Heated bathroom tile slight shock problem

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CAsparky

Member
Location
San Diego
A friend of mine has heated tile in his bathroom. When the heat is on and he turns on his faucet he gets a slight shock and he is barefooted. My helper and me took a quick look and could not feel the shock on our fingers. We touched our cheek to the faucet and could feel the tingle. I guess the the owner has sensitive lady fingers since he can feel the shock that way. The pipes are properly grounded. The shock only occurs when the heat is on and the water is running.

The heating system is low voltage with a transformer in the attic. It has the thermostat with the built in gfi. I think it is the mat type that unrolls and is under the thin set. Then the tile is laid. Any suggestions?
 

Cavie

Senior Member
Location
SW Florida
A friend of mine has heated tile in his bathroom. When the heat is on and he turns on his faucet he gets a slight shock and he is barefooted. My helper and me took a quick look and could not feel the shock on our fingers. We touched our cheek to the faucet and could feel the tingle. I guess the the owner has sensitive lady fingers since he can feel the shock that way. The pipes are properly grounded. The shock only occurs when the heat is on and the water is running.

The heating system is low voltage with a transformer in the attic. It has the thermostat with the built in gfi. I think it is the mat type that unrolls and is under the thin set. Then the tile is laid. Any suggestions?
Don't turn the heat on???.....sorry.......feeling a bit froggy today. Last day on the job today. Start new one on Monday:roll::roll::):):cool::cool:.
 
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Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
How does the gfci protect the low voltage wires after the transformer? My bet is the mat is compromised somewhere and is touching the water pipe but I am surprised they can feel the low voltage.
 

renosteinke

Senior Member
Location
NE Arkansas
Remember - just because you feel a shock, you still have no way to tell which way the current is flowing. Did the faucet shock you - or did you shock the faucet?

Those heating mats have extremely detailed instructions, requiring the mat be meggered, and the results recorded, at several stages of the project. Note that I said recorded. So I'd start by disconnecting the mat and megger testing the mat again- especially if no records were kept, or the testing was not done.

If the mat proves good, it's the piping that's energized.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
I'll go back to my fundamental question that applies in almost all such situations. Did it ever work properly, having been in service for some time and only now, for the first time, showing this symptom, or is this a brand new installation that exhibited this symptom as soon as it was first turned on? If the former, then I would want to know what has happened recently (e.g., new tile replacement, or new service panel replacement, or repair of heating system's power supply). If the later, then I would hand this problem to the company that installed the heating system.
 

handy10

Senior Member
Remember - just because you feel a shock, you still have no way to tell which way the current is flowing. Did the faucet shock you - or did you shock the faucet?

Those heating mats have extremely detailed instructions, requiring the mat be meggered, and the results recorded, at several stages of the project. Note that I said recorded. So I'd start by disconnecting the mat and megger testing the mat again- especially if no records were kept, or the testing was not done.

If the mat proves good, it's the piping that's energized.
Would it not be true that the mat must be shorted to the floor? We know that the only time a shock occurs is when the mat is energized. Since the EG and the neutral are not likely switched, there must be a short between the hot connection to the mat. If the plumbing is shorted to a hot, there would be a shock all the time.
 

renosteinke

Senior Member
Location
NE Arkansas
Measure. You have to measure.

There need not be a true 'short.' Many times a megger will reveal a fault that will not show with a simple continuity test. That is, the insulation might be able to hold back 9vdc from your meter, but applying 120VAC will lead to the breaker tripping immediately. That's why the mat makers insist on megger testing.

Since a house has two 'legs,' it's possible for the actual potential to be as high as 240v.

So, why doesn't the GFCI trip? Put aside any silliness about 'sensitive lady fingers.' You can easily feel current flow of less than 4mA. The only difference between a 'tingle' and becomming a statistic might be something as trivial as the socks you're wearing.

Sherlock Holmes reasoned that, once you've ruled out the possible, then you must look at the impossible. That's why I brought up the plumbing being the source of the power. For all I know, the source might prove to be a bad element in the water heater - but first I'd check the mat.
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
Megger testing mats is good practice however I the Mats I have installed do not require or even suggest using a megger. Suntouch or Nueheat that is.
 

renosteinke

Senior Member
Location
NE Arkansas
I know not of "Suntouch."

My NuHeat literature, as well as the installation video, are both adamant about megging the mat:
1) when you take it out of the box;
2) when you place it on the floor;
3) after covering with thinset;
4) after setting tile; and,
5) before powering up.

The paperwork also has a form for your use, to note the actual megger readings.

There's a certain logic to it; you want to discover damage as soon as you can, to minimize the costs of replacing the mat- as well as for assigning blame for the damage.

Over at the handyman forums, there is no shortage of threads on this topic. It seems that, despite the best efforts of the manufacturers, all manner of these mats are being 're-tasked' from their original intended use. The manufacturers say 'don't trim,' yet folks try to trim them. Damaged mats are fished from dumpsters- and, amazingly enough, they don't work very well. Folks try to power them up with something besides the factory control unit. It seems every trunk-slammer is out there trying to install these 'on the cheap.'

Sorry for the rant- but, good heavens, FTRTI issues cause more headaches than I can count.

(FIRTI = Failure To Read The Instructions)
 

Sierrasparky

Senior Member
Location
USA
Occupation
Electrician ,contractor
I just looked at the online manual for Nuheat I see it calls to measure ohms but I do not see where it calls out for using a meeger. We may not be talking about the same thing. When I speak of a megger I speak of the megger insulation resistance tester that shoots a hi voltage pulse through the conductor. My megger is electronic and has a 500v and 1kv test. I thought most people think of this when the name "megger" is used.
 

mkgrady

Senior Member
Location
Massachusetts
If I remember correctly, the instructions of one manufacturer asked for a post installation and pre-tile installation reading of ohms to ground (the shielded portion of the cable). After tile was laid completely the reading was to be taken again to make sure it is the same. If it were substantially different it would indicate damage occurred during installation of tile. I would expect the ohms value to be just a few (10 to 50ish)depending on how many watts it were rated. How are you going to get a megger to read a few ohms? Arn't they made to measure K-ohms and meg-ohms? I used a multimeter.
 

mkgrady

Senior Member
Location
Massachusetts
The heating system is low voltage with a transformer in the attic. It has the thermostat with the built in gfi. I think it is the mat type that unrolls and is under the thin set. Then the tile is laid. Any suggestions?
Did you actually see a transformer? I have installed a few brands and none had a transformer. The fact that the controller has gfi on the output makes me doubt the transformer existance. I don't see how it would work on the line side of a transformer.
 

electricguy

Senior Member
I just looked at the online manual for Nuheat I see it calls to measure ohms but I do not see where it calls out for using a meeger. We may not be talking about the same thing. When I speak of a megger I speak of the megger insulation resistance tester that shoots a hi voltage pulse through the conductor. My megger is electronic and has a 500v and 1kv test. I thought most people think of this when the name "megger" is used.

I have only seen the ohms measurements also in nu heat mats, I have never seen them requiring a megger test.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Did you actually see a transformer? I have installed a few brands and none had a transformer. The fact that the controller has gfi on the output makes me doubt the transformer existance. I don't see how it would work on the line side of a transformer.
I believe the GFCI must be there to protect the wire from the T-stat to the trany. You don't want the trany primary to short to the secondary. My guess.
 

hillbilly1

Senior Member
Location
Atlanta,Ga
Occupation
Field coordinator/ technical support
I believe the GFCI must be there to protect the wire from the T-stat to the trany. You don't want the trany primary to short to the secondary. My guess.
I agree, a fault from the primary to the secondary could be deadly if ground fault protection was not provided, as others have said, once it goes thru the transformer, the ground fault protection is nullified if theres no fault between the two windings.
 

hurk27

Senior Member
OK my guess:

This is an old house and the circuit the mat is tied to doesn't have a ground, and they used the neutral to bond the heating element shield, which now the voltage drop of the neutral is providing a small voltage that a person that is wet out of the shower can feel?

Don't laugh, had a home owner do this, and guess what, a GFCI won't protect against this either, because the voltage is coming from the line side of the GFCI.
 

Fulthrotl

~~Please excuse the mess. Sig under construction~~
I know not of "Suntouch."

My NuHeat literature, as well as the installation video, are both adamant about megging the mat:
1) when you take it out of the box;
2) when you place it on the floor;
3) after covering with thinset;
4) after setting tile; and,
5) before powering up.

The paperwork also has a form for your use, to note the actual megger readings.

There's a certain logic to it; you want to discover damage as soon as you can, to minimize the costs of replacing the mat- as well as for assigning blame for the damage.

Over at the handyman forums, there is no shortage of threads on this topic. It seems that, despite the best efforts of the manufacturers, all manner of these mats are being 're-tasked' from their original intended use. The manufacturers say 'don't trim,' yet folks try to trim them. Damaged mats are fished from dumpsters- and, amazingly enough, they don't work very well. Folks try to power them up with something besides the factory control unit. It seems every trunk-slammer is out there trying to install these 'on the cheap.'

Sorry for the rant- but, good heavens, FTRTI issues cause more headaches than I can count.

(FIRTI = Failure To Read The Instructions)
yep. all of that.
man knows whereof he speaks.

there is also a "supervisory device" that nuheat sells, that you are
flat nuts not to use... i think they are $30 each.... it's a battery powered
continuity tester that will sound an alarm if the resistance of the mat goes
either dead short, or open. after you have installed the mat and meggered
it, you put this critter across it, so when the tile guys screw it up, or the
plumber, or whatever... you get an alarm, that won't shut off.

you use one per mat, and after the job is done, it goes on a shelf somewhere
for the next time you need it.

now, i'm new, but it seems to me that "low voltage" as in less than 120 vac
seems like a sucky way to heat a floor, as you are gonna have to have much
larger guage wire to the mats.

now, for the box in the wall, for the nuheat controller, you will not be happy
trimming it unless you use a 4sd box, with a 1 1/4" two gang ring, set flush
with finish wall.

you'll want that extra volume of the ring, even in 1/2" sheetrock.


randy
 

electricguy

Senior Member
yep. all of that.
man knows whereof he speaks.

there is also a "supervisory device" that nuheat sells, that you are
flat nuts not to use... i think they are $30 each.... it's a battery powered
continuity tester that will sound an alarm if the resistance of the mat goes
either dead short, or open. after you have installed the mat and meggered
it, you put this critter across it, so when the tile guys screw it up, or the
plumber, or whatever... you get an alarm, that won't shut off.

you use one per mat, and after the job is done, it goes on a shelf somewhere
for the next time you need it.

now, i'm new, but it seems to me that "low voltage" as in less than 120 vac
seems like a sucky way to heat a floor, as you are gonna have to have much
larger guage wire to the mats.

now, for the box in the wall, for the nuheat controller, you will not be happy
trimming it unless you use a 4sd box, with a 1 1/4" two gang ring, set flush
with finish wall.

you'll want that extra volume of the ring, even in 1/2" sheetrock.


randy
I cant seem to find the word megger in the first link here

http://www.nuheat.com/customer-care/manuals.html
 
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