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For my work, I’m working on a project that uses a power supply that outputs 42A DC at 5V limit.

While I know that 5V is nothing if I were to come into contact, poor grounding can still cause flashes and burns.

So what are good safety tips when dealing with this sort of supply? Thanks!

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  • \$\begingroup\$ Always use wire with sufficient ampacity rating. Test all solder joints, or other connections for low resistance. If possible, avoid disconnecting wires with the power on, as there may be a significant "inductive kick". \$\endgroup\$ Commented Apr 24, 2021 at 17:37
  • \$\begingroup\$ Avoid under-rated contacts. \$\endgroup\$ Commented Apr 24, 2021 at 17:52
  • \$\begingroup\$ Avoid wearing metal rings or jewelry. Getting a ring across a 42A supply can get uncomfortable fast. \$\endgroup\$
    – John D
    Commented Apr 24, 2021 at 18:29

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5V, as said, is safe by all means (less than 60V, by IEC, CENELEC ad UL standards, ad less than 50 V, OSHA).

John D mentioned correctly the problem of burns, if you wear a metal ring.

Then you have to consider the way you interrupt the 42A and if there is a connector that should bring that current and may be extracted with current on. Usually I put several contacts in parallel. With 5V however arcing should be every limited. If I have to switch off 42A dc I would use relays with contacts in parallel: I have a heap of Omron G2RL and they perform quite well.

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IEC and UL norms states that you can touch with your finger, without health risks, the following 2 types of voltages with respect to the ground of the circuit AND with respect to EARTH:

DC voltages: max 60 VDC

Non DC voltages: max 42 Vpp (peak to peak)

Those are considered safe voltages that we all human beings can safely touch.


If your power supply is UL6950 or UL62368 compliant than you are safe even without plastic sole shoes.

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