I hate electrical faults....

[mike2016]

Two strange things happened in the last week I just want to run by people here and see if I have a real issue or not....?!

 

I was trimming cable into one of the attic power sockets I'm running off a repurposed shower circuit. The MCB is off so the live is dead but when cutting the wire down to size (2.5mm2) I heard the fuseboard trip, it was the main house fuse that had gone. I assume this is because of a temporary short between the neutral and earth caused by my tool? Ideally I'd not connect the wire up until all the trimming is done but is there a way to safely cut wire without risking shorting wires together when you are extending an existing circuit? I was just using a sharp pliers. I assume everything worked the way it was meant to? 

 

Second issue is last night I plugged in a brand new surge protector gang block with built in usb ports. Three hours later there's a bang and the radial circuit MCB has tripped. I unplugged the new gang block and reset the MCB, all good so far. My guess is this was caused by a single USB device I had plugged into it. I've heard of problems with some USB socket makes - maybe this is similar? I was going to wait until tomorrow to try the gang block again, to see if it still works, but not use any USB ports. Anyone had similar experiences? 

 

Just trying not to burn down my house!! Thanks!

[ProDave]

On any circuit with an RCD, shorting neutral to earth will cause some of the neutral current to go to earth instead and the RCD will detect the imbalance and trip.  That is normal and something you just learn to accept if you cannot or do not want to isolate all circuits.

 

The Bang and the MCB tripping could be anything. It won't be a USB device. It could be a faulty extension cable or could equally be a fault on the circuit such as a live wire pinched by a screw and on the verge of the insulation breaking down.  That's why you should do a high voltage insulation test on the wiring that will find that sort of fault.

[mike2016]

I think I'll write off the extension cable so....go back to the old one! Appreciate the insight into the RCD behaviour and the swift response! Helps me stay safe! Thank you! 

[Carrerahill]

1 hour ago, mike2016 said:

Two strange things happened in the last week I just want to run by people here and see if I have a real issue or not....?!

 

I was trimming cable into one of the attic power sockets I'm running off a repurposed shower circuit. The MCB is off so the live is dead but when cutting the wire down to size (2.5mm2) I heard the fuseboard trip, it was the main house fuse that had gone. I assume this is because of a temporary short between the neutral and earth caused by my tool? Ideally I'd not connect the wire up until all the trimming is done but is there a way to safely cut wire without risking shorting wires together when you are extending an existing circuit? I was just using a sharp pliers. I assume everything worked the way it was meant to? 

 

Second issue is last night I plugged in a brand new surge protector gang block with built in usb ports. Three hours later there's a bang and the radial circuit MCB has tripped. I unplugged the new gang block and reset the MCB, all good so far. My guess is this was caused by a single USB device I had plugged into it. I've heard of problems with some USB socket makes - maybe this is similar? I was going to wait until tomorrow to try the gang block again, to see if it still works, but not use any USB ports. Anyone had similar experiences? 

 

Just trying not to burn down my house!! Thanks!

The first issue you experienced is one of the biggest problems with working on RCD protected circuits that are only off at the MCB. For this reason individual RCBO's are good but certainly more expensive way of doing things. The only way to avoid this is to disconnect the neutral too or simply switch off the RCD too but that might not suit. Which is why next week when my new 20 something way Wylex hi-integrity board goes in there will be some non-RCD protected submains, some RCBO circuits (fridge freezers) and a good split between the two RCD's on the split way.

 

The second issue, well, it could be a few things. Does the surge protector still work OK? Assuming the circuit sits OK without the surge protector and USB adaptors then I would suggest it is safe to assume, however, assumption is never good when it comes to electrics - investigate until you know for sure.

 

 

Edited May 29, 2020 by Carrerahill

[mike2016]

I might try the surge protector again tomorrow and see how it behaves. Certainly gives me a perspective on how the consumer board COULD be arranged in a new build to make life easier for a small extra cost. Cheers!