[saspinski (OP)]

I was at a rented beach house last week when one of the phases collapsed. The system has 2 phases, one for everything but the electric shower, the other for the shower. Because I am still waiting for the energy supplier to fix the problem, I had to change the wiring in the electric distribution board and put all the house in the "good" phase.

All the house except for the (110 V) air conditioner, that has its own circuit breaker and get the "bad" phase direct from the electric meter. Measuring the Voltage, there are less than 70 V available for the air conditioner.

However, if I insert an light bulb in that power plug, it glows after some delay, and the voltage increases to about 100 V (

And if I plug the air conditioner in parallel, it works!

I wonder if there are loose wires in the transformer that reduces the tension from the city line to the house, and the delay results from an electromagnetic force joining them, when the current flows though the lamp, like a kind of relay.

[chris]

Sounds very dodgy to me!

[saspinski (OP)]

The guys from the electric supplier company finally came today and fixed the problem. I was not there, but according to my wife they blamed the "sea air" for a bad contact somewhere from the aerial cables out of the house before the meter.

[evan_au]

If the voltage varied as other appliances turned on and off, it might have been a fault in the neutral connection?

[Bored chemist]

A lamp needs some time to heat up. Normally that delay isn't noticeable, but if the voltage is low it will take longer than usual.

[saspinski (OP)]

If the voltage varied as other appliances turned on and off, it might have been a fault in the neutral connection?

in the days before before the company come, I connected all house in the "good" phase, and everything worked fine, so I donīt think there was a problem in the neutral.. I checked also the continuity between neutrals in the plugs and didn't find anyone disconnected from the electric distribution board,

[saspinski (OP)]

A lamp needs some time to heat up. Normally that delay isn't noticeable, but if the voltage is low it will take longer than usual.

But here the time delay was too big, and moreover the voltage at first dropped after tunrnig the switch on. After some time the lamp shined and the voltage increased above what it was when the switch was off.

[chris]

Is it normal for a beach house to be wired to two separate phases? That seems a bit like overkill? Unless you are running a cannabis farm and consuming prodigious energy for grow-lights or something, surely a single mains phase is perfectly adequate?

[evan_au]

But here the time delay was too big, and moreover the voltage at first dropped after turning the switch on. After some time the lamp shined and the voltage increased above what it was when the switch was off.

You may be seeing the very nonlinear temperature dependence of metals? Metals have a strong positive temperature coefficient.

When the metal filament is cold, it has a fairly low resistance. That means that it will have a very low voltage across the lamp, and most of the voltage drop will be across whatever other (accidental) load is attached to the working phase. In this state, it won't heat up quickly.

However, as metals heat up, the resistance increases, and more of the voltage drop will occur across the lamp, causing it to heat up even more, and eventually to glow visibly. But it won't reach full voltage/full brightness, as it is still in series with some other load.

Is it normal for a beach house to be wired to two separate phases?

Not in 230V countries, since one phase (plus a neutral) supplies enough power for most appliances.

However, in 115V countries (eg Americas), it is standard practice to deliver 2 phases of 115V AC (plus a neutral). Small appliances are connected to 115V, and large appliances (clothes dryers, etc) are connected across 230V.

[saspinski (OP)]

However, as metals heat up, the resistance increases, and more of the voltage drop will occur across the lamp, causing it to heat up even more, and eventually to glow visibly. But it won't reach full voltage/full brightness, as it is still in series with some other load.

But the increase of the resistance with temperature doesn't explain the fact that the final voltage: 100V was bigger than the open circuit voltage: 70V. 

[Bored chemist]

Is it normal for a beach house to be wired to two separate phases?

It's this weird American thing...
https://en.wikipedia.org/wiki/Split-phase_electric_power

[chris]

in 115V countries (eg Americas), it is standard practice to deliver 2 phases of 115V AC (plus a neutral). Small appliances are connected to 115V, and large appliances (clothes dryers, etc) are connected across 230V.

So presumably the power company need to be careful about which two phases they connect to each residence to ensure that they are correctly out of phase to produce the 230V potential?

I honestly did not know this. I knew that US supplies were 110V, allegedly on safety grounds, but I was unaware that they served two phases like that for the juice-hungry devices. I thought they'd just use thicker cables and run a higher current.

And does this mean then that some devices need to operate at 230V, or do they step down the higher voltage close to the appliance?

[evan_au]

So presumably the power company need to be careful about which two phases they connect to each residence to ensure that they are correctly out of phase to produce the 230V potential?

In the 3-phase AC supply envisaged by Nikola Tesla, the 3 phases are 120° out of phase.
However, for two 115V AC voltages to add to 230V, they must be 180° out of phase. So you can't supply 2 phases of the 3-phase supply.

This 180° is accomplished in the US by having a single-phase transformer with a center-tapped secondary.
- The primary winding is connected to just one of the 3 high voltage phases running down the street
- The center-tap on the secondary winding is connected to earth and also connected to the house as a neutral. The two other terminals on the secondary winding are each at 115V above ground, 180° out of phase, with 230V between these two wires.
- Within the house:
        - small appliances connect to one of the 115V phases or the other - it really doesn't matter, as long as both phases are roughly equally loaded
        - big appliances connect between the two 115V phases, producing a total of 230V

And does this mean then that some devices need to operate at 230V, or do they step down the higher voltage close to the appliance?

Resistive losses are quite high at 110-115V AC. So the stepdown transformer is located very close to the houses - from what I recall, a transformer on a pole often serves the 3 or 4 homes closest to that pole.

In 230V AC countries, resistive losses are lower, so they often use one large transformer serving many houses in a street. This transformer has 3 phases in at high voltage (eg 11kV), 3 phases out at 240V AC.
- Small houses connect to just one of the 230V phases
- Large houses (eg with high-power ducted air conditioning systems) connect to all three 240V phases, because 3-phase electric motors are more efficient than single-phase electric motors.