Engineering question

Status
Not open for further replies.
H

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
Lets say I have installation and its fused disconnect. I understand breakers would require EGC. Can the fuses function and open without equipment grounding conductor in circuit or does it require equipment grounding conductor? Does anyone know? Whats the theory behind it engineering wise?
 
"I understand" makes me chuckle :)
As bwat notes they are both OCP devices and follow the same current flow rules.
 
augie47 said:
"I understand" makes me chuckle :)
As bwat notes they are both OCP devices and follow the same current flow rules.
Click to expand...

I have seen fuses without EGC. Such as in appliance inside that protect the wire, utility uses them all the time and they dont have EGC

Why would fuse even require EGC? They have wire that blows if enough current flows in one of the phase conductor anyways
 
As in your other thread, an EGC makes the breaker or fuse behave with a line-to-ground* fault like a line-to-neutral fault.


* By "ground", I mean bonded conductive surfaces and enclosures.
 
LarryFine said:
As in your other thread, an EGC makes the breaker or fuse behave with a line-to-ground* fault like a line-to-neutral fault.


* By "ground", I mean bonded conductive surfaces and enclosures.
Click to expand...

Lets say you have line to ground fault and their is no EGC. You dont think their would be fault currents flowing thru the line? Would not that current be enough to blow the fuse without EGC?
 
hhsting said:
Lets say you have line to ground fault and their is no EGC. You dont think their would be fault currents flowing thru the line? Would not that current be enough to blow the fuse without EGC?
Click to expand...
It depends. Even without a NEC approved EGC, there might be a low impedance path back to the source, through things like pipes, building steel, hvac ducts, etc.

Suggest you look over post #5 again and study those different scenarios. Draw it out, analyze the current flow....
 
hhsting said:
Lets say you have line to ground fault and their is no EGC. You dont think their would be fault currents flowing thru the line? Would not that current be enough to blow the fuse without EGC?
Click to expand...
By ground it seems you're referring to earth and with that being the case just figure out the impedance back to the source and use ohms law

Roger
 
electrofelon said:
It depends. Even without a NEC approved EGC, there might be a low impedance path back to the source, through things like pipes, building steel, hvac ducts, etc.

Suggest you look over post #5 again and study those different scenarios. Draw it out, analyze the current flow....
Click to expand...

That path could also be the neutral if its bonded to can or enclosure and no EGC
 
hhsting said:
I have seen fuses without EGC. Such as in appliance inside that protect the wire, utility uses them all the time and they dont have EGC

Why would fuse even require EGC? They have wire that blows if enough current flows in one of the phase conductor anyways
Click to expand...
??
not quite sure what your saying here..

you mean line fuses on distribution lines?
EGC??
Fuses won’t blow unless current is flowing. For current to flow there has to be a circuit.
For a fuse to blow or trip in needs another phase, or neutral, or earth return to complete the circuit.
EGC or not...
 
hhsting said:
That path could also be the neutral if its bonded to can or enclosure and no EGC
Click to expand...
That's true but the neutral is only bonded at the service (or SDS) so you are dependant on an EGC path for fuses and breakers.
 
Are you perhaps confusing an EGC (Equipment Grounding Conductor) with a GEC (Grounding Electrode Conductor)? An EGC is there (mostly) as a safety measure to ground the conductive parts of a piece of equipment so that you don’t become an easier path to ground if there is a problem. The GEC is there to purposely create a ground reference for a SOURCE like a transformer or generator so that a line to ground fault will allow enough current to flow that an OCPD like a fuse OR circuit breaker will clear the fault.
 
Jraef said:
Are you perhaps confusing an EGC (Equipment Grounding Conductor) with a GEC (Grounding Electrode Conductor)? An EGC is there (mostly) as a safety measure to ground the conductive parts of a piece of equipment so that you don’t become an easier path to ground if there is a problem. The GEC is there to purposely create a ground reference for a SOURCE like a transformer or generator so that a line to ground fault will allow enough current to flow that an OCPD like a fuse OR circuit breaker will clear the fault.
Click to expand...
Perhaps you mis-typed the part in red? A GEC is not to operate an OCPD to clear a fault.
 
Lets say their is fault line to ground, line to line fault current is going to flow thru the line fuse.


There cannot be fault current flow thru the fuse or the line if their is no closed circuit or effective ground fault path whether the effective ground fault current path is thru Not an EGC or thru EGC.

Can you still get electrocuted if their is no effective ground fault current path back to the source? You don’t have closed circuit. Can you? How can current flow thru line to fuse to person and go where there would be no path back?


So how can one get electrocuted if their is no EGC and their is fault? Their has to be closed circuit i.e effective ground fault current path somewhere and if that close circuit is not thru EGC then still line currents flow from line to fuse to person to the closed circuit. How can fuse not open?
 
Last edited:
hhsting said:
Lets say their is fault line to ground, line to line fault current is going to flow thru the line fuse.


There cannot be fault current flow thru the fuse or the line if their is no closed circuit or effective ground fault path whether the effective ground fault current path is thru Not an EGC or thru EGC.

Can you still get electrocuted if their is no effective ground fault current path back to the source? You don’t have closed circuit. Can you? How can current flow thru line to fuse to person and go where there would be no path back?


So how can one get electrocuted if their is no EGC and their is fault? Their has to be closed circuit i.e effective ground fault current path somewhere and if that close circuit is not thru EGC then still line currents flow from line to fuse to person to the closed circuit. How can fuse not open?
Click to expand...
Grounded system for example. Live conductor has failed and touching unbonded “floating”metallic appliance.

Human comes by barefoot on garage concrete floor and touches metallic appliance.

Current now flows through human through concrete/earth back to the grounded source.

Magnitude and severity of shock and current flow depending on many things such as, weather conditions (wet/dry), resistance of the human under those particular circumstances.
 
Status
Not open for further replies.
Top