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Electric water heater - heating element design change.... Doug 02-04-2007
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Posted by Doug on February 4, 2007, 3:21 am




I've noticed a design change in terms of electric water heater made in
the last 10 years or less.

Prior to that it seems like that the standard heating element wattage
was 3800 per element. Now its 4600 watts per element.
Why the change? Faster recovery times, I suppose...

With 3800 watt elements, a 20 amp 240 v circuit was fine with maximum
current less than 16 amps.

With the 4500 watts elements, a 20 amp 240 v supply circuit is
marginal with a demand current of around 18.75 amps.

I've got a few places that still have electric water heaters on 20 amp
circuits.

I recently had to replace one during a weekend that was bitterly cold.
The 20 amp breaker kept tripping, as the heater switched from the top
to the lower element. I suspect that the surge current when the
element was cold was enough to trip the breaker.

Working in the bitter cold within a crawlspace to upgrade the circuit
to 30 amps was simply not, for the time being, an option.
I looked in vain for a breaker that weekend with a longer time delay.
Eventually I installed a 25 amp breaker keep the heater on.

YES, YES, I know, with a 20 amp circuit, on 12 gauge wire, that 25 amp
breaker is a code violation. You don't have to give me flack for
that...However, I'm not worried since it's only a temp solution and
there is no constant demand current over 18.75 amps. Also, an element
short will trip that 25 amp breaker almost as fast as a 20 amp one. In
the spring I'll put in a 30 amp circuit.

I'd never seen 25 amp 240 volt breakers until recently. There must be
a demand for them..

Anyone else have this problem?

Doug







Posted by RBM on February 4, 2007, 7:57 am


There has been no change. There are a variety of heaters and variety of
wattages. Typical full sized heaters are available in 3800,4500, and 5500,
some with duel wattage connections. The installer must use the tank
appropriate for the job and replace under sized feeders if necessary



>
>
> I've noticed a design change in terms of electric water heater made in
> the last 10 years or less.
>
> Prior to that it seems like that the standard heating element wattage
> was 3800 per element. Now its 4600 watts per element.
> Why the change? Faster recovery times, I suppose...
>
> With 3800 watt elements, a 20 amp 240 v circuit was fine with maximum
> current less than 16 amps.
>
> With the 4500 watts elements, a 20 amp 240 v supply circuit is
> marginal with a demand current of around 18.75 amps.
>
> I've got a few places that still have electric water heaters on 20 amp
> circuits.
>
> I recently had to replace one during a weekend that was bitterly cold.
> The 20 amp breaker kept tripping, as the heater switched from the top
> to the lower element. I suspect that the surge current when the
> element was cold was enough to trip the breaker.
>
> Working in the bitter cold within a crawlspace to upgrade the circuit
> to 30 amps was simply not, for the time being, an option.
> I looked in vain for a breaker that weekend with a longer time delay.
> Eventually I installed a 25 amp breaker keep the heater on.
>
> YES, YES, I know, with a 20 amp circuit, on 12 gauge wire, that 25 amp
> breaker is a code violation. You don't have to give me flack for
> that...However, I'm not worried since it's only a temp solution and
> there is no constant demand current over 18.75 amps. Also, an element
> short will trip that 25 amp breaker almost as fast as a 20 amp one. In
> the spring I'll put in a 30 amp circuit.
>
> I'd never seen 25 amp 240 volt breakers until recently. There must be
> a demand for them..
>
> Anyone else have this problem?
>
> Doug
>
>
>
>
>
>



Posted by Doug on February 5, 2007, 3:00 am


On Sun, 4 Feb 2007 07:57:16 -0500, "RBM" <rbm2(remove
this)@optonline.net> wrote:

>There has been no change. There are a variety of heaters and variety of
>wattages. Typical full sized heaters are available in 3800,4500, and 5500,
>some with duel wattage connections. The installer must use the tank
>appropriate for the job and replace under sized feeders if necessary
>


I beg to differ.

During the era of 10 + years ago, the standard residential home water
heaters supplied by the majority of local suppliers, in terms of tank
sizes from 30 to 85 gallons, all used 3800 watt elements. Obviously
other sizes could be special ordered. I know this because I installed
quite a few back then.

These days, those suppliers plus the big box stores only stock the
same sized heaters with 4500 watt elements.
And of course, yes, other sizes can still be special ordered.

When one is replacing one on an emergency basis on a weekend for
tenants, one has to use what's available on the shelf.

Ever since my state passed a state statute allowing for rather heavy
local taxation for on the shelf inventory, the suppliers have been
stocking only that which sells rapidily and in quantity.

Doug


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