Phase seperation and balancing

[brman]

I don't have much practical experience of 3 phase installations but someone just asked me a question I wasn't sure of the answer to so here goes......

If I have a 3 phase DB and I was to take off single phase circuits (eg for lighting, sockets etc) are there any actual regulations relating to keeping those phases separate and load balancing?
I've had a poke around and cannot find anything more than "good practice" recommendations to:
1) balance the load on the phases
2) keep to just one phase in a given area to avoid the risk of 400V (particularly on sockets)
However I've also understood that alternating phases on lights is sometimes used to ensure that not all the lights go on a fault.

As all this can become a bit contradictory I was wondering if there are any actual regs or whether it was more down to experience and judgement on what is best for a given installation?

btw. before someone gets worried I am not about to go out and design a large 3 phase installation - I am just curious

 

[telectrix]

you have it about right. if there are 2 phases in a switch position for ex., it should be labelled accordingly.

 

[Des 56]

Poorly balanced installations tend to waste pound notes as well

 

[brman]

Thanks guys.

Des: I assume the cost thing is because the meter measures the phase with the max load rather than being in affect 3 single phase meters?

 

[Knobhead]

Poorly balanced installations tend to waste pound notes as well

Why? ? ?

 

[Des 56]

I was thinking excess charges for exceeding max load agreements

 

[Knobhead]

Thanks guys.

Des: I assume the cost thing is because the meter measures the phase with the max load rather than being in affect 3 single phase meters?

The meter records the KW per phase and totals them not averages them. Imbalance will not make a blind bit of difference to the total bill.

 

[Knobhead]

I was thinking excess charges for exceeding max load agreements

That’s a totally separate argument. Not many places have max demand agreements. It would normally only effect large consumers.

 

[La Poste]

Why is it encouraged to balance the phases?

Is it just good practice?

 

[theroadblock]

However I've also understood that alternating phases on lights is sometimes used to ensure that not all the lights go on a fault.

Regarding the lighting, i believe there is actually a regulation for factories to use mixed phase supplies for high bay lights and the such to avoid the 'stroboscopic effect' caused which can fool the eye to believing rotating machinery is actually standing still.

Roady


# Found the regulation , stroboscopic effect regulation 559.9

 

[spark 68]

Why is it encouraged to balance the phases?

Is it just good practice?

Yes it is good practice to try and balance the phases as best you can, you will almost certainly not be able to exactly balance them anyway in normal mixed load and mixed SP+N and TP+N environments.

Another reason to try and balance is due to the N conductor in any Dist cables, in the worst case it is possible to overload the N conductor/s, as these at worst will carry twice the load current as the phase conductors in a highly un-balanced situation.

I will leave it for Tony to give you the maths.

 

[Darkwood]

Stroboscopic effect is only an issue with certain types of lighting in the inductive range, the main issue here is loading up 1 or 2 phases and leaving one nearly empty can create issues in terms of expansion or introduction of 3ph equipment, say you had a 72KVA 3ph supply (100amp) then you loaded ph1 to 75amps, ph2 to 60amps and lastly ph3 to 22amp then owner decides to buy a 3phase machine with a FLC of 35amps.... your stuck - had the loads been balanced you wouldn't have the need for possible expensive balancing work or upgrade of supply. The design of an installation should consider and allow for expansion, as to how much allowance should be implied is dependent on the premises and it uses also any additions to existing 3ph system should be incorporated with knowledge of the existing loading over the phases.

 

[theroadblock]

Stroboscopic effect is only an issue with certain types of lighting in the inductive range, the main issue here is loading up 1 or 2 phases and leaving one nearly empty can create issues in terms of expansion or introduction of 3ph equipment, say you had a 72kw 3ph supply (100amp) then you loaded ph1 to 75amps, ph2 to 60amps and lastly ph3 to 22amp then owner decides to buy a 3phase machine with a FLC of 35amps.... your stuck - had the loads been balanced you wouldn't have the need for possible expensive balancing work or upgrade of supply. The design of an installation should consider and allow for expansion, as to how much allowance should be implied is dependent on the premises and it uses also any additions to existing 3ph system should be incorporated with knowledge of the existing loading over the phases.

^Agree, though all things considered i am lead to believe its always good practise to leave room for expansion on any installation, :icon14: .

( When a kind person prior to me has left room for expansion on an installation its saved me some work before :smug: )

 

[La Poste]

I will leave it for Tony to give you the maths.

Thanks Buddy.

We did the maths the other night.

 

[Rockingit]

If you have an unbalanced load being fed from a generator, you can physically hear the poor thing struggle due to the imbalances placed on the armature.

 

[ian.settle1]

Large factoies are also charged a KVAR rate as well, thats why they have Power Factor Capacitors Banks at the incomer so another reason to balance the load.