Another Mains Electrical Earthing Situation.

Good morning,

I've chosen to start this new thread rather than hitch-hike on Georgineer's thread with a similar title.

I've recently been attending to my 1980s stack hi-fi equipment. This comprises the following 'separates': an amplifier, a CD player, an AM/FM radio and a compact cassette player, all by Pioneer, plus a Dual turntable. What prompted my creating this thread was my changing the mains plugs from Bulgin mini 6-amp 3-pin plugs to 'MasterPlug mini 10-amp 3-pin plugs. This wasn't done because of the increased current rating - the socket-strip for the MasterPlugs holds the plugs more securely than did the socket strip for the Bulgin plugs.

It was some 36 years since I bought and installed this equipment and I was surprised to discover that all the units had only two cores in their mains leads. There is a separate wire from the Dual turntable to a chassis terminal on the amplifier rear panel. Neither the loop AM antenna nor the FM ribbon feeder folded dipole antenna has an earth connection. I have not noticed whether any of the units bears a 'double insulated' badge. All the Pioneer units are effectively bonded together via the screens of their various audio cables and RCA phono plugs.

So, I've been operating this equipment for all these years with no connection to the 'circuit protective conductor' of the house supply. ( It is common knowledge that earthing of audio equipment has to be arranged with care in order to avoid hum-inducing earth loops. ) There's no easy way to connect the stack to the earth pole of the MasterPlug socket strip. The stack is housed in a purpose-built cabinet.

I'm interested to receive forum members' thoughts on this subject. Is this two-wire configuration peculiar to Pioneer equipment?

Best regards,

Swarf, Mostly!

I think (without looking at mine ) that you will find it is double insulsted and many of the units of this time were housed in wooden boxes. The main transformer will isolate and the working voltage will be low ie 5V, 12V or so. Ground loops are the problem. Noel

If your house has a modern RCB equipped distribution unit I would not worry about it.

regards Martin

I suggest you enrol and join Vintage Radio FOC, where there are some real experts on such matters. better to be safe than sorry John

Earthing is important whenever an appliance has a metal case because a live wire fraying or coming loose inside can electrify the outside of the unit. Very dangerous because metal cases provide a large contact area that greatly increases the current flow into the victim. Much worse than touching the end of a 2.5mm diameter wire.

An insulated case removes most of the risk, but care has to be taken to keep fingers out and to make certain control shafts, fixing screws and metal handles can't become live. Depending on the design, and earth might not be necessary.

Since plastics, many appliances come enclosed inside a fully insulated box. The risk of shock from these is minimal, and there's nothing users can touch that can to be earthed. The internal design also reduces the hazard in various ways. Earthing these does nothing useful.

Earths remain vital on metal appliances, but I suspect the majority of house appliances these days don't need or have one.

Signal and safety earth requirements are so different as to be almost two different subjects! I think it's safe to assume Pioneer understood both.

Dave

You can do nothing wrong by earthing all the matal cases to a mains earth or CPC. It is very unlikely that this will induce any noise or hum, but if it does, then you can think again! An installation with parralell paths to earth is a faulty installation! The problem with relying on the RCD to keep you safe is that it will only trip when someone touches the live metalwork and 30mA (or whatever) flows, and only if the trip is working as it should, Which is by no means a given. If the metalwork is earthed, the trip will operate as soon as the fault occurs, without anyone having to touch it. The old IEE regulations said "all extraeneous metalwork must be earthed" and "No mechanical device shall be fitted to any circuit as a SOLE means of protection" The use of RCD and MCB circuit protection breaks these regulations, and only time will tell us if this is a wise choice or not. If in doubt, earth it!!

Phil

Edited By Phil Whitley on 28/04/2022 10:03:51

Hi Swarf Mostly!, if you have Phono inputs on your amplifier, you should have the Earth post near to where the inputs are. Transcription decks (record player) with a magnetic pickup should have a thin wire with the phono input/output leads, this is done this way to prevent earth loop hum. The common connection from the pickup is totally insulated from the deck's metalwork and the thin wire, earth's the metalwork of the deck directly, rather than taking the long route round via the earth pin plugs, my Pioneer PL-3000 has only a twin mains cable and nothing on the users side has any connection to the thin wire and I've seen this with other decks with magnetic pickups, that I have had in the past. Although my Technics SU-3050 shows no earth connection through the mains plug on the schematic diagram, there is in fact a three core flex connecting it to the mains even though there is an isolating transformer that is the only part that connects to the mains.

I think both these where made before double insulation became more of the norm, as both the CD players plugged into the amp only have a twin plug-in mains flex and my double cassette player/recorder also only has a twin core flex connecting it to the mains.

Regards Nick.

Edited By Nicholas Farr on 28/04/2022 11:57:07