# Can someone explain 3-phase electricity?

#### Timmyp

##### Member
Hey everyone,

The first of what may seem like a lot of simple questions to some of you!!

Could you explain to me what 3-phase electricity is in relation to a standard electrical supply?

Timmy P

Timmyp said:
Hey everyone,

The first of what may seem like a lot of simple questions to some of you!!

Could you explain to me what 3-phase electricity is in relation to a standard electrical supply?

Timmy P

Hi Timmy - The standard power outlet that you have on the wall is a single phase 240V outlet. There is an active (hot) cable that sends 240V to the application plugged in and a neutral cable that returns the voltage. There is also an earth (ground) connector that is there to reduce your risk of electrocution should things go bad.

Three phase has 3 Active connectors and one neutral and one earth, although, some applications do not use a neutral but for theatre applications in the UK and Australia, you will need the neutral.

Each active phase is 120' out of phase to the next one which is why an electric motor can run from just the three actives and without a neutral, as one is at +240 one at -240 and one at 0 at any one point in the cycle. But for power, you need the neutral. When you see a three phase distro, this effectively takes three phase and splits it into several single phase outlets. Commonly, 3 to 4 10A single phase outlets will be branched off of each 32A three phase Active. Thus, you will see distro units with 9 or 12 single phase sockets on them and most will be marked as phase 1, phase 2 and phase 3. Often they will be marked with colour (ie, red 1 or white 3) or with numbers (ie, 1-1 or 2-3).

Three phase generally carries more current and is used in lighting and sound because you can power up more applications. For example, a common 3phase dimmer will have 12x10A circuits on it where a common 4pac dimmer will only have a total capacity of 10A.

That is a fairly basic explanation but I don’t want to go into more in depth discussion at this point until I know if you have any other questions. There is a lot more to know when it comes to distribution of three phase power but I don’t want to get to detailed at this point, without knowing your specific questions (if any).

Hope this was some help.

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Mayhem said:
Hi Timmy - The standard power outlet that you have on the wall is a single phase 240V outlet.
Readers should note that that's for the UK. The US is 120V rather than 240V.

Thanks a lot guys, all of the info you've given has been great

Am I right in understanding that another pro for using 3 phase in lighting and sound is that there is a smoother power output? Meaning that there is less chance of surges etc?

Thanks again

Timmy P

Not neccesarily. With 3 phases, there is just *more* power available to use.

MHSTech said:
Readers should note that that's for the UK. The US is 120V rather than 240V.

Yes - I should have pointed that out. My apologies.

The US is also different as it is 20 amp instead of 10 on a standard circuit.

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Mayhem said:
Correct - as you require twice the amps to get the same power. As power = voltage x amps.

Wait just trying to understand this and relate it to the energy unit in my physics class. I know that power is energy per time, so does that mean that amps are 1/time?

gabe said:
Wait just trying to understand this and relate it to the energy unit in my physics class. I know that power is energy per time, so does that mean that amps are 1/time?

Unless I am wrong, 1 watt = 1 joule per second and 1 volt = 1 joule per ampere per second and an ampere is an SI base unit.

soundlight said:
The US is also different as it is 20 amp instead of 10 on a standard circuit.

greetings.
I just wanted to throw in a quick clarification here. The word "standard" should be considered a relative term. For example, dimmers come in many different flavors. In one of my theaters, the standard dimmer outlet can only handle 10 amps. whereas in another theater here the rack is filled with 20 amp dimmers. having a rack, fitted with 6K. or even 12K. dimmers is not uncommon.

the amperage coming from wall outlets can differ as well. in many homes, especially older ones, the "standard" outlet could be rated at 15 amps.

take care, Scott

Scott C. Parker
Chair
NY Area Section of
The United States Institute of Theatre Technology
www.hstech.org

as i find in our theatre, 3 phase is cleaner and leads to cleaner single phase, simply because it is on a different lead and isolated from the single phase power found on the 120 volt wall outlets in the room or on the 240v plugs found elsewhere which is normally supplied to the sound equipement

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