Ground and neutral connections

[bbiandov]

Hi everyone,

I have seen so much convoluted content on this topic which leads me to believe that my sources are bad, comprised of those who really don't know the answer and divert attention away from the touchy topic:

Is the green ground wire the same as the white neutral wire? The criteria here is resistance between the two - if it's close to zero then a rational answer should be YES. And yes it should be since the utility company, at some point or another, does connect a grounding rod directly into the neutral wire right after the transformer so any possible resistance that one could measure at the house would be between their grounding rod and mine?

My objective is to answer a more practical question: in the absence of green wire in the electrical conduit is it OK to connect the available white neutral wire to both the neutral AND ground terminals on a 3-prong outlet?

 

[#12]

The white wire is there to carry current back to the transformer. The "bond" wire is a safety ground which does not carry current except under fault conditions. If you connect them together at the receptical, you cause problems instead of solving them.

The white wire commonly has a tiny AC voltage on it because of current flowing in it. Attaching that to the bond terminal attaches the tiny AC voltage to a place that everyone thinks is completely safe.

You might solve a problem I don't know about by attaching white to the green terminal, but it's much better to do it properly.

 

[Sceadwian]

You should never connect a saftey ground wire to neutral, in fact it probably violates electrical code, everywhere.
Just as an example say an appliance has an electric motor which develops an insulation fault and it's hot and neutral fault and the neutral gets disconnected, saftey grounds are often connected to pretty much every metal object on most appliance so since there is no no proper ground return the entire appliance will be electrically HOT, this is bad... With a valid saftey ground there would be a massive current into the ground line and a breaker would trip. Given the option between leaving it disconnected and connecting it to neutral leave it disconnected. There are many options for adding a ground at various locations, and it doesn't even have to be a massivly huge wire if you use a GFCI you can use a relatively thin ground wire, ANY current going into it over a few ma's will trip the saftey breaker.

 

[bbiandov]

You should never connect a saftey ground wire to neutral, in fact it probably violates electrical code, everywhere.

Ok so a realistic and credible safety issue only occurs in a double failure. Both internal fault must occur as well as the neutral must be broken. If only an internal fault occurred with the neutral being in tact that will be sufficient to trip the circuit breaker.

Then how is this different from the following scenario with 100% proper 3-wire system: electrical motor creates internal fault in an appliance AND the neutral wire breaks between the panel bond (that's where neutral and ground are bonded together) and the transformer. The motor fault will distribute current via it's perfectly working neutral back to the panel and from there to all grounded appliances with no low resistant path to complete a circuit (the earth rod resistance is way to high to provide viable amps to trip a breaker)?

 

[Sceadwian]

bbiandov. Why don't you hold on REAL hard to the device that fails and tell me why things like this are done, a person near a device like this in good physical contact would be DEAD, and possibly catch the area they were in on fire.

The difference is that in a saftey ground connected device the current has a place to go besides YOU. No ground is required for electrocution the capacitance and resistance of the human body will provide enough difference in electrical voltages at any two points to fry someone like bad pork.

If you doubt me please connect a large metallic object to live even if it AND you are isolated so that there appears to be no fault. Grab onto it with both hands, and please have paramedics standing by, even though they probably won't be able to help you if the pole was around the diameter of your hands and the muscles locked. You'd be DAMN lucky if blast from the moisture and surface tissue of your hands sent you clear of the heart stopping current of a few hundred ma.

Why do you think the saftey ground exists? This HAS happened before in the real world, so much so it's law.

Mind you even if it's not a person during a short circuit the phase difference between even otherwise neutral objects can cause them to be part of the short. This is why some shorts are just a large blast of sparks around a general area.

 

[#12]

Thanks Scead. This guy was making me dizzy.

 

[Sceadwian]

Just to reiterate this. It is NEVER under ANY circumstances okay to attach a saftey ground connection to neutral, EVER.

 

[Reloadron]

My response is really simple:

My objective is to answer a more practical question: in the absence of green wire in the electrical conduit is it OK to connect the available white neutral wire to both the neutral AND ground terminals on a 3-prong outlet?

No, it is not OK. To best understand why it is not OK would be to read completely through Article 250 (Grounding and Bonding) of the NEC (National Electric Code).

Back in 1962 it was adopted as law for very good safety reasons. The three prong polarized outlet with ground was developed for good reason.

You ask if it is OK? The answer is no, it is not OK.

Ron

 

[Sceadwian]

Thank you Reloadron, that can't be said enough.

 

[tcmtech]

Ok so a realistic and credible safety issue only occurs in a double failure. Both internal fault must occur as well as the neutral must be broken. If only an internal fault occurred with the neutral being in tact that will be sufficient to trip the circuit breaker.

Not necessarily. Your common return line could break or develop a bad connection between the device and the main junction box causing the current flow that should have gone back to the common point in the service panel to instead go back to the body of the device where then anything touching it and a suitable return circuit become the next available return path instead. One single point failure outside of the device is still enough to make it a potentially lethal problem even though the device itself has nothing wrong with it.

 

[BrownOut]

Not to mention that if the common return breaks, then one side is no longer "common" but has the full line voltage on it. Your body can then become 1/2 of a voltage divider, along with the load that's plugged in. Better hope the load alone is enough to keep you from being electrocuted.

 

[ronsimpson]

Some where in your house the ground and neutral are connected. They should be connected at the first panel and not connected in sub panels or any other place. They should not be connected at the plug!

In the first pose "in the absence of green wire in the electrical conduit", when I install conduit there is white & black in the conduit and the outside is metal piping known as ground. When installing a 3 wire outlet using conduit and metal boxes the screws connect ground to the outlet.

Most likely we are talking about a old house with two wire wiring and no metal conduit. In this case I have run a separate green wire through the walls. It is not easy!! I often have to take a very different rout with the green wire.

 

[KeepItSimpleStupid]

With all of the electronics in a home, one fails to realize that the ground is also a REFERENCE for your water pipes, your CATV and your COMPUTERS.

If, for instance, a fault to ground exists on one circuit, it will not raise the potential of others.

That's a simple explanation although a computer center was taken down because lightning can change the Earth's potential so the reference on each side of a building can be different. When you have devices that use as little as 5V to communicate, you have problems.

The fix, replace connections from one side of the computer center to another with fiber.

In ground Swimming pools require lots of attention because of ground potentials.