Electronic – Safety considerations designing a mains powered device

mains

I am building a device for hobby purposes- a 3D printer specifically.
It already uses mains (240V AC) powered heater elements to heat the build chamber (4 ceramic cartridge elements at 100W each).

The heater elements are switched on by opto-coupled relay board (something like this: http://www.ebay.com/itm/5V-8-Channel-Relay-Module-Board-Shield-for-Arduino-ARM-PIC-AVR-DSP-MCU-Uno-1280-/200807736090?pt=AU_B_I_Electrical_Test_Equipment&hash=item2ec112e31a one).

I would also like to heat the build platform the same way- using a mains-powered silicone heater mat at 1000W (I have a larger and heavier build platform than most of the other 3D printers- that's why I need so much power to heat it up in a reasonable amount of time).

The build chamber heater elements are not moving, so I'm less concerned about those.

But the build platform is moving, and I am worried that a broken live wire can basically put the build platform at 240V potential, which can be very hazardous to user, if mains connection is not earthed and protected by RCD.

I have come up with the following ways, which I think should protect against such failure:

  1. Use an isolation transformer, and power all heaters from that.

  2. Include a RCD in my device. This should limit the possibility of electrocution.

  3. Power heaters from a DC power supply. I don't like this option because of the price of DC power supply at required power levels.

What is the recommended way of designing such a device?

Best Answer

If the device is properly earthed then use a fuse. This is the tried and tested way. Proper earthing is important but if this cannot be achieved then an RCD doesn't cost very much. To be honest I'd be thinking of a low voltage heater that wouldn't be regarded as a health hazard - maybe 50V or thereabouts. Cost should not influence safety unreasonably and a 1kW AC to DC converter isn't beyond the reach of most folk.

Having said that, if you are considering an isolation transformer, then surely one can be foundf that isolates and drops the voltage to something reasonably safe.

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