Unbalanced jumpers

**FRENCHIE** · 10-Mar-20, 10:36 AM

Hi guy's
I am in desperate need of some logic to my problem.

We are using 95mm Wesbraid soft jumpers, from the one panel jumping across the room to another panel VIA a open cable tray, the jumpers are about 6 metres long, we have two of these jumpers in parallel for each phase.

Now for my problem.
The RED PHASE each jumper is carrying 250 Amps.
The WHITE PHASE each jumper is carrying 250 Amps.
The BLUE PHASE NOW THERE'S MY ISSUE,
The one jumper is carrying 500 Amps.
The other jumper is carrying sometimes 1 Amp,
Sometimes 5 Amp and sometimes 125 Amp,
Never more than that.

We looked and the lug to see for over heating and NO the insulation tape still intact.
We followed the jumper mm by mm to for burning and still intact.

The jumpers are same length.

Unfortunately the is a hospital and it's on the ESSENTIAL supply we have taken infrared scans and it is alarming we have on that STUBBY over 110 degrees.

We are making plans with new jumpers to replace the overheated one and the one that's giving us this issue.

IF ANYBODY OUT THAT MIGHT AN EXPLANATION IT WOULD BE GREAT.

THANKS
FRENCHIE

**ians** · 10-Mar-20, 12:49 PM

Do the jumpers go through individual metal holes or do they all go through the same hole?

Measure the voltage between the top terminal of the blue phase and the bottom terminal of the blue phase on main switch and circuit breaker in that circuit...and test the voltage on the other phases ...to check if it is the same.

**Justloadit** · 10-Mar-20, 01:00 PM

It sounds to me that there is a break in the cable, or one of the terminals not crimped properly, or the Busbar or bolt or.... something is mechanically wrong.
Swapping the physical positions of the terminations on one side then do a current measurement. If the reading changes then the cable is at fault, if the same position cable shoes the low reading then it is the point of termination that is the issue.

Some pictures of the connection & terminations will help to see if there is anything visual that may be picked up.

Only way to find out is to remove the said cable and to do a visual check.
Unfortunately once it is out of circuit, you may not detect the break with using a simple resistance tester, and may require a destructive removal of the plastic of the cable and inspect to see where the break is.

**Rifrug** · 10-Mar-20, 08:44 PM

That sounds like a bad crimped lug, if the copper wire is not making good contact with the lug it could give up and down readings as it heats and cools. Or the bolt are not tight. Thats my guess.

**FRENCHIE** · 10-Mar-20, 10:38 PM

Thanks Justloadit & Rifrug.
But Ian yes they are going through individual holes with plastic glands on a aluminium gland plate, and when you said that I must check across the main switch, which because the cables being in parallel I wouldn't get a different reading, but then I realised why there is no sign of a burning faulty crimped plug, is if you agree with me and would be the answer of my problem, is that you take a bus-bar which has a 1000amp going through it and you take a 1.5mm wire from the beginning of the bus-bar and you try and flash to the other end of the bus-bar it will not flash because the current is already going through the bus-bar and not through the 1.5mm wire, if what I am saying makes sense, please tell me what you think.
Eish sorry for the late call, this issue has had us spinning that we couldn't see any evidence of the fault.

**Dave A** · 11-Mar-20, 07:20 AM

To find the point of resistance in the faulty jumper using infrared scanning, you are going to have to disconnect the good jumper (the one that is taking the 500 amps). Obviously this will need some thought on how to load the faulty jumper without causing knock-on effects...

Without current, the point of resistance isn't going to generate enough energy to show up.

**ians** · 11-Mar-20, 08:47 AM

The first thing you must do is get rid of the aluminum gland plate...and replace it with a non metalic plate.

I do the main switch/circuit breaker test to check for bad connections inside the units... when i do thermal inspections and i dont find issues with the actual lug or terminations the next step is to do a voltage test ...i normally compare the reading top to bottom (line to load)...of each phase... and if 2 are 0.54 volts and 1 is 15 volts... i know straight away that the switch is faulty and there is an internal bad connection...or a problem with a point to point cable.

You can make a up a long tail and do the test at various point in the panel and between panel to pin point bad connections...the beuty about this kind of test ...it can be done without switching off the power.

**GCE** · 11-Mar-20, 06:25 PM

Aluminum gland plate is fine as it is non magnetic material and you will not get a heat build up due to eddie currents
Only happens on magnetic material

**ians** · 11-Mar-20, 10:08 PM

not being an electrical engineer ...when we start getting into this complex stuff... like eddy currents going around the cable and heat build up due to hysteresis ...circulating current along the cable being compounded by harmonics ...cable configurations and earth separation ...draining ... and all that stuff... personally i have only used bakelite to terminate large single core cables... never even considered aluminum.

It will be interesting to hear the outcome of this issue.

**GCE** · 12-Mar-20, 06:40 AM

We use aluminium especially on the larger generators - You are generally bringing in 120sqmm armour cable ECC which tends to crack Bakelite when there is a bit of movement and at the same time you are bringing in single cores from the alternator. With aluminium you still have earth continuity and a solid base to gland to and the single cores can go through separately without the eddy current problems.