Converting live chassis sets to earthed chassis

[boater sam]

I am perfectly happy working on sets where the chassis is connected to the neutral mains but do prefer sets with mains transformers and earthed chassis.
For some time I have considered changing an AC/DC set when it is being extensively rebuilt to have an earthed chassis without using an isolating transformer.
If all the ground connections could be taken to a "return rail" rather than chassis, then an earth could possibly be fitted.
There would be some care needed with regard to tuning capacitors, pilot lamp holders etc. but this should be plausible. It would avoid insulating/isolating knob grub screws, aerial, earth and gram connections and all the little bits like metal frets & trims.

Any view on this idea? Am I a heretic?
It would not be original but the changes would be difficult to spot on a casual look. Purists may pooh pooh the idea, but it would bring sets into a safer condition, more in line with modern regulations.

[AlanBeckett]

In the normal Domestic situation it really does depend on your (Electrical) Supply installation. I'm sure there are people on here who are much more familiar with the 17th Edition than I am. However, if your Installation has Protective Multiple Earthing (PME) then there will be a Tag near to the Meter saying so. If that's the case then Neutral is bonded to Earth at your Premises and you'll be OK. If that's not the case then you may well find that you can measure a significant Voltage between Neutral and Earth. If that's the case then joining them together with a relatively thin piece if Wire could produce exciting results.
There are more 'Interesting' installations out in the Boon Docks - ask Lawrence

Alan

[boater sam]

In the normal Domestic situation it really does depend on your (Electrical) Supply installation. I'm sure there are people on here who are much more familiar with the 17th Edition than I am. However, if your Installation has Protective Multiple Earthing (PME) then there will be a Tag near to the Meter saying so. If that's the case then Neutral is bonded to Earth at your Premises and you'll be OK. If that's not the case then you may well find that you can measure a significant Voltage between Neutral and Earth. If that's the case then joining them together with a relatively thin piece if Wire could produce exciting results.
There are more 'Interesting' installations out in the Boon Docks - ask Lawrence

Alan

TN-C-S installation in current terms. Without looking up the regs. I can't remember the allowable neutral conductor potential relative to true ground but it is small. Usually anything over 6 volts is reportable, and rectified.
In the distribution ONLY. Additional N to E connections not allowed on consumer side of incomer head. RCD/ELCB would trip anyway.
There would be no N to E in the radio.

[AlanBeckett]

There would be no N to E in the radio.

Yes, but there is the potential for such a fault.
I don't have any strong views on Authenticity but I'm not sure exactly what you would achieve.

Alan

[boater sam]

There would be no N to E in the radio.

Yes, but there is the potential for such a fault.
I don't have any strong views on Authenticity but I'm not sure exactly what you would achieve.

Alan

Surely no more likelihood of a N to E fault than in any other appliance with an earth? The domestic distribution is designed to cope with such faults, that's what RCDs are for, i.e. non Phase faults and leakage to earth faults that fuses and MCBs don't detect or clear.

With zero neutral volts, RCDs still detect a N to E fault and disconect.
But we seem to be drifting off thread here. Sorry.

[pwdrive]

"There are more 'Interesting' installations out in the Boon Docks - ask Lawrence"

On the consumer unit side of the meter ours is the standard stuff, the outside incomer at the outside meter box has neutral feed and earth feed to the consumer unit connected together and sealed (tamper resistant) within the meter box, the neutral on each utility pole is connected to a buried earth mat (might be a spike, not sure) which is buried close to each utility pole going back to the transformer and possibly beyond, we are about 3 to 4 poles away from the transformer pole.

On the AC/DC neutral conversion thing I guess it's up to what you want, I don't do mains AC/DC radios but if I did then it would be via a suitably rated isolating transformer.

EDIT: The original incomer had a PME tag or label attached to it in the meter box, they replaced the old original incomer cables (bare aluminium) due to them setting fire to the garden (old thread about that in this forum somewhere) They were replaced with fully insulated cables all the way back to the transformer pole, they are labeled CNE at the meter box.

Lawrence.

[Radio Fixer]

What you described in your original post Sam was the way many US sets were made in the 30's and 40's. The chassis still got connected to the -ve rail supply and neutral, for RF purposes, by a cap (typically .05 or .1) with a discharge resistor across it, typically 220K.

It can be done with Brit sets that weren't designed that way but there are certain problems as you have noted.

Gary

[Ed_Dinning]

Hi Gents, there have been Eddystone AC/DC sets manufactured as described above, with the chassis earthed and a "neutral" busbar insulated from chassis within the set. This busbar is linked to chassis and earth via a Y class capacitor.

It certainly can be done, but requires care and caution.

Ed

[boater sam]

Hi Gents, there have been Eddystone AC/DC sets manufactured as described above, with the chassis earthed and a "neutral" busbar insulated from chassis within the set. This busbar is linked to chassis and earth via a Y class capacitor.

It certainly can be done, but requires care and caution.

Ed

Thank you all for your input. I think that the effort to convert a chassis will be worthwhile if only to prove it is plausible.
I am assuming the capacitor between Neutral and earth is purely for RF suppression, in which case is there a case for a pi network of 1, X and 2, Y caps as used for motor suppression? That would take care of the modulation capacitor as well.
As I said, it is not for my safety but to establish that with modern components a better solution is available to the now frowned upon practice of 'live' chassis construction.
Agreed that the isolating transformer solution is good, but that seems to me like a patch rather than a cost effective design solution.