Earthing AC/DC live chassis radios - UK Vintage Radio Repair and Restoration Discussion Forum

YT2095UK · 5th Nov 2009, 5:14 pm

[Split from https://www.vintage-radio.net/forum/...d.php?t=47049]]

as for the chassis being Live, it Is wired to Neutral and Earth in the plug, and eventually will have a 3 core flex (Chassis Earthed) when it`s all put back together, I`m not a fan of `U` type valves and series heater sets, but this one has something special going on.
and she`ll not be able to Play with it as it`ll be on her bedroom shelf, besides, she has several trannies to play with anyway.

paulsherwin · 5th Nov 2009, 6:06 pm

Quote:

Originally Posted by YT2095UK

as for the chassis being Live, it Is wired to Neutral and Earth in the plug, and eventually will have a 3 core flex (Chassis Earthed) when it`s all put back together

NOOOO!

You should not earth the chassis of an AC/DC set. Mains neutral is connected to earth, but not in your house. It is earthed at the electricity substation, and there can be several volts between neutral and earth once the supply gets to your home. Earthing the chassis may cause all sorts of problems, the most likely being to trip the earth leakage breaker in your consumer unit.

AC/DC sets maintain safety by physically isolating all the metal parts that may potentially become live. If the cabinet has been well constructed and there is a suitable back then the radio will be safe in normal use.

I think Nick may have been concerned by the tendency of young children to take things to pieces and poke things into holes. I would be reluctant to allow a young child to use any valve radio unsupervised.

Paul

kalee20 · 5th Nov 2009, 6:17 pm

Quote:

Originally Posted by YT2095UK

as for the chassis being Live, it Is wired to Neutral and Earth in the plug

No, no, no!

If you do this you can have large circulating earth loop currents (assuming a circuit breaker doesn't trip). Earth and neutral should be the same potential, but in practice, voltage drops along neutral wires caused by currents flowing through them, can put neutral a few volts above earth by the time it gets to your house.

One thing I have done, is to take the earth lead in a 3-core cable, to the chassis via a 240V neon indicator. If the indicator lights, the chassis is live due to a neutral/live mix up somewhere.

YT2095UK · 5th Nov 2009, 6:23 pm

All of my 2 wire DC sets are like this, the only voltage difference is 0.178v between Earth and Neutral here.
my Shed wiring is also Earthed Propper (copper pipe burried), and so my House as a result is also Earthed localy as well as at the station.
no RCD problems here ever?
I find that Earthing the chassis of such sets also helps reduce Noise, and living in the middle of Town I need all the help I can get reducing unwanted RF noise.
it even helps pull the Signals up on SW too

I agree totally with the unsupervised part, she can use the radio here (in the workshop) and likes to see the valves light up in the dark and change channels, I expect this will go towards her fond memories of Valve radios too, I know I have plenty.

murphyv310 · 6th Nov 2009, 12:31 am

Hi YT.
Assume the neutral is cut somewhere after the substation grounding, where is all the current going? Yes right through that little 13 amp plug, if that scenario was to happen you could have a big bang or even worse.
Its also against the regulations.
Cheers
Trevor

YT2095UK · 6th Nov 2009, 12:18 pm

I`m struggling to understand exactly what you mean?
in your scenario all I can see happening is that my radio wired the way it is would continue to work as it`s now using earth in place of the Neutral, and will only draw the amount of current that it needs.
a bit like way back when many places were fed a single Live wire from the grid and other end of the potential was a local earth (a burried pipe or plate on the land), in fact some remote farms still use this.
don`t get me wrong, I`m not substituting Earth for Neutral here, I`m strapping earth TO neutral on 2 wire sets.

I`d like to understand what it is you guys can see that I`m failing to.

cmjones01 · 6th Nov 2009, 12:35 pm

The Neutral wire to your house is shared with lots of other people. Imagine it gets broken somewhere between your house and the substation. Where does the return current from everyone else's house flow then? Through the chassis of your radio and its mains lead. Now your local earth probably has a dangerous voltage on it and the mains lead has probably caught fire. That's why this arrangement isn't allowed!

Peter.N. · 6th Nov 2009, 12:53 pm

Its not the effect it could have on your radio that's the problem, its the effect on your house wiring, as already stated the load on the neutral wire between you and where it is strapped to earth at the transformer/substation could result in a difference of several volts between neutral end earth which could be a quite a high amperage, enough to heat up or even burn the part of the circuit that is in effect short circuiting the long run to the substation - that is assuming of course that your local earth has a very low resistance.

paulsherwin · 6th Nov 2009, 12:54 pm

To put it in even simpler terms, if there is a potential difference between neutral and earth in your house and you have them strapped together, a current will flow through your house wiring. In many cases this will be too small to be noticed unless a circuit breaker trips, but in the worst case a huge current will flow. If you're lucky a fuse will blow somewhere, but if you're unlucky your house will burn down

Paul

AlanBeckett · 6th Nov 2009, 1:07 pm

I think you're at cross purposes. YT2095UK, go to your meter and/or consumer unit and see if there's a tag or label on it saying it's a PME system. If so, then Earth and Neutral are bonded together at your house. If not then the above comments apply. Even if they are bonded there may still be problems. My istallation is PME. However, in my garage, which is on the end of a length of SWA at the bottom of the garden, there is sufficient potential difference between the incoming Earth and Neutral, when several things are switched on, to trip the garage RCD if they are connected together. So, in the house I can connect a set's Neutral and Earth, but both in the garage or greenhouse, which is even further away I can't.
Alan

YT2095UK · 6th Nov 2009, 1:16 pm

I just had a look, and earth IS neutral here?
2 wires come into the house, they go into a box with a 60A fuse in it and 3 wires come out, Earth, Neutral and Live, then off they go to the meter etc...
at that point (pre 60A fuse box) downstairs there can only be Live and Earth surely?
I`v also had a go at drawing out a circuit for the above scenarios and I think I can see what you mean, in a way it would be like supply all the current those houses hooked up to mine were using and drawing it through my Chassis Earth/Neutral wire.
and while it May not make any difference in our house the way it`s wired up, if I ever gave a set away to someone...
I`ll undo it asap

how about this then, a pair of 0.1uF caps from Live and Neutral to the earth wire?
it Does help pull up signals on my SW set, so it gives a HF AC path, but nothing harmfull or dangerous should the local substation fail.

paulsherwin · 6th Nov 2009, 1:21 pm

Your house supply will be live and neutral. The earth is provided by an earthing point in your house. There will not normally be a connection between N and E in your house.

Your capacitor idea shouldn't do any harm. You should use X2 rated caps for safety.

Paul

julie_m · 6th Nov 2009, 1:26 pm

In a town, the earth and neutral conductors will be joined together at each house where the cable enters from the street. This is known as protective multiple earthing (also called TN-C) which helps guard against "disconnected neutral" scenarios.

Also, the residual current detector in or next to your consumer unit relies on every milliampere supplied by the live wire returning via the neutral wire. If there is more than 30mA difference, it trips and cuts off the supply (on the assumption that whatever unauthorised route the current is taking might be via you). If you have joined earth and neutral somewhere downstream of the RCD, then you have provided another return path and run the risk of tripping it.

In fact, I'm surprise you haven't already. Save your work, and go and test your RCD right now. (And do your smoke alarms on the way back.)

ppppenguin · 6th Nov 2009, 1:45 pm

Quote:

Originally Posted by ajs_derby

In a town, the earth and neutral conductors will be joined together at each house where the cable enters from the street. This is known as protective multiple earthing (also called TN-C) which helps guard against "disconnected neutral" scenarios.

My italics. PME (TN-C) is widely used for both urban and rural supplies. TN-C-S, where the cable armouring is used for earthing, is also common, especially in urban underground supplies.

This wikipedia article is a decent introduction to the subject.
http://en.wikipedia.org/wiki/Earthing_system

YT2095UK · 6th Nov 2009, 1:51 pm

my smoke alarms (and extinguishers are all fine) I check them 1`st of every month, I`m a bit paranoid like that.
for testing an RCD, would a 7W pygmy bulb Live to earth do it (that draws about 30ma), or is there a better way?
I can`t do it until my wife gets back as she needs to turn off her computers first.

cmjones01 · 6th Nov 2009, 1:56 pm

Quote:

Originally Posted by paulsherwin

Your capacitor idea shouldn't do any harm. You should use X2 rated caps for safety.

I might have missed something, but aren't capacitors between L/N and E supposed to be class Y rated? Their failure could (in theory, at least) expose someone to electric shock.

julie_m · 6th Nov 2009, 2:00 pm

Quote:

Originally Posted by YT2095UK

for testing an RCD, would a 7W pygmy bulb Live to earth do it (that draws about 30ma), or is there a better way?

The test button on the RCD is usually the easiest way ..... It works by connecting a resistance from live on the "outgoing" side to neutral on the "incoming" side, so the fault current never leaves the live/neutral pair. This avoids the risk of imposing a potential on metalwork that should be earthed, but isn't due to some other fault.

paulsherwin · 6th Nov 2009, 2:09 pm

Quote:

Originally Posted by cmjones01

Quote:

Originally Posted by paulsherwin

Your capacitor idea shouldn't do any harm. You should use X2 rated caps for safety.

I might have missed something, but aren't capacitors between L/N and E supposed to be class Y rated? Their failure could (in theory, at least) expose someone to electric shock.

I'm not familiar with the regulations, and you may be right. I can't see the safety issue myself but that doesn't mean it isn't there.

I would expect a SC cap failure in these positions to cause a blown fuse or tripped breaker rather than a safety hazard

Caps used to isolate aerial and earth sockets are certainly supposed to be class Y.

Paul

cmjones01 · 6th Nov 2009, 2:20 pm

I did a quick Google and turned up:
http://www.justradios.com/safetytips.html
which, though from a Canadian perspective, indicates that class Y should be used from L/N to E. I guess the dangerous condition only arises if there's a high-impedance earth fault at the same time as a capacitor failure.

Semi-relevant anecdote: when I moved into this house, the whole electrical installation wasn't actually earthed, though it looked like it was. It's a TN-S installation with the sheath of the incoming cable used as earth, but the earth wire (such as it was) from the assortment of fuse boxes was waving in the breeze somewhere near the cable sheath! I think the surveyor's report recommended 'a brief electrical test'. Yeah, right! One of the first things I did was rewire the place...

Radio_Dave · 6th Nov 2009, 6:10 pm

Quote:

Originally Posted by YT2095UK

I find that Earthing the chassis of such sets also helps reduce Noise, and living in the middle of Town I need all the help I can get reducing unwanted RF noise. it even helps pull the Signals up on SW too

Quote:

Originally Posted by YT2095UK

I just had a look, and earth IS neutral here?

I can't see how you notice an improvement in reception if you earth an ac/dc set when you claim the earth and neutral are tied together in your house?

I really am no expert, but neither are the many others (some with even less knowledge) who visit this public forum. Therefore, I hope somebody will clarify the correct and only way to wire and connect an ac/dc set to the mains supply. I don't think the households supply/consumer unit is relevant as a radio is a portable device

David

5th Nov 2009, 5:14 pm	#1
YT2095UK Retired Dormant Member Join Date: Sep 2009 Posts: 487	Earthing AC/DC live chassis radios [Split from https://www.vintage-radio.net/forum/...d.php?t=47049]] as for the chassis being Live, it Is wired to Neutral and Earth in the plug, and eventually will have a 3 core flex (Chassis Earthed) when it`s all put back together, I`m not a fan of `U` type valves and series heater sets, but this one has something special going on. and she`ll not be able to Play with it as it`ll be on her bedroom shelf, besides, she has several trannies to play with anyway.

5th Nov 2009, 6:23 pm	#4
YT2095UK Retired Dormant Member Join Date: Sep 2009 Posts: 487	Re: a "Unique" Murphy 198M All of my 2 wire DC sets are like this, the only voltage difference is 0.178v between Earth and Neutral here. my Shed wiring is also Earthed Propper (copper pipe burried), and so my House as a result is also Earthed localy as well as at the station. no RCD problems here ever? I find that Earthing the chassis of such sets also helps reduce Noise, and living in the middle of Town I need all the help I can get reducing unwanted RF noise. it even helps pull the Signals up on SW too I agree totally with the unsupervised part, she can use the radio here (in the workshop) and likes to see the valves light up in the dark and change channels, I expect this will go towards her fond memories of Valve radios too, I know I have plenty.

6th Nov 2009, 12:31 am	#5
murphyv310 Dekatron Join Date: Sep 2006 Location: Kilmarnock, Ayrshire, UK. Posts: 5,422	Re: a "Unique" Murphy 198M Hi YT. Assume the neutral is cut somewhere after the substation grounding, where is all the current going? Yes right through that little 13 amp plug, if that scenario was to happen you could have a big bang or even worse. Its also against the regulations. Cheers Trevor __________________ Cheers, Trevor. MM0KJJ. RSGB, GQRP, WACRAL, K&LARC. Member

6th Nov 2009, 12:18 pm	#6
YT2095UK Retired Dormant Member Join Date: Sep 2009 Posts: 487	Re: a "Unique" Murphy 198M I`m struggling to understand exactly what you mean? in your scenario all I can see happening is that my radio wired the way it is would continue to work as it`s now using earth in place of the Neutral, and will only draw the amount of current that it needs. a bit like way back when many places were fed a single Live wire from the grid and other end of the potential was a local earth (a burried pipe or plate on the land), in fact some remote farms still use this. don`t get me wrong, I`m not substituting Earth for Neutral here, I`m strapping earth TO neutral on 2 wire sets. I`d like to understand what it is you guys can see that I`m failing to.

6th Nov 2009, 12:35 pm	#7
cmjones01 Nonode Join Date: Oct 2008 Location: Warsaw, Poland and Cambridge, UK Posts: 2,679	Re: a "Unique" Murphy 198M The Neutral wire to your house is shared with lots of other people. Imagine it gets broken somewhere between your house and the substation. Where does the return current from everyone else's house flow then? Through the chassis of your radio and its mains lead. Now your local earth probably has a dangerous voltage on it and the mains lead has probably caught fire. That's why this arrangement isn't allowed!

6th Nov 2009, 12:53 pm	#8
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	Re: Earthing AC/DC live chassis radios Its not the effect it could have on your radio that's the problem, its the effect on your house wiring, as already stated the load on the neutral wire between you and where it is strapped to earth at the transformer/substation could result in a difference of several volts between neutral end earth which could be a quite a high amperage, enough to heat up or even burn the part of the circuit that is in effect short circuiting the long run to the substation - that is assuming of course that your local earth has a very low resistance.

6th Nov 2009, 12:54 pm	#9
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,966	Re: Earthing AC/DC live chassis radios To put it in even simpler terms, if there is a potential difference between neutral and earth in your house and you have them strapped together, a current will flow through your house wiring. In many cases this will be too small to be noticed unless a circuit breaker trips, but in the worst case a huge current will flow. If you're lucky a fuse will blow somewhere, but if you're unlucky your house will burn down Paul

6th Nov 2009, 1:07 pm	#10
AlanBeckett Rest in Peace Join Date: Dec 2008 Location: Burton upon Trent, East Staffordshire, UK. Posts: 1,686	Re: Earthing AC/DC live chassis radios I think you're at cross purposes. YT2095UK, go to your meter and/or consumer unit and see if there's a tag or label on it saying it's a PME system. If so, then Earth and Neutral are bonded together at your house. If not then the above comments apply. Even if they are bonded there may still be problems. My istallation is PME. However, in my garage, which is on the end of a length of SWA at the bottom of the garden, there is sufficient potential difference between the incoming Earth and Neutral, when several things are switched on, to trip the garage RCD if they are connected together. So, in the house I can connect a set's Neutral and Earth, but both in the garage or greenhouse, which is even further away I can't. Alan

6th Nov 2009, 1:16 pm	#11
YT2095UK Retired Dormant Member Join Date: Sep 2009 Posts: 487	Re: Earthing AC/DC live chassis radios I just had a look, and earth IS neutral here? 2 wires come into the house, they go into a box with a 60A fuse in it and 3 wires come out, Earth, Neutral and Live, then off they go to the meter etc... at that point (pre 60A fuse box) downstairs there can only be Live and Earth surely? I`v also had a go at drawing out a circuit for the above scenarios and I think I can see what you mean, in a way it would be like supply all the current those houses hooked up to mine were using and drawing it through my Chassis Earth/Neutral wire. and while it May not make any difference in our house the way it`s wired up, if I ever gave a set away to someone... I`ll undo it asap how about this then, a pair of 0.1uF caps from Live and Neutral to the earth wire? it Does help pull up signals on my SW set, so it gives a HF AC path, but nothing harmfull or dangerous should the local substation fail.

6th Nov 2009, 1:21 pm	#12
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,966	Re: Earthing AC/DC live chassis radios Your house supply will be live and neutral. The earth is provided by an earthing point in your house. There will not normally be a connection between N and E in your house. Your capacitor idea shouldn't do any harm. You should use X2 rated caps for safety. Paul

6th Nov 2009, 1:26 pm	#13
julie_m Dekatron Join Date: May 2008 Location: Derby, UK. Posts: 7,735	Re: Earthing AC/DC live chassis radios In a town, the earth and neutral conductors will be joined together at each house where the cable enters from the street. This is known as protective multiple earthing (also called TN-C) which helps guard against "disconnected neutral" scenarios. Also, the residual current detector in or next to your consumer unit relies on every milliampere supplied by the live wire returning via the neutral wire. If there is more than 30mA difference, it trips and cuts off the supply (on the assumption that whatever unauthorised route the current is taking might be via you). If you have joined earth and neutral somewhere downstream of the RCD, then you have provided another return path and run the risk of tripping it. In fact, I'm surprise you haven't already. Save your work, and go and test your RCD right now. (And do your smoke alarms on the way back.) __________________ If I have seen further than others, it is because I was standing on a pile of failed experiments.

6th Nov 2009, 1:51 pm	#15
YT2095UK Retired Dormant Member Join Date: Sep 2009 Posts: 487	Re: Earthing AC/DC live chassis radios my smoke alarms (and extinguishers are all fine) I check them 1`st of every month, I`m a bit paranoid like that. for testing an RCD, would a 7W pygmy bulb Live to earth do it (that draws about 30ma), or is there a better way? I can`t do it until my wife gets back as she needs to turn off her computers first.

6th Nov 2009, 2:20 pm	#19
cmjones01 Nonode Join Date: Oct 2008 Location: Warsaw, Poland and Cambridge, UK Posts: 2,679	Re: Earthing AC/DC live chassis radios I did a quick Google and turned up: http://www.justradios.com/safetytips.html which, though from a Canadian perspective, indicates that class Y should be used from L/N to E. I guess the dangerous condition only arises if there's a high-impedance earth fault at the same time as a capacitor failure. Semi-relevant anecdote: when I moved into this house, the whole electrical installation wasn't actually earthed, though it looked like it was. It's a TN-S installation with the sheath of the incoming cable used as earth, but the earth wire (such as it was) from the assortment of fuse boxes was waving in the breeze somewhere near the cable sheath! I think the surveyor's report recommended 'a brief electrical test'. Yeah, right! One of the first things I did was rewire the place...