Naked Science Forum

General Science => General Science => Topic started by: Christopher King on 23/03/2009 12:30:02

Title: Why don't hot plates cause an electric shock?
Post by: Christopher King on 23/03/2009 12:30:02

Christopher King  asked the Naked Scientists:
   
How come electric hot plates conduct heat but not electricity which would of course kill Jamie Oliver doing a fry up.

Ta.

What do you think?

Title: Why don't hot plates cause an electric shock?
Post by: RD on 23/03/2009 18:21:35

I think the design will be like that of an electric kettle element:
An electrically heated coil of wire is encased in ceramic (an electical insulator) which is encapsulated in an outer shell of metal,
 i.e. the metal on the outside of the heating element is not electrically connected to the mains.

So the big-tongued chef is safe from electrocution.   [xx(]

Title: Why don't hot plates cause an electric shock?
Post by: Karsten on 23/03/2009 20:13:58

I agree with RD, the element is encased in ceramic. But how about those hot wire cutters that are designed to cut styrofoam. Their wire is not encased in anything, electricity flows through and I wonder if one could get shocked if one touched it. I never did since the thing gets so hot. But would it zap me?

Title: Why don't hot plates cause an electric shock?
Post by: RD on 23/03/2009 21:06:12

Hot wire foam cutters use low voltages (6/12 volts), unlike mains electricity (110/240 volts),
 so the hot bare wire is not an electric shock hazard, just a burn/fire hazard. 

Title: Why don't hot plates cause an electric shock?
Post by: Karsten on 24/03/2009 00:53:49

So should I assume there are a whole bunch of electrons flowing, just not very fast? High amps, low voltage? Something needs to make this wire hot and hot fast. Harmless to me but plenty to make that wire hot?

Title: Why don't hot plates cause an electric shock?
Post by: techmind on 07/12/2011 22:11:49

Quote from: Karsten on 24/03/2009 00:53:49

So should I assume there are a whole bunch of electrons flowing, just not very fast? High amps, low voltage? Something needs to make this wire hot and hot fast. Harmless to me but plenty to make that wire hot?

Depending on the resistance of the wire, it might be an amp or two at 2 or 3 volts.

Title: Why don't hot plates cause an electric shock?
Post by: CliffordK on 07/12/2011 23:03:57

Your skin's electrical resistance is great enough that it is essentially impossible to get shocked with less than 12V unless you you have a break or penetration in the skin (two of them), or you touch it to a mucous membrane (in theory).  Clothing will also provide a fair amount of insulation at low voltages.

Keep in mind that the handle of the hand-held device is likely insulated, so you would have to touch it near the electrode.  Which is the path of least resistance?  Through the skin, or through the wire?

Some appliances have bare wires, not encased in ceramic.  They are generally covered with something so that they are not easily accessible.  Perhaps the inside of a toaster?

In that case, assuming the appliance frame is grounded (or both you and the electrical system are grounded)...  and you are running 110V (double if 220V).

• Anyway, if you touch the frame to a place near the "HOT", you would get a 110V shock.
• If you touch the frame to the heating element near the ground/neutral wire, the potential difference would be near 0V, and you wouldn't feel a shock.
• If you touched the frame to a place in the middle of the wire, the potential difference would be about 50 or 60V, and you may feel a shock (in the USA).  The difference would be 110V or 120V in Europe, and you would probably get a shock.
  

Of course, if you let it heat up too long, you will also get a nasty burn which may break the skin, and could cause you to get a shock at a lower than normal voltage.