Grounding of a sink basin

Status
Not open for further replies.
Dennis Alwon said:
Larry, you will always receive a shock on a gfci but hopefully it will trip before it kills you. On an ungrounded system it can protect you esp. if you are grounded by something else.


A gfci in an ungrounded circuit will not trip with a tester but it can protect a person.
Click to expand...

See previous response.
 
LarryFine said:
A GFCI device is useless on an ungrounded system, and will not function. A person must receive a shock for one to trip.
Click to expand...

True but the only 120V ungrounded system we would use would be a 517.160 Isolated Power System which by it's nature eliminates the need for a GFCI.

Roger
 
There's almost always a specific exception to a generalization, but you're making my point in your example: a GFCI device requires that one circuit conductor be intentionally grounded to function.

The "need" for a GFCI is eliminated because it would not react to a contact by personnel. Like an ungrounded power source, two accidental contacts would have to occur for there to be an issue.
 
LarryFine said:
There's almost always a specific exception to a generalization, but you're making my point in your example:
Click to expand...
And I meant to.
​
LarryFine said:
a GFCI device requires that one circuit conductor be intentionally grounded to function.
Click to expand...
Well it doesn't actually have to be grounded, it can be any third current path.

​
LarryFine said:
The "need" for a GFCI is eliminated because it would not react to a contact by personnel. Like an ungrounded power source, two accidental contacts would have to occur for there to be an issue.
Click to expand...
Agreed.

BTW, don't think I'm trying to correct you Larry, I know you know how it works. :thumbsup:

Roger
 
A large ungrounded system can have enough capacitance to ground to provide a fatal shock. A GFCI on such a system should work.
 
don_resqcapt19 said:
A large ungrounded system can have enough capacitance to ground to provide a fatal shock. A GFCI on such a system should work.
Click to expand...

Again, we're talking theoretical, which means generalizing. I did not mean to imply that a hazard can never exist on an ungrounded system. Yes, if a current to earth can be created, a shock can occur.

However, for a GFCI device to trip, there would need to be a sufficient difference of current between the lines involved and the earth created by the accidental contact, requiring one line to be better coupled to earth than the others.

If all phases have the same coupling to earth, which is necessary to avoid nuisance tripping, no shock current would flow outside the current sensor. Any current to earth through a person would travel through all lines equally.
 
Last edited:
K8MHZ said:
Are we maybe confusing an ungrounded system with a 2 wire receptacle? Or is it just me?
Click to expand...

It's just you. :p So far, I've only been discussing the former.

Still, the same holds true for the latter: supply must have a grounded conductor.
 
LarryFine said:
However, for a GFCI device to trip, there would need to be a sufficient difference of current between the lines involved and the earth created by the accidental contact, requiring one line to be better coupled to earth than the others.

If all phases have the same coupling to earth, which is necessary to avoid nuisance tripping, no shock current would flow outside the current sensor. Any current to earth through a person would travel through all lines equally.
Click to expand...

Thinking about it, a shock current from an ungrounded system as a whole could trip a GFCI as long as the supply (line side) conductors is well-coupled to earth.

However, wouldn't any difference between capacitive coupling on the line and load sides of the GFCI be seen as leakage current and cause nuisance tripping?


Thinking about it even more, wouldn't any capacitive current be seen as leakage current?
 
LarryFine said:
Thinking about it even more, wouldn't any capacitive current be seen as leakage current?
Click to expand...

Yes it is.
That is partly why you see main feeder GF protection set in Amps, while mA levels are typically only used for 'people' protection or for small branches.
 
LarryFine said:
There's almost always a specific exception to a generalization, but you're making my point in your example: a GFCI device requires that one circuit conductor be intentionally grounded to function.
Click to expand...

This is not _quite_ true, but close enough for 120V systems. For a GFCI to function current needs to flow in an imbalanced fashion on the sensed conductors. I've seen residual current detection trip because of capacitive coupled currents, using impedance grounding. I presume that if you had a large enough 120V ungrounded system, the capacitive charging current could be large enough to present a shock hazard and a GFCI would detect the residual current from contact.

Back to the original 'bucket' scenario. If a hair dryer drops into an insulated bucket of normal tap water, some current will flow through the water from one AC terminal to the other. If a person were to somehow interpose themselves in this current path, they would feel a shock and the GFCI would not detect it. In the case of the hairdryer these terminals are very close together, and it would be difficult to get a finger close enough to intercept appreciable current. A grounded drain would actually _increase_ the hazard, because now there is a path for current to flow through a larger volume of water...though it would increase the chance of the GFCI tripping.

Because tap water is not a very good conductor, the current might be limited to the point that the GFCI doesn't trip.

-Jon
 
GoldDigger said:
And if for some reason there is a voltage gradient in the water (more likely with a pool or tub than a sink) putting two hands in the water can cause a serious shock, but not a GFCI trip.

Sent from my XT1585 using Tapatalk
Click to expand...

keeping in mind swimming pool water is required to have a ground reference by the required bond to a branch circuit equipment ground
not that i think every plastic sink should have the same
 
Status
Not open for further replies.
Top