Cases for Amplifiers

[BobDraper]

It's possible to buy high quality aluminium cases on ebay/amazon which come from China. They fit together well and usually have output/input sockets and an on off switch included. There's a problem however - these cases are usually in sections and each part is coated in a substance that insulates it from the adjacent sections. Up to now I've spent a lot of tiiime rubbing off paintwork in a bid to try to make an electrical connection for the whole case and cross wiring between the different parts.

So my query is this - Is all this work really necessary? Does the whole thing have to be connected for safety and or screening?

 

[ctrlx]

yes.

all conductive metal casework needs to be connected to mains earth.

 

[gholl]

Unless everything inside is double-insulated!

 

[techtool]

Try external tooth lock washers on the fasteners to bite through painted or anodized surfaces to provide conductivity.
This is the method used by the makers of painted industrial cabinets like Wiegmann, Hammond, etc.

 

[BobDraper]

Sorry to be slow getting back.I just bough a NAD 902 power amp which has no earth wire. The on;y thimg I can see which makes this safe is binding of the ht wires with cable ties. It seems to me that should the primary to secondary short on the transformer the case could become live with only a layer of paint as protection. What is more thia seems to apply to every commercial bit of hifi equipment I've seen since the valve era IE metal case an no earth wire.

Thanks for the info on lock washers and other replies. I'll look into that, The Chinese do apply a very thick layer of paint though.

 

[gholl]

If the transformer/power supply has double insulation (signified by two [concentric] squares) there's no need for an earth wire. In case of a shorted secondary a fuse should blow and occasionally there might be a temperature fuse within the transformer. Worry not.

 

[Mooly]

Sorry to be slow getting back.I just bough a NAD 902 power amp which has no earth wire.

Its called 'Double Insulated' and must meet very exacting standards to be able to be classed as such.

See Class II here:
https://en.wikipedia.org/wiki/Appliance_classes

It seems to me that should the primary to secondary short on the transformer the case could become live with only a layer of paint as protection.

Its not going to happen with the manufacturer specified parts (transformer, mains switch etc etc). Fit non approved replacements and all bets are off and what you describe could happen. With the correct parts it will not.