Busbar & Tap off box - power loss & Over-voltage issues

[marconi]

What is odd is the way the busbars have been connected to the live conductors viz: Brown, Blue, Black, a gap then Grey. This is wrong.

One would expect Brown, Black, Grey, a gap, then Blue so that the electromagnetic fields of the three lines combine to reduce in magnitude the resultant field around them. The Grey out on a limb to the right markedly stops this happening.

In the correct order Brown, Black, Grey a gap and then Blue, the effective situation is two parallel conductors ( one made up by the 3 lines and the other the neutral), with the current flowing in them being in opposite directions so the net em field produced by each current is minimised/cancelled out. This cannot happen as well in the actual set up shown in the pictures because the Grey is separated.

So, as well as the advice from others about dodgy connections the busbar ordering of live conductors exacerbates the electromagenetic effects of any transient currents. From Lenz's law rapidly changing strong EM fields around conductors induces high voltages. Perhaps this is the cause of the arcing.

You might want to investigate the nature of the loads on the failing tap off boxes and look for similarities between them not seen with the remaining tap off boxes.

 

[marconi]

You ought to check whether the busbars are actually correctly connected to the lines and neutral but it is the tap off box which is incorrectly wired to the busbars ie: Black, Grey and Blue (- if Brown is correctly terminated you would expect to see the Black on the second from left and then Grey which your image does not show ). The isolator might be switching the neutral feed which is not intended. You'd get some odd voltages if this was the case AND A DANGEROUS SITUATION.

 

[Andy-1960]

It also looks as though those bus bars are tinned or plated to improve conductivity, filing the bars will have removed this.

 

[marconi]

You ought to check whether the busbars are actually correctly connected to the lines and neutral but it is the tap off box which is incorrectly wired to the busbars ie: Black, Grey and Blue (- if Brown is correctly terminated you would expect to see the Black on the second from left and then Grey which your image does not show ). The isolator might be switching the neutral feed which is not intended. You'd get some odd voltages if this was the case AND A DANGEROUS SITUATION.

IGNORE MY #17. I have got myself addled with the above post but cannot edit it because 20 minutes has passed. What I want to say is go back to fundamentals and confirm the energisation of the busbars with respect to the three supply lines and neutral and then check how the connections at the top of the isolator have been made to them.

 

[davesparks]

the neutral in the Tap off box is secure on both sides of the isolator and there are no signs of damage to the cable. Could it be the neutral at the origin of the busbar is the issue, and if this is the case, why is only this tap off and one more affected on another run?

It’s not the connections inside the isolator that I am talking about, it is the connection to the busbar itself. You can see burning on the busbar itself and not inside the isolator, therefore the problem is at the point at which is connects to the busbar.

The tap off will need to be replaced and moved to an undamaged part of the busbar. Fitting a new one in the same location will result in it burning out again due to the damaged busbar.

 

[Simonslimline]

You ought to check whether the busbars are actually correctly connected to the lines and neutral but it is the tap off box which is incorrectly wired to the busbars ie: Black, Grey and Blue (- if Brown is correctly terminated you would expect to see the Black on the second from left and then Grey which your image does not show ). The isolator might be switching the neutral feed which is not intended. You'd get some odd voltages if this was the case AND A DANGEROUS SITUATION.

The last job i was on had some crappy legrand busbar system installed throughout the multi story carpark and main building. The connections were, L1-N-L2-E-L3 Where the SWA,s terminated in to the feeder box for the busbar.



I have looked online but cant find the same busbar.

 

[Fozzy0207]

The last job i was on had some crappy legrand busbar system installed throughout the multi story carpark and main building. The connections were, L1-N-L2-E-L3 Where the SWA,s terminated in to the feeder box for the busbar.



I have looked online but cant find the same busbar.

This is the standard confirmation for busbar I have worked on. Mainly Eaton and E&I. The pitting on the bar will be as a result of a poor contact between the tap off fingers and the bar itself. Depending on the damage you will need to move the tap off position and potentially change out the length of bar as well. The fingers on the tap off are probably slack and will need replacing. A quality issue and may be covered under warranty. If you can’t move the tap off position I would change the fingers and depending on the damage clean up the bar and reinstate making sure to use good contact grease.

 

[Lucien Nunes]

Is this tinned aluminium busbar by any chance? (MPB is available with either copper or ali bars). If so, once damaged, the aluminium is exposed and will not make proper contact with the tap fingers even if it is cleaned up and tightened securely. Aluminium forms an insulating oxide layer instantly on contact with air, which requires abrasion under a layer of anti-corrosive paste to eliminate. A tap clamped on to bare ali could certainly make such poor contact that arcing would begin at low currents, or just be high resistance without arcing.

I don't have the MI's to know the official termination procedure but as above, I would start with a new set of fingers in a new position and make sure to proceed carefully regarding maintaining plating integrity.