leaving conductors exposed

s · 2010-12-11T14:12:01+00:00

i got a desk lamp from ebay like the one in the image link below. thebulb is held up by two adjustable telescopic rods, exactly the sametype as you would find on the aerial of a FM radio. they are metal.i saw the double insulated symbol on the bottom, which go me thinking.how did they get the wiring through these rods double insulated, theyare pretty thin. then i examined the rods. they had joints in them.they werent even hollow! there was no wiring. they were theconductors.a quick check with the meter gave 20V AC. thats how it was designedto light the bulb .my question is can you have the double insulated symbol on a productwith exposed 20V AC conductors?if interested this is a description of a similar product , which showsthe conductors are exposed by design:

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Brenda Ann 15 years ago

You're right in principle, but it's difficult to think of /any/ situation in which 14 volts could pump enough current through a human body to kill its owner. You'd need a net resistance (across the heart) of 140 ohms. Not likely.

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A direct current path through the heart (e.g. attached electrodes) will cause fibrillation at as little as 10uA. A somewhat less detailed description is found in Wikipedia:

Ventricular fibrillation A domestic power supply voltage (110 or 230 V), 50 or 60 Hz AC current through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60 mA. With DC, 300 to 500 mA is required. If the current has a direct pathway to the heart (e.g., via a cardiac catheter or other kind of electrode), a much lower current of less than 1 mA (AC or DC) can cause fibrillation. If not immediately treated by defibrillation, fibrillations are usually lethal because all the heart muscle cells move independently instead of in the coordinated pulses needed to pump blood to maintain circulation. Above 200 mA, muscle contractions are so strong that the heart muscles cannot move at all.

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lsmartino 15 years ago

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Take into account the fact that fake electrical chinese products almost always have fake certification labels. I have seen countless of useless power strip with fake UL labels, or badly constructed computer cases with a fake CE seal stamped over the chassis. I have seen even fake circuit breakers made in China with UL marks, so don=B4t assume that a poor quality electrical chinese product has been properly inspected just because it bears a UL or CE label.

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lsmartino 15 years ago

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Can you illustrate a real life situation where a 12V battery electrocutes a human being? I posted a skin resistance table that makes that possibility higly unlikely.

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Spehro Pefhany 15 years ago

Unless it is defective.

Best regards, Spehro Pefhany

"it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com

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Wild_Bill 15 years ago

Maybe you're not familiar with the expression.. Never Say Never.

Being a repair newsgroup, many folks have likely encountered damaged battery chargers, and not knowing every possible fault, including improper previous repairs, one never knows if an electrical device has a fatal fault or not until it's been examined and tested.

Nearly every electronic equipment service manual printed in the last 40 years (at least), includes a method to test line operated equipment for hazardous leakage levels that can be fatal. Safe levels of leakage for line operated equipment fall within the uA microamp range.. that's Less than a mA milliamp.

I believe that actual current threshold determined to be hazardous is about

35mA, across the heart, which can interrupt normal heart rythyms.

So, with a small voltage applied to fingers of one hand with the other hand grounded, the additional skin resistance of the arms will decrease the possibility of a fatal shock. That same voltage, applied to points near the heart will increase the possibility of a fatal shock.

By following standard safe practices, one can be confident that they are working safely.. one hand in pocket, standing on dry, insulated material, good lighting, concentrating on what you're doing with no distractions or practical jokers around.. and one of my own personal habits which is to not have anyone standing behind you. You can't see or predict that person's movements, so tell 'em to move where you can see them.

FWIW, a number of years ago there was a safety recall of some Dewalt cordless power tool battery chargers (not a car battery charger), because one of the battery terminals was not isolated from the AC line (by poor design). That model definitely presented a deadly fault, so don't always expect that new items are perfectly safe, either.

-- Cheers, WB .............

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William Sommerwerck 15 years ago

We were not talking about defective equipment. Yes, OBVIOUSLY, defective products can electrocute you. And it's good sense not to do things that might expose you to equipment faults.

Many years back I had a GE toast-r-oven repaired, and the tech didn't check the leakage. When I accidentally touched the toaster and the faucet, I got a shock. Removing the metal side panel showed that a bare wire was touching the metal.

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Dave Plowman (News) 15 years ago

I've never quite understood why such things aren't grounded in the US? Or perhaps they are now?

*A bartender is just a pharmacist with a limited inventory. Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound.

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William Sommerwerck 15 years ago

The product was purchased 35 years ago. Household appliances generally did not have chassis grounds.

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leaving conductors exposed

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