UK Ska busbar tapoff help

[COSMICSUN]

Hi everyone
Iam installing a 25A supply to a machine from a canalis busbar system the machine is Tpn and earth. I have a 5 way tapoff unit . Should I be using a four pole breaker so I issolate the neutral or should a 3pole breaker be fine. The busbar system is a ska 800amp system which governs more equipment around the building. Iam thinking of unbalanced loads and current on the neutral
Cheers Cosmicsun

 

[westward10]

I personally wouldn't isolate the neutral unless the machine specs suggest it or the earthing system dictates it.

 

[COSMICSUN]

I personally wouldn't isolate the neutral unless the machine specs suggest is or the earthing system dictates it.

 

[COSMICSUN]

Thank you. for your reply. I feel a bit better for your answer. If I was going straight from a sub main I wouldn't even be asking and would not even contemplate disconnecting the neutral. My busbar use is quite limited but not virginal. I just wanted to check out both what other sparks thoughts are and if there is a general use of 4 poles when adding just one machine and not sub main boards
So many thanks for you input.
Iam most grateful.
Cosmicsun.

 

[Lucien Nunes]

Agreed, if there's no local need to break the neutral, use a 3-pole.

 

[COSMICSUN]

Agreed, if there's no local need to break the neutral, use a 3-pole.

Cheers. We have a generator back up system at source which is automatic should we loose the grid. Breaking the neutral is good practice for the generator take over. But this is already in hand in the automation part at the incomes.
Thankyou for easing my mind
Cosmicsun

 

[pc1966]

In the UK at least any generator transfer switch must break neutral as there is only one N-E link permitted (from supplier-side, or generator, not both).

Breaking neutral without a switch that has a special make-first / break-last contact on N carries the risk of a short over-voltage on switching an unbalanced load if some L are on but not N.

I have a few 4-P isolators at my work place but that is due to an up-front RCD so I wanted to isolate any N-E faults down-stream quickly so main (or backup) power could be restored before UPS run out.

As above, for most TPN systems there should be no real need for N isolation.

 

[pc1966]

Just spent the last 15 mins looking at the Canalis KSA catalogue! Not played with those before, but always something that might be handy to know about for the future.

 

[COSMICSUN]

In the UK at least any generator transfer switch must break neutral as there is only one N-E link permitted (from supplier-side, or generator, not both).

Breaking neutral without a switch that has a special make-first / break-last contact on N carries the risk of a short over-voltage on switching an unbalanced load if some L are on but not N.

I have a few 4-P isolators at my work place but that is due to an up-front RCD so I wanted to isolate any N-E faults down-stream quickly so main (or backup) power could be restored before UPS run out.

As above, for most TPN systems there should be no real need for N isolation.

 

[COSMICSUN]

My concern is that connecting into the busbar system would my machines cables neutral carry any unbalanced load
That may be present as the loading on the busbars around 360amps at present going to all different subs around the building both, will 3 phase and single phase loads. Any unbalanced load will be travelling along the neutral bus bar back to the incomers. If I end up working on the machine and my 3pole breaker is locked off would there could there be current on the neutral
I hope I have explained that so you get my way of thinking.
Thanking you in advance
Cosmicsun.

 

[pc1966]

My concern is that connecting into the busbar system would my machines cables neutral carry any unbalanced load
That may be present as the loading on the busbars around 360amps at present going to all different subs around the building both, will 3 phase and single phase loads. Any unbalanced load will be travelling along the neutral bus bar back to the incomers. If I end up working on the machine and my 3pole breaker is locked off would there could there be current on the neutral
I hope I have explained that so you get my way of thinking.

So you worry about the few volts of N drop possibly causing trouble of a good few amps if it gets shorted to earth/CPC?