Things That Go Bang in the Night!

[RBZ5416]

I have a Siemens CU fitted with an 80A/30mA RCCB that covers the whole ring main & cooker.

A couple of nights back there was a bang like a power supply letting go & the RCCB tripped. The bang seemed to come from the general direction of the kitchen but I can't be sure. No physical evidence or nasty smells so I reset the RCCB. All appliances in there appeared to still be working, as was everything else in the house.

Next day it tripped again without any bangs but couldn't be reset. I systematically unplugged everything & kept trying. Last two things (it's always the last right?) were the dishwasher & washing machine. After they were disconnected I could reset the RCCB. Plugged them back in one at a time, the RCCB didn't trip & both devices appeared to be functioning.

I left the WM disconnected & connected DW via a plug-in breaker, also rated at 30mA. Next day the CU RCCB tripped again & the breaker on the DW had also tripped. The DW as idle at this point so it looked like a fault with the DW. Except I reset everything & ran a cycle on the DW & it completed without incident!

So I guess I need to strip the DW out & check around for any signs of what caused the bang. But I'm confused as to how it's still working & tripping the RCCB is only intermittent?

Last time I had anything like this was many years ago when an iron turned out to be the culprit. I just put that down to the mains cable likely breaking down with the constant flexing. But the DW hasn't moved in the 10 years since the kitchen was refurbed.

 

[wwwebber]

Happened to me years back. Would regularly get a bang in the kitchen and the CU tripped. Isolated it to a dishwasher so we replaced it. Only for it to happen again - it was the plug socket that the dishwasher was plugged into - it had a loose connection

 

[RBZ5416]

I'm assuming that as the plug-in RCD also tripped that it must be the DW side? But happy to be educated if not.

 

[EFLImpudence]

I'm assuming that as the plug-in RCD also tripped that it must be the DW side? But happy to be educated if not.

That would appear to be the case - although strange things do happen.

Can you leave the DW unplugged and see what happens?

As the MCB is not tripping, it suggests a Neutral to Earth fault but that would not normally involve a bang.

 

[crystal ball]

I was called to similar problem, eventually found a very wet socket under the sink behind a mountain of clutter, sink drain was leaking and had been for years as it had rotted the floorboards

 

[RBZ5416]

That would appear to be the case - although strange things do happen.

Can you leave the DW unplugged and see what happens?

As the MCB is not tripping, it suggests a Neutral to Earth fault but that would not normally involve a bang.

Will do but as with all things intermittent, it may not be conclusive.

I was called to similar problem, eventually found a very wet socket under the sink behind a mountain of clutter, sink drain was leaking and had been for years as it had rotted the floorboards

Socket appears in good condition but when I get chance, I'll open up & check connections are tight.

I'm beginning to wonder if the source of the bang was one of our furry friends having a nibble of the cable? Maybe when I pull it all out I'll find partially vaporised mouse!

 

[AndyPRK]

The big filter capacitor thing maybe? inside the DW


A little late now, but reminded me of this tool (for finding small leaks). Am I the last to know about these lol?

 

[JohnD]

cold water tanks and WC cisterns are more likely to overflow at night or when the house is empty, if the valve is dripping a bit and no water is being used to drop the water level.

I also had this happen when a change in household meant the washing machine was no longer used every day, and a dripping fill valve allowed the tub to fill up and spill over.

 

[ban-all-sheds]

A little late now, but reminded me of this tool (for finding small leaks). Am I the last to know about these lol?

1. Who are the target market for such a tool?
2. Do (1) really need a laboured explanation of what RCDs do, how the test works, etc?

 

[333rocky333]

I'm assuming that as the plug-in RCD also tripped that it must be the DW side? But happy to be educated if not.

If its an ACTIVE plug in Rcd then it would have gone off due to loss of power when the main Rcd went off, only PASSIVE Rcds stay latched.
If unsure plug it in and turn the power off at the Rcd to see if it stays on or goes off

 

[Echo the husky]

^ Beat me to it!

 

[sparkwright]

That would appear to be the case - although strange things do happen.

Can you leave the DW unplugged and see what happens?

As the MCB is not tripping, it suggests a Neutral to Earth fault but that would not normally involve a bang.

Sound advice.

The op has done well to narrow it down to two appliances, but the plug-in RCD may be a red herring and perhaps shouldn't have been used.

RCDs can do some seemingly odd things.

 

[ericmark]

With a neutral earth fault the faulty appliance does not need to be switched on. Being plugged in is often enough. So damp bread stuck in toaster, plugging toaster in RCD does not trip, switch on kettle it trips, but fault in toaster not kettle, but kettle uses more power so fault shows when kettle is used.

I am lucky I have a portable appliance tester and a couple of insulation resistance testers so easy enough for me to test, but latter uses 500 volt, so not really for DIY use, cheap enough start at around £35 but mine can use 250 or 500 or 1000 volt to test with, clearly there is a danger.

So maybe best idea is call an electrician?

 

[JohnW2]

Will do but as with all things intermittent, it may not be conclusive.

Well, it would be pretrty conclusive as far as the DW was concerned if trips continued when it was unplugged!

Kind Regards, John

 

[ban-all-sheds]

So damp bread stuck in toaster....

But bread does not come into contact with the elements.