Science Questions

How do the filaments in a toaster work?

Sun, 25th Jul 2010

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Chris Smith asked:

When you look at the glowing filament in the toaster, are each of those wires in the toaster actually running at 240 volts or does the toaster step the voltage down? Are they all in series so as this big voltage drops, the actual potential in each of them is quite low, so how does it work?


Dave: - It’s basically just a very long piece of fairly high resistance wire. I've taken a toaster apart recently so I know this. It starts at one end and kind of zigzags up one side, then the current flows down and then zigzags up along the other side, and then it’s attached to the neutral wire.  So, one end of it is going to be at 240 volts.  The other end is going to be at about earth.  So, if you stick something metal anywhere near the 240 volts, even 100 volts, you're going to get a big shock.

Chris: - But if you were lucky and you got it to the neutral end, the potential there is a bit lower.  So if you were making a toaster, hopefully, you'd design it with the most inaccessible bit of the high resistance filament, furthest away from where the knife’s going to go.

Dave: -  Looking at how the toaster worked, one of the holes is going to be more dangerous than the other one, but they didn’t seem to have made any particular attempt to make one side more difficult to get at than the other.

Chris: -  They assume people have got some common sense after all.

Ben: -  Exactly.  I guess if the general rule and the general understanding is, “Don't stick metal cutlery in your toaster” then the other safety features are probably obsolete!


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Erm, I think they are usually referred to as elements rather than filaments. No idea why... Geezer, Tue, 27th Jul 2010

Most heating elements use Nichrome 80/20 (80% nickel, 20% chromium) wire, ribbon, or strip. Nichrome 80/20 is an ideal material, because it has relatively high resistance and forms an adherent layer of chromium oxide when it is heated for the first time. Material beneath the wire will not oxidize, preventing the wire from breaking or burning out. Pumblechook, Tue, 27th Jul 2010

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