How do electrical circuits work?

edindie

This morning my wife plugged in the toaster and tripped the switch on our fuse box. I turned it back on again, and it tripped again when she tried to toast something again a few minutes later.

What does this mean? I assume if the toaster had a broken fuse it just wouldn't work rather than keep tripping the switch on the house's fuse box. Does the fuse act as a bridge between the toaster and the mains, therefore meaning when the fuse is broken the device can't connect to any power?

I imagine I will have to buy a new toaster, but I thought I'd also take this chance to educate myself a bit on how electricity in the home works.

So, anyone want to teach me something?

Owain_Moneysaver

When you say 'tripped the switch' which switch do you mean - a MCB (circuit breaker for an individual circuit) or an RCD (residual current device which usually serves a group of circuits or the entire house, and will have a test button and instructions to "test regularly")?

Both types of circuit breaker operate much faster than a fuse.

In particular the RCD will trip in a fraction of a second with any leakage to earth; a plug fuse can carry tens of amps for quite a long time.

Have you tried emptying the toaster of crumbs and ensuring that it's completely clean and dry? Also that the flex isn't frayed at any point.

edindie

It was the master switch on the fuse box, not the one related to the downstairs plugs.

I've not tried cleaning the toaster as I didn't think crumbs could carry current! I'll give that a go and see if it trips the switch again.

There is no fray in the flex as it is a relatively new toaster.

muckybutt

If its the main switch RCD by the sound of it then it will almost certainly be a fault to earth on the toaster - IF its only the toaster causing this, it may be coincidental the tripping when you used the toaster.

With the RCD main switch tripping and no other fuses / mcb's blowing it will be a fault between Neutral and Earth.

Have you tried plugging the toaster into another socket, or ried anything else in the same socket as the toaster ? that will rule out the socket being faulty.

If the toaster trips it again - throw it away and get a new one.

edindie

Sadly my wife is one step ahead of you there. Whilst I was trying to work out what went wrong, she had gone and got a new toaster!

southcoastrgi

prob just crumbs & needed cleaning out as Owain said

ohreally

An element shorting to earth?

Myser

ohreally wrote: »

An element shorting to earth?

I have seen this on old toasters before - where the bread tray lifts up when the toast is ready, it would trip the RCD. As the bread tray (earthed) springs up it momentarily touches a loose element wire - not worth repairing!

ohreally

10 minutes and a few £'s http://www.ebay.co.uk/itm/ROWLETT-TOASTER-ELEMENT-NEW-/110461282144

Myser

ohreally wrote: »

10 minutes and a few £'s http://www.ebay.co.uk/itm/ROWLETT-TOASTER-ELEMENT-NEW-/110461282144

I'm not so sure about 10 mins? On a few toasters I have seen, it is very difficult to open them up. They use deep recessed screws, bend metal tags around the plastic casing and tight fitting plastic buttons/dials. The buttons/dials can break as they aren't really designed to be removed after being fitted during manufacture.

The one that I saw causing the RCD to trip had the element wire wrapped around a heat-resistant sheet material. The sheet had cracked so some of the element wire was loose. Given the cost of a new toaster, I suggested to the owner that a new one be purchased!

These days, you can buy a toaster for less than £5. Cheaper than a new element! I suppose it's a different story if it's a Dualit or something expensive.

Rockingit

Have to say that I'm shocked (no pun) at some of the advice being handed out here....mostly wrong with the technicals, but also no consideration being given to other factors.

For starters, a fuse will not 'take tens of amps for ages', neither will an MCB respond faster. A BS1361 fuse will take roughly 3 x In (rated amps) for 5 secs whereas as a BS-EN 60898 B (commonly found domestic MCB) will take roughly 5 x In /5s....therefore meaning that a fuse is actually 60% faster amp for amp than an MCB.

An MCB or fuse may not (normally) trip under an earth fault condition as they are designed for over-current protection, not earth fault protection.

Likewise, an RCD is designed to activate on sensing an earth fault and may not respond at all to a severe overload fault. It is in no way a 'master' switch, simply a reflection that due to the expense of them then commonly we will split a dwelling into two or three sections and have multiple MCB's fed from one device.

But, back to the OP.....yep, bin it buy a new one!