question on BONDING 2

[rrzzan]

Bonding is the connection of all electrically conductive materials (which are likely to be energized) to each other and to the neutral conductor in order to create a low impedance fault current path, back to the source.

My question is.
1. Since the neutral conductor also has current in it, will it not allow current to flow on the surface of the metal surface, which may give a shock to any individual touching it?
2. For a properly bonded system- If someone touches the charged metal surface, then bulk amount of current will find the low resistance path (effective ground-fault current path) which will trip the circuit breaker.

But if the person touches the ‘hot’ wire then? All the current will try to find its path to the source via ground and he will not be protected…..?? Is bonding not intended to protect it somebody touches the ‘hot’ conductor?

Please help me clear my doubts.

 

[DanDel]

There seems to be some basic misunderstandings of electrical systems in your questions.

The neutral carries the return current, and typically does not have much of a potential (voltage) to ground. The neutral is grounded in (hopefully) one place, near the source to keep this potential low. The neutral conductor provides the lowest-impedance path back to the source, not a person touching it or something grounded (bonded to ground). If the neutral were disconnected from the return, then there would be a potential of the system voltage between that wire and ground (in a grounded system).

In your 2nd question, you somehow assume that a properly bonded system is 'charged'. A properly bonded system is one which has nearly zero voltage to ground. This is the same voltage a person would have if he touched it, so there is no current flow.

Someone touching a 'hot' conductor now becomes part of the circuit, between the line and return of the system. This is why live parts are insulated and people are protected from them. A solidly grounded and properly bonded system is necessary to cause a device trip upon a ground fault which will remove the hazard to personnel.

 

[rrzzan]

Thanks DanDel,
Clear about my 1st doubt.

In my second question,
First paragraph-I assumed that there is a ground fault ( a hot conductor touching a metal surface). It is just a background anyway.

Second paragraph-I am assuming that the conductor is not insulated and somebody intentionally touches only the ‘hot’ conductor…then bonding should not work for him, right?

 

[DanDel]

Bonding is not intended to prevent someone from touching a live wire.

 

[davidbeach]

Bonding is also NOT made to the neutral conductor (limited exceptions grand-fathered in) but rather to the ground conductor.

 

[waross]

Have you ever seen a breaker trip because a motor burnt out and went to ground? How about a loose wire touching the side of a junction box or the frame of an appliance? Grounding is supposed to both limit the voltage on exposed conductive surfaces to close to ground potential and trip the breaker. Without bonding, the examples given above may result in injury or death to someone touching the outside of a junction box or a motor frame in the event that a hot conductor contacts the inside of the exposed metal.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rrzzan]

Davidbeach,

What do you refer a 'ground' conductor? Terminology is NEC is confusing. Here's how I interperate,

ungrounded = hot
grounded = neutral
grounding = ground

 

[rbulsara]

rrzan:

I would try to answer your question in the original post in sort of reverse order.

Your last statement in the OP is correct to the effect that if someone touches the live wire on a grounded ssytem and he is in contact with the grounded surface also he will get the electric shock! It also true that if he was insulated from the ground or the system was a truely ungrounded (there is no such thing but that a different subject) he may not get a shock (just as birds sitting on live wires survive). This was one of the arguments for ungrounded system in old days, but the history has proved that benefit of a grounded system far outweighs ungrounded system. A solidly grounded system allows rapid clearing of a fuse/breaker in case of unintentional touching of hot wire to a ground before it turns in to a fire and other shock hazard. So the key is not to touch a live wire and so on.


2. Bonding means just that connectio between two elements. Neutral supposed to be "bonded" to ground only at one point that is at the source. Look up "main bonding" jumper in NEC 250. All other non-current carrying surfaces are supposed to be bonded to a ground or a grounded surface such as buildong steel. Idea is to bond all surfaces within reach of a persons span to be bonded together to create a equipotential surface to minimize shock hazard even from static electricity.

1. This the most puzzling statement to me. Current in neutral is not intended to keep it out of grounded surface. Neutral with normal currents are part of a normal circuit to make a complete circuit from source terminal to the load and back. The insulation on neutral conductor is there to keep the current from going through the ground. If someone just connects a load to the ground instead of neutal may or may not cause a shock but is not desirable or permitted by code for safety reasons.

Hope this is somewhat helpful. I hate writing long responses.

 

[davidbeach]

Neutral is a normally current carrying conductor, not used for bonding. Ground is used only to carry fault current and for bonding purposes.

 

[jghrist]

What do you refer a 'ground' conductor? Terminology is NEC is confusing. Here's how I interperate,

ungrounded = hot
grounded = neutral
grounding = ground

You are basically correct. The neutral is grounded, but only at one point.