Tell me about trip switches (and washing machines)

Like most folk, our house has a trip switch; I vaguely remember an electrician, doing some work for us, telling us that ours was particularly sensitive (which I took to be a good thing). The last couple of times it’s tripped have been heating elements burning out in our electric oven. Also, at some point, I remember reading a piece suggesting that if you mowed over your mower’s cable, a good trip would cut in before you got electrocuted (although this may be urban myth).

Perhaps I’ve been naively assuming that we’ve been protected from all electrical mishap.

Yesterday our washing machine started making an awful noise, followed shortly by the smell of burning and smoke. It appeared that the drum had seized but the motor was determinedly trying to spin it at 1400 rpm. Fortunately we were in (not always the case) and turned it off.

Once we’d settled down from the realisation that the whole house could have burnt down if we hadn’t have been in, I realised that the trip switch had done nothing; I would have assumed that straining motor would tripped it. I am clueless around electrics, but should it have done so?

I suppose that a supplementary question is whether there should have been a fuse or cut-off mechanism (perhaps a heat sensor) in the washing machine itself. It had a programable timer which rather invites you to set it to run when you’re not around.

I suppose that a

Interesting question and one I’d like to know the answer to.
The EV Electricity tariffs with cheap electricity in the middle of the night means that it’s tempting to set washer and dishwasher to run whist we are asleep. What protection options are there?
Would an RCD help?

An RCD trip switch detects voltage leaking to earth from live.
An oven element shorting out is a classic for tripping the RCD.

The breaker will protect against overload but it’s not going to know that your washing machine drawing more current than normal (you could plug a heater into another socket on the ring). It’s own 13amp fuse isn’t likely to protect it either. Most of the smoke from the washing machine was probably the rubber belt slipping and getting hot.

Mowing over a cable…I’d hesitate to say it would stop you getting a shock, but it would stop you getting a sustained shock. A plastic body lawnmower probably wouldn’t transfer the shock at all.

Protection options. Smoke detectors for when you are in. Or internet connected detectors if you want an alert on your phone when out of the house (such as Nest Protect which will do a voice alarm over the whole house ‘smoke in the laundry’). I’ve bought a pair so the house one will alert me if the campervan has smoke in it (although I’ve not installed the house one yet)

The description ‘trip switch’ may cover various types of device. The one that disconnects power and stops you from being electrocuted is an rcd or rcbo. This works by measuring the current that goes into a circuit on the L and what comes back on the N. If they’re with 30mA (typical rating) of each other then it won’t trip, if it’s greater than that the only place that current can usually go to is to earth, sometimes through a metallic appliance or a person, both of which are good conductors. It’ll then disconnect the power as 30mA is insufficient current to cause fatal electrocution in a healthy adult person. Note that it’s different for children/babies and animals.
The other type of ‘trip switch’ is a circuit breaker
This won’t necessarily trip quickly enough in the event of an earth fault like the above, it simply limits the current from rising above the rating, typically 32A for a socket outlet circuit; its duty is actually to protect the cable from damage from overheating.
In the circumstances above it’s unlikely that either will have operated as neither scenario (rcd or cb) fits the fault. The plugtop fuse (13A) would normally operate to disconnect the power, although that’s not guaranteed. I’d imagine that eventually the WM motor windings would burn out, maybe that was the smell, but I’m not a WM engineer.
Modern properties are being encouraged to now fit AFDDs (arc fault detection devices); these disconnect when they see any kind of arcing that may lead to a fire, either in an appliance or the fixed wiring of the property.

The RCD deals with earth faults, there is usually only one or two protecting a load of other trips. The MCB trips do their thing like a fuse, ie when overloaded.

However, the trips are rated to protect the circuit of several sockets lights whatever so are rated higher than 13A on a sockets circuit. That’s when the appliance fuse should protect the individual appliance, however a washing machine fuse will be rated at 13A, and you can spin a stuck belt quite happily with 13A!

The stench is quite possibly the burnt belt.

I fitted a slower trip for my garage circuit as the welding kit was constantly tripping the trip as it’s quite a spiky load, everything has been fine since.

It didnt trip as it was a mechanical, rather than electrical fault.
If the motor had seized, either the fuse on the plug, or the circuit breaker would have tripped. The RCD would not trip, as the RCD detects an imbalance between Live and Neutral. When you have an overload, the live and neutrals are still equal, if you have a fault, the RCD trips.
Think of it like this: You have a lightbulb that can take infinite power, but, you run it at 6 amps normally to give the light required, the circuit breaker is a 10 amp one. If you have a dial to turn up the power, your lightbulb will take more power, and make it so bright that the sun looks dim. But, it will not trip the circuit breaker or rcd, as it is not using more than 10 amps, the size of the circuit breaker. This is what was happening with your motor, it was using a bit more power to make it turn, but, it wasnt using enough to trip the circuit breaker.
The RCD works differently. That trips when there is an imbalance between live and neutral, and if the motor is spinning there will be no imbalance, as power out on live = power back on neutral. The RCD is there to protect you if you touch a live terminal, and earth at the same time. If you do cut through your mower cord, it may not even trip. But it will trip when you tough the live ends, as some of the current will be going through you, rather than back through the neutral wire.
It wont stop you getting an electic shock, but it does limit the time you have that shock for. So dont pick up the cable when you cut through it with your mower, as it may still be live. Yes really.

And back to your washer, I brought this up last week. Appliances can be rubbish. They are made to a price point, and safety has little to do with that price point. Dishwashers and dryers are regular sources of house fires. A fridge caused the Grenfell fire. I dont hear cries of get them sorted by the victims, but I do hear the (valid) claims about the cladding that spread the fire (which was another price point decision by the builders).