Discuss Odd problem on IR Test. in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

Raptor0014

Esteemed
Reaction score
1,261
Doing some testing today on a Wet Room installation.

Fed from its own small CU. And consists of

2 x seperate 50A (for 10.5kw shower) circuits
1 x 20a radial for underfloor heating. This runs direct from CU to a fused spur and then from the fused spur to the UFH controller.
1 x 20a radial for 2 x sockets in a storage cupboard and a fused spur from this for the heated towel rail.
1 x 6a light circuit.

Everything fine until I got to the L-N IR test. It kept giving me a reading fluctuating between 0.08 & 0.37 MOhms. L-E and N-E just fine.

Nothing is going bang as it would with a L-N dead short. So it’s not that.

The 2 fused spurs have neons as do the 2 pull cords for the showers All of these I ensured were switched off as I know neons can cause an issue.

However this didn’t solve the issue on the global IR and I’m scratching my head.

The board is a Fusebox RCBO board. I tried doing the test on the supply side of each RCBO to see if that made a difference. But it didn’t.

I thought it may be the UFH controller so I disconnected that completely yet still got the same problem.

I have traced every single cable as it is still at the first fix stage. Sockets etc have just been added as the plasterer and tilers etc aren’t in for another month. Nothing is damaged. All the connections are sound and terminated correctly in the sockets and spurs, the shower cables have a wago on each conductor and are taped up. Towel rail isn’t yet connected but the supply cable is terminated in the fused spur.

What I can’t work out is why every single circuit is being affected by whatever is causing this fault.

Anyone ever experienced this? I could understand one circuit having the issue, but not every circuit.
 
That’s the only thing I can think to do when I go back tomorrow. I’ve never had an issue before with Fusebox RCBOs and can’t see why it would cause an issue now.
 
Are you doing a global IR? Or have the board fully terminated and relying on turning off each circuit to test?

For IV I'd always be individually IR testing circuits, before I teminate them into a board.

I too can't work out how this is happening unless you are.

And if you are think things like lighting drivers, fans etc.

Might be a faulty RCBO.
 
Are you doing a global IR? Or have the board fully terminated and relying on turning off each circuit to test?

For IV I'd always be individually IR testing circuits, before I teminate them into a board.

I too can't work out how this is happening unless you are.

And if you are think things like lighting drivers, fans etc.

Might be a faulty RCBO.
Yes I’m doing a global IR.

Main switch off, SPD MCB off, all 5 RCBO on and all accessories on apart from the 4 switches with neons. There are no lights or fans in the installation. There are 2 standard MK sockets that are terminated correctly. The fused spurs are terminated correctly and the shower switches are terminated correctly. Only other thing is the UFH controller and I disconnected it.

Tested L-E, N-E & L-N from the isolated side of main switch.

I’ve never had any issue doing it this way before. Just seems odd with this board.

I then tried each individual RCBO from the load side and got the same result.

I’m back there today so will take out each circuit and test at the conductor. I had to leave yesterday to get the kids from school otherwise I would have carried on.
 
Yes I’m doing a global IR.

Main switch off, SPD MCB off, all 5 RCBO on and all accessories on apart from the 4 switches with neons. There are no lights or fans in the installation. There are 2 standard MK sockets that are terminated correctly. The fused spurs are terminated correctly and the shower switches are terminated correctly. Only other thing is the UFH controller and I disconnected it.

Tested L-E, N-E & L-N from the isolated side of main switch.

I’ve never had any issue doing it this way before. Just seems odd with this board.

I then tried each individual RCBO from the load side and got the same result.

I’m back there today so will take out each circuit and test at the conductor. I had to leave yesterday to get the kids from school otherwise I would have carried on.
Just a quick check with the board isolated is to look at the RCBOs.

With them off check incoming Live terminal to outgoing Live terminals for continuity and outgoing L-N. Shouldn't be any.

I'm thinking there may be a rouge RCBO that's causing all your issues.

Either that or there's something you've missed and disconnecting each circuit from its RCBO and IR testing will narrow it down.
 
Out of interest is this an EICR or IV? I'm guessing EICR as you have loads connected.
Tested L-E, N-E & L-N from the isolated side of main switch.
The board is a Fusebox RCBO board. I tried doing the test on the supply side of each RCBO to see if that made a difference. But it didn’t.

Were they the compact double pole RBCO's or the taller single pole RCBOs? In other words were you repeatedly sending 500v between every circuit's N and the CPC bar for each circuit you tested?

I'm also considering that the N-E test would have had been sending 500v to the N and PE terminals of the SPD I think, as N wasn't isolated? I currently can't see what harm that would do though.

My working theory is that they are single pole RCBOs, and the N-E test has damaged something connected in an unusual way.

My general fault finding rule is that if all else fails, start looking at what does work. It can help focus the mind! So in this case everything out of RCBO's, leave the CPC's in for now, and see what happens. If still no logic disconnect CPC's. If still no logic disconnect bonding.

For some reason I'm half expecting everything to test clear until you put it back in...!
All the best with it, I'm sure you'll crack it tomorrow.
 
Been back today. Turns out to be 2 of the RCBOs.

With all circuits disconnected from RCBO they all get the expected >999 Mohm across L-N

The 2 x 20A RCBO however give a reading of 0.08Mohm, even with the conductors removed. The 2x 50A & 1x 6A don’t. 🤷🏼‍♂️

So I’m going to speak to Fusebox on Monday and ask why. I could see 1 being a faulty one. But 2 and from the same supplier so likely the same batch. It’s odd that they would give that reading.
 
Been back today. Turns out to be 2 of the RCBOs.

With all circuits disconnected from RCBO they all get the expected >999 Mohm across L-N

The 2 x 20A RCBO however give a reading of 0.08Mohm, even with the conductors removed. The 2x 50A & 1x 6A don’t. 🤷🏼‍♂️

So I’m going to speak to Fusebox on Monday and ask why. I could see 1 being a faulty one. But 2 and from the same supplier so likely the same batch. It’s odd that they would give that reading.
have you checked the instructions do not forbid insulation testing?
 
Doing some testing today on a Wet Room installation.

Fed from its own small CU. And consists of

2 x seperate 50A (for 10.5kw shower) circuits
1 x 20a radial for underfloor heating. This runs direct from CU to a fused spur and then from the fused spur to the UFH controller.
1 x 20a radial for 2 x sockets in a storage cupboard and a fused spur from this for the heated towel rail.
1 x 6a light circuit.

Everything fine until I got to the L-N IR test. It kept giving me a reading fluctuating between 0.08 & 0.37 MOhms. L-E and N-E just fine.

Nothing is going bang as it would with a L-N dead short. So it’s not that.

The 2 fused spurs have neons as do the 2 pull cords for the showers All of these I ensured were switched off as I know neons can cause an issue.

However this didn’t solve the issue on the global IR and I’m scratching my head.

The board is a Fusebox RCBO board. I tried doing the test on the supply side of each RCBO to see if that made a difference. But it didn’t.

I thought it may be the UFH controller so I disconnected that completely yet still got the same problem.

I have traced every single cable as it is still at the first fix stage. Sockets etc have just been added as the plasterer and tilers etc aren’t in for another month. Nothing is damaged. All the connections are sound and terminated correctly in the sockets and spurs, the shower cables have a wago on each conductor and are taped up. Towel rail isn’t yet connected but the supply cable is terminated in the fused spur.

What I can’t work out is why every single circuit is being affected by whatever is causing this fault.

Anyone ever experienced this? I could understand one circuit having the issue, but not every circuit.
My guess would be that L-N IR dc test damaged the rcbos internal circuitry
 
If it makes you feel any better I managed to kill a freezer once doing a global IR test. For EICRs and board changes I stick to L+N to E!
I was fitting Hager ones yesterday and they have a little sticker on them saying you can IR test at the outgoing terminals....
So thanks for reminding us to check the instructions.
 

Reply to Odd problem on IR Test. in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock