GFCI and extension cords in temporary installation

M

marcosgue

Senior Member
Location
Tampa
Occupation
Electrician
The use of gfci devices during stages of construction is mandatory according to article 590 and I've seen the use of extension cord without the ground pin.
I think this is osha violation, but my point is if using gfci is enough to protect the personnel during the event of ground fault even though using this type of extension cord without ground pin?
 
The GFCI device will function properly to protect personel without the cord being connected to the EGC. Same thing would apply when using equipment that is equipped with a factory installed 2-wire power cord.
 
I'm agree. I think most of equipment with 2 wire power cord are rating double insulation and they don't need the use of egc, but in my opinion the use of gfci devices in temporary installation do not release the use of extension cord with egc. Is this correct?
 
marcosgue said:
I'm agree. I think most of equipment with 2 wire power cord are rating double insulation and they don't need the use of egc, but in my opinion the use of gfci devices in temporary installation do not release the use of extension cord with egc. Is this correct?
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Yes, the ground pin on the cord is required and if broken off (like many cords on construction sites) it should be disgarded. Good news is that the GFCI protection upstream from the broken cord will still function.
 
The presence of the EGC will change the probabilities around the GFCI's function.

GFCIs specifically detect detect current that flows out of the circuit, say through a person to ground. And this function will be completely intact even without the EGC in the cord.

But if a cord or tool gets damaged, and there is an intact EGC, then the leakage current can flow to ground via the EGC and trip the GFCI before current flows through the person.

Also if the EGC is not present, then you have a greater chance of a hot to neutral shock, where current flows from hot, through the person, to neutral, and a GFCI cannot detect this sort of shock.

-Jonathan
 
winnie said:
Also if the EGC is not present, then you have a greater chance of a hot to neutral shock, where current flows from hot, through the person, to neutral, and a GFCI cannot detect this sort of shock.
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Well in this scenario you do not have a ground fault and there isn't path back to the source and the ocpd will remain close. Could you clarify some common hot to neutral shock where the gfci can't detect this electrical shock?
 
marcosgue said:
Well in this scenario you do not have a ground fault and there isn't path back to the source and the ocpd will remain close. Could you clarify some common hot to neutral shock where the gfci can't detect this electrical shock?
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Didn't you ever make one of those electric hot dog cookers in shop class?

 
winnie said:
The presence of the EGC will change the probabilities around the GFCI's function.

GFCIs specifically detect detect current that flows out of the circuit, say through a person to ground. And this function will be completely intact even without the EGC in the cord.

But if a cord or tool gets damaged, and there is an intact EGC, then the leakage current can flow to ground via the EGC and trip the GFCI before current flows through the person.

Also if the EGC is not present, then you have a greater chance of a hot to neutral shock, where current flows from hot, through the person, to neutral, and a GFCI cannot detect this sort of shock.

-Jonathan
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Thanks Jonathan, Can you point me in the right direction about another scenario when the gfci do not respond beside the hot-person-neutral?
 
marcosgue said:
Thanks Jonathan, Can you point me in the right direction about another scenario when the gfci do not respond beside the hot-person-neutral?
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Not really. If you have leakage to ground the GFCI will respond. And in most situations, if a person touches hot they will also touch something else that will be in contact with ground, and you will have sufficient ground leakage to trip the GFCI.

You'd need a particular bad set of circumstances (dunno, tool falling into a bucket of water on a scaffold? plastic bathtub with plastic pipes?) that is insulated from ground so a person comes in contact with hot and neutral without contact to ground.

My only claim is that having the EGC makes this already unlikely situation even less likely.

The 'hot dog cooker' is a perfect example of what the GFCI can't detect: if you have contact with hot and neutral, but isolated from ground, the GFCI just sees normal load current. It has no smarts to determine that the load current is flowing through some meat. In fact I've used one of those presto cookers on a GFCI outlet.
 
winnie said:
Not really. If you have leakage to ground the GFCI will respond. And in most situations, if a person touches hot they will also touch something else that will be in contact with ground, and you will have sufficient ground leakage to trip the GFCI.

You'd need a particular bad set of circumstances (dunno, tool falling into a bucket of water on a scaffold? plastic bathtub with plastic pipes?) that is insulated from ground so a person comes in contact with hot and neutral without contact to ground.

My only claim is that having the EGC makes this already unlikely situation even less likely.

The 'hot dog cooker' is a perfect example of what the GFCI can't detect: if you have contact with hot and neutral, but isolated from ground, the GFCI just sees normal load current. It has no smarts to determine that the load current is flowing through some meat. In fact I've used one of those presto cookers on a GFCI outlet.
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Thanks for your response and clarification
 
GFCI work by only measuring the unbalance between the energized conductor and the grounded conductor. In other words on a 120 Volt circuit if either of these two conductors draws more then 4 to 6 milliamps ( 0.48 to 0.072 VA ) then the other conductor GFCI will trip believe in under 1/30th of a second. On old GFCI receptacles black & white wire went thru a torrid coil to pick up any unbalance. Most shocks occur between the energized ( black wire ) and the ground. The ground pin is the most important point of connection. First made, last to break for a reason. You would never want to be holding a drill with a metal housing where the ground pin was broken. Extension cords & all tools & equipment with a broken ground pin must not be used until repaired. For power tools we would measure the resistance from ground pin to tool body then megger it. On equipment usually only measured ground pin to equipment frame resistance.
.
 
marcosgue said:
Thanks Jonathan, Can you point me in the right direction about another scenario when the gfci do not respond beside the hot-person-neutral?
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GFCI essentially monitors hot to neutral current balance, it has to be off by more than 4-6 mA to initiate trip. If all current is going from hot to neutral it will never initiate trip, it has no idea where current is actually going it just sees what current goes out on one protected conductor is coming back on the other protected conductor.

Back to the missing ground pin on a cord, this likely somewhat one reason long ago they started requiring GFCI protection on receptacles for temporary use. It offers some shock protection where the missing EGC may not have had the opportunity to help clear some fault but was not intended to be a reason to not still have EGC in the cords used. At a construction site you may have several sub contractors doing various parts of the construction and who knows what condition their cords may be in. Larger projects maybe the owner or GC is more observant of OSHA compliance by the sub contractors, if not they get by if nobody is observing such things. I put in temp services on my projects which all are rather small projects, and may not be back to do any other work for some time. I have no idea what some guys might plug in or what condition it is in, GFCI still gives pretty good protection, if they have rigged up stuff with ground faults or just simply in poor condition, how can I control that unless I am there to watch every move they make with what they plug in? If they tamper with my GFCI as some work around and then get injured or killed, I'm probably in an investigation at very least, but hopefully the EI will be able to say it passed inspection and in order to do that it had GFCI protection. A good start on my side, still may be more difficult to prove someone else tampered with it though.
 
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