H & M Clipper help required

[Nearholmer]

I usually enjoy "electrical" threads, but the beginning of this one went badly ...... anyway.......

 

Andy

 

In case nobody has answered in the interim, the name RCD (residual current device) is actually very good, and highly descriptive, and it describes a class of device, not a particular piece of equipment.

 

Such a device measures the difference (the residual amount) between the current entering a circuit, and the current leaving, by the intended paths. If everything is working as intended, the difference will be zero. If a difference exists, it implies that current is flowing via an unintended path (which could include a person), and the device is then arranged to initiate interruption of current flow (break the circuit).

 

It is a simple matter to detect a difference between 'in' and 'out' currents in an a.c. circuit, to very great accuracy, so RCDs can be used to initiate circuit interruption at very low current difference, even in a circuit carrying a very large current (mA difference in kA currents). It is far easier to do this than to detect current flows via earth directly, and it is far better to do it this way, because not all 'escaping current' faults flow through earth (if some poor soul, wearing thick-soled carpet-slippers was to bridge direct line to neutral, for instance). 

 

Devices based on the residual current principle have been used almost since the dawn of electrical engineering, and are used to detect, for instance, tiny leakages from major power transmission and distribution circuits, and within major equipment such as power transformers, as well as to help protect people in domestic circumstances.

 

I'd be surprised/worried if, whatever they are called there, the devices used in homes in the USA aren't RCDs.

 

Kevin

[AndyID]

59 minutes ago, Nearholmer said:

I'd be surprised/worried if, whatever they are called there, the devices used in homes in the USA aren't RCDs.

 

 

Hi Kevin,

 

Yes, they work the same way except that such a device here is usually called a GFI for Ground Fault Interrupter. I think that's a less erudite description more easily understood by people who don't know much about electricity, but that's just my personal opinion

 

Andy

[Junctionmad]

The term GFI , stems from a device called Ground Fault Circuit Interrupter on e etc in the early 60s in the USA , where the original name has continued to be used and is encapsulated in the US NEC , The device is exactly the same as a RCD , albeit subject to various regulatory specifications 

[Il Grifone]

On 21/09/2019 at 14:22, mossdp said:

Were there are any more variable Transformer controllers other than the Safety Minor and Powermaster?  I do not think there were any more than these two from H and M but were there some from other manufacturers that people know from seeing the specifications or from seeing the insides to  know for sure. I think the vast majority of old controllers were variable resistance types.

 

The Hornby Dublo Marshall II & III were/are variable transformers too, but use tappings of the transformer rather than a wiper like the Powermaster. The II is pretty useless as it only has four speeds in each direction.

 

I've only fought through about half the thread up to now, but would make the following points.

 

RCDs  detect the difference in current between the two poles of the mains supply. They are universally 30mA despite the lethal current being 15mA (hence the modification to leak 15mA). I have never understood this....

 

The problem with resistance controllers is that the load on the motor is constantly varying and any series resistance with lower/raise the

applied voltage with increasing.decreasing load (i.e. positive feedback). The variable transformer limits the series resistance to that of the transformer plus any safety device so minimising this effect. A feedback controller can be designed to eliminate it completely or even reverse it (possibly not a good idea).

 

The recommended fuse rating for any product should not be exceeded. Unfortunately the standard values (others are available) are 3A and 13A (a designer involved?) and many  appliances require other values. For our trains even 1A is too high and an old (pre-flat screen) TV really needed 5A (which we always fitted).

Conversely Continental plugs (US/Canada too AFAIK) do not have fuses at all.  I was reading a post on the 'net the other day about the dangers of treading on the UK plug (which invariably falls prongs up as we all know). Apparently people have actually managed to impale themselves on them!

 

Selenium rectifiers are prone to going short circuit and emitting toxic fumes. However the smell is an effective warning. At the time it was all we had . (TVs used either a large valve or a string of the things to rectify the mains!) The introduction of silicon rectifiers was welcomed with open arms. They are not a direct replacement as the selenium diode drops 3 volts and the silicon only 600 millivolts. I thought this would give a little more omph to a train controller, but was disappointed when it seemed to make no difference !  ??   It is nevertheless worthwhile. However, don't drill out the rivets unless you know what you're doing! My Powermaster has screws. Was this an early production or a mod. by an earlier owner?

 

Ancient electrical devices can suffer from insulation breakdown and should therefore be treated with respect. Any rubber insulation has to go and ideally a thermal cut-out should be fitted. Modern transformers have these, but unfortunately have a tendency to trip. not a problem if a solid state device which rests itself, but soldered links are common. Failure of these usually causes the transformer to be written off (they are designed to be non-repairable!) and usually a replacement (if available) costs more than the equipment is worth (hardly 'green' - more 'planned obsolescence').

 

Kirdon units used acetate plastic and are now seized up (collectible or bin).

 

PAT testing involves a 5000 volt insulation test - not a good idea for a transformer (or a TV set). This will damage the insulation even if it passes the test!

 

Probably no-one is still reading, so I'll shut up now!

 

Edited October 15, 2019 by Il Grifone

[RobjUK]

10 minutes ago, Il Grifone said:

PAT testing involves a 5000 volt insulation test

 

I think you have a typo there - 500V not 5000V!

 

[Crosland]

40 minutes ago, Il Grifone said:

The recommended fuse rating for any product should not be exceeded. Unfortunately the standard values (others are available) are 3A and 13A (a designer involved?) and many  appliances require other values. For our trains even 1A is too high and an old (pre-flat screen) TV really needed 5A (which we always fitted).

 

The fuses in UK 13A plug tops are there solely to protect the lead to the appliance. The appliance should contain it's own protection, as required.

[melmerby]

1 hour ago, RobjUK said:

 

I think you have a typo there - 500V not 5000V!

 

Yes 500v.

My last place of electrical employment used to do a PAT on mains electric hand tools whilst they were running.

Work that out (N.B I know how it was done)

 

Edited October 15, 2019 by melmerby

[Il Grifone]

Perhaps my source was dodgy,because it definitely stated 5000V??  500V is certainly less damaging to a transformer (or the EMI protection circuit in a TV). It was quite a while ago!

[Il Grifone]

On 21/09/2019 at 11:05, Pacific231G said:

I have one of those section switch modules  (though I got rid of my H&M controller long ago and my Kirdon Major ever longer ago); I might even find a use for it someday.

 

The Powermaster was introduced by H&M in September 1957 and heavily advertised at four guineas i.e. 84'- (postage 2/6 extra) until well into 1958.

 

I have RM for that year and, as well as H&M's two page advert and immediately before it, the September edition included  a full  article introducing it. This article incorporated "plan of the month" in the form of a couple of point to point layouts with the six feeds from the Powermaster and common returns marked. Cyril Freezer  was obviously quite impressed by this controller, which he said they'd tested extensively on their own layouts both at home and at work, and the variable transformer  did work well. They'd not been able to test the built in section switches as their layouts were already fully sectioned but he obviously saw that, for modellers not well versed in layout wiring, it would cut out several steps of the process. The obvious downside of this would have been that, if one of the section switches failed or simply became dirty the whole unit might be rendered useless as there would be no way of getting at the circuit selectors inside the riveted case to fix them. Looking at my H&M section switch module which appears to use the same switches, I think they would have been vulnerable to dirt and corrosion. 

 

Rather curiously, Freezer's main plan - for a terminus to terminus L wih an intermediate non passing station- was supposed to have two "cabs" one at each terminus but the whole thing only used six section switches marked 1-6. 

 

The other oddity was in the H&M advert that advertised the uses of the "full-volts boost button" as  including  freeing difficult motors, overcoming dirty contacts  and reversing A.C./D.C. motors. The output didn't include voltage controlled AC so it clearly couldn't reverse A.C. motors such as Märklin's but were there still non permanent magnet DC motors in use at that time? I did wonder whether H&M were possibly considering an AC version for Märklin users- presumably the advantages of a variable transformer would have been just as relevant.

 

FWIW my own policy on electrical equipment- I use mains lighting equipment for filming- is that if it's not worth the modest cost of getting it PAT tested it's not worth keeping, There may be instances where you still need to use obsolete equipment- the reel to reel tape recorder mentioned before for example- but at least use it with an RCD socket; they're very cheap though be aware that while they may protect you from say a chassis or a low voltage output going live mains they won't protect you  from becoming a load in a live to neutral circuit.

Despite constant nonsense about "Elf n Safety" gone mad (usually not based on anything actually said or done by the HSE), H&S isn't about not taking any risks, it's about understanding and assessing risks and then minimising them.

 

The usual way (back then at least) was that each 'cab' would have a switch to feed each section. In the event of two cabs selecting a section, a short would operate the cut-out - not quite the best way of going about things!

 

The low series resistance is just as relevant for AC motors.

As to the 'full volts boost button', I've never managed to use it to persuade stalled motors to start. It might work, but... I couldn't see how it could persuade an AC motor to reverse, but found it would reverse a Trix locomotive. It actually first disconnects the supply then boosts and then interrupts again before returning to normal. Since Trix motors reverse by cutting the supply, this works OK. Märklin on the other hand, use an over-voltage pulse of about 20V to operate the reverser, which the Powermaster does not supply. My solution for both makes involves a bridge rectifier to supply the field winding. It no longer works on AC, but does reverse properly!

 

The section switches are quite robust and mine have never given any trouble. (Famous last words....)

 

My trackwork has the common return connected to earth. This aids both safety and minimises radio interference.

[sharris]

3 hours ago, Il Grifone said:

Perhaps my source was dodgy,because it definitely stated 5000V??

 

It can be quite nail biting when you're taking equipment to BSi to be tested to EN60601 standards (medical equipment electrical safety) and they start zapping it with 2kV spikes on the mains and 8kV ESD pulses on all the ports.

 

 

[cliff park]

In the early days of PAT we once had a contractor come into our (electronics) workshop, fail all 17 of our computer monitors (old fashioned tube type) and cut all the mains leads off. Why? Because he was doing a check to see that metalwork was earthed, put one probe on a screw in the case and the other probe on the earth pin of the plug. But the screw he picked simply screwed 2 pieces of the plastic case together. He had had the PAT course the day before, we were all apprentice trained electronics engineers, but what we said meant nothing to him.

[RLWP]

1 hour ago, cliff park said:

In the early days of PAT we once had a contractor come into our (electronics) workshop, fail all 17 of our computer monitors (old fashioned tube type) and cut all the mains leads off. Why? Because he was doing a check to see that metalwork was earthed, put one probe on a screw in the case and the other probe on the earth pin of the plug. But the screw he picked simply screwed 2 pieces of the plastic case together. He had had the PAT course the day before, we were all apprentice trained electronics engineers, but what we said meant nothing to him.

 

When worried about the effect of PAT testing on our computers, we kept an eye on the tester. We eventually caused him a problem by pointing out the new SUN machines we had had separate leads, so labelling the plug was a bit pointless

 

He stopped testing and went to ask for advice, I don't remember seeing him again

 

Richard

[kevinlms]

1 hour ago, cliff park said:

In the early days of PAT we once had a contractor come into our (electronics) workshop, fail all 17 of our computer monitors (old fashioned tube type) and cut all the mains leads off. Why? Because he was doing a check to see that metalwork was earthed, put one probe on a screw in the case and the other probe on the earth pin of the plug. But the screw he picked simply screwed 2 pieces of the plastic case together. He had had the PAT course the day before, we were all apprentice trained electronics engineers, but what we said meant nothing to him.

We all received new soldering irons once, because the double insulated ones we had prior, all failed the continuity to earth test! We tested the new ones and if the same guy had been around, he ought to have failed the new ones as well.

[PatB]

I got a free disc and belt sander when it got PAT (or local equivalent) tested at thecollege MrsB was attending. It was genuinely faulty, but all that had happened was that the self tapper securing the earth to the frame had fallen out (or never been installed at the factory). Into the skip it went, to be later retrieved by yours truly, fitted with a new 2c self tapper and a mains lead off a scrap motor from my mill. Technically naughty, but as it hasn't caught fire or electrocuted me yet 10 years onI'm fairly confident of my judgement. 

[MarkC]

3 hours ago, cliff park said:

In the early days of PAT we once had a contractor come into our (electronics) workshop, fail all 17 of our computer monitors (old fashioned tube type) and cut all the mains leads off. Why? Because he was doing a check to see that metalwork was earthed, put one probe on a screw in the case and the other probe on the earth pin of the plug. But the screw he picked simply screwed 2 pieces of the plastic case together. He had had the PAT course the day before, we were all apprentice trained electronics engineers, but what we said meant nothing to him.

I bet he was popular with whoever had to pony up for repairs/renewals...

[melmerby]

Oh Dear.

RMWeb topic drift warning.

[AndyID]

4 hours ago, melmerby said:

Oh Dear.

RMWeb topic drift warning.

 

I think it was last seen near the Azores several pages ago.

[Il Grifone]

I think PAT testing is very relevant to elderly electrical equipment.

 

IIRC I forgot to mention that transformers of this era will not have the thermal cut-outs fitted in accordance with modern regulations. The risk is small, especially if they are not left unattended (switch off at the mains or, better still, unplug).

I did have a car battery charger* fail recently. Investigation showed that the thermal cut-out had become detached from the transformer and was thus unable to trip when the transformer overheated. No harm done, but....

 

* These work rather harder than model train equipment of course

[Colin_McLeod]

 

15 hours ago, melmerby said:

Oh Dear.

RMWeb topic drift warning.

 

Remind me again. What is the topic?

 

 

This always happens when someone asks a question about older equipment but that's life.

Edited October 17, 2019 by Colin_McLeod

[Hroth]

19 hours ago, cliff park said:

In the early days of PAT we once had a contractor come into our (electronics) workshop, fail all 17 of our computer monitors (old fashioned tube type) and cut all the mains leads off.

 

Ummmm....

 

If they were the "usual" sort of computer monitor, they'd surely have electric kettle type mains cords.  Not too hard to replace once the P(R)AT tester had vacated the premises......

 

 

[sharris]

2 hours ago, Hroth said:

 

Ummmm....

 

If they were the "usual" sort of computer monitor, they'd surely have electric kettle type mains cords.  Not too hard to replace once the P(R)AT tester had vacated the premises......

 

PAT testing was a result of the Electricity at Work Regulations 1989 which came into force in 1990, but became more like what we know them as today after 1994 with the HSE Guidance Note HS (G) 107 which was the first guide to periodic testing. 25 years ago I seem to remember there were still a fair number of CRT monitors that had fixed mains cables. 

 

[melmerby]

2 hours ago, Hroth said:

 

Ummmm....

 

If they were the "usual" sort of computer monitor, they'd surely have electric kettle type mains cords.  Not too hard to replace once the P(R)AT tester had vacated the premises......

 

 

Depends how long back, the Euro type connectors weren't universal, some equipment had hard wired leads.

My first computer monitor was such an item.

 

[RLWP]

2 hours ago, Hroth said:

 

Ummmm....

 

If they were the "usual" sort of computer monitor, they'd surely have electric kettle type mains cords.

 

Not so, if you go back to my post just after Cliffs, you'll see the expectation was the lead was part of the equipment. Kettle leads post date his (and my) anecdote

 

Richard

[kevinlms]

19 hours ago, melmerby said:

Oh Dear.

RMWeb topic drift warning.

According to the OP the thread went off topic, right from the start!

[Crosland]

7 hours ago, Il Grifone said:

I did have a car battery charger* fail recently. Investigation showed that the thermal cut-out had become detached from the transformer and was thus unable to trip when the transformer overheated. No harm done, but....

 

* These work rather harder than model train equipment of course

 

As a cash strapped teenager, one of my Model railway power supplies WAS a car battery charger, LOL!