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?

--
|WARNING: Due to extreme spam, googlegroups.com is blocked. Due to ignorance |
| by the abuse department, bellsouth.net is blocked. If you post to |
| Usenet from these places, find another Usenet provider ASAP. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |