making an Earth / Ground connection. rema: 2005 Stereo B;
I am replacing the mains power cable on this set. As is normal, the original cable does not include a ground/earth wire. I would like to connect the ground/earth wire that is in the replacement cable, to the set. This is mainly for audio reasons, and also safety reasons. I am in the UK where earth is standard on mains power sockets.
I have some years experience with audio and electrical wiring, but am not familiar with vintage equipment from the DDR, and thought this may be a good thing to check with the wise folks of the RadioMuseum.
My questions are:
1 Is this likely to be a good/safe idea?
2 If so, What is the best place to connect it to? Do I simply make a really strong connection to a solid part of the radio's metal chassis?
3 I would also like to do the common hi-fi practise of connecting the earthing cable (NOT the audio cable screen) from another peice of audio, a turntable, to the same connection point on the radio. Is this likely to be a good/safe idea?
4 Are there any capacitors, or anything else, that should be discharged, or otherwise made safe, before handling/soldering the power connections?
5 Is it best to wait some time after disconnecting the power plug, before working on it?
It's great to make my first post on RadioMuseum - I'm very glad to see there's no such thing as a stupid question!
as long as your radio is mounted inside an "insulating enclosure" after repair, e. g. in a wooden casing, there is no reason to connect the metal chassis with PE. This applies also if such a radio will be connected with a CD-player or turntable, which are usually equipped with a two wire mains cable without PE as well.
Your question is general and not limited to the United Kingdom and has nothing to do with the former "DDR" . You can assume that this radio was produced according to the standards valid at that time ("state of the art"). If you made no fundamental changes regarding the power supply (and I think you did not), electrical safety is ensured further on.
Thank you very much for your reflections.
It is good to know the apparatus is safe without a PE.
However, with respect, my questions are about the possible issues involved in the ADDING of a PE to it.
To be clear:
This was made at a time, and in a country, where there was no earthing system incorporated in the infrastructure of the electricity system.
I intend to add an earth to it, and connect it to an electricity system which incorporates earth as standard.
It seems straightforward, and this may be a stupid question, but we are dealing with high voltages here, and I am checking if anyone thinks there may be any problems or difficulties which are likely to arise - both in the fitting of a new power cable (which is necessary, with or without this modification), and in the operation of a set so modified.
Surely someone here has attempted a similar modification?
I am aware this is quite a general question, yet I include details about the set, the country of origin, and its present location, in order to provide as much potentially relevant information as possible for those who would try to help me.
Thanks in advance,
Although your question is simple the answer is surprisingly complex and depends on many factors. In this particular case we are talking about a radio manufactured in Europe during the 1960’s. The set is AC only and therefore probably uses a mains transformer, which might isolate the chassis from the mains supply. However this should not be taken for granted as some sets use auto-transformers that provide no isolation. It is necessary to ascertain if it is isolate and exactly how. If it is not isolated by a transformer then attaching a “Protective Earth” should not be considered.
Some sets particularly AC/DC sets have chassis isolated by capacitors. If the chassis were to be connected to the PE several problems could arise: -
- The isolating capacitors would be stressed & if original liable to failure.
- The PE may introduce electrical interference (noise).
- A small current would flow to the PE via the isolating capacitors. If the mains supply is protected by a “Residual Current Breaker” as is now common then this small leakage could increase the likelihood of nuisance tripping.
Even with transformer isolated chassis problems may arise such as: -
1. If the transformer is very old it may become stressed & fail.
2. The PE may introduce electrical interference (noise).
Most European countries have had PE available in homes for just as long as in Britain, but usually just for high risk appliances such as washing machines etc. In Britain it was normal to attach a PE to any appliance that had any exposed conductive surface. This could result in complicated wiring of Hi Fi audio systems as introducing a PE often caused hum. In recent years if not decades the use of PE for domestic electronic equipment in Britain has declined & is no longer used in most cases.
If your concern is safety then an insulation test should be perform between any exposed conductor & the mains terminals using an insulation tester. Such tests are normally carried out using a test voltage of 500v DC.
Providing the set has sufficient insulation a PE is not only unnecessary but a possible source of problems.
I would strongly recommend that PE should not be added without understanding all the issues. However proper insulation testing is worth considering. Indeed within the UK it is illegal to sell any electrical appliance including second hand radios without a certified electrical safety test. Something, which is often ignored. Another consideration is that any person making alterations is legally responsible for any injury caused as a result.
the earth connection you are proposing is strongly advisable. Old equipment may have poor insulation in the primary side, damaged rubber wires, or unsafe paper capacitors. The earth wire can be connected to the chassis close to the entry point of the power cable. A clean job can be done with the use of Euro IEC-320 connector/filter, connecting the earth wire from the filter to one of its locking screws. In this way, you have also a noise filtering action, fully compliant with the latest safety standards, on the mains wires. You can then remove old and unsafe paper capacitors from the primary of the power transformer and the chassis. Another way is to use a bathtub style line filter, when it is impossible to fit the IEC socket. These solutions will also provide properly insulated turrets to terminate the transformer primary wires. You can give a look to various existing models at http://www.corcom.com/Series/PowerLine/K/. Otherwise you can use a terminal board to terminate the power cable.
No matter the solution you choose, remember to firmly lock the entering cable, so it cannot move if you pull the power cord. Other important safety rules are to do good joints and to insulate hot wires, so that they cannot be inadvertently touched. Crimped insulated faston terminations are advisable.
About charged capacitors, there are no big capacitors on the primary side. It is however good practice to wait several minutes after having unplugged the cable, to allow all capacitors to discharge, before starting to work inside the chassis. Do not try to manually discharge them (you can do it only if you already have experience): just check with a voltmeter the voltage across them before touching anything under the chassis.
Thank you, Keith and Emilio, very much.
At first I want o point out that I fully agree with the detailed information from Keith Staines, including the possible danger of hum, thank you for your support!
But I have a problem with the general statement "the earth connection is strongly advisable". Old industrially manufactured equipment is not unsafe in principle or only because of its age. As far as I remember we had many discussions like that in German language.
There were mentioned some typical faulty components which always occur in connection with old electrical equipment.
It is exactly the task of the restoring person to replace or repair such parts during restoration because they are a potential risk and the main reason for possible, or better, for typical damage later on.
- Nobody who feels responsible for himself and other people would leave "damaged wires, paper capacitors, etc." inside the power supply of a radio which he intends to operate again. That means, operational safety must be ensured before the intended use begins.
Later, after operational safety was reached, one could think about additional earth/ground connections, RF-filters and so on. But never rely on such "additional safety means" before establishing operational safety according to original manufacturer's instructions and documents.
In other words : Of course one could try to mount air bags inside a 30 or 50 years old car. But at first one has to carry out an accurate inspection and repair of all safety related components like brakes, tyres, steering mechanism.
The question was raised whether one gets additional safety with the proposed measures or not. In my opinion there is no general response existing for that. It is your turn, Keith Dobson, to judge that, perhaps after reading all answers once again.
In the years after 1950 earth/ground connections were carried out for e. g. heating and cooking appliances. It was well known that electrical safety could be improved this way. But these appliances usually had no transformer/galvanic separation from power line as many radios already had at that time.
And now my question to you, Keith Dobson: Does your radio contain a mains transformer in its power supply or not ? I had a look on the pictures and saw two output transformers, but no mains transfomer. Maybe it is under the chassis. And we have no schematic diagram, that is missing.
Thank you Rolf for shedding more great light on this fascinating subject.
The unit does have a transformer power supply. It is housed separately to the radio. I will try and add photos now. All forum friends' opinions of it will be gratefully received. There is a schematic for the mono version (Rema 2005), but I don't know how much of that would be common to both versions.
The question "whether one gets additional safety with the proposed measures?" is a point I find very interesting, and obviously extremely worthy of discussion in this forum.
Yet, with respect, it is not one of the questions I have been asking in this thread.
You have confirmed my thoughts, that if the radio is properly maintained, it has an adequate level of safety, without a PE. The question of ADDITIONAL safety is not really of consequence in the context of my current project.
The questions I have asked seem very similar to the point you have discussed, but are effectively quite different. I believe these original questions are also very interesting and, again with respect, I think it would be correct for this thread to stay focussed on them, rather than the "additional safety" issue.
I apologise for any confusion from me, and thank you deeply for taking the trouble to communicate in my language.
To clarify, the main questions I raised are:
1 might it actually be UNSAFE in some way/s to add a PE?
2 might it actually be UNSAFE in some way/s to add a chassis connection from this radio to another piece of audio gear?
This is why I ask:
In my original post you will see I am considering this step mainly for audio reasons.
I feel I should explain that a bit:
When I connect a (1970's) record player to an (1970's/1980's) audio hi-fi amplifier, it is necessary also to connect an earth cable between the two.
Each piece of my hi-fi equipment has a terminal, usually connected to it's chassis, provided for this purpose.
Not all the pieces incorporate a PE, but in those that do, the connection follows through to earth.
When the earth cable (between the equipment) is disconnected, background noise tends to increase. By a lot.
(This is not the same as the signal earth, or screen, which is in the signal cable).
I am not sure when this convention started. It seems common on hi-fi from the 1970's and 1980's.
Now when I connect a record player to the input of the Rema 2005, there is a lot of background noise (buzz, hum, etc). But there is no earth terminal as standard on the Rema to connect to. If I create one and connect the two units, the buzz may disappear like magic. Or, it might get worse. I have found, with some audio grounding issues, that sometimes you cannot know until you try.
What I don't want to do, is go bang.
I need to replace the old power cable in any case. I would like to know if the option of connecting PE would be safe, because it may improve the noise floor. Or, it may make it worse. I don't know until I try it.
What I want to know is, - is it safe to try?
All of the responses above are very helpful, and illuminating.
I will be checking all of the points raised above, and making any components safe before proceeding.
Any more thoughts gratefully received. Thanks to you all!
The answer to both your questions is I think Yes it might be unsafe. The difficult question is why.
Firstly if a set has connectors designed to be used by an operator without tools or specialist knowledge then provided the set is working correctly to the original design performance it should be safe to use such connectors. However if the manufacturer provided no connector then it would be unwise to make a DIY connection without thorough investigation & consideration. Some of the issues I have already mentioned & I will not repeat them.
In your particular case do any of the audio connectors on the chassis have pins electrically connected to chassis? If yes then the chassis is probably designed to be connected to other equipment, in which case it should be safe to connect the chassis to earth. If you wish to try this without fear of it going bang then I would suggest first measuring the voltage between the chassis & earth. You will probably measure a voltage if using a modern high impedance meter. A simple electricians tester using a light bulb would probably be better. If the bulb does not glow then I would risk connecting a temporary earth to evaluate any hum. As an additional safeguard a light bulb in series with the mains works very well at limiting fault currents & giving warning by glowing.
The types of audio equipment you mentioned have bonding terminals in addition to audio signal connector. The bonding point is not necessarily a PE point as you observed. Bonding metal casing of audio equipment usually helps reduce hum etc by screening the circuits. but can introduce hum if more than one item is connected to a PE (earth loop). Some turntables for instance used a PE for the motor, but this was insulated from the turntable chassis. The chassis was then bonded to the amplifier, which might be connected to PE. So the decision to provide a PE may also be dependant on the combination of audio units you wish to use. Perhaps a knowledgeable audio enthusiast can provide more information on this subject.
Should you decide to fit a bonding terminal & a PE cord I would suggest you connect the earth wire of the mains cord or IEC socket directly to the bonding terminal. Otherwise as suggested by Emilio.
A word of warning many individuals especially musicians have been electrocuted using audio equipment. A problem is that many mains powered items are used together; if one becomes live and an adjacent item is earthed but the two items are not bonded then a user operating both is liable to electrocution. Ironically in this case the danger is increased by having the earth, however bonding would have been better. Incidentally when I connect a lead between two items of equipment I never touch any conducting parts of the lead & the equipment. I may be paranoid but I am alive & I know others who are not.
first I wish to underline that many of the old equipment, no matter if industrial or house appliances were unsafe at all. I remember transformerless radios or record players, with cabinets and knobs made of vile plastic, generally crushed after a short use. When I restored ANIE qualified Italian radios for some friends that want to use them, I first added a good insulation transformer inside the cabinet. And how many equipment I have seen, that used flammable parts or, even better, asbestos inside to prevent fire! More, I also remember to have replaced two ground-fault safety interrupters not working at all, one with melted contacts!
The planning of the job to do to restore any old equipment may be subjective and depends upon a careful evaluation of the actual status. Nevertheless, creating a low-impedance path between the chassis and the earth, to prevent shocks in case of poor insulation, is one objective safety rule.
From the pics loaded by Keith, I see two tar-sealed paper capacitors. Of course, I cannot know if they are on the primary side, but tar is swollen and partially melted: these capacitors should be replaced. Well, how many people really know what kind of dielectric can be specified for a RFI filter capacitor from the mains to the chassis? How many people really know the availability and the use of class X or class Y capacitors? I suggested the use of a IEC filter, just because its manufacturers certainly had the proper experience to have made a safe, foolproof component. In addition, in a stereo amplifier noise is kept lower by a ground connection, and a good RFI filtering helps to reduce clicks due to i.e. neon lamps.
About the second item, the grounding of other auxiliary equipment, the answer is a bit more complex. The ground wires should be connected together, but loops must be avoided. This means that if a common connection already exists through the power cable no additional connections should be made between the metallic chassis. Or, if you are using a 5-wire connection cable, with an earth wire, you should not use 3-wires power cable on the second unit. In other words, you should avoid any loop that may be coupled with external magnetic fields, says transformers or even mains wires, otherwise loud hum may result.
Bravo Keith, Emilio and Rolf.
It never fails to amaze me just how complicated the subject of earth is.
I will be re-reading all of the above contributions, over and over.
I do realise the importance of insulation and other testing, and replacing the paper capacitors, before proceeding.
I hope this thread is found by others in the future, looking to understand exactly this issue.
Thank you Keith for your stressing of caution for the inexperienced. I am very sorry to hear of your colleagues. In the 70's and 80's I received more horrible shocks on stage than I could number, and very nearly lost a friend that way myself.
Maybe it should be stated here for the benefit of others that, in cases where PE is part of equipment's original design, the PE connection should obviously NEVER be removed as a quick way to reduce noise. There are other methods (many not covered in this thread) that may be employed to solve earth related noise problems. Although this is a very complicated and confusing subject, finding those other ways; or just putting up with the buzz; are far better options than risking your life by disconnecting the earth wire.
I will post an update when I have done the work, with photos and results of the experiments.
At this point, I think that if the sound is clean enough without PE, I might be tempted to just leave it at that!
Kind regards to all,
first, thank you for understanding. You are right, this issue is complicated and interesting, but also very time consuming. In particular for me because I have to communicate in a foreign language.
And now, after talking about several details, we should try a new approach as you suggested under the precondition that the "basic electrical safety" as intended from the manufacturer 50 years ago was ensured by your restoration. And we should stick to our hobby (equipment), that means to our radios.
What can we do additionally ? What increases safety ? What could be dangerous ?
I thought about how to examine these questions and came to the conclusion that it would be best to seperate this onsiderations from our discussion with the advance that one would be able to continue this from time to time, please look here. Today I read your response and saw that you came to a similiar conclusion regarding the fact that our thoughts and considerations should be simply to find from others who might be interested now or in future.
With regard to filtering I support Emilio's approach to use industrial manufactured products according to the relevant standards.
With regard to possible hum problems we got the statements from Keith Staines and Emilio about the connection of the radio with other equipment (record or CD player). If you carefully read their explanations you could arrive at the following conclusion: To avoid hum due to a so called earth loop only one single PE-connection, if any, is allowed : At the power supply of the (AF-)amplifier. Additionally I would like to recommend the publication of the US American expert, Mr. R. G. Keen, titled "Star grounding in tube amplifiers". I was (and I am) very enthusiastic about it and translated it therefore into German language.