Three phase sockets office environment.

[threephase123]

I can not understand how three phase works in an office environment. If the supply is 400v then how do you get it to drop down to 230v for office equipment such as computers etc?

 

[steptoe]

change it to single phase.

 

[m4tty]

Three phase is 400v between phases but 230v between each phase and earth so 230v is achieved by using one phase hth

 

[Doc Hudson]

I can not understand how three phase works in an office environment. If the supply is 400v then how do you get it to drop down to 230v for office equipment such as computers etc?

The same way it works in houses. Office environment is irrelevant to this question surely? if you understand three phase at all you will understand what the relative potential difference is between the neutral, star, or earth point, (dependent upon what some people may call it) and the relative phase shift between the peaks on each of the three phases and thus where your 400v & 230v are from. The 230v we use in out homes is generated as 3-phase. Are you aware how this becomes 230v nominal at the distributors cut-out?

Doc H.

 

[green-hornet]

As this is asked in the correct area of the forum I would like to indulge in a simplified easy to understand explanation.

3 phase supplies are a standard, every street in the UK is supplied via a 3 phase supply, which is why during some power outputs some houses are affected and some are not. This is because each phase is shared and balanced along the length of the street, as most houses do not require more than 100 amps there is seldom any need to provide more than a single phase supply. However, some commercial properties use more power and industrial units even more. With this also comes the need for 3 phase motors and higher demand.

If you are presented with a 3 phase supply you have in effect 3 single phase supplies which must be balanced amongst the loadings. As each phase will be metered it is best that a balanced 3 phase is shared amongst all circuits. A 3 phase board is usually presented with a 125 amp main switch, but some can be higher depending on the supply and needs, each phase can then be connected to the main switch in the correct order. L1, L2 and L3. If any 3 phase equipment is used within the property then a 3 phase MCB will be used, this breaker will be a connected unit that connects across all 3 phases, therefore taking up 3 slots in the distribution board.

Any single phase circuits will only take up 1 slot in the distribution board.

If we then go to basics, each phase will represent 230v to earth, so we now have a problem if we say each phase is 230v to earth surely we have a supply with 690v and not 400v?

In short no we do not, simply because a 3 phase supply is made up in degrees offset to each other, we would require another live cable to get 690v.

The next problem we have with a 3 phase supply is the distribution of circuits, I have already mentioned balance, but we have another consideration and that is when two phases are taken to a single outlet or within reach of each other, potentially we could have a much higher voltage than the 400v presented, and any enclosure should be rated to account for this higher voltage. In close proximity one phase should be labelled as 400v between this and another phase.

3 phase is more versatile and much easier to work with than single phase providing all loadings are correctly balanced. Remember, if you use all three phases its 400v, if you use one phase its 230v and in the words of those TV Meercats simples.