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Update: Freddo has been very busy but managed to attend the sports ground with the defective swa cable last weekend. We had some conversations on my test rig and how to use it in the private area which I have copied below:
Good morning. A 25mm2 conductor has a resistance of 0.000727 Ohms/m. When a current of circa 75A flows through it the voltage drop is 75 x 0.000727 = 0.055V/m. Not much. A 40m length of 25mm2 conductor will drop a voltage of 40 x 0.055 = 2.2V Thus when you measure the near and far voltages with your dvm you will need to drop down in range scale in order to obtain the necessary resolution. My dvm has a 2000mV range which would be ideal for example.
We are using a variation of the 4 wire resistance measurement method. It is important that the 'voltage sense' connections are on the 'outside' of the near and far current loop connections. See para 2 of :
4 Wire Testing | Resistance Measurement to within 1mΩ | How-To - https://www.camiresearch.com/Campaigns/Web-Articles/4-wire-testing.html
So at the far end the Henley is wired with the middle terminal to black and right to red - the current loop - and the sense connection blue is made to the left of the black to the middle terminal.
A nice feature of this set up is that the near readings will be negative voltages and the far ones positive due to the negative terminal of the dvm being connected to the point of fault. You should see this when you do the on arrival survival tests with the three 3.3R test resistors.
After measuring R-Y, I recommend you swap the SWA for the Yellow and take the R-SWA measurement. Finally swap the Yellow for the Red and take the Y-SWA measurement.
You need to know the length of the cable in order to use the data to divide it into near and far. Say Near is 250mV Far is 1850mV Distance to fault from start of cable is length of cable x 250/(250 + 1850). My example in the image indicates the cable is damaged only in one place. The most likely region is as I have shown.
When I have the voltage measurements I will do the sums.
Good morning. A 25mm2 conductor has a resistance of 0.000727 Ohms/m. When a current of circa 75A flows through it the voltage drop is 75 x 0.000727 = 0.055V/m. Not much. A 40m length of 25mm2 conductor will drop a voltage of 40 x 0.055 = 2.2V Thus when you measure the near and far voltages with your dvm you will need to drop down in range scale in order to obtain the necessary resolution. My dvm has a 2000mV range which would be ideal for example.
We are using a variation of the 4 wire resistance measurement method. It is important that the 'voltage sense' connections are on the 'outside' of the near and far current loop connections. See para 2 of :
4 Wire Testing | Resistance Measurement to within 1mΩ | How-To - https://www.camiresearch.com/Campaigns/Web-Articles/4-wire-testing.html
So at the far end the Henley is wired with the middle terminal to black and right to red - the current loop - and the sense connection blue is made to the left of the black to the middle terminal.
A nice feature of this set up is that the near readings will be negative voltages and the far ones positive due to the negative terminal of the dvm being connected to the point of fault. You should see this when you do the on arrival survival tests with the three 3.3R test resistors.
After measuring R-Y, I recommend you swap the SWA for the Yellow and take the R-SWA measurement. Finally swap the Yellow for the Red and take the Y-SWA measurement.
You need to know the length of the cable in order to use the data to divide it into near and far. Say Near is 250mV Far is 1850mV Distance to fault from start of cable is length of cable x 250/(250 + 1850). My example in the image indicates the cable is damaged only in one place. The most likely region is as I have shown.
When I have the voltage measurements I will do the sums.
