Electrical Safety - Shocks - Model Answer?

[Chantry09]

Homework Statement

a) You have been asked to design a convector heater (electric radiator) which has a metal body. Detail an appropriate method of preventing electric shock for users of this product, and show how such a protection strategy could be implemented in your design. (15)

b) Describe the effects of electric current on the human body. (5)

2. The attempt at a solution

For part A would i just mention about connecting the Earth wire to the metal casing and describe how the Earth wire stops the user from getting a shock? I could also talk about insulating the live components so that the user isn't able to easily touch them. Is there anything else i should be talking about? Its 15 marks so i think i need more.

For part B what five things should i be mentioning? I found this on the internet, if i put this in the exam do you think that would be enough?:

More than 3 ma painful shock

More than 10 ma muscle contraction 'no-let-go' danger

More than 30 ma lung paralysis- usually temporary

More than 50 ma possible ventricular fob. (heart dysfunction, usually fatal)

100 ma to 4 amps certain ventricular fibrillation, fatal

 

[TVP45]

You might also look at some of the UL standards (or CSA or whatever your home country). A heater like this would have to meet one or more of those standards in order to be sold. There are some fairly simple things about insulation, creepage distances, finger penetration, etc.

 

[Chantry09]

Thank you for the reply. The question is worth 15 marks through, despite what i already know and what you have told me do you really think that will be enough?

 

[TVP45]

If you simply rewrite what I told you, that will not be enough. If you actually look at the standards I suggested and follow those in a design, it should suffice. Do you have a design yet? Can you share it?

 

[Chantry09]

Ill find the design tomorrow in the exam but it will be to late then :P.

Should i just look up what these safety standards entail then?