Eli5: What’s the difference between a single phase electric current versus a 3 phased one?


Eli5: What’s the difference between a single phase electric current versus a 3 phased one?

In: 18

It’s like a rope, one phase is just one so can lift only so much (supply limited power) , 3 phased is like a 3 ropes tied together – you can lift something big or untangle it and lift 3 smaller things at tge same time (suply more power)


An interesting fact not mentioned here is the phase shift occurring in three phase power.
The voltage in one phase shifts between -240V and +240V constantly.
When you now attach one phase to a motor, it will induce a magnetic field in the metal wires inside.This will help a motor to turn itself since it is a magnet that gets attracted from the resulting electromagnetic field.
If you now use three phases, the voltage is 120 degree shifted which means, that every phase will reach the 240V at a different point in time.
This makes it easy to construct a motor that spins 50 times a second using three coils and the three phases. You now just need to arrange the coils in a triangle and put a magnet in the middle. The magnet will rotate in the frequency of the power network.

PS: living in Europe so voltage may be different but the concept is the same.

Am not an Electrician ( do we have an acronym for that yet?)

But when I moved into my current (no pun) house five years ago, we had single phase. Lights and regular fans working fine, but we had to choose between Hot shower (one of those wall mounted things) or the Fridge being on. We had to choose between the wife having a hot shower or my work Desktop functioning. (I would have included an anecdote with microwave ovens for Americans, but we haven’t used, needed nor missed them for over a decade – microwaves I mean… I think).

We got a three phase installed a week later and every ran smooth. Still does five years later.

For power coming into the house, we use AC – alternating current. The voltage alternates between positive and negative, following a sine wave (what you imagine a wave looks like).

We talk about waves as having a phase. This just means where in the cycle we start/are. For a sine wave, the start, labelled 0°, is usually when it’s in the middle and about to go up. We label the phase from 0° to 360° because the height of a sine wave is just the height you’re at when you go round a circle anticlockwise from horizontal.

Three phase AC uses three different wires to carry the electricity in, each at a different phase. They are spaced 120° apart. You could think of the extra phases as starting ⅓ and ⅔ along the wave, or as starting 120° and 240° around the circle.

Because maths, a properly controlled 3-phase system has a *total* voltage of 0V at all times. E.g. one wire will be very negative and the other two will be slightly positive, so the voltages all add to 0. This means in theory if you grabbed all 3 phases in one hand, you’d be safe. You might get an injury on your hand, but the electricity wouldn’t flow through the rest of your body and kill you. I wouldn’t recommend testing this…