How Crazy Can the Corporate World Be? - Page 1
Forum section: electronics / general

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 18, 2016, 02:54:11 am
content: My son will be working with 100+VDC supplies at his place of employment. The employer has mandatory safety training for employees who will be exposed to high voltage (don't know exactly what their threshold is.). So far this sounds sensible.Then he attends the training and at one point they recommend that if you don't know how high the voltage of a particular wire is, you should touch it with the back of your hand. Two reasons: First, there are fewer nerve endings there so it won't hurt so much. Second, if your muscles involuntarily spasm they won't curl around the wire.He couldn't believe his ears, and then noted that this advice was included in the written material.What were they thinking? I told him to go immediately to the law and finance departments to get them to prepare for the large lawsuits and judgements that will follow anyone actually following this advice.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: November 18, 2016, 04:02:12 am
content: Seems like for the last 75 to 100 years or so the rule should be if you don't know don't touch.Simple tools like a light bulb or a neon bulb with wire probes would be better than the back of your hand. And Simpson's have been available for nearly that long for anyone who should be working on unknown wires.There are really few excuses for not knowing the possible voltage on a wire, the only real doubt is whether it is hot or not. Easy to check without using yourself as a fuse. In the cases where the voltage really is unknown it also likely to be a REALLY bad idea to touch random wires.

author: VulcanBB18
author_rank: Contributor
timestamp: November 18, 2016, 05:22:11 am
content: I have heard this "back of the hand" advice from old sparkies and hobbyists, but NEVER seen it printed in official material!And it is internally consistent - there are fewer nerve endings there, and you will pull away (instead of grip-on), however......unless it was a life-and-death situation to test that wire, and there was no multi-meter or test-lamp available, then yes I'd do it.Otherwise, I'm not intentially giving myself an electric shock! I mean what year is this...1916??cheers,

author: Red Squirrel
author_rank: Super Contributor
timestamp: November 18, 2016, 06:01:19 am
content: It does sound like something that would be against most if all safety regulations but it's more sensible than grabbing the wire with palm of hand... I personally use my fingers, one finger to ground then to what I want to test, but I only do that test AFTER I've used a multimeter. It's basically a final test before I grab the wires and start working on them. I also test the multimeter in a known working outlet before to make sure it's working correctly.

author: Fsck
author_rank: Super Contributor
timestamp: November 18, 2016, 06:26:52 am
content: in what situation do you have to touch a wire but don't have any tools? can't even use your belt, shoelaces, pen?

author: Brumby
author_rank: Unknown
timestamp: November 18, 2016, 08:43:32 am
content: I'm aware of this 'guideline' - but I've never used it.If I don't know what I'm dealing with, I won't touch it.

author: Zero999
author_rank: Super Contributor
timestamp: November 18, 2016, 09:06:02 am
content: Quote from: CatalinaWOW on November 18, 2016, 02:54:11 amOf course you should never touch something with a potentially dangerous voltage on. Apart from being foolish, the hand test is unreliable. The tiny current leaked by a switched mode power supply may feel like pins and needles but it's not harmful, yet you wouldn't feel anything when touching connected to a floating 600VDC battery bank.Quote from: blueskull on November 18, 2016, 03:01:59 amThat 50VAC or 50VDC?

author: dmills
author_rank: Super Contributor
timestamp: November 18, 2016, 10:51:32 am
content: The back of a hand thing CAN, ONCE IN A BLUE MOON, be a good idea.I ended up on a boat slowly filling with sea and needing to repair a pump control circuit, now the three phase supply came in via a contactor, and we had the control supply switched off, but I still got a nice belt (To the back of the hand).It was because the contactor control switch (Which we could get to easily) actually controlled a remote Thyristor and and a junction box had flooded allowing enough gate current to flow, stupid bit of 'design', especially as the status indicator showed switch not contactor status.Sometimes you need to get the fix in NOW, not go looking for tools.But I would never advocate it on land, bit like the way marine firefighting has a very different view or risk to the land based sort (Land based, you can stand back and let it burn, does not usually work so well on a cruise ship).It is a trick worth knowing, like using the back of a hand on a potentially hot metal hatch if you have a fire aboard (Substantially the same reasoning), but one with very limited use outside of messy situations, and probably not something for newbie safety training.Regards, Dan.

author: tszaboo
author_rank: Super Contributor
timestamp: November 18, 2016, 11:03:32 am
content: I thought the proper procedure top check if a wire has high voltage was to give it to an intern or a lab assistant...I much rather like the very sensible other rule they give: If you work on mains powered stuff with a permanent electrical cord, put the end of the cord into your pocket. That way, neither you, nor someone else can accidentally plug it in. Unless you have awkward colleagues, who steals cable ends from your pocket.

author: Psi
author_rank: Super Contributor
timestamp: November 18, 2016, 12:03:43 pm
content: Check the wire with a meter first.Then, if the meter says it's safe, touch the wire for the first time with the back of your hand.This may save your life if the meter is faulty.I suspect this was the intent of what they said. It probably got twisted and misinterpreted

author: CraigHB
author_rank: Regular Contributor
timestamp: November 18, 2016, 12:17:25 pm
content: Quote from: Psi on November 18, 2016, 12:03:43 pmThat's what I do when working on household utility stuff, check with a meter first then brush with finger as a final backup just in case the reading is not correct. I actually got nailed by that once changing out an electric water heater. Flipped the breaker, checked with meter and indicated flat, but still hot. Don't know why meter read flat. Could have been deadly, but wire contact occurred with water heater chassis first, breaker popped. Dodged a bullet on that one.

author: jonovid
author_rank: Super Contributor
timestamp: November 18, 2016, 12:21:50 pm
content: a shocker if it failsupdate-a simple solution to the problem

author: Brutte
author_rank: Frequent Contributor
timestamp: November 18, 2016, 02:08:20 pm
content: Quote from: CatalinaWOW on November 18, 2016, 02:54:11 amPerhaps that was a training with Bear Grylls..If the only two choices are to either touch a wire with a palm or with the back of your hand then sure - pick the latter, makes sense then. However is just hard to imagine a real life context in which someone voluntarily does such things.

author: zapta
author_rank: Super Contributor
timestamp: November 18, 2016, 02:11:18 pm
content: Quote from: CatalinaWOW on November 18, 2016, 02:54:11 amSince we don't have the exact text of the training material, it's hard to judge it here.I see value in telling people that touching with the inner part of the hand is even more dangerous than the back of the hand.

author: Jeroen3
author_rank: Super Contributor
timestamp: November 18, 2016, 05:09:59 pm
content: No. the only way a safety trainer is allowed to teach is using the appropriate safety tool.For low voltage (<1000): you use eg, a fluke T90.For high voltage (>1000): you ask the high voltage certified personell. If you are not certified, you are not insured.And thus liable!

author: ajb
author_rank: Super Contributor
timestamp: November 18, 2016, 05:15:52 pm
content: Quote from: Psi on November 18, 2016, 12:03:43 pmMany training materials recommend a three-step test:1- Check a known-live circuit with the meter, verify that the meter indicates it's live2- Check the unknown circuit3- Check the known-live circuit again, verify that the meter still indicates it's liveThis will verify that the meter is functional, and the third step will catch things like one of the leads coming loose from the meter or the setting switch getting bumped between steps 1 and 2. For bonus safety points, measure both circuits from the same reference (ie, live or neutral) where possible and leave the reference lead in place through the whole process.