I read that teflon tape should never be used on the threads of a water
heater anode rod because it electrically insulates the anode from the
tank and prevents it from protecting the tank. But I recently bought a
State brand heater containing two anode rods. One rod screws in the
normal way, but the other hangs from the hot water outlet by a 1" piece
of plastic, and it's definitely insulated from the tank. So does this
mean that the anode doesn't have to directly contact the tank?
I have always used a single wrap of teflon tape around the bottom
threads of the sacrificial anode rod, figuring that the top threads
would provide the circuit continuity. I don't see how an electrically
isolated anode would offer any electrical (current flowing) cathodic
protection. Some chemical protection, maybe. Do the instructions give
you a clue as to the purpose of the insulated rod?
The whole idea of a sacrificial anode is to force the electrical charge to
plate off the least noble of metals, which in a water heaters case, is zinc
or some composite thereof. So I cannot imagine why it would be isolated. Try
calling the manufacturer at their 800 number and ask for tech
support...perhaps they can enlighten you and perhaps me too....Ross
Is there any possibility that that "second piece" is somehow in the
wrong place and it's really the "drop tube" for the cold water inlet?
You did call it a "rod" and not a tube, so excuse me if I'm making a WAG
in the wrong direction. But I too would like to know its function if
it's really insulated from the tank shell.
Maybe the plastic hanger is conductive? It wouldn't have to be really
low resistance to work, the current flow to an anode rod is only a few
hundred microamps. And, they do make conductive plastics, like the
static discharging laminates used on workbench tops to prevent
electrostatic charge damage of sensitive electronic stuff.
Re the teflon tape; I ran a short series of experiments years ago to
answer just that question. They showed that a reasonable wrapping of
teflon tape would not electrically insulate a pipe joint made up to
normal tightness. The teflon squeezed right out where there would be
metal to metal contact on the flanks of the threads and stayed where it
was needed to plug the "spiral leak path" between the truncated crest of
the male threads and the sharp bottoms female thread.
The second anode rod looks a lot like this:
Only with mine the plastic between the nipple and anode is blue instead
of white. The big horizontal hole through the plastic is for letting
water flow out of the heater. I measured infinity ohms between the
nipple and anode (digital meter), so I don't think that the plastic is
Roger that, I guess we're hopefully going to learn something new about
galvanic protection, but HEY, maybe it ISN't actually an "anode" to
retard galvanic corrosion?
I practically flunked chemistry, but I'm thinking maybe there's ways of
inhibiting NON-galvanic corrossion of the tank by the nasty chemicals in
some water supplies, by putting a "more easily corroded" material inside
Like, maybe if you've got a dish of acid it'll eat up a piece of steel
you drop in it, but if you dump in some strong base the acid will get
neutralized and not bother the steel as much?
I hope this thread continues until someone "in the know" educates us
about that second rod.
BTW, your excellent photo shows the plastic extending through the inside
the nipple right to top. That may just be to give it a "good grip" but
I'm betting it's also to prevent water from touching the inside of the
nipple. If the top end of an unlined steel nipple is attached to copper
piping, the galvanic corrosion will be at its absolute worst inside the
The anode in the tank won't do shite to protect the nipple because the
sacrificial current flow won't go very far up inside the nipple. (The
same reason it's hard to get electroplating to "throw" inside the holes
on a workpiece without having to stick additional anodes into the holes.)
I may have posted this here before, but at the risk of repeating myself,
here's a photo of the inside of one of the galvanized steel nipple I
used the last time I replaced my electric water heater. I'd dutifully
bought a pair of dielectric (insulated steel/brass) unions and steel
nipples and replaced the copper parts which were there before.
"Everybody" said to use dielectric unions to prolong the life of the new
In less than six months both of the steel nipples were nearly clogged
with clumps of rust and one had started a pinhole corroded through the
"thin spot" at the root of an exposed thread.
That's when I started thinking about what I'd done and realized that
because the heater tank and the house piping were both connected to
ground per code, the galvanic unions were "shorted out" and (worse than)
I put the all copper parts back in.
Later, I stumbled onto this document from Rheem, a major water heater
manufacturer, which confirmed what I'd figured out on my own.
This is getting curiousor and curiouser...
I posted the question on the forum section of the web site you swiped
that photo from and received one answer already. But I'm not sure I
believe it, it's too hard for me to envision how that steel sleeve he
mentions isn't visible *somewhere* in that photo.
But I'm not sure I believe the answer, it's hard for me to believe that
steel sleeve he mentions isn't visible *somewhere* in that photo, and
where it contacts the metal of the nipple, but anything's posible I suppose.
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