On Thursday, March 15, 2018 at 10:43:03 PM UTC-4, Oumati Asami wrote:
On 16/03/2018 09:08, trader_4 wrote:
On Thursday, March 15, 2018 at 10:10:11 PM UTC-4, Oumati Asami wrote:
On 15/03/2018 17:57, trader_4 wrote:
On Thursday, March 15, 2018 at 6:09:18 AM UTC-4, Oumati Asami wrote:
On 15/03/2018 09:38, trader_4 wrote:
On Wednesday, March 14, 2018 at 10:38:55 PM UTC-4, Oumati Asami wrote:
How does this circuit work?

This house has 3 phase power.

I was replacing a downlight and found it having two black, two neutral,
and one blue incoming wire.

If the light switch was on, the blue wire was energized.
If the ceiling fan was on, one of the incoming black wire was energized.

Why/how do both light and fan work when both are on?

incoming downlight
a) ================(black)------------------
b) ================(GROUND)----------------
c) ----------------(blue)------------------

IDK why a house anywhere would have 3 phase power. But there is a wire for the light, a wire for the fan, two neutrals, so what's the issue?

Sorry, the diagram was wrong. I mistakenly labelled ground as neutral.
It is now corrected.

When both fan and light are on, both the blue and black wires are
energized.

So, again, you have a hot for the light, a hot for the fan and a neutral. What's the issue?

When both fan and light are on, there are two hots. Where is the neutral?

Same place it's always been? You said there was a neutral.

Sorry. I made a mistake in the original post. The neutral in the
original should be ground. There is a blue wire, hot when light is on,
two ground wires, and two black wires, one of them hot when fan is on.
Please see the corrected diagram above.

The light is a ceiling recess light, not one on the ceiling fan.

The ground wire should be connected to the metal frame of the fan and light.. The fan and light have a hot on one side and the other side is the neutral. Like someone else said, if that wire is another green/yellow then it is serving as the neutral and should be marked as that. Whether it is correctly run and terminated on the other end, who knows.