Electric code or UL question, SPST relay on pump

Making one that provides reliable mains safety isolation is not so easy - but adding a couple 100p,F 5kV ceramics is cheap & simple.

FYI: a TV antenna mounted outdoors, on a dry day, in a high wind can easy acquire a 10kV static charge. Punches right through plastic or enamel insulation.

.... Phil

Just wondering, how you would have 10 kV across a _folded_ dipole as implied by the 300 ohm impedance level. In addition to the loop formed by the dipole, the center of the top part is often grounded, so no great potential difference between the folded dipole and ground.

An open HF wire dipole can indeed produce several kilovolts and there can be several centimeter long sparks between the downlead terminals, when the feeder is disconnected from any equipment.

That was the issue with the "All American Five". Never use a pair of pliers instead of the volume knob. That sort of thing hasn't been allowed for fifty years.

tabbypurr:

safety,

It's not that simple.

is far from foolproof. That is why class II was invented.

yes, but bear in mind one of those layers can be air.

order to work. The second layer ( called reinforced insulation ) protects the user in case of failure of the first layer.

ery safe. The ones that do have exposed metalwork take special precautions so live parts and exposed metalwork can never come into contact - unless th e item has suffered obvious damage.

must be designed and rated for such use - where their failure could render exposed metalwork live. The design rules and test procedures for class II r ated supply transformers are elaborate, involving fire proof insulation and the use of regular plus thermal fuses so no possible overload condition re sults in a hazard to the user.

Fireproof insulation? Not in UK, it's probably different in US/Aus.

r soaked class II power tool must not be operated nor a class II hair dryer dropped into an occupied bath tub.

NT

In this case the basin won't be connected to anything else and is closed (lid). But of course someone could open the lid. But that would pretty much require a double fault plus a violation.

No, line and neutral except maybe for some isolated very local historic generators. They should have polarized the connectors. If I were in a standards commission I'd flag that immediately because it is so obvious.

But woe to those who used the fingers to turn a partially broken tuner knob where the set screw was exposed.

snipped-for-privacy@downunder.com wrote: Phil Allison

Fact is, a supply isolating, antenna balun must be able to tolerate such a massive voltage without insulation failure.

.... Phil

You don't even need to do that. The wax over the grub screw was often missing, so one drop of water on your hand and you'd get bitten.

NT

Please tell me - why are so many pommies such complete pricks ? I'm sure an expert pommy prick like you knows the answer to that.

.... Phil

Are you certain of this? I thought Class II appliances must have both basic and supplementary insulation whereas "reinforced" insulation is sufficient by itself.

It would of could have the necessary creepages etc to be equivalent?

BICBW

I don't think you're coming across very well here. Pot, kettle black as Limeys would say.

The standards I have read also permit a single, very thick layer of insulation, known as "reinforced insulation".

The IEC-based standards that I have read use the term "Basic" and "Supplementary" for the two layers of insulation that are required in a class II appliance, or "reinforced" insulation if it is a single very thick layer that is supposed to do the same job. They reserve the term "Functional" for insulation that is so poor/thin that it does not meet the requirements of even "basic" insulation, and is used where it makes absolutely no difference to safety, but where it helps the product to work.

Do you know which standard this is for the transformers? I am curious because this is something that has worried me in the past when I have seen transformers without thermal fuses and with thermoplastic split bobbins, or toroidal transformers that probably don't have anything fireproof between the windings. I've also noticed that some transformers for the US market don't even seem to have split bobbins although they are UL recognised etc.

Single layer insulation of sufficiently generous proportion might be termed "reinforced" in some documents. Your point is pedantic - at best.

.... Phil

Maybe you're off your meds again.

NT

k.

The second layer is called variously "protective" or "supplementary".

Single layer protection has various names too - zzzzzzzzzzzz..

" Approval and Test Specification - Isolating and Safety Isolating Transfor mers "

It has enough confusing details to give any transformer maker the willies - but suffice to say a properly Class 11 complaint design is no walk over.

It is rare indeed to see a class II toriodal transformer - I doubt I have e ver seen one. The test requirements of AS3108 for example make it near impo ssible to design one that will pass.

Smallish E-Core transformers without thermal fuses can pass class II requir ements - providing they use adequate fire proof insulation between primary and secondary plus primary and core. Testing involves allowing samples to l iterally burn down until the primary goes open while at no time permitting the safety insulation to fail.

Some small transformers pass the testing by never heating to a dangerous te mp even with the secondary hard shorted - IOW they self current limit to a tolerable level for the insulation used.

.... Phil

I think you are making my point. The issue is that once one of the two barriers is no longer protecting you and you have not aware of this, it is the same as having only one barrier to begin with. One failure and you are at risk.

Seems to me there should be some way of alerting the user one layer of protection has failed.

The difference is that with 1 barrier by design, lots of end users are at risk. With 2, few are.

No need. Mains electrical appliances have a very low electrocution rate, single figures per year in UK. There are much more useful rabbits to chase.

NT

Actually that's why they put like a 2.2 meg resistor across it, to dissipate the charge but not cause too much line leakage.

Lightning?