And yet Desco still puts one megohm resistors in all
of their straps, as do your competitors.  Why do this
if not for safety reasons?

This can't be to increase discharge time, because 
equipment is hard grounded, while only our people are 
grounded through 1 megohm.

Surely there are lots of ways that electricity can
hurt us, and it makes sense for UL to caution people not
to do anything stupid.  But putting some resistance in 
the path to ground seems a reasonable precaution.

And UL and ESD association specs still require a minimum 
resistance to ground.  Probably OSHA too (I've seen OSHA
compliance asserted in data sheets, but there's no specific
documents referenced).

-Joe

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gene Felder
Sent: Wednesday, May 20, 2009 6:07 PM
To: [log in to unmask]
Subject: Re: [TN] ESD Heel Strap / Shoe Checker - low resistance

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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