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?
On Thursday, March 15, 2018 at 7:58:01 AM UTC-4, Dean Hoffman wrote:
first lets clarify your picture
does a represent TWO blacks wires and only one is energized when the fan is on? what about the other black wire? are the two black wires connected together?
does b represent TWO white? are they connected together?
and c looks like it is ONE blue wire that is on when the light is on?
On 15/03/2018 19:22, firstname.lastname@example.org wrote:
Yes. Only one black is energized when fan is on. The two black wires are
connected together. The parentheses represent a connector. It is like
== where wires go into the  from top and bottom
To put the connector into the top diagram, turn the connector (==)
90 degrees. So, from left to right is a, b, and c.
In this part of the world, ground is yellow/green. They are connected
There is only one blue wire and it is on when light is on.
So, when both fan and light are on, both a and c are energized.
Just by looking, I suppose. Assuming the motor has two wires,
one wire is the hot wire feeding the motor. What is the other, second, wire
coming out of the motor connected to? It should be hooked to a neutral
eventually going back to your panel. It shouldn't be hooked to any
metal in the motor housing or frame.
The same thing applies to the light. A hot wire feeding it, a
neutral going back to the panel, and a separate ground wire connecting
metal to metal in the various boxes containing lights, outlets, etc.
The easiest way to cheat would probably be to connect the second
of the devices to the metal. Then the ground would be carrying the
should be carried by the neutral.
I am not sure/don't think both black wires are from the fan. When I
separated the two black wires and turned on the fan, one of the black
wire was energized and the fan wasn't turning. That's all I know. the
other black may serve as the neutral for both the fan and the light.
On Thursday, March 15, 2018 at 10:13:37 PM UTC-4, Oumati Asami wrote:
he neutral? It must be
If the ground was used as the neutral, it would trip for sure when the ligh
t or fan was turned on. It would probably trip even without being turned on
. Like I said, the wire might be green, but it could be otherwise correctly
used as the neutral.
It never occurs to me that people would use ground as neutral. Would
that make the fixture energized when on? I just tested the light
fixture, it was not energized when light was on, nor when both were on.
On Thursday, March 15, 2018 at 11:06:00 PM UTC-4, Oumati Asami wrote:
he neutral? It must be
The fixture would not be energized as long as the wire is connected all the
way back to the panel and connected to the neutral there. But if it got d
isconnected, the light and fan would not function and the metal would be en
ergized. Which is why it's not allowed by code for that kind of circuit her
e in USA at least.
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.
On Thursday, March 15, 2018 at 10:43:03 PM UTC-4, Oumati Asami wrote:
ire for the light, a wire for the fan, two neutrals, so what's the issue?
ral. What's the issue?
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 neutra
l. 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 correct
ly run and terminated on the other end, who knows.
On Wednesday, March 14, 2018 at 11:09:04 PM UTC-4, trader_4 wrote:
I can answer that for one location.
In a housing development at what is essentially a campus, we fed 3 phase power to individual houses because of going to 208V airconditioners. I think we got a better price on a bulk buy of the units.
What we found is that everybody complained their dryers didn't work right and their ovens took too long to warm up. Their appliances expected 240.
For a straight thermal load like an over or dryer, that drop
from 240 to 208 is actually pretty messy.
At first glance you'd think that 208/240 = 0.8666.., or about 13 pct,
so to first approximations 13 pct longer to heat up.
However, wattage is amperage times voltage. And both of these [a]
are dropping by that 13 pct.
So the final wattage is.. 0.86... times 0.86... = 0.73.
So more than 25 percent longer.
[a] neglecting the very real issue that in many of these
items the resistance changes with temperatur...
As a side note, we installed a "240v" air conditioner i
a NYC building that had three phase, so it was being fed
at the equivlanet of 208.
We very specifically asked the sales rep AND the manufacturer
if this would be a problem. They said it was fine.
Knowledge may be power, but communications is the key
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