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-   -   GFCI on 2 wire systems (https://www.nachi.org/forum/f19/gfci-2-wire-systems-44946/)

thowell 11/9/09 5:39 PM

GFCI on 2 wire systems
 
Looking for some help on clarification. My understanding is a GFCI will prevent elec shock in a 2 wire system. I have seen them in bathrooms and kitchens. The part that trips me up is, a 2 wire system is still not grounded. That should be a safety concern, but not unsafe with a GFCI installed. (correct?)
Second part of question, in a home with 2 wire outlets why couldn't a person put GFCIs in all the locations? Like the living room for example. I was ask this question the other day. The occupants would be protected, correct?
Thanks folks.

mlarson 11/9/09 6:17 PM

Re: GFCI on 2 wire systems
 
He can.

cevans 11/9/09 6:31 PM

Re: GFCI on 2 wire systems
 
I wouldn't say they prevent, but rather that they reduce the potential for someone to get shocked. People can always find ways to electrocute themselves.

Many older homes' electrical systems are not grounded, however, short of fully rewiring the house, GFCI can be an effective way of providing improved protection against shocks and maintain "code" compliance with three prong outlets (use the "no equipment ground" stickers).

As Mike said so succinctly, he can install them on most circuits for enhanced protection. Don't need to install on every outlet, just lead outlet on each circuit. Change the other outlets to three prog, install stickers and he's good to go.

Of course, I would advise him to use a qualified, licensed electrician to do the work vs. Bubba that handy guy.

mlarson 11/9/09 6:34 PM

Re: GFCI on 2 wire systems
 
Quote:

Originally Posted by cevans (Post 580683)
I wouldn't say they prevent, but rather that they reduce the potential for someone to get shocked. People can always find ways to electrocute themselves.

They prevent a fault current in excess of 5 mA from going through a person.

That is sufficient to prevent electrocution in most of the population.

Those at risk are ones that have a pathway via inter-venous lines or a compromise layer of skin.

GFCI outlets in non three wire systems need to be labeled appropriately.

belliott 11/9/09 6:36 PM

Re: GFCI on 2 wire systems
 
Tim a grounded system is to protect the equipt and not you.

Not sure I would want a bunch of GFCI outlets with stickers everywhere that no one will pay attention to when they plug things in.

If this place has real conduit, a switch to grounded outlets is easy.

mlarson 11/9/09 6:37 PM

Re: GFCI on 2 wire systems
 
Conduit in Iowa?

Come on Bob get real.

belliott 11/9/09 6:39 PM

Re: GFCI on 2 wire systems
 
Quote:

Originally Posted by mlarson (Post 580695)
Conduit in Iowa?

Come on Bob get real.

Do you assume Mike? or have you been there.
I have not.:)

For all I know they are using Tesla coils to beam it all through space.

mlarson 11/9/09 6:41 PM

Re: GFCI on 2 wire systems
 
Quote:

Originally Posted by belliott (Post 580696)
Do you assume Mike? or have you been there.
I have not.:)

For all I know they are using Tesla coils to beam it all through space.

Got relies their Bob.

mgratton 11/9/09 6:46 PM

Re: GFCI on 2 wire systems
 
Quote:

Originally Posted by mlarson (Post 580691)
They prevent a fault current in excess of 5 mA from going through a person.

That is sufficient to prevent electrocution in most of the population.

Those at risk are ones that have a pathway via inter-venous lines or a compromise layer of skin.

GFCI outlets in non three wire systems need to be labeled appropriately.

True, but GFCI's are not going to protect the 60" Plasma, microwave oven, computer, fridge,...

mlarson 11/9/09 7:16 PM

Re: GFCI on 2 wire systems
 
Quote:

Originally Posted by mgratton (Post 580700)
True, but GFCI's are not going to protect the 60" Plasma, microwave oven, computer, fridge,...

Never said they were for equipment protection.

Follow the mfgs. instructions for appliances.

rbrady 11/9/09 7:49 PM

Re: GFCI on 2 wire systems
 
I'm sorry, but it really bugs me when people state that GFCI will reduce the risk of (or worse yet - prevent) electrical shocks.

GFCI PROTECTION DOES NOT REDUCE THE RISK OF ELECTRICAL SHOCKS!!!!!

They reduce the risk of death by electrocution, but have absolutly no affect on electrical shocks in general. A 5ma shock is still VERY painful (from what I have read).

belliott 11/9/09 7:52 PM

Re: GFCI on 2 wire systems
 
Not really

Now 220 kinda bothers you.
110 just tickles.

rbrady 11/9/09 7:56 PM

Re: GFCI on 2 wire systems
 
Quote:

Originally Posted by belliott (Post 580742)
Not really

Now 220 kinda bothers you.
110 just tickles.

Have you ever tripped a GFCI with your body (across two fingers doesn't count)? I don't recommend trying it, but would be interested in hearing if anyone has.

From what I have heard, at least 220 will knock you off, unlike 110 which just makes your muscles hold tighter.

belliott 11/9/09 8:11 PM

Re: GFCI on 2 wire systems
 
I have been shocked many times ,so I do not count as I may have built an immunity.

In used to experiment from the time I was a kid.

None the less I would not depend on any devise to always do its job.(haven't we all inspected bad GFCI)?

mlarson 11/9/09 8:21 PM

Re: GFCI on 2 wire systems
 
Resisting going there. ;-)


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