Grounding & bonding prevents Arcing

[jaggedben]

I would say that your tactic of editing my comments so that they make your point is poor etiquette. If you were to include the whole comment you would read that I have not contradicted myself.

I was just trying to keep the thread from being too cluttered and I did not remove anything that would change my opinion about your comment. I did forget to mention that I do not think that lightning is what the insurance inspector in the OP had in mind.

Bonding reduces arcing vs not bonding for a ground fault by reducing the duration the arc is allowed to persist. An object that is not bonded could arc indefinitely until starting a fire.

Why would an object that is supposed to be bonded but is not bonded arc indefinitely and start a fire? I cannot think of a situation in residential AC wiring where this would be meaningfully true. Moreover, there are types of arcing (e.g. series arcing), that bonding can play no part in stopping.

An object that is bonded will arc for a very short time because the OCPD will trip on a ground fault.

And an object that is not bonded won't arc at all if not in contact with other bonded objects. It could be energized and thus a potential shock harzard or arc hazard to other objects, and that is certainly dangerous, but that situation is not accurately described by the phrase 'bonding prevents arcing.'

This point you are trying to make is only relevant to ground faults.

I think the point I'm making is relevant to the entirety of low voltage wiring, and perhaps the entirety of wiring under the scope of the NEC. Perhaps I'm wrong, but no evidence has been presented in this thread to convince me otherwise.

There are other reasons why bonding and grounding help reduce arcing. Do you dispute these as well?

Not entirely, but I have not seen any examples given that seem relevant to the 240V residential wiring involved in the OP, or even any that fit within the scope of wiring covered by the NEC. Again, it seems to me that the primary intent of bonding in the NEC is to cause arcing when there is a fault, with the intent of tripping protective devices.

The OP made a reference which I believe was intended to convey that the home inspector had no idea what he was talking about. I believe the OP is substantively correct on that point.

 

[jaggedben]

exactly the reason
to keep devices equipotential

extreme
no bonding, broken wire/connection
100 A cb
480 fault to frame 277 to ground
no trip
1000 ohm individual touches frame
277 mA flows and he's dead

True, and very important to understand, but there's no arcing in this example.

less extreme
poor bond 5 ohm
same fault 55 A flows
no trip 55<100
frame will have 277 on it with 277 dissapated across the gnd cond
touch = zap

Again, no arcing in your example.

we ground monitor all ckts to trip cb if >=2.7 ohm
We use a 15 ngr
frame under fault 2.7 x 15 = 40 vac to gnd
40 mA is survivable and close to let go
and v and i relays on the ngr which will trip and save him

if a conductor shorts to duct/pipe and is not bonded same scenario
the person becomes the ground path
if bonded the cb trips before contact

Yes, all true, but not about reducing arcing.

 

[jaggedben]

Arcing may be a side effect at times but creating arcing is not the reason for bonding. We bond things for 2 reasons.

1. To bring bonded items to equal potential.

2. To create low impedance paths for fault current to travel through should there be a fault, which ultimately we are bonded somewhere to the system grounded conductor and this allows high current to travel and cause quick opening of overcurrent protective devices.

Yes, all true, and "arcing may be side effect at times" is precisely why I don't accept that 'bonding prevents arcing'.

 

[kwired]

Yes, all true, and "arcing may be side effect at times" is precisely why I don't accept that 'bonding prevents arcing'.

I wasn't sure what your position on this "bonding may reduce arcing" statement for a little bit there. But yes, bonding isn't an intent to increase or decrease arcing, arcing is just something that happens when we don't have a solid connection at an intentional or non intentional junction/contact point in a current path. You must have current or there will be no arcing.

 

[iwire]

Okay, again I ask... seriously?

To my mind, the purpose of bonding is generally to cause arcing, under the theory that an overcurrent or other protective device will detect a problem and de-energize the circuit.

Once again yes.


Why do you think we bond service raceways to enclosures?

It is not to trip the non-existent OCPD.


Why do you think we bond around concentric KOs on 480 volt circuits?

It so the concentric KO does not become a fuse and blast sparks out before the real OCPD opens.

 

[mbrooke]

Arcing only can take place between a difference of potential, bonding brings things to the same potential. In fact in operating rooms where flammable anesthesia was used decades past, the room was practically a Faraday cage. Even the cart had chains that bonded it to the floor if I recall correctly.

 

[romex jockey]

This thread is all over the road with 'arc'

Please describe 'arc' for me in detail less anecdotal ,more lab setting.

Then apply bonding, ground fault, to it

~RJ~

 

[Fitzdrew516]

I think there is some confusion because the term "arcing" is being used differently than we would commonly use it. I think the inspector is accurate (for the arcing item), but I have heard this referred to as "side flashing". i.e. - lightning strike travels through the up the ground rod and if it gets to a point that is not bonded it will jump/side flash/arc to the nearest thing it can. Anyone have an NEC reference for this or is this all under the umbrella of NFPA 780?

 

[iwire]

Seriously we are asking what an arc is?

Try Googling it.

 

[Sahib]

Seriously we are asking what an arc is?

You need to be content with what it does rather than what it is. In that respect, you need to know that once an arc is established between conductor and ground, OCPD may not be always able to clear it.

 

[Ingenieur]

True, and very important to understand, but there's no arcing in this example


Again, no arcing in your example.


Yes, all true, but not about reducing arcing.

sure there is
the connection causing the high Z could be lose, this is typical
or a broken/damaged wire within insulation
this would cause an arcing fault, the most common kind
solid bolted faults are rare

people have given you a dozen valid reasons
including the NEC opinion (not mandatory)
you r3efuse to acknowledge them
that doesn't invalidate them

 

[mbrooke]

Seriously we are asking what an arc is?

Try Googling it.

I did:


https://www.google.com/?gws_rd=ssl#q=electrical+arc+

https://en.wikipedia.org/wiki/Electric_arc


One is left to wonder what exactly constitutes as "plasma discharge" especially when several different stages of electric discharge are defined all determined by variable like voltage, air pressure and distance:

https://en.wikipedia.org/wiki/Electric_discharge_in_gases

Air pressure can be assumed constant through out, but voltage and distance determines what type or if its even possible to sustain an arc.

 

[mbrooke]

You need to be content with what it does rather than what it is. In that respect, you need to know that once an arc is established between conductor and ground, OCPD may not be always able to clear it.

Can you elaborate further on this? Im a bit dull in that regard :dunce::ashamed1:

 

[kwired]

Bonding conductive objects together will minimize arcing between those objects. Only in cases of extremely high voltage like a lightning event is where you may still have arcing between those objects even though they are bonded. 600 volt and below it it not happening.

It will do nothing to prevent arcing to objects that are intentionally at a different potential - like an exposed ungrounded conductor.

 

[iwire]

Bonding conductive objects together will minimize arcing between those objects. Only in cases of extremely high voltage like a lightning event is where you may still have arcing between those objects even though they are bonded. 600 volt and below it it not happening.

Really?

I have to disagree, please take a look at this old thread of mine.

http://forums.mikeholt.com/showthread.php?t=112421

 

[kwired]

Really?

I have to disagree, please take a look at this old thread of mine.

http://forums.mikeholt.com/showthread.php?t=112421

did not read through all the posts, but are you referring to the signs of arcing between locknuts and enclousures and the bolts between components shown in the OP?

If so there obviously was voltage drop across a connection - meaning the bonding was not as good as it could have been.

I just saw the other day a bolt on hub that had the heads of the bolts nearly burned off from fault current passing through them. That was on supply side of service disconnect and should definitely have been better bonded - but was also something around 45 years old and my expectations were not that high for it in the first place.

 

[iwire]

did not read through all the posts, but are you referring to the signs of arcing between locknuts and enclousures and the bolts between components shown in the OP?

Signs of?

Obviously it arced and spit sparks out.

If so there obviously was voltage drop across a connection - meaning the bonding was not as good as it could have been.

:slaphead:

 

[mbrooke]

Bonding conductive objects together will minimize arcing between those objects. Only in cases of extremely high voltage like a lightning event is where you may still have arcing between those objects even though they are bonded. 600 volt and below it it not happening.

It will do nothing to prevent arcing to objects that are intentionally at a different potential - like an exposed ungrounded conductor.

I agree, bonding brings objects to the same potential. And Id say that even with an ungrounded conductor, bonded objects will remain at the same potential and trip a breaker where a low impedance path back to the source exists through the bonding.

However, when you have a typical home with multiple sections of duct work joined together and going through dampers, do you bond each section? Every connection point adds impedance, so to be truly safe you would have to bond each section.

 

[MD84]

Regarding kwired and iwire comments above. Kwired is saying properly bonded objects will not arc when nominal voltage is <600v.they can arc even when bonded at voltages >600v.

This is my interpretation anyway. Just making sure there is not a misunderstanding there.

 

[iwire]

Regarding kwired and iwire comments above. Kwired is saying properly bonded objects will not arc when nominal voltage is <600v.they can arc even when bonded at voltages >600v.

This is my interpretation anyway. Just making sure there is not a misunderstanding there.

And my point is simply this.

We bond around service raceways and concentric KOs to prevent a more spectacular arc from happening than the ones shown in my pictures when there is a ground fault.

Even below 600 volts.

I am not saying in any way that there some sort of continuous arc, I am pointing out bonding is often done to prevent arcs during a ground fault.