DIYbanter - View Single Post - Wiring new 220v circuits into fuse box

danny burstein

In writes:

On Sun, 15 Sep 2019 03:14:01 +0000, Bud Wilder
om wrote:

replying to RBM, Bud Wilder wrote:
I am installing a new electric hot water heater in a home that was built in
1936. The fuse box is the old conventional type, not circuit breakers. Please
direct me as to how to connect the wire running from the 220 v plug directly
to the existing fuse box.

Probably can't be done. Is there a 30a pull out that is not being
used?
Other than that there is no legal way without doing something with
that box.

FIrst, if you're asking the question in this manner, chances
are you really should NOT be even thinking of dealing with
wiring into a fuse box.

That being said, if you're more familiar with electricity
than your simplistic post suggested, there is a _possible_
alternative you might be able to use.

Now... IF... you're talking about the US (or Canada) where
the standard voltage is 120, and to get 240 (you said 220,
but that's a common issue), you have to do some modestly
but common (in _newer_ homes) trick stuff, there's another
option, maybe, for you.

How much hot water do you actually use, and how quickly
do you need more?

The reason: The 240V water heater will warm up the
water sitting in the tank (how large is it?) and keep
it hot until used. Then... it will take the new,
incoming, and cold water... and heat it up.

This "recovery rate" is based on the wattage (plus
the incoming temperature, etc).

Now... you (if you really know what you're doing)
can rewire that 240V water heater so that it runs
off "only" one of the 120V legs.

This will significantly reduce the recovery rate,
that is, it will take a _lot_ longer to heat
up that big tank of cold water. [a]

However, if you have a large enough tank and
don't pull too much at a time, and don't
need a hefty second chunk too soon, it might
work out.

[a] you'd at first think that reducing the voltage
by half means twice as long for the hot water,
but it's actually four times the duration.

Reducing the voltage by half _also_ reduces the
amperage going through by half, so the actual
wattage (voltage times amps) is cut by 3/4 [b]

[b] there are some modest additional variables
due to the temperature swings, but they're lost
in the noise.

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