There is no connection to ground, either? ...like your aquarium example? In that case, I don't think you have anything to worry about. I don't think there is anything to worry about anyway, as long as it's designed for a US 120V circuit.
There are a lot of old installations one has to worry about, too.
The discussion was about static rain.
Even if the folded dipole is hit by the lightning, the _differential_ voltage is pretty small, unless the lightning blows out the other conductor.
The _common_mode_ voltage is huge with a direct lightning hit, but then you have much greater problems to worry about than the input stage of the TV tuner.
Interesting - many people seem to use them as though the output could be SELV (safe extra-low voltage) that could be touched - e.g. input connectors on audio equipment, lab instruments etc., and I have seen them sold for halogen downlights where the output is accessible also. I wonder if this is really allowed, and whether they had thermal fuses added. If the secondary winding is thick enough then I suppose earthing one end of the secondary could ensure that the input fuse would blow before any part of the secondary becomes hazardous live, but that would only work for very thick windings.
I have not seen this stuff discussed in any catalogues or books.
** I cannot deal with "examples" that you claim to have seen but I have not.
Transformers for halogen downlights require *type approval* in Australia for that purpose and I have not seen a toroidal that has been given that approval.
** Just adding a thermal fuse is not good enough to pass all the test procedures for class II. The polyester insulation barrier between primary and secondary normally fails too fast. ** Huh ?If the output winding is grounded for safety - then it ain't class II.
.... Phil
There are plenty of 60601 approved Torids. That require double insulation between Pri/Sec.
Cheers
Lightning could easily blow out a conductor but there isn't much you can do to save a direct hit. But insulation isn't primary to primary, obviously. The issue is common mode.
Direct hits aren't the only problem. The insulation has to withstand what the arrestor(s) can't handle.
When I was a kid, I had several dipoles. I'd always disconnect the feeds from the equipment. During a storm it wasn't unusual for sparks to jump across the PL-259 plugs.
We'd like to also use this for 240VAC is possible. There is PE which also grounds the pump motor housing.
Yes, and generator situations where the installers weren't anywhere close to licensed electricians.
-- Regards, Joerg http://www.analogconsultants.com/
For 240V, I think you'll need a two-pole switch. Grounding the motor housing is a good idea but it doesn't really change things. The issue is that you need to switch the "hot" and not the "neutral". Otherwise, I think you'll have to do something like double-insulation.
Oh, sure. A friend bought a house and discovered all of the basement wiring was done with zip cord.
We are currently checking whether the pump motor has double-insulation.
A German TV crew in France started the lights for an interview in a home. Phssss .. zzooosh and the wall paper was charred along the track where the power line went under the plaster.
-- Regards, Joerg http://www.analogconsultants.com/
Ok fair enough. Most of the ones I know are old, and not in Australia. E.g. Marconi signal generators - not class II but accessible parts on the secondary side.
Do audio power amplifiers often use toroidal transformers? If so, how do they get away with it? I know those are usually not class II, but AIUI, even in class I, if there are accessible parts, these still need to be separated from the mains by double insulation unless the parts are protectively earthed. I know that often speaker terminals are not accessible, perhaps nothing else is either.
Yes, the toroidal ones I had seen were in Europe, and it was a long time ago, before they all went switched mode, then changed to LED.
Yes, I imagine that fibreglass tape and fibreglass sleeving of the primary wires as they pass between the secondary wires might be needed as a minimum, and I haven't seen that done.
All the same, products like this:
Perhaps the newer standards are less rigourous than the old AS3108.
Yes, I was more interested in whether or not the output of a transformer is safe to touch (SELV / PELV), not specifically class II.
I have in the past wondered whether it is allowed (or whether it is common practice) to rely on grounding a terminal of the secondary winding as the means of making it safe to touch. For example, the output of PC power supplies is not isolated from the mains, but might usually be safe to touch. Often hobbyists want to put several of these in series to get a higher voltage, so they modify ATX power supplies by removing the earth connection from the DC output (or more stupidly, they just cut the mains earth wire). Even in the better situation with the casing still earthed, I have wondered whether the transformer in these has proper double insulation from primary to secondary, or if they rely on the very sturdy secondary winding being solidly earthed at its centre tap, so that any failure of the transformer insulation would blow the fuse. It was of interest because I wanted to know whether the modified power supplies would still be as safe as they should be.
Chris
Why? Assuming that the motor wiring would have been legal and safe
*without any relay at all* and running the pump continuously, (and that the instructions specify that the plug is pulled rather than turning off the relay for maintenance), how could adding a single-pole relay make it more dangerous than no relay? More to the point, which clause of which standard says so?It almost seems like arbitrary bargaining with the regulations - oh that relay looks mighty convenient - surely can't be allowed unless we make it inconvenient by - hmm lets see - double insulation in the motor, double pole switching, and hmmm maybe if you wear high-visibility boots, and a traffic cone on your head. Yes, that will do it, four points of random safety inconvenience balances out one convenient relay.
My criticism is not directed at you in particular, just everybody who doesn't explain how the single pole relay could make it less safe than no relay, and suggests some random extra safety feature, and doesn't explain what fault mechanism could be prevented by $arbitrary_inconvenient_safety_feature, nor any other good reason for doing it such as a specific clause of a specific standard.
Regulators would consider the relay a purely functional switching device, so yes SPST should be fine. If there were a manually operated switch then that could have a role in safely isolating the load so a double pole switch would be wiser choice. I do not think relays are considered reliable to use for circuit isolation, anyone working on the pump should be able to use a separate means of disconnection.
What do your competitors do in their pumps?
piglet
** Practically every one is chassis earthed and so is the PSU common.
A few have "earth lift" switches on the back that removes the PSU link - a feature I believe would make them fail an approval lab test since it breaks "all accessible metal parts must be earthed" rule.
** Nope - speaker and input connections are handled in normal use.** A class II transformer must fail safely when the secondary is overloaded or shorted. This means the internal thermal fuse must open before the wind ings and insulation are damaged. Since toroidals use thin, polyester tape f or insulation, with the primary buried under the secondary and held under p ressure, passing such a test is a problem. Under shorted a secondary conditions, the heat dissipation of a typical tor iodal transformer increases by a huge factor ( 100 times or more) compared to the rated load condition. The primary temperature rises so rapidly that there is not enough time for a thermal fuse to act before the temp rise exc eeds the safe maximum for the insulation. ** Fraid I cannot see any indication either the above are class II approved .
** It is never safe to touch the secondary of a transformer that is NOT cla ss II. All plug-pak transformers are class II types by law.
** Standard practice for decades..... Phil
It says it in the datasheets:
I suppose there is an important distinction between a class II transformer and a class II appliance. In many cases a class I power supply contains a double-insulated (class II) transformer. Many laptop power supplies have the negative output terminal grounded (so it is class I), yet the barrel connector that provides power to the laptop does permit you to touch at least the negative terminal of the output (which is grounded).
I did have a product knocked back by a test house because it was possible to touch a 5VDC power rail, and the standard to which that product was tested used a human body equivalent circuit that had a 2kOhm DC resistance, and the limit of touch current was 2mA in that standard. Therefore they would pass it if the accessible voltage was less than 4 Volts, but not if the accessible voltage was above 4 Volts. Different products have different limits, e.g. somehow they got things like the Raspberry Pi approved, and many PCs allow you to open the case without tools and touch the motherboard with its 12V traces referenced to earth.
This seems to contradict your previous statement.
I think I need to read some more standards, but I'd probably have to buy them first.
** It is very obvious that the above units are *standard* toroidals.
Not even a primary thermal fuse in sight.
The Chinese makers are playing fast and loose with terminology.
** Wonder how they can sell 9V batteries ....** Really ??
Teasing me into debating *YOUR* opinions with *YOU* is not gonna work.
You are welcome to them.
... Phil
The human body equivalent circuit used in the testing had one side earthed. My "mistake" was that my 5V power supply had its negative output pin connected to earth too. If I had earthed one terminal of a 9V battery, that would have failed testing against IEC60598.1 at this test house. If the 9V battery is floating, then it is ok, as no current flows in the touch current test. Also, next time I need to run some 5V logic, I would be better off connecting it between plus and minus 2.5V supplies!
I think that the standard authors originally intended it to forbid access to things which had a touch current greater than 2mA AND an open circuit voltage aboove 34V, but they left out the "AND" in the text, and later on some unthinking do-gooder inserted an "OR" into the sentence.
I remember I used to check 9v batteries using my tongue. Current would flow through it even when the battery was floating. Probably the only reason I am still alive is that the current did not pass through my heart?
Yes, I get that, but it is *far* from "safe" if the barriers can fail with no indication. With a grounded metal case the fuse blows when the tool is plugged in making it clear there is a problem. Finding out that your insulation has failed by being electrocuted is no fun.
I guess if you are chasing rabbits, we are not having the same conversation.
-- Rick C
Is it possible that your product is "outside the scope" of this standard due to the low voltage? I think that is the case for e.g. the EU "low voltage directive" which is for 50 < V < 1000 AIUI.
-- John Devereux
That sounds like a valid argument. Thanks.
There are no competitors for this stuff, it is a new (and not yet disclosable) market. Also, in other industrial markets I have seen too much stuff that apparently never saw an agency compliance lab review so one cannot rely on other's gear to be 100% legit.
However, when looking at other applications for pumping where people have access such as sump pumps I have seen float switches from reputable sources that are single-pole. Sometimes SPDT to allow for use in up as well as down pumping applications.
-- Regards, Joerg http://www.analogconsultants.com/
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