Buzzzz!

Huge explained on 26/11/2016 :

It seems unlikely that the buzz is anything to do with the electrician doing his thing, just coincidence.

The only way to track down an RCD trip left to you, is to fully isolate one item / one circuit at a time until it no longer trips. I would though have expected an electrician with a Megger to have found the cause. That means isolating both live and neutral, a neutral leak to earth can cause the trip, as easily as the live to earth. On a ring with 13amp sockets, you can isolate by completely unplugging rather than switching off at the socket - which leaves the neutral connected.

This is just a guess, but does it sound like ground loop hum? Easy way to test for that is a 1:1 audio isolating transformer, or an old microphone transformer.

Could potentially be related to nuisance RCD trips...

I'd have thought with that number happening, if it was one circuit you could isolate them in turn to identify it within a few days.

If it's the cumulative leakage from multiple appliances across all your protected circuits, maybe some experimentation with a 13A plug and some resistors could find how close to 30mA you are, and which circuit is contributing most?

I don't believe in coincidences.

I fear this is the case.

Me too. But after weeks of isolating/unplugging stuff, we've come to the conclusion it's ...

Oh, that's easy - the oven. Disconnect it and all this goes away. Not very convenient, though. Sparks Megger'd the cable (couldn't do the oven without frying its electronics) and said it was fine.

That's why we're thinking about splitting the load across multiple RCBOs rather than a single RCD.

Probably via the amplifier.

With apologies if it's teaching granny...

Is it a typical Dell with audio sockets at the front and back? If so, do you get the same hum using t'other socket?

IIRC you may be able to set it in software to send different signals to the front and rear sockets so that may be summat else with which to fiddle about.

Not at all.

Yes and yes.

:o(

Already looked and there seems to be no way of doing this. I'm running Linux Mint 17, BTW.

In fact I thought I'd sorted it by plugging into the back instead of the front and it briefly stopped. Then came back. Wonder if it really is a dodgy mechanical earth somewhere?

Buy a USB sound 'card' for a fiver, or call it a USB DAC and spend a grand.

In message , Lee writes

Rather than search for some sort of isolating transformer, I'd see if I had any sort of battery powered amplifier that I could plug in - maybe some sort of radio or cassette recorder with aux input?

Even that doesn't work well with earth neutral shorts.

Isolating one link may stop the trip, but the short may still be on another spur.

And there are other cases where the trip is a whole-house issue. Lots of electronic kit with RF suppression puts a lot of capacitance between live neutral and earth. Transients due to starting high loads plus high impedance feeds from e.g. old transforners that are over worked, can trip a whole house RCD.

I would

Meggers don't see capacitance

That means isolating both live and neutral, a neutral leak to

Exactly. You need to isolate each ring to check E-N shorts, and megger it to check L-E shorts.

If that doesn't reveal the issue, then you need to up the main RCD to something like 150mA slow blo and RCBO anywhere that needs RCD for safety reasonsn.

Oven elements leak when damp. Give it a good run.

I have to say that my old PC started doing similar after some kind of power cut, And then the ethernet got irrational and wouldn't work.

New motherboard.

If yours is modern, the processor and ram may be swappable into a new board.

Otherwise i=use it as an exceuse to get more RAM and a more modern CPU..:-)

Don't need a megger.

check neutral earth short on a stock resistance meter. Disconnect elements one by one till it changes, then replace last element...disconnected.

Ah, yes, well, I am afraid I was thinking of Windows drivers/software ;)

Anyhow, still in full-on Kamikaze mode:

a. same with the UPS taken out of the loop?

b. same hum on the L/R surround socket if you have it?

c. same with a different connecting cable?

d. I had an intermittent hum from a Dell once which went away when I changed the power lead so ...

Or simply test whether a pair of standard headphones plugged into the PC have the hum. If that is clean then induced voltage on ground seems plausible, from where becomes the question though :)

Plug headphones into the headphone socket. Is the hum there or not?

Depending on your CU it may be possible to swap just the socket side of things to RCBOs and do away with the existing RCD.

This may be an easy DIY job[1] depending on the CU you have. Depending on the age and make of the CU it could also be a nightmare cost-wise for the RCBOs.

If a new CU is needed [2] then I would suggest that you spent a couple of extra pounds for a Hager one as

1. Hager prices are actually not that bad.
2. Their quality is bloody good.
3. Hager do not change their MCBs and RCBOs every few years to piss you off if you need a new one.

Post a photo of your CU (or feel free to email one) and I'll be able to tell you if a new CU or RCBOs are the best option without you having to look up RCBO prices etc.

Cheers

Or I might just get another Squeezebox if eBay can provide.