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?

  • \$\begingroup\$ Double-insulate the wires? Also, you generally don't need a RCD to detect a short to earth. Assuming you have a proper earth connection, it should blow a circuit-breaker, since the earth and the neutral are both connected together at the distribution panel. \$\endgroup\$ Feb 23, 2014 at 11:34

1 Answer 1


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.

  • \$\begingroup\$ AC-DC converter seems to be a waste of resources- heater doesn't really care if it's driven by AC or DC. \$\endgroup\$
    – fest
    Feb 23, 2014 at 12:07
  • \$\begingroup\$ AC-DC converter seems to me like a waste of resources (heater doesn't really care about voltage regulation), and they start at 500EUR/700$ for 1kW which is a tad expensive for my purposes. It seems to me that a transformer with 48V secondary and fuse should basically offer the same level of protection as a properly designed AC-DC converter, right? I am not trying to cut cost at the expense of safety- I am looking for a cost-effective solution which is still safe. \$\endgroup\$
    – fest
    Feb 23, 2014 at 12:19
  • 1
    \$\begingroup\$ I spent some more time thinking about this, and realized that going low-voltage is the way to go. \$\endgroup\$
    – fest
    Feb 25, 2014 at 12:56
  • \$\begingroup\$ @fest good luck with it dude. \$\endgroup\$
    – Andy aka
    Feb 25, 2014 at 13:38

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