PAT safety testing of old record players

[emeritus]

This reminds me that when I was with GEC, one of the secretaries had an old GEC fan heater that, although it had a metal case, was clearly marked with the double insulated symbol. At some point in its history the flex had been replaced by three-core, the earth having left disconnected at the plug, the earth wire having been cut back. It was failed at one of the annual inspections for lack of earth. Out of interest, I had a look at it, and the construction was in effect an inner metal case within the outer metal case, the different layers being spaced apart by insulating spacers. I assume that the presence of these insulating spacers fulfilled the double insulated requirements, as there were two sets of insulators in the path between the live wires and the outer case, and that it should therefore not have been failed. They got her a new one anyway, and I now have the old heater in my shed, the supply to which is RCD protected.

[dseymo1]

I'm certainly no expert in this area, but would think that the typical autochanger is practically double-insulated, having a motor wound with enamelled wire on an insulated bobbin, the whole thing suspended from grommets. Isolation of the signal cable is, of course, another matter.

[trh01uk]

Originally Posted by flyingtech55

Sorry...I'm not going to get involved in semantics...I don't really do them very well.
I'm not quite sure what you are implying in your final sentence but if you're saying I'm relatively non-skilled I'm glad no-one else has spotted it in the last forty years I've been professionally employed in electrical/electronic and mechanical engineering. Whew, lucky escape there then!

Tim,

the comment you quote doesn't refer to you - specifically - at all. Since I don't know you I am unable to say whether you are competent or not.

I can only react to what you actually write. I was merely pointing out the inconsistency of what you said. You said you are "not a design authority" (I'm not now, but I certainly have been in the past, as probably many others on here are/have been), so you tell us that you can't test the earthing efficiency of a product. You then go on to tell us that you can work out that an item that was never designed to meet class II standards does actually meet them.

What the job of making vintage equipment safe involves is "someone competent" (which may well be you) deciding that the equipment is safe. And I suggest that working out that "double insulation" is in place and adequate is far harder than checking that bits of metal are electrically joined together, and that the earth wire to the mains socket is adequate size and properly connected. For one thing in the latter case, you can actually see the earth connections and check the wire is not frayed, etc. And for another, you can take your PAT tester and check the adequacy of the connections - its designed to confirm that the resistance of any connection is less than 1 ohm.

It is - by contrast - far harder to check the adequacy of an insulator. You can hit it with a high voltage (megger for instance) - but as far as I know the standard PAT tester can't supply this sort of test. There's another nasty problem with insulators, and that is the build up of conductive dirt which can track across/through an insulator, and which can be totally invisible.

I respectfully suggest that the method - of earthing otherwise unearthed bits of metal that may be touched by the public - is the better one, and less risky overall.

Richard

[matthewhouse]

All Pat testers have built in insulation testers, they wouldn't be much good otherwise! More advanced testers have the ability to carry out flash testing at 1500V for class I 3000V for class II. This would be required after modification of an appliance, and is supposed to be carried out after appliances are repaired. This test is skipped if the appliance has RFI suppression capacitors.

[Okto1984]

Instead of removing the plug, perhaps removing the cable from inside the appliance would be sufficient to dissuade anyone from trying to use it? You could also place warning labels over the case screws (like the warranty labels on some items). This would give two levels of discouragement, which I would hope is enough.

Removing the plug or cable however does mean if anyone is determined to use it, they're more likely to do something that could make it dangerous. So, less likely to happen, but more risks if it does. It's hard to weigh that up.

[kalee20]

Originally Posted by dseymo1

I'm certainly no expert in this area, but would think that the typical autochanger is practically double-insulated, having a motor wound with enamelled wire on an insulated bobbin, the whole thing suspended from grommets. Isolation of the signal cable is, of course, another matter.

That's as may be, but it wouldn't necessarily meet 'double insulated' standards.

Enamel on wires is considered to be functional insulation only - makes the thing work - not safety insulation.

An insulated bobbin may meet the standard's requirements, if sufficiently thick (I believe 2mm is the minimum but correct me if I'm wrong). It would then count as 'reinforced' insulation. Thinner material would be OK if capable of withstanding a certain voltage (basic insulation), provided it was backed up by additional insulation also capable of minimum voltage withstand criteria (supplementary insulation).

There are also minimum clearances to be maintained between live conductors and user-accessible metalwork, and also minimum creepage distances across the surface of insulating materials - the figures 8mm for both stick in my mind for standard mains voltages.

Complying with the double-insulated standard isn't just carrying out an insulation test, it's also confirming that these internal minimum construction requirements have been complied with.

[flyingtech55]

Originally Posted by trh01uk

I can only react to what you actually write.
You then go on to tell us that you can work out that an item that was never designed to meet class II standards does actually meet them

Err...I've read my original post very carefully and I don't see the part where I said that the item would meet class II standards.

Originally Posted by trh01uk

And presumably you then attach a class 2 label to the item for the benefit of PAT testers who come after you?

I most certainly would not attach such a label for the simple reason that it is not and could never conceivably be Class II.

TimR

[trh01uk]

Originally Posted by matthewhouse

All Pat testers have built in insulation testers, they wouldn't be much good otherwise! More advanced testers have the ability to carry out flash testing at 1500V for class I 3000V for class II. This would be required after modification of an appliance, and is supposed to be carried out after appliances are repaired. This test is skipped if the appliance has RFI suppression capacitors.

As far as I recall, such flash testing was phased out over 10 years ago - at least for routine PAT testing of manufactured equipment. There may well be specialist "advanced" equipment around that can do these tests, but its hardly applicable on an amateur forum like this one.

And I wouldn't be applying 3000V to vintage equipment. There is a danger that insulation in place will in fact flash over, and then track. Once that happens its very hard to repair the damage without replacing the insulated part completely.

Standard PAT tests, apply 500V DC, with the option of reducing to 250V DC to avoid triggering surge suppressors.

Of course, fitting extra insulation and then flash testing what you have fitted is possible (if you have the equipment). But I suggest that it is in fact a lot easier to fit earth bonding straps, and establish that the overall earth system resistance is less than 1 ohm.

The latter method needs just wires bonded to metal, and can be checked with a good DVM (you don't need a PAT tester at all in fact). The former method needs specific bits of insulation made and fitted (some of which may be visible to the end user) and then checked with specialist equipment.

At the end of day, the task needs a new "design authority" to effectively redesign the vintage equipment to meet modern standards.


Richard

[matthewhouse]

Agreed, I've only once carried out flash testing on one appliance, the feature is still present on several modern testers (but not on the one I use frequently). The latest book says dielectric testing should only be performed where it will not weaken insulation or create a hazard. dielectric testing should not be used for in service inspection and testing. In some cases equipment returned to service after general repair and maintenance may require a dielectric strength test, if in doubt seek advice from the manufacturer of the appliance.

As with all the electrical regulations, they are so by vague and basically leave decision making up to the person doing the work. Twice we have phoned the IET asking for clarification of two different regulations, but they just read the regulations out of the book and couldn't provide any clarification.

As you say earthing is certainly the easiest way to go, converting a class 0 appliance to class II would definitely need flash testing to prove that the insulation is up to the job.

Originally Posted by flyingtech55

This a tricky one. As it has no earth it should be tested as a class 2 item. However, it will obviously not have the 'proper' double insulated symbol on it.

From the current code of practice for in service inspection and testing of electrical equipment it states that if class II, it should carry the double insulated symbol. If it is not know whether an item of equipment is class I or class II, it should be treated as class I.

So if the deck was not earthed the appliance would fail as it did in post one. (Because it's class 0) If it was earthed it could technically pass. But would really need type testing in a test house after any modification to check compliance with the current standards. As type testing often results in the destruction of the appliance, this would be pointless.

I doubt many appliance test people are going to be checking if the cartridge tags are suitably isolated from a live chassis amplifier either. Fortunately I've not come across any such equipment during testing, with the exception of an old tape recorder. The flex was so perished it failed straight away.

I would however not allow the general public to operate such equipment, and would certainly remove the flex if it was being hired out for stage use etc.

In Skamanuk's case it's probably best to accept that the record player can't meet the current standards of construction, and to use such appliances for personal use or as made safe display items only. You are then safe in the knowledge that you can't be held liable, as nothing can go wrong. (except maybe someone trapping their fingers in the lid!)

For personal use I take sensible precautions and use common sense (not that common sense is allowed any more). A good internal and external visual inspection, an earth bond test for class I, and then an insulation test. If it passes then I'm happy. Then I would put a record on it and enjoy listening to the thing, that's what it's for! You have to take some risks in life or it's not worth living, and the rule making and work hindering, office idiots win. It's happening where I am right now.