extremely small risk percentage multiplied by this risk increase is still very small. But I'd rather go for the smaller of these.
GFCI (Ground Fault Circuit Interruption) protection can cover many of the cases that EGC also protects from, and it can also function and even be tested without an EGC present. It's not a complete solution. But it is better than not having GFCI, especially when EGC is absent. GFCI can be added to older wiring more easily since it does not involve tearing out walls to rewire.
The EGC needs to run along with the associated current carrying conductors, either as part of a cable assembly together, or inside the same conduit. This ensures that should there ever be a high current fault, the current will not induce voltage in other wiring, nor acquire inductance that could result in a delay or failure of the overcurrent protection from opening the faulty circuit fast enough. Adding an "extra separate ground wire" is not the correct way, even if it is parallel but outside of existing cables. Only a complete rewire brings an older system up to today's standards of safety.
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|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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wrote:

The problem is voltage drop. In the case of the neutral the "drop" is actually a rise as referenced to ground. The farther you get from the main panel where they are connected together and the higher the load on the conductors the more difference you would have between neutral and true ground. If you were holding a metal tool, "grounded" to the neutral out in the yard it might give you quite a bite if you were sitting in damp soil. If there was also a bad connection somewhere in your neutral that rise would be 120 volts and you would be holding a hot tool. By making the ground wire totally dedicated to "earthing" the tool there will be no voltage drop (rise) on it and no current flowing throug it unless you have a fault. That fault should trip the breaker.
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On 12/5/06 6:17 PM, in article snipped-for-privacy@corp.supernews.com, "Mike"

Many places are wired just as you think they should be--no separate protective ground wire. The ground wire was added for extra safety as described in many other posts. Sometimes conductive conduit served as a ground. BX cable is one example.
As a kid, and even later, I remember seeing open wiring on knob insulators where no separate grounding is in sight. I suppose if I went to look at some antique buildings, I still may see such dangerous installations.
I do remember insanely dangerous ad/dc radios with screws at line voltage that went through plastic cabinets to a metal chassis.
Bill -- Fermez le Bush
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Mike wrote:

If you use a single wire for both the neutral and the safety ground, a single fault - open neutral between the appliance and the service panel - can put the metal body of the appliance at 120 volts with respect to ground. It would require two faults for that to happen when you use a separate EGC. The EGC (equipment grounding conductor) would have to be open, *and* there would have to be a fault in the appliance to bring the metal case to 120 volts with respect to ground.
Ed
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wrote:

In the US, there are many old power tools some 40-50 years old with metal cases and 3 prong grounded plugs. In many cases, the operator, when faced with a 3 prong plug that will not fit in a 2 prong socket would bend or saw off the 3rd grounded prong, or sometimes use one of those 3 to 2 wire grounded adapters and not connect the green ground wire to a true ground.
Believe or not, this still causes electrocutions according to the Consumer Product Safety Commission.
Originally, the power tools had only two prong non-polarized plugs and metal housings.
After years of electrocutions, injuries, shocks, stunned workman falling off of ladders, etc. it was decided to ground these metal housings with the third prong.
Then it was discovered (as described above) that many would attempt to circumvent the protection of the ground by cutting the 3rd prong off at the connector.
Double insulation became popular on power tools and much of the power tool industry went back to two prongs.
My wet-dry shop vac is all plastic and double insulated, but I notice that it has a 3 prong plug.
Beachcomber
Conclusions:
1. Grounding is better (safer) than not grounding. 2. The neutral should not be used at a safety ground 3. The neutral should never carry line current 4. A GFCI protected circuit with a true safety ground is a good thing. 5. A GFCI circuit without a true safety ground is not quite as good, but still better than no GFCI at all. 6. Switches that break the neutral wire, but not the hot wire to control a device, can be very dangerous.
QUIZ QUESTION -
You want to hire an electrician to wire a garage light and and garage receptacle outlet. The light should be able to be switched on or off from either the garage or the house (a total of 2 locations). The garage receptacle outlet must be always be on.
You receive 3 bids. You are told you will need two 3-way switches, a receptacle outlet, a light socket and some wire.
Electrician A says - No problem, I can do that job with 5 wires for $300 Electrician B says - No problem, I can do that job with 4 wires for $250 Electrician C says - No problem, I can do that job with 3 wires for $200
(the number of wires is the number of conductors between the garage and the house. The power source is in the house. Safety ground wires are not included in the count.)
Question - You want the installation to be legal according to the NEC, but also you also don't want to spend more than you have to.
Which electrician to you give the job to?
(more rules - Safety ground wires don't count in the numbers mentioned above and may not to be used to carry current - No Insteon - X10 - or radio controlled switches)
Beachcomber
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Beachcomber wrote:

I think you'll want to change #3.

$250
Ed
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OK assuming this is an AC circuit not DC (No diode tricks!):
Excluding the ground, 4 wires are needed., hire electrician B, or write a performance specification requiring the finished product to meet NEC, switch three ways, the outlet to be continuosly hot (On both top and bottom sets of terminals), and not use Insteon or X-10 type trickery, save $50 and hire electrician C.

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Joe Leikhim K4SAT
"The RFI-EMI-GUY"
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Anybody knows you shop the prices around a few minutes before the bids close, one of them will do it for 5% less than the other guy.
j
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Beachcomber wrote:

You can use 3 wires if you use a single pole switch, a 3-way and a SPDT relay.
4 wires can be used in conduit. If using a cable, like UF, it has to be 4 wire cable, else a 2 wire cable and a 3 wire cable.
So what are we missing?
Perhaps more interesting is the same problem but lights at both ends that are switched together. Can be done with a 4 wire cable. Otherwise I believe it takes 2 - 3 wire cables.
-- bud--
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| Since the neutral wire and the Ground wire are both connected together at | the Service entrance, why are they both needed? Instead of connecting the | ground wire to the case of appliances, connect the neutral wire to the case | and throw the ground wire away. I have never been able to get an answer on | this. I've Googled this to death. Can anybody out there clear this up?
Looks like an ungrounded mailbox:
action not taken: mailbox unavailable (in reply to RCPT TO command)
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
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IIUC Live and Neutral wires in British systems carry the load from and to the power station and the earthing systems at the stations/substations. The earth is directed to earth, and is used only where the appliance has some part that may come into contcat with the operator if some short or failing in the wiring causes a live wire to contact a conducting case. If the live wire shorts to the earthed case the system passes current directly from the supply to earth and hence has practically negligible resiostance and draws all available current thus blowing the fuse. It's a safety device for domestic consumers. Not so much needed on all plastic devices such as plastic kettles and vacuum cleaners for there isd no way the current in the live wire touching the case could overcome the resistance of the insulating case without there being too much current for the fuse to accomodate.
The earth is always dormant unless the system breaks down. The neutral carries current back out to the electrical grid's earths, probably at the sub station.
It's organised and thus we know where everything is.
--
Billy H



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