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May 2009

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Subject:
From:
Gene Felder <[log in to unmask]>
Reply To:
Date:
Wed, 20 May 2009 15:07:21 -0700
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UL agrees with Rex.  See below "It will not reduce or increase your risk of
receiving electric shock".

Wrist Straps and Foot Grounders covered by our listing are to note this UL
Underwriters Laboratories listing caution warning:
"Note: This product is not recommended for use on equipment with operating
voltage exceeding 250 VAC.
CAUTION: The ESD Series is for electrostatic control. It will not reduce or
increase your risk of receiving electric shock when using or working on
electrical equipment. Follow the same precautions you would use without
wrist straps or foot grounders, including:
. Make certain that equipment having a grounding type plug is properly
grounded.
. Make certain that you are not in contact with grounded objects other than
through the ESD Series."

Gene Felder
[log in to unmask]

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Rex Waygood
Sent: Wednesday, May 20, 2009 2:53 PM
To: [log in to unmask]
Subject: Re: [TN] ESD Heel Strap / Shoe Checker - low resistance

Your work environment should not present an electric shock risk, if it  
does then fix it. If that risk exists then there are as many ways for  
electrocution to occur bypassing the resitance of the wrist strap or  
heel grounder.

The first esd standard was written to have no risk of electrocution.  
Unfortunately it was unworkable.

Rex



Sent from my iPhone

On 20 May 2009, at 21:30, "Kane, Joseph E (US SSA)"
<[log in to unmask] 
 > wrote:

> As has been mentioned here, LOW resistance indicates
> a safety problem.  If the operator has resistance of
> less than 1 megohm (nominal) to ground, then they
> risk electrocution if they touch 110V hot.  Without sufficient
> current limiting resistance, it's like having your guy
> standing around in a puddle of water.
>
> With one megohm resistance in series, 110 volts will give
> him a good shock, but the current is limited to less
> than 1 milliamp (I=V/R), which is not enough to stop his
> heart.
>
> Lotion and more sweat will lower the resistance, not
> increase it.  You could have him wear insulating socks
> inside those shoes, but that won't be very comfortable and
> probably won't last for long, as sweat builds up.  In fact,
> some ESD-protective shoes are deliberately built so that they
> don't "breathe" very well, facilitating buildup of a sweat layer.
>
> We've had issues with conductive shoes failing low, because
> the shoes were too conductive for some people.  We replaced
> those shoes with ones that meet spec.
>
> If heel straps are failing as well, that's a puzzle, because
> something is circumventing the 1 megohm resistor.  The only
> way this can happen is if there's another parallel path to
> ground.  Are you testing with both feet on the conductive
> surface at once?  The spec says to test each foot individually,
> because a person keeps only one foot in contact with the floor
> at a time when walking.  If your footwear tester doesn't have
> independent footplates, have this person lift one foot at a time
> while pushing the little button.
>
> As for the wrist straps, that's another head-scratcher.  If this
> person is wearing conductive footwear on a conductive surface
> while he's testing the wrist strap, there's your other path
> to ground.  Try having him stand on an insulating pad.
>
> Joe Kane
> BAE Systems
> Johnson City, NY
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
> Sent: Wednesday, May 20, 2009 3:59 PM
> To: [log in to unmask]
> Subject: Re: [TN] ESD Heel Strap / Shoe Checker - low resistance
>
> Most shoe testers are checking for a range of 1 meg to 10 meg.  
> Anything
> in between is a pass. Over 10 meg is too much resistance in series
> between the "touch button" and the shoe/strap floor plate, which is  
> the
> operator, the sock, and the shoe or heelstrap. Under 1 meg is too  
> little
> resistance between same. Most people fail high due to dry feet, loss  
> of
> conductivity in the shoe, or their hands are too dry. People that fail
> low are unusual.
>
> If your warehouse worker is working in a warehouse that is not air
> conditioned and he sweats heavily his socks and his shoes can actually
> become saturated to the point where the reading is "too conductive"  
> and
> he will fail low.
> Applying lotion to the strap will exacerbate the situation. If he  
> put on
> someone else's shoes and walked around in them with damp socks plus  
> the
> lotion is still on his socks and skin he could possibly saturate  
> someone
> else's shoes, but I doubt it.
> If his shoes are saturated with any oils or chemicals or metal
> filings/nails from the warehouse or loading dock area they would also
> fail low.
>
> A portable ESD checker can be used to measure the actual resistance
> between the bottom of his shoe and his finger. If it is below 1 meg  
> you
> may wish to have him wear thicker socks and make sure the heel strap  
> is
> worn on the inside of his shoe, but not on the inside of his sock.
>
> I suspect that he is really failing high, in which case he may need a
> good foot lotion, non-acrylic (thin wool or cotton) socks, and  
> possibly
> even a hand lotion. Be sure the lotion is something like I.C. lotion
> from R&R products or the equivalent and does not contain any  
> silicone or
> lanolin.
>
>
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Helena Pasquito
> (Cobham DES SSA)
> Sent: Wednesday, May 20, 2009 1:53 PM
> To: [log in to unmask]
> Subject: [TN] ESD Heel Strap / Shoe Checker - low resistance
>
> Hello Tech Net,
> Assemblers and techs check their shoes on an ESD Shoe checker, each  
> day
> before the start of their shift. We have one person that works in the
> warehouse that always fails low (resistance). We have tried new heel
> straps, walking for an hour or two in regular ESD shoes, even wearing
> someone elses shoes that had just passed. Nothing seems to work. He  
> has
> also tried to apply lotion to the strap that sits inside his sock. Do
> you know of any tricks we can try to employ? Have you seen issues like
> this before? I think some of the steps we took may have helped for a
> high resist fail but not a low resist. Even the wrist strap test fails
> for him (multiple wrist straps).  Any suggestions would be much
> appreciated.
> Helena Pasquito
> Training Specialist
> Certified IPC Trainer
> Cobham Electronic Systems
> 1001 Pawtucket Blvd., M/S 160
> Lowell, MA 01853
> 978-442-5024
> [log in to unmask]
>
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