mbrooke
Batteries Included
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- United States
- Occupation
- Technician
In light of a few GFCI threads on Mike Holt's, I thought Id post this Email I wrote up a while back and sent to a friend. I am not here to bash anyone on this forum, but over time I have realized that few know the reasoning (in depth) behind why GFCIs were mandated.
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Although to be fair most people-including many professionals- don't understand why GFCIs were mandated. GFCIs were not mandated because water somehow caused an explosive melt down- but rather between the 1900s through the 1950s people did not understand electrocution, or that 120 volts could kill you. I know of old text books which recommended electricians test for power by licking their fingers and then grabbing the wire in question; or openly saying anything under 150 volts- or even 250 volts could not kill you; or that an ungrounded delta was safe to work live. As a result metal cased tools/appliances were made without an EGC and codes/standards never bothered mandating it.
However after the 2nd world war with the rapid proliferation of urban electrification and electric appliances an increased number of deaths began being documented in areas where people were barefoot, wet, near metal, ect; like basements, garages, kitchens, outdoors, ect. Contrary to what we have been lead to believe, most of these users were not misusing their tools or appliances in any way (like using them in the rain, or swimming with them for example)- but rather being victim of an internal hot wire touching the metal case. Indoors on carpet/wood sub floor you could usually let go, but else where not so much.
The preferred solution would have been making sure every new appliance had a 3 prong plug and every home had 3 prong outlets, however this would not take care of the massive amount of existing appliances already in use, which back then lasted you a life time. As a result, the best solution to take care of both existing and new appliances- in addition to homes which would never see an EGC for 150 years but would see some new outlets- would be the creation of a 5ma current differential device in a receptacle form,(GFCI).
Code began mandating them in areas with the most electrocutions took place and going on from there in pecking order. Deaths began plummeting from faulty appliances and the occasional misuse.
Take in to perspective the UK. EGCs and 3 prong plugs were mandated in the UK since at least the 40s meaning post WWII everything with a metal case had an EGC- including outlets that would not take a plug missing its ground pin. This resulted in GFCIs (or RCDs) being delayed up until the late 90s. In fact RCDs were predominantly pushed not as much as to protect against electrocution at the time, but rather to protect against the increased fire hazard associated with 240 volts line to ground. IE, the UK got its AFCIs. :thumbsup:
That is however not to say GFCIs/RCDs do not have their place in the modern US and the modern UK, despite 3 prongs now found on nearly all none double insulated appliances. GFCIs and RCDs still protect against two less likely but still possible dangers:
1. The loss of the 3rd pin or EGC.
a. It happens. Ground pins breaker off, crap happens:
http://forums.mikeholt.com/showthread.php?t=172466
b. Unqualified personnel hooking up hot tubs and pool motors. Ground wire optional for none electricans
2. Damaged cords. This can happen regardless of working EGC. Cord plugged in, hot wire insualtion damaged and exposed. Person picks up damged section and becomes energized. A GFCI in this case will be a life saver.
In the UK this is known as a "direct contact"
http://image.slidesharecdn.com/unive...?cb=1282450904
So pushing aside everything you know about GFCIs, they were simply- and still are- another type of EGC. They were created and mandated soley to address the issues asociated with missing EGCs. Not water or mositure.
..............................................................................................................................................
This helps back the above:
http://www.necconnect.org/resources/gfcis/
..................................................................................................................................
Although to be fair most people-including many professionals- don't understand why GFCIs were mandated. GFCIs were not mandated because water somehow caused an explosive melt down- but rather between the 1900s through the 1950s people did not understand electrocution, or that 120 volts could kill you. I know of old text books which recommended electricians test for power by licking their fingers and then grabbing the wire in question; or openly saying anything under 150 volts- or even 250 volts could not kill you; or that an ungrounded delta was safe to work live. As a result metal cased tools/appliances were made without an EGC and codes/standards never bothered mandating it.
However after the 2nd world war with the rapid proliferation of urban electrification and electric appliances an increased number of deaths began being documented in areas where people were barefoot, wet, near metal, ect; like basements, garages, kitchens, outdoors, ect. Contrary to what we have been lead to believe, most of these users were not misusing their tools or appliances in any way (like using them in the rain, or swimming with them for example)- but rather being victim of an internal hot wire touching the metal case. Indoors on carpet/wood sub floor you could usually let go, but else where not so much.
The preferred solution would have been making sure every new appliance had a 3 prong plug and every home had 3 prong outlets, however this would not take care of the massive amount of existing appliances already in use, which back then lasted you a life time. As a result, the best solution to take care of both existing and new appliances- in addition to homes which would never see an EGC for 150 years but would see some new outlets- would be the creation of a 5ma current differential device in a receptacle form,(GFCI).
Code began mandating them in areas with the most electrocutions took place and going on from there in pecking order. Deaths began plummeting from faulty appliances and the occasional misuse.
Take in to perspective the UK. EGCs and 3 prong plugs were mandated in the UK since at least the 40s meaning post WWII everything with a metal case had an EGC- including outlets that would not take a plug missing its ground pin. This resulted in GFCIs (or RCDs) being delayed up until the late 90s. In fact RCDs were predominantly pushed not as much as to protect against electrocution at the time, but rather to protect against the increased fire hazard associated with 240 volts line to ground. IE, the UK got its AFCIs. :thumbsup:
That is however not to say GFCIs/RCDs do not have their place in the modern US and the modern UK, despite 3 prongs now found on nearly all none double insulated appliances. GFCIs and RCDs still protect against two less likely but still possible dangers:
1. The loss of the 3rd pin or EGC.
a. It happens. Ground pins breaker off, crap happens:
http://forums.mikeholt.com/showthread.php?t=172466
b. Unqualified personnel hooking up hot tubs and pool motors. Ground wire optional for none electricans
2. Damaged cords. This can happen regardless of working EGC. Cord plugged in, hot wire insualtion damaged and exposed. Person picks up damged section and becomes energized. A GFCI in this case will be a life saver.
In the UK this is known as a "direct contact"
http://image.slidesharecdn.com/unive...?cb=1282450904
So pushing aside everything you know about GFCIs, they were simply- and still are- another type of EGC. They were created and mandated soley to address the issues asociated with missing EGCs. Not water or mositure.
..............................................................................................................................................
This helps back the above:
http://www.necconnect.org/resources/gfcis/
