Why does code note require gfci breakers on electric water heaters? - Page 3 - Contractor Talk - Professional Construction and Remodeling Forum

bwalley · 09-27-2009, 09:40 PM

Quote:

Originally Posted by protechplumbing

It would only trip the breaker if the heater was grounded. Since the heater was not grounded, the circuit was not complete and therefore no current could flow to trip the breaker. The circuit was only closed to ground when he touched the faucet that was attached to the heater via the potable water distribution system. The only path to ground was thru his body at that point.

If the circuit was shorted, then it would have tripped the breaker even if the water heater wasn't grounded.

In this case it sounds like neither the water heater or the potable water distribution was grounded and there was leaking voltage.

A GFCI breaker in this case may not have corrected the bad installation.

If the element is leaking voltage to the water and the water heater and the potable water lines are properly grounded, it should trip the breaker or go to ground before going to a faucet as electricity will always take the path of least resistance.

protechplumbing · 09-27-2009, 09:54 PM

Really? Where did the current flow to after it exited the section of bad element?

FYI, the breaker usually does NOT trip when a heater blows an element. That is the whole reason for having the double poled high limit thermodisk in the upper thermostat. A blown element can in some cases cause the breaker to trip if there is a length of element short enough that is touching the element jacket it may have an ohm value low enough to trip that leg of the double pole breaker. Many times though the current isn't enough to trip the breaker and the blown element continuous to heat the water thru one side of the element until the water temperature rises to the point (160f) that the high limit thermodisk in the upper part of the upper thermostat opens both poles.

In case you are wondering, this isn't something that I read out of a book, it something that I have witnessed first hand several times when responding to a "no hot water" repair call.

Quote:

Originally Posted by bwalley

If the circuit was shorted, then it would have tripped the breaker even if the water heater wasn't grounded.

In this case it sounds like neither the water heater or the potable water distribution was grounded and there was leaking voltage.

A GFCI breaker in this case may not have corrected the bad installation.

If the element is leaking voltage to the water and the water heater and the potable water lines are properly grounded, it should trip the breaker or go to ground before going to a faucet as electricity will always take the path of least resistance.

protechplumbing · 09-27-2009, 09:55 PM

Tub drain for one.

Quote:

Originally Posted by 480sparky

What ground? How?

480sparky · 09-27-2009, 09:59 PM

Quote:

Originally Posted by protechplumbing

Tub drain for one.

So it was an all-metal DWV system?

bwalley · 09-27-2009, 10:01 PM

Quote:

Originally Posted by protechplumbing

Really? Where did the current flow to after it exited the section of bad element?

FYI, the breaker usually does NOT trip when a heater blows an element. That is the whole reason for having the double poled high limit thermodisk in the upper thermostat. A blown element can in some cases cause the breaker to trip if there is a length of element short enough that is touching the element jacket it may have an ohm value low enough to trip that leg of the double pole breaker. Many times though the current isn't enough to trip the breaker and the blown element continuous to heat the water thru one side of the element until the water temperature rises to the point (160f) that the high limit thermodisk in the upper part of the upper thermostat opens both poles.

In case you are wondering, this isn't something that I read out of a book, it something that I have witnessed first hand several times when responding to a "no hot water" repair call.

The high limit switch on the upper element is not meant to take care of electrical shorts, it is there in case the thermostat sticks and it keeps heating the water, it will then trip due to temperature.

I am sure you have seen some strange issues like this, my point is if the 120v line was shorted, it should have tripped the breaker or went to ground before the guy was shocked using the faucet in a kitchen.

Water heaters are grounded through the case as well as the water line, unless it is CPVC or pex, which is one of the bad things about non metalic water lines.

protechplumbing · 09-27-2009, 10:05 PM

I believe so. It's been a while though.

Quote:

Originally Posted by 480sparky

So it was an all-metal DWV system?

protechplumbing · 09-27-2009, 10:08 PM

I don't think you comprehended my previous posts. I'll give you a minute to go re-read all of them before I correct you. I'm trying to avoid talking in circles with you.

Quote:

Originally Posted by bwalley

The high limit switch on the upper element is not meant to take care of electrical shorts, it is there in case the thermostat sticks and it keeps heating the water, it will then trip due to temperature.

I am sure you have seen some strange issues like this, my point is if the 120v line was shorted, it should have tripped the breaker or went to ground before the guy was shocked using the faucet in a kitchen.

Water heaters are grounded through the case as well as the water line, unless it is CPVC or pex, which is one of the bad things about non metalic water lines.

bwalley · 09-27-2009, 10:14 PM

Quote:

Originally Posted by protechplumbing

I believe so. It's been a while though.

If it was a metal water line, why didn't the current go to ground before shocking the guy?

Even if it lost it's main ground, the water lines are usually grounded in more than one area.

If the water lines were run under the slab like most houses are, wouldn't that also act as a ground?

bwalley · 09-27-2009, 10:16 PM

Quote:

Originally Posted by protechplumbing

I don't think you comprehended my previous posts. I'll give you a minute to go re-read all of them before I correct you. I'm trying to avoid talking in circles with you.

I am pretty sure I did comprehend what you are saying, I think you are just using the term "short" when you may have had leaking voltage.

protechplumbing · 09-27-2009, 10:21 PM

Post #13

Quote:

Originally Posted by bwalley

If it was a metal water line, why didn't the current go to ground before shocking the guy?

Even if it lost it's main ground, the water lines are usually grounded in more than one area.

If the water lines were run under the slab like most houses are, wouldn't that also act as a ground?

protechplumbing · 09-27-2009, 10:24 PM

You are correct. Short is not the right term. I should have used th word "fault". I'll give you that.

Quote:

Originally Posted by bwalley

I am pretty sure I did comprehend what you are saying, I think you are just using the term "short" when you may have had leaking voltage.

protechplumbing · 09-27-2009, 10:32 PM

I'm going to ask you a hypothetical question to illustrate my point. Lets say that I remove the wire connected to the un-switched side of the upper element and connect a new wire that is connected to ground. What will happen? Why?

Quote:

Originally Posted by bwalley

If the circuit was shorted, then it would have tripped the breaker even if the water heater wasn't grounded.

In this case it sounds like neither the water heater or the potable water distribution was grounded and there was leaking voltage.

A GFCI breaker in this case may not have corrected the bad installation.

If the element is leaking voltage to the water and the water heater and the potable water lines are properly grounded, it should trip the breaker or go to ground before going to a faucet as electricity will always take the path of least resistance.

480sparky · 09-27-2009, 10:33 PM

Quote:

Originally Posted by protechplumbing

I believe so. It's been a while though.

I can't think of any other path. Unless he was standing on a tile floor that had an imbedded electric heat cable in it.

But just because someone comes in contact with an energized 'something' does not automatically mean they're going to get, or even feel, a shock.

protechplumbing · 09-27-2009, 10:39 PM

Agreed. The amount of shock felt will vary depending on the voltage and the resistance to ground.

Quote:

Originally Posted by 480sparky

I can't think of any other path. Unless he was standing on a tile floor that had an imbedded electric heat cable in it.

But just because someone comes in contact with an energized 'something' does not automatically mean they're going to get, or even feel, a shock.

bwalley · 09-27-2009, 10:42 PM

Quote:

Originally Posted by protechplumbing

I'm going to ask you a hypothetical question to illustrate my point. Lets say that I remove the wire connected to the un-switched side of the upper element and connect a new wire that is connected to ground. What will happen? Why?

If you hook up a ground wire to the unswitched side, nothing will happen until the thermostat closes, then it will trip the breaker because 1 leg has a direct path to ground which is called a "Short".

protechplumbing · 09-27-2009, 10:48 PM

Incorrect

protechplumbing · 09-27-2009, 10:58 PM

120v will be applied to the 12.8 ohm (4500w) heater element and 18.75 amps will flow from one pole of the double pole 30 amps breaker thru the element to ground. Since only 18.75 amps is flowing it will not exceed the breakers 30 amp trip point and the current will continue to flow thru the element uninterrupted generating heat until the water is heated to the set point of the upper thermostat. At that point, the thermostat will reroute voltage to the lower thermostat away from the upper element and all heating from the upper element will cease.

Now that we have established that, let me go the next step and ask the question again but with a new twist this time:

Let’s say that I remove the wire connected to the switched side of the upper element and connect a new wire that is connected to ground. What will happen? Why?

bwalley · 09-27-2009, 11:03 PM

Quote:

Originally Posted by protechplumbing

Incorrect

It will be a short circuit to ground.

I will test your theory on a water heater tommorow, and I guarantee you it will trip the breaker.

bwalley · 09-27-2009, 11:08 PM

Quote:

Originally Posted by protechplumbing

120v will be applied to the 12.8 ohm (4500w) heater element and 18.75 amps will flow from one pole of the double pole 30 amps breaker thru the element to ground. Since only 18.75 amps is flowing it will not exceed the breakers 30 amp trip point and the current will continue to flow thru the element uninterrupted generating heat until the water is heated to the set point of the upper thermostat. At that point, the thermostat will reroute voltage to the lower thermostat away from the upper element and all heating from the upper element will cease.

Now that we have established that, let me go the next step and ask the question again but with a new twist this time:

Let’s say that I remove the wire connected to the switched side of the upper element and connect a new wire that is connected to ground. What will happen? Why?

When the circuit is closed it will trip the breaker, again because the 120v line has a direct path to ground.

protechplumbing · 09-27-2009, 11:15 PM

You forget that I'm a local bud. If you really doubt these basic electrical concepts (ohms law) you aren't qualified to even comment on this thread.

There is no doubt in my mind that the breaker will NOT trip in that experiment. I am speaking from both an electrical theory stand point as well as 10 years of first hand experience servicing electric water heaters on an almost daily basis.

No one who has any experience/training servicing electric water heaters would debate what I just said. If you understood Ohm's law (the most basic electrical concept there is), you would not even need to waste your time with such an experiment. I'm not trying to insult you or make you feel dumb, it's just obvious to anyone who knows what's what that you are not schooled or vetted in this particular subject.

I'll just go ahead and answer my old hypothetical questions for tonight for the sake of educating anyone else who may be reading this thread.