where to connect the shield - Electronic Circuits Projects Diagrams Free

balkesli · 18th February 2008, 09:12 PM

hi,
we designed an electronic card which is supplied by a dc adapter(i.e. no safety ground connection). the card is in a box and the box is shielded. i wonder where should i connect the shield? because there is no earth connection.

RadioRon · 19th February 2008, 09:18 AM

The shield can function correctly even if it is not earthed. In your situation it might be best to connect the shield to the circuit reference on the card (ie. DC ground). However, it would be useful to know a few things first. Are there cables passing into and out of the box? Is it likely that a person would touch the sheild metal in normal use? Is the sheild there for a specific purpose, or just general protection?

balkesli · 20th February 2008, 11:22 AM

the shield is for emc purposes. to block em waves. does it function properly if i connect it to the DC ground?

Boncuk · 20th February 2008, 02:03 PM

The best bet would be to get a real earth (not the articial "earth" taken from neutral) shield connected to the box. The shielded cable should only be connected at the box to leave the other end unconnected.

The shielding in that particular case is not AF which requires shielding on both sides. Shielding AF cables on both sides is a cripple. A third neutral wire and an extra shielding is much better.

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18th February 2008, 09:12 PM	(permalink)
balkesli	where to connect the shield hi, we designed an electronic card which is supplied by a dc adapter(i.e. no safety ground connection). the card is in a box and the box is shielded. i wonder where should i connect the shield? because there is no earth connection.

19th February 2008, 09:18 AM	(permalink)
RadioRon	The shield can function correctly even if it is not earthed. In your situation it might be best to connect the shield to the circuit reference on the card (ie. DC ground). However, it would be useful to know a few things first. Are there cables passing into and out of the box? Is it likely that a person would touch the sheild metal in normal use? Is the sheild there for a specific purpose, or just general protection? __________________ RadioRon

20th February 2008, 11:22 AM	(permalink)
balkesli	the shield is for emc purposes. to block em waves. does it function properly if i connect it to the DC ground?

20th February 2008, 02:03 PM	(permalink)
Boncuk	Shielding The best bet would be to get a real earth (not the articial "earth" taken from neutral) shield connected to the box. The shielded cable should only be connected at the box to leave the other end unconnected. The shielding in that particular case is not AF which requires shielding on both sides. Shielding AF cables on both sides is a cripple. A third neutral wire and an extra shielding is much better.