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In alt.engineering.electrical Tzortzakakis Dimitrios
wrote:

| ? ?????? ??? ??????
| ...
| In alt.engineering.electrical Tzortzakakis Dimitrios

| wrote:
|
| | Professional washing machines. One of my very first days 'in the
field'
| was
| | to connect some of them. They have a large heating element, you can
| connect
| | it single phase, or 3 phase, it just heats up faster (of course) when
| you
| | connect it 3 phase. (they have a single phase motor, so it works also
in
| | pure 230 V).
|
| If it has 3 elements rated for 230 volts, with 3 separate connections
that
| would be to three separate phase for a three phase feed, and all
connected
| to the one phase for a single phase feed, then it should heat up at the
| same
| speed, while drawing three times the current (not accounting for the
| motor).
|
| I don't know why it should heat up faster in three phase, or why you
would
| say "of course" about it. I would think it would heat up faster if you
| took
| it over to London and hooked it up to a 240 volt supply.
|
| Maybe you connected with single phase just one element? The rest two
| remained unconnected? (3 230 volts elements, connected wye). I'm sure it
| heated up faster, in 3 phase connection.

You were the one who said "it just heats up faster (of course) when you
connect it 3 phase."

I would disagree.

But the fact that you said "(of course)" seems you presume that to be the
general case. Now your most recent comment at least acknowledges that if
not all elements are connected, it won't heat up as fast.

In the simple case, each of 3 elements is individually wired, so you have
a total of 6 leads. When connecting to three phase, one lead of each is
connected to neutral, and each of the other leads is connected to separate
phases. When connecting to single phase, they are all wired in parallel.
Both cases always involve one of the leads from each element connected to
neutral, so those 3 leads can be pre-connected together. So you could
have
just 4 leads. The common neutral lead needs to be rated for all the
current
together for it to be rated properly for single phase.

It should apply the same voltage (230V) to each element, and they should
each
draw the same current. How would you believe this would be slower to
heat?

If the 3 elements were wired _internally_ in star without a neutral lead,
it would still work fine on three phase as long as all elements were equal
impedance. But on single phase, you could only activate 2 of the
elements,
and that would be 2 in series fed with 230 volts. You'd only get 1/6 the
power that way.

Are you assuming the elements would be wired that way? That would clearly
NOT be intended for single phase connection.

The 3 elements could be wired _internally_ in delta. In this case, these
would have to be 400V elements. Connecting 2 leads to 230 volts would
still
give you only 1/6 the power (but more evenly distributed in this case).

So what is the situation that makes _you_ believe that 3 elements
connected
to single phase _will_ draw less power to heat the water than when
connected
to three phase?

I have no idea, we didn't even open up the washing machines as they were
under guarantee. I know that the landlady's electrician connected the wms
single phase, and I connected (in the distr.box) all 3 phases. I suppose it
has 3 elements connected wye, and single phase is 1 element, plus motor and
automation.



--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr