Am working on a Ratcliff 200A signal generator which happily is now up and running. The mains power cord has been replaced with a modern one for safety reasons.

There is a proper earthing of the mains with a certain combination of nuts/bolts/washers and lugs.

Would appreciate details of this and where the components could be purchased.

Thanks for any info.

In this particular case I would put one 3/16 bolt through the bottom or back of the cabinet and terminate the earth wire with a suitable crimp lug that will fit that bolt. Put the lug on the bolt first, followed by a flat washer, spring washer and nut or just the flat washer and a nylock nut, done as tight as possible without stripping the thread. This should be sufficient. Using the bolts that hold the transformer in place is electrically possible but illegal - a separate bolt needs to be used.

I do valve radios in a similar manner.

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A valve a day keeps the transistor away...

Thanks Brad, that is what I was after and will get the bolts, washers etc. Understand the necessity of using a bolt separate from any other assembly.

My Query would be why is it illegal to use the bolts from the transformer? There must be a good reason.

There are a couple. The bolts can work loose and the connection resistance can be higher than a separate connection. It isn't illegal to earth the body of the transformer, in fact it is a good idea but that particular connection can't be the only one.

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A valve a day keeps the transistor away...

QUOTE: Using the bolts that hold the transformer in place is electrically possible but illegal - a separate bolt needs to be used.

That rule is similar to the electrical code in the USA. The rule saying that a metal wiring box shall be connected to the grounding wire with a machine screw attached to the box, and that screw shall serve no other purpose. The hole for this screw in the box is tapped.

In the USA, all house wire connections are always done inside metal or plastic boxes. Idea being that if a connection goes bad, any sparks that happen will be contained inside the box, and won't ignite the innards of the house wall.

In the USA, all house wire connections are always done inside metal or plastic boxes.

In 2015, the UK mandated metal breaker boxes (which they call "consumer units") for all new installations.

QUOTE: The change to enclosures made from a non-combustible material is due to the rise in deaths from consumer unit house fires, which London Fire Brigade (LFB) has recorded. In 2013/14 alone there was a record 253 fires involving consumer units. This is a steep increase from 71 fires in 2011/12. LFB reported that the reason for the rise in fires was due to ‘substandard cable connections made by the electrician’, which led to the plastic enclosures overheating and igniting.

They must have a lot of dodgy sparkies in the UK. We've had plastic breaker boxes in Oz for decades and I have yet to hear of one causing a house fire, let alone 253 in a year!

The poms love their anachronistic ring main circuits. Maybe there's a connection (no pun intended).

All plastic used in electrical installations in Australia and probably elsewhere must be self-extinguishing.

That sort of regulation re fire did extend to transformers even in 1937, where the insulation material was not to support combustion. I tend to use, the shake proof washers, not so much for is shake proof feature but to bight into the metal and is more corrosion resistant.

A nut that cannot come loose is desirable otherwise lock nut. (two nuts). It is always desirable, as far as I am concerned, to ground a chassis where there is a shielded transformer. Anything with an MOV here sees it in a box that will not set a fire, if the MOV explodes (and they can). With a conventional nut & bolt arrangement: Transformers vibrate. Vibration loosens things.

Metal boxes and conduit, have killed especially where its got cloth rubber wiring in it. Several years back, two electricians were killed by it. I still consider cloth rubber wire to be implicated in burning down "Notre Dame Cathedral". Lengths of that early stuff will get a charge on it, as often joined lengths will get corrosion & bonding issues & with that old deteriorating wire can become "alive" especially if disturbed, like stood on.

Marc

Please excuse me if I'm digressing at all, but the Topic here included Earthing of Radios !
I only wanted to point out that Australian (240v) and USA (110v) radios can cause problems, especially if the USA units are 'Transformerless'. (Including all the filaments in series etc etc). Not to mention the often case in the USA of non-polarised plugs/circuits! As such, one can find problems with identifying an Active/Neutral, such that a Chassis actively becomes 'live'. (You don't want to Ground that). It can get messy using an isolated 240/110 v transformer, that doesn't relate to an earthed chassis.

There are European sets that have ballasts not transformers and hot chasses, we have AC /DC sets and a few hot chassis sets here. When working on, or, assessing (first move) sets: Caveat Actor always applies. If the Monkey's have been at it, even that it has a transformer: It could still be a death trap.

Seen plenty.

OBL,

AC/DC mains sets were also made here and can hide a few dangers for the unwary. Yes, it is not wise to earth the chassis of a transformerless receiver and most of the experienced collectors and restorers who have dealt with these are fortunately aware of the problems involved.

The big issue is inexperienced people delving into these and simply adding a new cord - the results will not usually be good ones and we continually warn these people not to touch AC/DC mains sets aside from giving the cabinet and front face features like knobs and dials a restoration so the set is able to be displayed.

Because Australia has a polarised pin layout, the possibility of incorrect connections is less than the US and some other countries however there is no guarantee that a correctly wired radio will not be plugged into an incorrectly wired socket. Some home handymen ignore the possibility of a $22,500.00 fine (NSW) for doing unlicenced electrical work and try their luck and sometimes one will get the odd electrician who just bangs in that extra power point and doesn't test his work. So the risks with AC/DC sets remains.

An AC/DC receiver, even when restored correctly, should only be used with an isolation transformer.

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A valve a day keeps the transistor away...

An AC/DC receiver, even when restored correctly, MUST only be used with an isolation transformer.

I am a moderator on an American radio forum & they have piles of transformerless sets. Lots of those have two pin NEMA plugs & they in most cases can be reversed, so its an outright raffle as to where Active (line) ends up. Not everything is wired by electricians over there.

I have seen it here on a signal generator even that it had a transformer for one, but it is common to see a capacitor/s line to metal chasses and cases. That, when line is reversed, can also see AC active actually put onto the chassis. The older caps are not always a line cap.

I do keep a plug in tester for polarity as its convenient and safe and a quick test for plugs & cables. I often do Tag & Test at the local Mens Shed & of donated (in good faith or dumped) cables & such I would find around ten percent faulty and /or scrap.

My Isolation transformer, aside from line filters (RF), there are circuit breakers both sides of the transformer a pair of bezels to show that both sides are live and more importantly a KILL switch.

It should also be reiterated that a Slide transformer (Variac tm) is an Auto transformer not an isolation transformer.

Marcc

More modern AC/DC radios had all enclosing plastic or wood cabinet, with plastic knobs (and vent slots on the back cover). And any metal chassis had a bypass cap to the B- line, which was usually connected to the power line through the power switch. Only hazard is when you are doing repairs with the radio outside the cabinet.