Circuit protection advice

67ttamerya · Sep 7, 2015

Hi everyone - I am new to the forum , I'm hoping I have come to the correct place to post! I am not an electrician, I have reasonable electrical understanding and know how circuits like ring/radials work,how consumer units protect the circuit etc but little more.....

Recently our drying machine tripped the RCD on our consumer unit(17th edition). After leaving the dryer for a few days I tried it again. It was fine for a few cycles until we started hearing an occassional electrical bang coming from the dryer, but it was still operating. When I turned it off at the wall it again popped/banged. RCD did not trip. Later I turned it on at the wall( I know), the unit still has power and fuse in plug is not blown.

Dryer is now unplugged and out of use. Clearly there is an issue with the dryer but that is not really my question as we will either have it checked by an appliance technician or simply replace it if too costly.

What i am trying to understand is three things,

Why something like that could happen without tripping the RCD or blowing the fuse in the plug?
Is there some sort of overheat or other protection built into dryers that could cause it to make a large electrical bang but not trip anything else? Otherwise how could an electrical disturbance as strong as a bang not cause a current fluctuation large enough not to trip the RCD?
I would like to get a socket tester which can test the socket but also trips the RCD so i can see if the consumer unit will trip ( both RCD's trip when using the test button). Advice needed on which type/brand of socket tester is needed?

I look forward to any thoughts!

Octopus · Sep 7, 2015

67ttamerya said:
Hi everyone - I am new to the forum , I'm hoping I have come to the correct place to post! I am not an electrician, I have reasonable electrical understanding and know how circuits like ring/radials work,how consumer units protect the circuit etc but little more.....

Recently our drying machine tripped the RCD on our consumer unit(17th edition). After leaving the dryer for a few days I tried it again. It was fine for a few cycles until we started hearing an occassional electrical bang coming from the dryer, but it was still operating. When I turned it off at the wall it again popped/banged. RCD did not trip. Later I turned it on at the wall( I know), the unit still has power and fuse in plug is not blown.

Dryer is now unplugged and out of use. Clearly there is an issue with the dryer but that is not really my question as we will either have it checked by an appliance technician or simply replace it if too costly.

What i am trying to understand is three things,

Why something like that could happen without tripping the RCD or blowing the fuse in the plug?

Is there some sort of overheat or other protection built into dryers that could cause it to make a large electrical bang but not trip anything else? Otherwise how could an electrical disturbance as strong as a bang not cause a current fluctuation large enough not to trip the RCD?

I would like to get a socket tester which can test the socket but also trips the RCD so i can see if the consumer unit will trip ( both RCD's trip when using the test button). Advice needed on which type/brand of socket tester is needed?

I look forward to any thoughts!

You need about £250 minimum for a MFT or hire a local competent spark for 30 minutes!

67ttamerya · Sep 7, 2015

could you give me any ideas why it is not tripping the rcd or blowing fuse?

cheers!

Octopus · Sep 7, 2015

Hum.... Not possible to diagnose over the net. You need somebody to look at it

67ttamerya · Sep 7, 2015

ok ... i m not really wanting a diagnosis as i am going to get a qualified person to look at it. i have no idea how to fix it nor do i want to. What im wanting is some pesonal understanding of how this is possible.... assuming the RCD is working correctly.

cheers

Richard Burns · Sep 7, 2015

If the fault is occurring between line and neutral then this should not affect an RCD.
However you can get high current spikes that will cause a bang in the internal circuitry but may be too fast for an MCB to trip or a fuse to blow.
The other thought is that it could be arcing from a damaged switch, an arc across two contacts would not affect an RCD an MCB or fuse.

Lucien Nunes · Sep 8, 2015

Many appliances contain an interference suppression capacitor or 'delta capacitor' across the input terminals. These can have partial short-circuits which make a bang but the affected area of metallised film in the capacitor blows itself clear with less energy than it takes to blow the fuse. In extreme cases the capacitor case will shatter and bits of disintegrated film come flying out, while the appliance carries on working.