Electronics > Repair
Monitor Speaker tripping the mains circuits (UK) insulation test ok, what next?
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Reprobyte:
Hello, purchased a used pair of JBL 705p monitor speakers, and I have found that 1 of them has tripped circuits 4 times.

1st time plugging in, tripped upstair circuit.
2nd time switching off switch next to IEC cable, tripped whole house.
3rd and 4th time on downstairs circuits, tripped when the extension that its plugged into was turned on at the wall with the rest of the setup.

This is over the course of a couple weeks.

I got out the Megger BM80 and tested the insulation and it’s at 370MegaOhms both poles to ground.

The device works fine when on, seems to be in a state of powering on or powering off. I have not yet opened the unit up as I am unsure if its the unit or something on my house, advice needed.

Any more tests I can do here, only really had a similar issue with a 1500VA step down transformer in the past doing the same thing.

All advice is greatly appreciated.
Roehrenonkel:
Hi Reprobyte,
 
what kind of breakers do you have (Amperage and characteristic)?
What RCDI (whole house on one RCDI is a bad idea, imho)?
370 Meg Iso seems reasonable.

Good luck
Reprobyte:
Hope this helps, these are the ones that tripped, I don't know if that explains. House electrics are not my strong point, I can wire the sockets but never messsed with the main box.
George Edmonds:
It sounds to me that you have a fault with the entire house installation that need checking out by a good competent electrician who understands RCD’s and RCBO’s, NOT one of the part P brigade.

G Edmonds
Gyro:
You appear to have highlighted the first floor lighting MCB. I hope you mean the ground floor sockets MCB next to it!

My first thought is inrush current. MCBs can get tired with age, especially if tripped multiple times. When breakers are in close proximity, it is possible for the magnetic field from one to affect the adjacent one on a heavy current surge. The first floor sockets MCB is right next to the RCD that tripped. It could be a magnetic interaction rather than an earth leakage fault, especially as the other RCD, feeding the ground floor sockets MCB didn't trip.

It's curious that one speaker trips the circuit and the other one doesn't (?). It would be worth comparing the innards to see if the NTC thermistor has been bypassed on the tripping one - assuming that the PSUs are SMPS.

Other thoughts, Have you got anything plugged into the signal inputs? If so, disconnect and try again. It would be worth checking for continuity (I wouldn't risk HV insulation test yet) between the signal ground and the primary side.
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