Proper way of grounding in plastic chassis? - diyAudio
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Old 1st March 2010, 02:03 AM   #1
maurycy is offline maurycy  United States
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Default Proper way of grounding in plastic chassis?

I have small 1W amplifier that runs on 12V. To power it, I am using laptop power supply 125V 0.7A -> 12V 1.6A. Now, my case is all plastic. The AC plug is two prong. So, what's the proper way of grounding in this case? The AC/DC adapter has fuse but I need to splice live 110V wire and connect it thru an on/off switch.

Thanks.
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Old 1st March 2010, 09:05 AM   #2
wwenze is offline wwenze  Singapore
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There is no real need to ground actually. Grounding is only necessary when you have high voltages running in an equipment that isn't double-shielded. 12V isn't high enough to hurt unless you lick it with your tongue.
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Old 1st March 2010, 10:21 AM   #3
wwenze is offline wwenze  Singapore
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My bad, I didn't notice the 110V on/off switch. Guess that's where to question comes from.

Though in this case it's still rather safe due to the plastic chassis, you have to make sure the live wire would not touch any metal parts in case of failure. Adequate spacing, securing the cables, plus another layer of insulation.
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Old 1st March 2010, 11:12 AM   #4
AndrewT is offline AndrewT  Scotland
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Hi,
if the power supply is certified as double insulated, then the power supply does not need a Safety Earth (Protective Earth).

The audio side does not need a Safety Earth. But, if there is anything inside the box that in the event of a worst case fault that could put mains onto any wire then the exposed conductive parts must be connected to Safety Earth.

If you modify the certified PSU, it no longer meets certification.

If the PSU is mounted, unmodified, outside the amplifier box, then there can never be mains voltage inside the box and then the Audio Ground does not need to be connected to Safety Earth.
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regards Andrew T.
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Old 1st March 2010, 01:39 PM   #5
maurycy is offline maurycy  United States
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Join Date: Dec 2005
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Thanks for replies.

I did remove the PSU from its plastic case so I guess it is not safe anymore. Now, I have another laptop power supply (125V 4A) that it is all original so I could use this one.

My only concern is that if I break the 12V wire instead of 125V one to install on/off switch, even in off position, the power supply would still draw power from the wall. Am I correct?
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Old 2nd March 2010, 11:49 PM   #6
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Yes. If you leave power attached to your power supply brick, it will draw a standby current.
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