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I got a question about safety standards:

I'm designing a consumer device and I'm not sure whether I need an earth wire.

I have an AC-DC converter plug that outputs 5 V and up-to a maximum of 1 A current. This plug goes from NEMA 5-15P to a barrel plug.

The main device is made out of (exposed) metal.

At this level of voltage/current do safety standards require that I ground the enclosure to earth ground?

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  • \$\begingroup\$ Edit: Even if we do have isolation between the input and the output (this is an external AC-DC converter) wouldn't the possibility of a 1A shock be dangerous enough? Or is 1A not that dangerous at 5V? \$\endgroup\$ – loves_electrons Jul 21 '19 at 6:06
  • \$\begingroup\$ Generally any DC less than 60V isn't an explicit shock hazard. If your AC/DC converter has double or reinforced insulation and has some inherent protections (OV/thermal) you should be fine. \$\endgroup\$ – Adam Lawrence Jul 22 '19 at 18:16
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The AC-DC section needs to meet applicable safety standards. One of those parameters is isolation between primary (AC) and secondary (DC). If the secondary is properly isolated, and has acceptable leakage that is below the limits allowed in the applicable standards, then it need not be earth connected.

This is a complicated topic and I suggest you consult a compliance engineering specialist to be certain.

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  • \$\begingroup\$ Thanks for responding so quickly! I'll double-check the isolation and you're right, I should get in touch with a certification specialist. \$\endgroup\$ – loves_electrons Jul 21 '19 at 5:54
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If you bring AC mains into your product, then yes, you need a ground. If hot or neutral touched the chassis, then it would need to exit through the ground.

By the sound of it you are using an AC-DC converter, so this would minimize testing.

A good way of doing this is by using an external AC-DC converter. We did this on a product and avoided many of the saftey tests during ETL regulatory testing.

My advice to you would be to get a regulatory consultant, they will save you money in the end.

Another note, if you are going to get your product certified it could cost anywhere from 2k-8k USD depending on the testing you need (another reason to get a consultant).

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  • \$\begingroup\$ You can use AC from a 2-wire plug, a safety ground is not required. The basic requirement is that line/neutral side needs to be double-insulated. \$\endgroup\$ – hacktastical Jul 27 '19 at 0:33
  • \$\begingroup\$ At our ETL they still wanted to test to 601010, so we used an external AC to DC. Sometimes you get the wrong person. It also depends on exactly how the AC mains is brought in. \$\endgroup\$ – Voltage Spike♦ Jul 27 '19 at 1:02
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If that 5v power supply with a barrel plug that itself has exposed metal meets electrical safety standards, then your metal-cased appliance will also be safe.

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