GFCI protection with modern PVC plumbing

[woody75]

In a modern bathroom with PVC plumbing, how much protection does GFCI protected circuits provide?

Example: Lets say you're in the bathtub and a plugged-in hair dryer falls into the tub. In a modern residential house and bathroom that uses all plastic piping, where would the power drain to for the GFCI to trip? Even if you are sitting in a half-tub of water, the drain plumbing and water plumbing attached to the fiberglass tub wouldn't provide a path to ground... Light fixtures in shower stalls, small appliances on the sink, all sources of live power that should be GFCI protected, but without a path to ground while sitting in the water, would the GFCI function as intended? Is there a sufficient enough ground in plastic plumbing to trip a GFCI?

 

[Jraef]

You seem to have an incorrect understanding of the dangers of electric shock and electrocution. It’s not only about the pipes being metal.

At a very basic level, even in your “all plastic pipe” scenario, at SOME POINT SOMEWHERE the water is making contact with a grounded metal surface. Doest really matter how far up or down the line it is.

But besides that, when current flows, contrary to popular belief it is not flowing only to the “path of least resistance”, it flows in all paths simultaneously, just in different amounts. So when you “drop the toaster in the bathtub”, it has a Hot and a Neutral connection, so the water in the tub will carry current across that connection, it doesn’t need for the pipes to be grounded. If you are in the tub, you are part of that circuit too.

 

[woody75]

You seem to have an incorrect understanding of the dangers of electric shock and electrocution. It’s not only about the pipes being metal.

At a very basic level, even in your “all plastic pipe” scenario, at SOME POINT SOMEWHERE the water is making contact with a grounded metal surface. Doest really matter how far up or down the line it is.

But besides that, when current flows, contrary to popular belief it is not flowing only to the “path of least resistance”, it flows in all paths simultaneously, just in different amounts. So when you “drop the toaster in the bathtub”, it has a Hot and a Neutral connection, so the water in the tub will carry current across that connection, it doesn’t need for the pipes to be grounded. If you are in the tub, you are part of that circuit too.

I am aware of this, which is why I never mentioned electrocution or even shock.

I am asking about whether or not a GFCI would trip if a device was thrown into a tub of water, no water flow, just standing water in a non-conductive tub connected to non-conductive pipes, with no good path to ground.

 

[retirede]

I am aware of this, which is why I never mentioned electrocution or even shock.

I am asking about whether or not a GFCI would trip if a device was thrown into a tub of water, no water flow, just standing water in a non-conductive tub connected to non-conductive pipes, with no good path to ground.

Define “no good path to ground.”

 

[jim dungar]

with no good path to ground.

Actually a GFCI does not look for current flowing on grounding conductors. A GFCI looks at the current between the hot and the neutral and trips if there is more than a 5mA difference.

So in your example of a totally isolated body of water that has a toaster dropped into it, a GFCI would not trip until another current path was established even if that current path did not involve "ground". This is why bathroom devices, like hair dryers, have a Leakage Detector incorporated in their supply plug.

 

[ptonsparky]

If my brother in law was alive you could ask him about an energized cu water line, a old cast iron enameled tub and a bit of soapy water flowing through a plastic sewer line to the old black iron line. The tub faucets were in the wall above the tub. He lived through it but it was a long time before he used that tub again.

 

[steve66]

In a modern bathroom with PVC plumbing, how much protection does GFCI protected circuits provide?

Example: Lets say you're in the bathtub and a plugged-in hair dryer falls into the tub. In a modern residential house and bathroom that uses all plastic piping, where would the power drain to for the GFCI to trip? Even if you are sitting in a half-tub of water, the drain plumbing and water plumbing attached to the fiberglass tub wouldn't provide a path to ground... Light fixtures in shower stalls, small appliances on the sink, all sources of live power that should be GFCI protected, but without a path to ground while sitting in the water, would the GFCI function as intended? Is there a sufficient enough ground in plastic plumbing to trip a GFCI?

I think its a good question. If a bathtub full of water is truly isolated from any ground (plastic tub and plastic piping), and an energized hair dryer is dropped in, the GFCI would not do anything.

Even if someone was in said tub, and was getting shocked by current flowing from the hot conductor, through the water, through the person, and through the water back to the neutral wire, the GFCI would do absolutely nothing. (Edit: Not going to try and calculate how much current might actually be available to shock someone like this, or if it would be enough to be dangerous, or even above the point of perception. Too many variables. )

That's why we bond the pool water in swimming pools.

Still, having a GFCI will always be safer than no GFCI because there are so many ways (other than plumbing) to get a shock by coming into contact with a hot conductor and a ground.

Last thought - maybe hair dryers should be required to have a grounded plug, and a ground connection to facilitate GFCI tripping when they are dropped in a sink or tub??

 

[woody75]

Define “no good path to ground.”

good enough to trip a GFCI circuit.

This is all just a hypothetical situation. I'm a commercial/industrial electrician, so it was just a topic that came up that made us go "hmmm..." We know how GFCIs work, we know this is an unlikely situation anyway, and in our industrial work space we'd never come across it. It was a general curiosity... Would a GFCI trip in a residential environment if the plumbing fixtures are not effectively grounded (assuming the water isn't flowing to provide a path to earth.) Like standing in a filled tub, water is turned off, and someone grabbed a suspended (chandelier style) light fixture that a homeowner decided to hang in their bath stall, but all the plumbing is in non-conductive plastic piping..

No flowing water... no grounded plumbing fixtures... just a dude in a tub coming in contact with a electrical device that was protected by a GFCI.

 

[retirede]

good enough to trip a GFCI circuit.

This is all just a hypothetical situation. I'm a commercial/industrial electrician, so it was just a topic that came up that made us go "hmmm..." We know how GFCIs work, we know this is an unlikely situation anyway, and in our industrial work space we'd never come across it. It was a general curiosity... Would a GFCI trip in a residential environment if the plumbing fixtures are not effectively grounded (assuming the water isn't flowing to provide a path to earth.) Like standing in a filled tub, water is turned off, and someone grabbed a suspended (chandelier style) light fixture that a homeowner decided to hang in their bath stall, but all the plumbing is in non-conductive plastic piping..

No flowing water... no grounded plumbing fixtures... just a dude in a tub coming in contact with an electrical device that was protected by a GFCI.

In the exact scenario you describe, there is no hazard. Exposed parts of the fixture are not energized unless there is an internal fault. If there is an internal fault, there is no path to ground through his body.

 

[hillbilly1]

No current flow = no shock
Current flow outside the neutral/hot= trip

 

[Seven-Delta-FortyOne]

You are correct in that a GFCI device does not protect against a person putting themselves in series with the circuit.

Since the GFCI uses a CT to measure differential potential between hot and neutral, if you are in series with the circuit, you could have 100% of the current flow through your body and kill you, and the GFCI would never trip.

 

[VirutalElectrician]

There was a similar discussion like this here a couple weeks ago. I posted a video of one of these old hotdog cookers as a great example of electrocuting flesh where a GFCI would not provide any protection.

https://www.facebook.com/video.php?v=982946219760462

 

[Jraef]

This is the exact scenario you describe.


This image has been floating around for years and was done specifically to demonstrate this issue. The problem is, it was a CAREFULLY staged setup.

 

[kwired]

If my brother in law was alive you could ask him about an energized cu water line, a old cast iron enameled tub and a bit of soapy water flowing through a plastic sewer line to the old black iron line. The tub faucets were in the wall above the tub. He lived through it but it was a long time before he used that tub again.

I had client that wanted me to check out tub/shower. She said she could feel something strange in her legs when using it, not distinct enough that she called it a shock but knew something wasn't right. Her husband never felt anything when using same tub/shower. Was an older house that had updates and additions. Cast sewer pipe leaving the house but plastic drain piping in vicinity of tub/shower. I took measurements and found nothing. She asked me to check into it again sometime later. That time I still had nothing, but then decided to run the shower. Once water was flowing in the drain piping I started getting voltage between water piping and the metal drain adapter. This was basically neutral to earth voltage that also showed up at service and wasn't enough to be too alarming. Don't recall exactly what but was in range you might find almost anywhere at any given time from what I recall. I made up a bonding jumper between that drain fitting and the water piping and she said she no longer had that strange feeling in her legs while using the shower.

Water in a plastic pipe will conduct some current. How well depends on water chemistry.

 

[ramsy]

it has a Hot and a Neutral connection, so the water in the tub will carry current across that connection, .. If you are in the tub, you are part of that circuit

Excellent point, since we know flesh conducts electricity better than fresh water, but neither trips thermal/magnetic breakers.

If the GFCI is useless, the only thing that saves you is pissing in the water, since urine is more conductive than fresh water, and jumping out before the urine dilutes.

If you can’t pee while being electrocuted, the only other thing that saves you is a Dormatory unit bathtub built per 2023 NEC 210.12(C).

Since the required AFCI trips with the resistance of the flesh, or fresh water, similar to arc-fault resistance.

 

[kwired]

You seem to have an incorrect understanding of the dangers of electric shock and electrocution. It’s not only about the pipes being metal.

At a very basic level, even in your “all plastic pipe” scenario, at SOME POINT SOMEWHERE the water is making contact with a grounded metal surface. Doest really matter how far up or down the line it is.

But besides that, when current flows, contrary to popular belief it is not flowing only to the “path of least resistance”, it flows in all paths simultaneously, just in different amounts. So when you “drop the toaster in the bathtub”, it has a Hot and a Neutral connection, so the water in the tub will carry current across that connection, it doesn’t need for the pipes to be grounded. If you are in the tub, you are part of that circuit too.

With electrically insulated tub the bulk of any current will flow between the hot and neutral. The entire tub of water however will likely have near same potential to ground as the ungrounded conductor as will you if sitting in it. Should you touch something of different potential you will have current flow through you, GFCI should protect you if current reaches trip level. GFCI won't prevent you from feeling any shock in such incident, it just limits how long it lasts once enough current to cause a trip begins to flow.

in an insulated tub there can be capacitive current depending on conditions. Many times it may be a pretty weak capacitor and not enough current to be too significant, but as conditions change capacitance could change.

 

[ramsy]

The entire tub of water however will likely have near same potential to ground

The inverse-square law should apply in water, so more current flows near the electric arc, or toaster in the tub.

Any body part electrocuted tends to paralyze the entire nervous system.

 

[ramsy]

She said she could feel something strange in her legs

Once water was flowing in the drain piping I started getting voltage between water piping and the metal drain

Excellent troubleshooting.
Thanks for sharing.

If her legs were near center of tub length while feeling neutral-to-earth voltage at tub drain, imagine how 120v line voltage would feel.

 

[garbo]

Two side notes 1) If a house had PVC running to a fiberglass or other non metallic septic tank doubt that their would be way less then the required 4 to 6 ma required to trip a GFCI . 2) Same thing as above but over 100' of PVC waste line feeding into a municipal cast iron waste line. If my area our water is fairly soft and guessing hard water with more minerals would conduct electricity a little better. Back in the late 1960's our great Vo Tech school took us to a large Electrical Expo. As soon as you walked thru the doors they had a beautiful model in a bikini standing in a bathtub of water operating a two wire double insulated hand drill. Don't think they would be allowed to do nowadays even if they had GFCI protection.

 

[winnie]

If a running hairdryer falls into an insulated tub, I'd expect that potential of the water to be about 60V, because the water will be roughly equally coupled to both the hot conductor and the neutral conductor. IMHO the 'potential field' of the water would be 120V right near the hot conductor, 0V right near the neutral conductor, smoothly varying between those two values between the conductors, and roughly 60V when distant from the conductors anywhere in the tub.

You will also have a 'current field' in the tub. This current field will be highest right between the two conductors, and will fall of very rapidly as you go away from the two conductors. My hunch is that at distances greater than the spacing between the two conductors the fall off will be faster than inverse square. (The inverse square law strictly applies to point radiation sources, but the electric current we are considering is a near field effect, not radiation, and the source isn't a point.)

But as others have said: if current flows from hot to neutral without any leakage, the GFCI can't detect it.