Intermittent MCB trip puzzler

[lathelad]

Hello all, hoping for some answers, please, to an (intermittent) electrical problem I’m experiencing:

I run a small lathe-cutting outfit (for cutting records) which is based on the ground floor in a rented space in an old Edwardian building.  The electrical supply to my room – or at least to the sockets - is via a modern looking consumer unit with MCBs. The MCB marked ‘Ground Floor Power’ supplies my room as well as a couple of other rooms on the Ground Floor.

My lathe setup comprises a number of interconnected audio appliances and a motor-driven lathe, but the problem component appears to be a stereo amplifier which is rated at 380 watts per channel.  Basically, the problem is that when I arrive in a morning, upon switching all the appliances on (in the same pre-determined order), when I get to this amplifier, it trips the MCB.  After resetting the MCB however, the amplifier is able to be switched on OK, and functions normally.  This usually takes only one reset – but sometimes as many as three.  I’ve fitted an RCD adaptor to the amplifier’s plug – but this does not seem to have had any effect either way. 

I should mention that this problem doesn’t occur every time I switch on the equipment for the day – maybe once a week, and when all is switched on OK, I can use my equipment all day without there being any further cut-outs. All components are correctly earthed.

The problem occurs both when I’m alone in the building, and also when the other rooms on my floor are occupied and in use.

The power to my equipment is via a single wall socket which feeds a 20-long socket strip, used mainly for reasons of reducing hum.

So, where’s the problem likely to be, please? The amplifier or the consumer unit/supply: or both, or something else?  I’ve asked my landlord to investigate the consumer unit/supply and resolve, but so far, no response has been forthcoming!

Thanks in advance for any advice you can give, and please let me know if you need more information. Apologies for any incorrect terminology used...

Jon

 

[ProDave]

Try turning the amplifier on as the first item?

I am guessing it has a big linear power supply and has a very high inrush current as it charges some big DC capacitors.

What is the rating of the MCB that is tripping?  It will have a letter and a number, something like B32.

 

[lathelad]

Try turning the amplifier on as the first item?

I am guessing it has a big linear power supply and has a very high inrush current as it charges some big DC capacitors.

What is the rating of the MCB that is tripping?  It will have a letter and a number, something like B32.

Thank you for your fast response, ProDave ... I'll try turning the amp on first when I go in tomorrow.  Regarding the MCB rating, it looks like B16

 

[Geoff1946]

Have you worked out the total wattage of all your gear?

 

[lathelad]

Have you worked out the total wattage of all your gear?

Hi Geoff, no I haven't ... that's another task for me tomorrow !  I'll make an inventory and report back

 

[ProDave]

B16 sounds a bit low to run all your gear and other people's as well. Perhaps you need to have a word with your landlord about upgrading the supply. That may be as simple as changing the MCB or it may need some other work, but it would definitely need a competent electrician to look at what is there.

It would be better if each room was on it's own circuit.

 

[lathelad]

B16 sounds a bit low to run all your gear and other people's as well. Perhaps you need to have a word with your landlord about upgrading the supply. That may be as simple as changing the MCB or it may need some other work, but it would definitely need a competent electrician to look at what is there.

It would be better if each room was on it's own circuit.

Thanks, Dave, I'll  certainly suggest this to my landlord, and I agree, it would be advantageous if each room was on its own circuit!

 

[SPECIAL LOCATION]

Thank you for your fast response, ProDave ... I'll try turning the amp on first when I go in tomorrow.  Regarding the MCB rating, it looks like B16

The 'B' bit relates to the MCB's operating characteristics around how fast it will operate in the event of an overload fault.

The '16' bit is the current.. ie.  16Amps..

Power = Current (Amps) x Volatge..  which in your case, suggests the circuit is only designed for 16A x 230V = 3680Watts..  (just over 3.5KiloWatts)

As ProDave says this sounds very low..

AND in-rush currents when you amplifier is turning on from cold...

Plus the other equipment you have already turned on, could well momentarily exceed the MCB's specification.

Once the amplifier has charged up it capacitors the current it draws will have levelled off hence you don't get further problems during the day...

You can get a basic impression of how much initial charging is needed for the capacitors..

by seeing how long the amplifier can carry on outputting sound after you have disconnected the mains supply..

(e.g. use some battery powered device to put an audio signal into the amplifier, then turn the mains off with the audio input still playing.)

Often they can continue on playing for what seems quite a while, as the same capacitors that have to initially charge up when you first switch it on...

now start to discharge again when they no longer have a mains supply.

(not scientific or technical but can give you practical illustration that your amplifier has to store up some electrical charge to prevent your audio output being affected by fluctuations in the mains supply).

Guinness   

 

[lathelad]

As ProDave says this sounds very low..

AND in-rush currents when you amplifier is turning on from cold...

Plus the other equipment you have already turned on, could well momentarily exceed the MCB's specification.

Once the amplifier has charged up it capacitors the current it draws will have levelled off hence you don't get further problems during the day...

All this makes a great deal of sense, thank you for your detailed explanation, I feel confident to tackle my landlord on this issue now

 

[lathelad]

I've noticed that the MCB for the power circuit for the first floor of the building, is rated B32 ... In the meantime, while waiting for my landlord to respond, I'll take an extension cable in over the weekend, plug in to a socket on the first floor, run it down to my studio and see if my kit runs OK off this supply

 

[Murdoch]

I've noticed that the MCB for the power circuit for the first floor of the building, is rated B32 ... In the meantime, while waiting for my landlord to respond, I'll take an extension cable in over the weekend, plug in to a socket on the first floor, run it down to my studio and see if my kit runs OK off this supply

be warned your extension will only have a 13A fuse so it may not prove anything.

BUT you do need to get your landlords spark involved

 

[tomsw18]

The 'B' bit relates to the MCB's operating characteristics around how fast it will operate in the event of an overload fault.

The '16' bit is the current.. ie.  16Amps..

Power = Current (Amps) x Volatge..  which in your case, suggests the circuit is only designed for 16A x 230V = 3680Watts..  (just over 3.5KiloWatts)

As ProDave says this sounds very low..

AND in-rush currents when you amplifier is turning on from cold...

Plus the other equipment you have already turned on, could well momentarily exceed the MCB's specification.

Once the amplifier has charged up it capacitors the current it draws will have levelled off hence you don't get further problems during the day...

You can get a basic impression of how much initial charging is needed for the capacitors..

by seeing how long the amplifier can carry on outputting sound after you have disconnected the mains supply..

(e.g. use some battery powered device to put an audio signal into the amplifier, then turn the mains off with the audio input still playing.)

Often they can continue on playing for what seems quite a while, as the same capacitors that have to initially charge up when you first switch it on...

now start to discharge again when they no longer have a mains supply.

(not scientific or technical but can give you practical illustration that your amplifier has to store up some electrical charge to prevent your audio output being affected by fluctuations in the mains supply).

Guinness   

Just to add to this good answer, the inrush is probably what is tripping the breaker so changing this from a B32 to a C32 will likely prevent the tripping.

Some people may say turn the amp on first, but I understand that this might cause pops, etc.  

 

[phil d]

Just make sure you get an earth loop test before swapping from a type B to a type C MCB the maximum value of loop is different for them both, if you are at the top end of the value for a B type you may possibly be over the value for a C type.