I'm hooking an RFID reader up to an antenna. The reader operates at 134kHz and, due to its resonant circuit design, it can produce up to 350V (peak to peak) across the antenna terminals, with max current of 200mA.

Other answers on this site suggest that you need to start thinking about safety at voltages over 50V (or 30V in some posts).

Apart from avoiding touching the antenna terminals, and surrounding portion of the circuit, what else should I do to make sure I'm safe?

Secondly, if I did get a shock from this circuit, how bad is it likely to be? (I.e. how dangerous is this?)

(FYI The reader is a RFIDRW-E-TTL from Priority 1 Design)

  • 1
    \$\begingroup\$ Is there any metal at all within ten feet of this thing? 35W in the right place could cause burns... \$\endgroup\$
    – user16324
    Mar 20, 2016 at 1:19
  • \$\begingroup\$ Regarding "..if I did get a shock from this circuit..": 80mA is typically taken as the nominal current that can stop your heart. 350Vpp is definitely enough to force a dangerous, painful, and/or potentially lethal current through your body; your RFID reader should be treated with care. \$\endgroup\$
    – uint128_t
    Mar 20, 2016 at 2:03
  • \$\begingroup\$ Are people allowed anywhere near the antenna? \$\endgroup\$
    – Steve G
    Mar 20, 2016 at 4:57
  • \$\begingroup\$ I don't think I want my anything I own scanned by this RFID reader. Especially if it is on my person. \$\endgroup\$
    – user65586
    Mar 20, 2016 at 11:36
  • \$\begingroup\$ There's nothing unusual about this reader. All RFID readers use a tuned inductor/capacitor combination and, as far as I can tell, most of them would have antenna voltages and currents similar to this one. I.e. it's perfectly normal. The only reason I asked about this particular one is that it's the one I happen to have, because it's good for interfacing to Arduinos etc. Dave's answer did a good job of explaining why its not the shock hazard I feared it was. Neither is there any hazard re radiation (that much I do know). At this frequency, it makes nothing but a very short range mangetic field \$\endgroup\$
    – wombert
    Mar 21, 2016 at 8:02

1 Answer 1


I think your concerns are overblown. According to the datasheet, this module only consumes 38 mA at up to 15V, or at most about 500 mW.

While the maximum voltage and current in the antenna coil are 400 V and 200 mA, respectively, this represents the internal circulating energy of the high-Q L-C tank circuit, and this is a very high-impedance circuit node. If you were to come in contact with this node, you would destroy the resonance, and the voltage would immediately collapse to a much lower value.

That's not to say that there are no safety issues — you do need to insulate the coil properly to prevent accidental contact (or internal breakdown).

  • \$\begingroup\$ Thanks. For the clear comprehensive answer and for your time in looking up the datasheet. \$\endgroup\$
    – wombert
    Mar 21, 2016 at 7:52

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