Buzzing RCBO

[Deleted member 9648]

Staff accommodation in a large hotel, was asked by maintenance guy to look at a DB. MK board with 3x RCBO's serving rings, and the rest lighting MCB's. One of the RCBO's was making a very noticeable buzzing noise,but otherwise worked fine. Disconnected cables and the buzzing stopped, IR circuit...nothing untoward. Reconnect cables and the buzzing starts again...with or without load. Was going to go and pick up a replacement straight away, but maintenance guy insisted on leaving it to the morning as he was already overtime.... 'and anyway,it's been like it for weeks'!

Any suggestions as to the cause of the buzzing?

 

[Pete999]

overload????? near the limit on the over current side

 

[telectrix]

try switching the circuits from the buzzing RCBO with another. if the buzzing stays with the original RCBO, replace. if it follows the circuit, then it's a circuit problem. one other possibility is to move the RCDO position so as to be next to a different device than the one it's next to at present (harmonics).

 

[Dave OCD]

It's more than likely the RCBO itself, had this on the older 'plug in' Wylex type MCBs before as well.

 

[Deleted member 9648]

Thanks fella's.....didn't have a lot of time as I said....it was last knockings after an afternoon repairing hot cupboards in the hotel, but definitely not overload as it did it with no load at all. I suspect faulty RCBO, will find out in the morning.....just seems odd that as soon as cables disconnected it stops,and clamp meter showing zero amps on the circuit

 

[telectrix]

maybe the letters "MK" are a clue.

 

[ruston]

maybe the letters "MK" are a clue.

Remember the ad they used to use "You can tell a good electrician by what they throw away."
Times have changed since then.

 

[Darkwood]

Is this buzzing RCBO for a lighting circuit and are the lights dimmed ??? - swap the dimmer out with a normal switch and see if it stops.

 

[Dave OCD]

Is this buzzing RCBO for a lighting circuit and are the lights dimmed ??? - swap the dimmer out with a normal switch and see if it stops.

No he said it's for a ring.

 

[Darkwood]

My Bad - read it too quickly :13:

 

[richy3333]

I reckon twill be bees or wasps!?

 

[telectrix]

or a happy RCBO.

 

[Dave OCD]

Staff accommodation- could be a rogue Rampant rabbit.:laugh3:

 

[Marvo]

As already mentioned, high load current and some kind of PWM electronics such as dimmers or maybe a fan speed controller etc are the causes I've come across. As per Tel's suggestion swap the circuits or even RCBO's around and see if the buzzing follows one in particular. I had a similar problem with an MCB once and two new replacements did exactly the same, I had to use a replacement from a different manufacturer eventually. There was obviously a compatibility issue with something on the load side that caused resonance with that particular MCB design.

 

[PEG]

Staff accommodation- could be a rogue Rampant rabbit.:laugh3:

He said it was a ring...which means the pleasure aid you speak of,is corded...

I make it a rule,not to use a mains powered device of this type...caused a right mess last time...:wings:

 

[ruston]

He said it was a ring...which means the pleasure aid you speak of,is corded...

I make it a rule,not to use a mains powered device of this type...caused a right mess last time...:wings:

Ah , the slack female syndrome.

 

[Deleted member 9648]

Oooer Missus!.......we've gone a little off piste so to speak!.......will have a check for rampant rabbit chargers tomorrow and will report back on how the replacement RCBO fares.
Thanks for all the replies chaps.

 

[Dave OCD]

Oooer Missus!.......we've gone a little off piste so to speak!.......will have a check for rampant rabbit chargers tomorrow and will report back on how the replacement RCBO fares.
Thanks for all the replies chaps.

Don't get caught checking out knicker drawers ffs !!:smilielol5:

 

[Lucien Nunes]

If you can't measure any real load on the circuit, but yet can't prove conclusively everything is disconnected, it does strongly suggest phase-angle control turned down low like Darkwood's lighting dimmer (perhaps a standard lamp with inline dimmer) But also possibly something electronically controlled that isn't supposed to be variable in which the triac is barely firing (fan timer?), or even the internal ballast of a dead CFL or a faulty SMPSU with one half of its rectifier open-circuit. I can think of all sorts of electronic things that might be persuaded to generate a load current waveform that would buzz the current coil of an MCB but look open-circuit to a multimeter continuity test. How about an internally arcing delta-cap in an appliance - usually still in circuit with the appliance off. That probably wouldn't last long without going bang though.

It'll be interesting to hear the outcome...

 

[UKMeterman]

He said it was a ring...which means the pleasure aid you speak of,is corded...

I make it a rule,not to use a mains powered device of this type...caused a right mess last time...:wings:

Go and google Hitachi

 

[Deleted member 9648]

Update.
Swapped the RCBO this morning and the new one buzzed exactly the same. Unfortunately there was no access to the rooms untill tomorrow morning so further investigation had to wait but at least the possibility of a faulty breaker has been eliminated.
Thanks again for the suggestions of causes,will be going round tomorrow unplugging/disconnecting loads and try to pin it down that way. If that doesnt work some more extensive testing may be required.

 

[Marvo]

It's the kind of issue that you'll probably find by elimination, ie unplugging or disconnecting loads rather than actual testing. TBH if RCBO is not getting warmer than usual I wouldn't worry about it, it's not something that's likely to be a safety issue, just an anomaly or an annoyance at worst.

 

[Farmelectrics]

Did you try moving the rcbo away from the breakers next to it

 

[Deleted member 9648]

Sorted.
Tracked down an FCU on the ring serving two high level son floods, neither of which have apparently worked for some time. As soon as these were disconnected the buzzing ceased and resumed when re-instated. I'll leave the technicalities of how these affected the RCBO to those with more technical knowledge than myself,as no further investigation was carried out. They were left disconnected pending replacement with 50w LED floods.

 

[Darkwood]

Possible the striker constantly trying to strike a duff lamp at a guess or a ballast sat energised generating a few transients back down the circuit... like I say just a guess.

 

[Lucien Nunes]

Aha so I was fairly close with my florry ballast suggestion. I'm with DW it was probably the igniter just breaking over, generating nice little current spikes without using any real power. Glad you found it.

 

[Marvo]

Sorted.
Tracked down an FCU on the ring serving two high level son floods, neither of which have apparently worked for some time. As soon as these were disconnected the buzzing ceased and resumed when re-instated. I'll leave the technicalities of how these affected the RCBO to those with more technical knowledge than myself,as no further investigation was carried out. They were left disconnected pending replacement with 50w LED floods.

Glad you found it and thanks for letting us know, it's one of those little interesting ones I'll remember for next time I get a buzzing protective device.