Gainclone - Grounding

[Mareus]

Hello,
i managed to build my first LM3886 Gainclone successfully.

However, there are some questions about the grounding left.
My aim is to achieve maximum protection from electrical surges!

My Gainclone uses a central grounding star in which the +26V tail of one "powerrail" and the -26V rail of the other "powerrail" are connected.

Now I am thinking about how to ground the case? Due to my oppinion there are three posibilities:

1. Grounding the case to the groundingstar.
2. Grounding the case to the "mains-earth" from the power connector.
3. Grounding to case to the groundingstar and connect the groundingstar to the "mains-earth" of the power connector.

What would be the safest solution?

Thank you

Mareus

[Puffin]

Just look up the page a little bit to "chip amp power supply".

[Mareus]

Due to the fact that I am a bloody beginner, I am not able to understand everything which is written in the Gainclone PSU FAQ.

Could someone please give my an easy, failsafe explanation how to do the grounding? Just to be 100% sure.

Thanks!

Mareus

[Mr Evil]

The most important thing is that you must connect a metal case to earth, for safety. I recommend reading Rod Elliott's earthing article.

[pacificblue]

Originally posted by Mareus
1. Grounding the case to the groundingstar.
2. Grounding the case to the "mains-earth" from the power connector.
3. Grounding to case to the groundingstar and connect the groundingstar to the "mains-earth" of the power connector.

What would be the safest solution?

The case must be connected to the mains earth in such a way that
- it cannot come lose by itself.
- it need not be unfastened during maintenance to disconnect other wires, e. g. ground wires on a star grounding point.
- it provides a low resistance to eventual short-circuit currents. The resistance must be so low that the short-circuit current that flows is big enough to trip the fuse or circuit-breaker for that circuit in less than 0,2 s. This means you have to know the rated current of the fuse/circuit-breaker and its characteristic, which is maybe asking too much. As a general rule use a wire from the power connector to the case that has at least the same wire gauge as the other wires in the supply cable. In Germany 1,5 mm² is generally used as smallest good practice value, because it not only provides a low resistance, but also a good mechanical stability against damage.

Then take a wire from the case's earth point to the star-ground, so that the earth connection remains intact, even, if you disconnect wires from the star-ground.
An alternative approach is to use the same bolt for earth and star-ground, connect the earth first, secure it with a nut and connect all other wires on top of that nut with a second nut. That way you can unfasten the ground wires, while the first nut maintains the earth-wire connected to the chassis.