Dull thud, and all the lights dim momentarily.

The zombie they buried under rhe floor is reaching out to get powered up?

Might be a damaged incoming underground.

Where's the refrigerator? My late mother had a fridge that used to create some sort of pulse when the thermostat switched it off. I imagine a capacitor had died, or something. (Probably the 'or something.') The lights would flicker and the TV would get confused for a moment or two and then everything would be normal until the next time.

Nick

I should have added that it made a loud noise and then shivered with the vibration as the motor ran down. Hence, noise, lights, EMP etc.

Does it happen all the time, e.g. including all through the night, or only during the day? What about weekends?

Well, it could still be something next door, interfering with the local mains supply.

Could the bang be a breaker tripping off next door?

Is the flicker a momentary brown-out, or a momentary surge (which can happen if there's a short circuit on another phase which momentarily yanks the neutral part way to that phase voltage)?

Brown-outs and surges can show up better with mains filament lamps, because they amplify the effect.

Aye, I don't like the description of the sound as a "dull thud" that is too much like a muffled explosion for my likeing.

Think I'd be getting onto the local REC, even on Saturday. If it is an underground cable fault it could make considerably more than a dull thud and a little flicker of the lights.

Thanks Andrew. The lights dim not brighten so brownout.

Certainly does it past midnight, and at weekends so 24/7 AFAIK

Neighbour sad she hasn't noticed anything amiss, I am sure she would have mentioned having to intervene at her CU several times an hour.

A Kentucky Fried Chicken was wrecked by a supply cable fault, which was basically a fire/arc before the main cutout which they couldn't put out.

Usually these things eventually turn into a good enough short circuit to blow the upline fuse (typically 400A on a residential street supply), or they end up burning out the cable leaving it open circuit. Until one or other happens, it can be pretty difficult to locate. One of my work colleagues used to do this in the 11/33kV network, but I suspect that doesn't mess around with just the occational pop for so long!

This is my thinking too.

My friends house is on an ordinary suburban street with underground distribution. Is it likely his incomer cable will enter from other than the front of the house? If it does enter at the front there is no chance the supply main runs where I can hear the noise, but it's still a worry.

I am wondering about the power to the conservatory. If the cable(s) were undersized and the loop impendence high enough could you think of some momentary short circuit scenario that would cause these symptoms but not blow a 30A wire fuse?

It could well be that the problem is next doors, I just cannot tell.

If his house is like mine (1930s ex-council), the incoming mains cable runs along the end of the 4 house terrace, then along the back wall, branching off to each hosue as it goes.

The freezer starting up?

I still reckon it sounds like my mum's old fridge.

Nick

Given where the noise apears to come from I would say not unless the local mice are keeping their cheese fresh in one.

I see what you mean, and maybe Nick had this in mind too. It might account for the timing intervals, the inrush surge of the motor starting acting as the cartelist to set whatever it is off upstream. Still odd though because where I hear the noise is not between the kitchen and the CU, Quite the opposite direction in fact.

The inrush for an induction motor can be enough to dim the lights for the whole house just on its own...

She would say that. What she's not telling you is the basement and attic are full of dope plants and the thud-flicker are when the contactor for the lights cuts in and out via a timer.

Depends. When I had a 1947 vintage lump of iron up a pole to supply me the microwave would do that all on its own.

And trip the RCD when I installed a load of computers and other s*it on it

NOW I have a freezer sized personal transformer to supply the house, that doesn't happen :-)

I'd appreciate your view on what might be causing the thud John.

Actually all the plant nursery's the police have raided in the last few years are on my road.

Are you a southerner?

Bill