Husnen Rupani:
Hi everyone, this is Hus, and I have with me, Andy Holman, who is a highly experienced electrician and trainer and assessor. In this video, Andy will show us how to do an IR test on an installation properly while avoiding the RCD capacitor charging. Let’s get started.

Andy Holman:
All right, Hus, not a problem. All right, so we’ll start off with the first thing is by going round the house in question, turning on all the circuit switches, making sure that appliances are disconnected. All of our breakers on. Out to the garage, breakers on. We’re now going to short all the incoming mains.

Husnen Rupani:
I might interrupt and ask some questions, Andy, if that’s all right?

Andy Holman:
Yep.

Husnen Rupani:
Why are we shorting the incoming mains?

Andy Holman:
We’re putting these three active conductors together and then shorting to the neutral. What we’re going to do is when we apply the 500 volts from the mega, we’re going to be putting it over all the live conductors together in relation to earth. So effectively there’s no potential difference between the active and neutral conductors, so therefore any capacitors in the circuit or any electronics are not going to see the 500 volts as a potential across them to do any damage or charge.

Husnen Rupani:
Makes sense.

Andy Holman:
So we’ve got that in place. All right, important we disconnect the MEN link or else everything will fail. The MEN link across. Because we’ve got everything shorted here, back at the switchboard by connecting to the neutral bar, when we apply the 500, it’s going to go out the neutral, join to the actives, come back into the board, and also go out to all the circuit switches. So we’ll apply the 500 volts, and unfortunately we’re going down to zero. So we’ve got a fault somewhere in the circuit.

So now we’ve got to determine whether is the fault in the underground wiring coming into the board or is it somewhere in one of these circuits? And the easiest way to do that now is we will turn around and separate the main neutral conductor and turn off our main switch. So we’ve now cut the circuit in half. And we can effectively now go back and do that same check from our earth onto our outgoing neutral, and we find that that one is now clean. It’s gone up and it’s sitting on infinity.

Husnen Rupani:
So what does that prove?

Andy Holman:
That’s showing that there’s no fault in any of the mains cable in relation to earth. Now that we’ve done that, while we’re at it, we’ll go down and we’ll now remove all the bridges. And because most underground cables there is no earth wire within, they’re in plastic pipe, we also want to check and do a phase-to-phase check as well to make sure there’s no breakdown in the insulation between the phases. And finally, blue to black, all clean. So what we’ve proved now is there is no breakdown between any of the live conductors, actives or the neutral, in the line. So our mains have passed. The fault is going to be somewhere downstream in our board.

Now, we’re lucky in the majority of the cases here, I’ll screw that back in so I don’t forget it, the RCDs employed here break both the active and the neutral conductor. So therefore, by turning that off, we can then isolate between the RCD and the other circuits. So by knocking all the breakers off, we can now turn round and go through and bridge out the active and neutral again because we don’t know what’s in the circuit downstream. There could be electronics, LED drivers, dimmers, et cetera. So by bridging out those active and neutral conductors on each outgoing circuit, we now, when we do the insulation test, I have a failure on that first circuit. I have a pass on the second circuit. I have a pass on that third circuit. And unfortunately a fail on that fourth RCD circuit.

Husnen Rupani:
What about sub-mains?

Andy Holman:
Sub-mains and all the rest of it are slightly different. Because, once again, we’ve got a neutral and a common going to out, we would need to pull out the sub-main neutral, bridge it and then redo the checks out to the other side.

Husnen Rupani:
So it’s the same thing.

Andy Holman:
Same process as what we’ve just done with air. So we would pull out. Now, whether we want to go through that stage or we want to stop.

Husnen Rupani:
No, I think we’ll just look at the two that failed.

Andy Holman:
Yep. All right. Now, the two that failed. We’ve now identified that the circuit has failed. What’s it connected to? What’s involved? Does it matter that the active or neutral has got the fault on it? For the purposes of installation testing, we have now failed that circuit, so it can’t be connected to supply. We would now have to move over and move into the fault-finding and diagnosis, start splitting the circuit down and breaking it up section by section to find out where that actual fault is to repair it. So at this point in time, we failed the circuit, we don’t go any further.

Husnen Rupani:
No worries. There’s one thing I want to mention, that the RCDs that we have here have a note on them that the insulation resistance test can be carried out at load terminals with device in off position. And that’s exactly what Andy has done, where he turned it off and then conducted the test on the load side of the circuit. By shorting active and neutral, he implemented the same thing as we did at the start, where now the potential across the active and neutral is going to be the same. So the 500 volts is not going to go through the circuit, but-

Andy Holman:
Over the circuit.

Husnen Rupani:
Over the circuit.

Andy Holman:
That’s it.

Husnen Rupani:
Thank you, Andy.

Andy Holman:
No worries. Thanks, Hus.

Husnen Rupani:
Thanks for watching.