Proper way of grounding in plastic chassis?

maurycy · 1st March 2010, 01:03 AM

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.

wwenze · 1st March 2010, 08:05 AM

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.

wwenze · 1st March 2010, 09:21 AM

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.

AndrewT · 1st March 2010, 10:12 AM

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.

maurycy · 1st March 2010, 12:39 PM

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?

Rainwulf · 2nd March 2010, 10:49 PM

Yes. If you leave power attached to your power supply brick, it will draw a standby current.

1st March 2010, 01:03 AM	#1
maurycy diyAudio Member Join Date: Dec 2005 Location: NJ	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.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
plastic cases and grounding - shielding	then_dude	Solid State	2	13th October 2007 02:15 PM
Proper grounding method...	69CamaroSS396	Tubes / Valves	14	11th August 2007 04:40 PM
Proper Grounding Scheme	PaulHilgeman	Parts	38	14th October 2003 05:00 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

1st March 2010, 08:05 AM	#2
wwenze diyAudio Member Join Date: Mar 2008	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.

1st March 2010, 09:21 AM	#3
wwenze diyAudio Member Join Date: Mar 2008	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.

1st March 2010, 10:12 AM	#4
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	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.

1st March 2010, 12:39 PM	#5
maurycy diyAudio Member Join Date: Dec 2005 Location: NJ	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?

2nd March 2010, 10:49 PM	#6
Rainwulf diyAudio Member Join Date: Feb 2009	Yes. If you leave power attached to your power supply brick, it will draw a standby current.