Burned out water heating element providing undesirable connection between common (or maybe hot) & ground

[gary j zingle]

With recent discussion on the seperation of ground and common wiring,
I dug out the burned out water heater element I recently replaced and
tested it.
>
Clearly within this particular burned out element hot, common and ground
were electrically connected (checked with an ohm meter, 450 to 500 ohms
resistance between not only hot and common but also between one of the
element leads and ground).
>
I find it interesting that despite this connection when the burned out
element
was in the coach and turned on it did not trip the breaker!
>
Although I cannot say that all element failures would result in the above=

it
certainly causes one to think.
>
Even if hot water is not required I certainly would recommend replacing a=
ny
burnt out element for safety reasons. Alternately If a burned out element=

cannot
be replaced immediately it might be best if it were disconnected to preve=
nt
any accident from occuring.
>
Gary Zingle
1973 GMC 26 foot
Another beautiful day without snow in this part of Alberta

 

[john dolan]

> I find it interesting that despite this connection when the burned out
> element was in the coach and turned on it did not trip the breaker!

The reason is that the breaker is a fairly dumb device (all we had for a
while, but still fairly dumb). The breaker did not trip because all it
was seeing was a load of 500 ohms drqwing less than 1 amp. As far as it
was concerned, it was just a very slow water heater element! When you
said there was no hot water even though it was getting voltage and
drawing current, I said it needs to draw a lot of current to heat water
(in a reasonable amount of time).

A smarter device is the GFI that Edgar Kremer has protecting certain
circuits in his GMC (in later years some models had a GFI protecting the
bath, the galley, and the outside outlet). His GFI kept triping and he
couldn't immediately figure out why. He said recently, that he had to
isolate every circuit in the motor home to figure out why. When he said
he discovered it was a 2000 ohm short to ground in the water heater, I
said to myself I should have asked him if the water heater was working.
But the next day, Edgar came back and ask if anyone had a good source for
a water heater element.

> Although I cannot say that all element failures would result in the >
> above it certainly causes one to think.

So Gary is right, all you folks who buy or build a inline GFI and have it
keep triping, as soon as you hook it up, check your water heater
element... (but seriously any lower resistance short to ground than
Edgars 2000 ohm short or Gary's 500 ohm short puts AC on the frame of the
Motor home with enough current to electrocute. We have all felt these
little tingles from time to time (I'm deadly serious now). Those are
often caused but something like this and they don't electrocute anyone
because the current is limited by the resistance of the short and the
resistance of the human body which is much higher than that. But if you
were a little girl and stepped out of the motor home into a puddle of
water from a rainstorm with bare feet, your resistance is dramatically
reduced. And now what was a funny tickle won't let you let go. And now
what was a higher resistance short, because of a leak with water driping
on some wires with worn insulation, becomes a lower resitance short which
will carry enough current to electrocute someone.

Regards,
John

- --
"I do whatever my Rice Krispies tell me to..."
John said, from inside a 1974 Glacier on the
Potomac, just north of the White House.