Short vs dead short vs ground fault vs short circuit

[teufelhounden91]

I have another spine tingling Yum Yum discussion to get into. Are you ready?

In the industry we often hear of shorts versus dead shorts. In the codebook it only ever talks about short circuits and ground faults. I don't believe it ever mentions the term dead short or deadbolt short, or even short for that matter. Only short circuits and ground faults.

My quandary then is on terminology and straightening out with the terminology means. Shouldn't we be using the terminology short circuit or ground fault to describe what is going on in the circuit? Not short and dead short. Correct me if I'm wrong but if a hot touches a neutral somewhere before the load this is a short circuit. Regardless if there is an arc or some other huge resistance/voltage drop and it takes awhile to trip the OCPD (short) or if it is directly touching and the OCPD trips instantly (dead short), it is still just a plain old short circuit. A ground fault on the other hand is when a hot touches ground regardless if there is an arc or it is directly touching.

My boss says a powerline laying on the ground is "a short, not a dead short." I disagree, I believe this is a ground fault. However technically he is not wrong because current is leaving source traveling through ground and getting back to the source neutral. There's no load in the circuit unless you view a swing set and chain link fence on fire as resistors. So if we take the swing set and fence out of it, this becomes a dead short?

https://www.youtube.com/watch?v=28Xq3JulV1o

And while we're on it, what about when a hot touches another hot? Is that still considered a short circuit?


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[teufelhounden91]

Short vs dead short vs ground fault vs short circuit

Also then, how much resistance must happen in a circuit before we start calling it a dead short versus short? I believe the terminology we are using for a dead short means there's zero resistance. Technically the entirety of planet earth has zero homes so there would be no resistance there as well… technically. But again, this is a ground fault...which is still a short circuit back to source. Even if a hot wires touching a neutral wire there is a resistance in that neutral wire back to source because of the length of the wire. So I still don't see a dead short as being a valid way to explain short-circuit versus short. To me it's all the same. Although knowing what we call a dead short versus knowing what we call a short helps us troubleshoot and find a problem better.


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[zbang]

It's a sunny afternoon and I should be out cleaning the gutters, so I'll take a stab at this-

"short circuit" - an unintended connection between two circuit conductors that "shortens" the electrical path or connects to something that it shouldn't. In some cases, this is not necessarily a bad thing (constant-current airport runway lights, for instance).

"Dead short" - usually means a very low resistance (or "high quality") short, can probably carry enough current to trip the OCPD.
I don't see any reason to differentiate between these; whether it's 0.0004 ohm or 0.1 ohm doesn't really matter much if it shouldn't be there at all.

"bolted short" - a connection so good that is effectively bolted together so it'll carry as much fault current as available. Term is only useful for fault current analysis.


"ground fault" - an unintended path between a circuit conductor and the EGC or GES. Usually causes current to flow in the EGC. An unintended connection between groundED and groundING conductors is still a "ground fault".

"powerline laying on the ground" - is just that. If it's insulated then nothing happens; if un- or badly insulated (or higher voltage) it can cause current to flow from that conductor through the earth and into the GES of whatever's supplying the conductor. I wouldn't call this a "ground fault" though.

"arcing fault" - a fault that forms an arc , usually higher resistance than zero but produces lots of heat.

See also:
http://forums.mikeholt.com/showthread.php?t=168701&p=1640283#post1640283
https://en.wikipedia.org/wiki/Fault_(power_engineering)

(Back to the gutters, sigh.)

 

[mbrooke]

"arcing fault" - a fault that forms an arc , usually higher resistance than zero but produces lots of heat.

Wouldn't this be a simple short circuit that sputters a bit before tripping the breaker?

 

[big john]

You have overloads, short-circuits, and opens. All other faults are subsets of each of these.

A ground-fault is just a type of short circuit that descrubes the return path.

I consider dead-short and bolted fault to be functionally equivalent, but "bolted fault"has a bit more technical legitimacy because it describes a condition where there is basically no imoedance between the phase and return conductor.

As far as short versus dead-short, I'd say a dead-short would always cause instantaneous protection to operate, wheras a simple short would go out on short-time pickup or even long-time depending on the impedance.

 

[ActionDave]

My boss says a powerline laying on the ground is "a short, not a dead short." I disagree, I believe this is a ground fault. However technically he is not wrong because current is leaving source traveling through ground and getting back to the source neutral. There's no load in the circuit unless you view a swing set and chain link fence on fire as resistors. So if we take the swing set and fence out of it, this becomes a dead short?

Fun conversation to have when you're putting tools back in the truck, but nothing worth arguing with the man about.

And while we're on it, what about when a hot touches another hot? Is that still considered a short circuit?


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I would say yes. I would use the term phase to phase fault for clarity.

 

[teufelhounden91]

FYI - this is what Google defines it as...

In an electric power system, a fault or fault current is any abnormal electric current. For example, a short circuit is a fault in which current bypasses the normal load. An open-circuit fault occurs if a circuit is interrupted by some failure.


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[teufelhounden91]

Fun conversation to have when you're putting tools back in the truck, but nothing worth arguing with the man about.
I would say yes. I would use the term phase to phase fault for clarity.

I'm fortunate to have a boss who cares enough to have these debates. A lot of masters out there aren't open to debates on how they understand theory.

I'm at a point in my experience that I'm realizing there are a lot of misnomers about theory so I want to clarify my understanding to be as correct as possible for when it is my time to teach others about this stuff.


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[ActionDave]

......I'm at a point in my experience that I'm realizing there are a lot of misnomers about theory so I want to clarify my understanding to be as correct as possible for when it is my time to teach others about this stuff.


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Good for you.

There are a lot of electricians out there that have some pretty silly ideas about electricity.

 

[jaggedben]

A ground-fault is just a type of short circuit that describes the return path.

I don't agree with that at all.

A short circuit is a connection between circuit conductors that allows current to flow without passing through the intended load. It's not a short circuit if current doesn't flow.

A ground fault is a connection between the circuit conductors and ground. A ground fault is still a ground fault, in my opinion, even if current doesn't flow because the grounded parts aren't bonded to provide a path back to the source, or because the system is ungrounded.

A ground-fault is only a short circuit if it occurs between an ungrounded conductor and ground on a grounded system. If the grounded conductor is faulted to ground, potentially causing current to flow on grounded parts between the fault and the point where the conductor is grounded, that is a ground fault but it is not a short circuit. In an ungrounded circuit where one conductor faults to ground, that potentially energizes the grounded parts but does not cause current to flow through them until another fault occurs on another conductor. The latter would typically need to be detected by some type of ground-fault protection device in order to prevent associated dangers or to alert people to the fault.

If all ground-faults were short circuits then we wouldn't need GFCI outlets, GFDI on PV systems, ground-fault protection devices on large services, etc. etc.

 

[GoldDigger]

I would also make a distinction between a ground fault, which may carry fault current and an unintended ground in an ungrounded circuit, which will not carry current if it is the first one.
So an ungrounded system is required to have a ground detector, not a ground fault detector.

 

[big john]

Fair point, I didn't consider ungrounded systems when I wrote that

If all ground-faults were short circuits then we wouldn't need GFCI outlets, GFDI on PV systems, ground-fault protection devices on large services, etc. etc.

But the vast majority of ground faults are short circuits. Those devices exist primarily because by monitoring the fault path for the presence of current that shouldn't exist, we can clear the fault at much lower energies than if we had to rely on far less sensitive "conventional" short circuit protection that is looking for a much larger fault current.

Just thinking about it: What do we call the wiring fault were multiple neutrals make unintended contact?

 

[ActionDave]

.....Just thinking about it: What do we call the wiring fault were multiple neutrals make unintended contact?

Undesirable, unbalanced, neutral current on a parallel, insulated, conductor....?

I call it a scab neutral or bootleg neutral. Not very scientific but I'm comfortable with it.

 

[jaggedben]

But the vast majority of ground faults are short circuits.

How do you know that? There are probably millions of neutral-to-ground faults out there on old house wiring that are not being detected because no GFCI is installed on that circuit. It stands to reason that half of the random ground faults on 120V 2-wire circuits would be neutral-to-ground faults, but if no GFCI is installed then typically no one knows. Heck, I've encountered enough DYIer work in which it was simply connected that way in the first place.

Also, in my work (PV systems), a high-resistance ground-fault on either DC conductor of the system results in parallel current on the EGC (and gets detected and shutdown by the GFDI). It'd better not be a short circuit on the DC side or you have an arc that no breaker or fuse will interrupt.

Those devices exist primarily because by monitoring the fault path for the presence of current that shouldn't exist, we can clear the fault at much lower energies than if we had to rely on far less sensitive "conventional" short circuit protection that is looking for a much larger fault current.

Yes, they still monitor for ground-faults though.
Short circuit protection is not ground fault protection, or vice versa. They really only overlap on a hot-to-ground fault.

Just thinking about it: What do we call the wiring fault were multiple neutrals make unintended contact?

I'd call it a neutral-to-neutral fault. Same question can be asked about line-to-line faults of the same leg.

 

[big john]

Shot circuit protection is not ground fault protection, or vice versa.

I never said they weren't different forms of protection, I said that many ground faults are short circuits and the presence or absence of GFP doesn't change that.

 

[JFletcher]

It's a sunny afternoon and I should be out cleaning the gutters, so I'll take a stab at this-

"short circuit" - an unintended connection between two circuit conductors that "shortens" the electrical path or connects to something that it shouldn't. In some cases, this is not necessarily a bad thing (constant-current airport runway lights, for instance).

"Dead short" - usually means a very low resistance (or "high quality") short, can probably carry enough current to trip the OCPD.
I don't see any reason to differentiate between these; whether it's 0.0004 ohm or 0.1 ohm doesn't really matter much if it shouldn't be there at all.

"bolted short" - a connection so good that is effectively bolted together so it'll carry as much fault current as available. Term is only useful for fault current analysis.


"ground fault" - an unintended path between a circuit conductor and the EGC or GES. Usually causes current to flow in the EGC. An unintended connection between groundED and groundING conductors is still a "ground fault".

"powerline laying on the ground" - is just that. If it's insulated then nothing happens; if un- or badly insulated (or higher voltage) it can cause current to flow from that conductor through the earth and into the GES of whatever's supplying the conductor. I wouldn't call this a "ground fault" though.

"arcing fault" - a fault that forms an arc , usually higher resistance than zero but produces lots of heat.

See also:
http://forums.mikeholt.com/showthread.php?t=168701&p=1640283#post1640283
https://en.wikipedia.org/wiki/Fault_(power_engineering)

(Back to the gutters, sigh.)

Good explanations. I've typically thought of a "short circuit" as two things: 1) a circuit that is unintentionally interrupted or incomplete via a broken or loose conductor... literally "short of a complete circuit". 2) a temporary shorting of hot>neutral or hot>ground, like when a loose receptacle touches the inside of its metal box when something is plugged in. Dead short, to me, is when there is something more substantial, like a screw/nail thru a wire, screwing a tie-bar tube down onto the hot wire(s), etc, where it will insta-trip the breaker or burn thru the faulty wiring.

 

[kwired]

Just thinking about it: What do we call the wiring fault were multiple neutrals make unintended contact?

Well GFCI's and AFCI's with GFP seem to think they are ground faults and they trip

Good explanations. I've typically thought of a "short circuit" as two things: 1) a circuit that is unintentionally interrupted or incomplete via a broken or loose conductor... literally "short of a complete circuit". 2) a temporary shorting of hot>neutral or hot>ground, like when a loose receptacle touches the inside of its metal box when something is plugged in. Dead short, to me, is when there is something more substantial, like a screw/nail thru a wire, screwing a tie-bar tube down onto the hot wire(s), etc, where it will insta-trip the breaker or burn thru the faulty wiring.

Your condition #1 most would call an open circuit.


I always figure a short circuit is a condition where the only impedance in the circuit is the source impedance plus conductor impedance - no load impedance to put any limits on current flow. A dead short or bolted short - are just ways of indicating that there will be minimal contact impedance at the fault point.

Of course I have many customers that claim "there must be a short in it" whenever something isn't working correctly regardless of what the symptoms may be.

 

[jaggedben]

Well GFCI's and AFCI's with GFP seem to think they are ground faults and they trip

.

Yes, well they certainly can't tell the difference, and from a safety standpoint it makes sense. (Supposed a 100A neutral faults to a 15A neutral. The latter could be overloaded.)