Drew is correct. Here's applicable section sof ESD association documents.
When working with voltages over 250 VAC, ESD personnel grounding should not
be used, rather ionization may be required to neutralize electrostatic
charges.
Per ESD Handbook ESD TR20.20-2008 Wrist Strap section 5.3.2.6 "For personnel
safety, wrist straps should not be used in situations where there is an
exposed electrical circuit of 250 volts or higher.
NOTE: Several publications exist (beyond UL) that provide varying limits of
allowable current for personnel safety. For example, most power supplies are
current limited to 5 mA. For this reason, the user should check with local
safety personnel to determine requirements for their particular area. Refer
to the personnel safety section of this handbook for further guidance."
Per ESD Handbook ESD TR20.20 section 5.3.6.1 Introduction and Purpose /
General Information "The primary method of static charge control is direct
connection to ground for conductors, static dissipative materials, and
personnel. A complete static control program must also deal with isolated
conductors that cannot be grounded, insulating materials (e.g., most common
plastics), and moving personnel who cannot use wrist or heel straps or ESD
control flooring and footwear.
Air ionization can neutralize the static charge on insulated and isolated
objects by charging the molecules of the gases of the surrounding air."
As important as ESD control is, it is of secondary importance compared to
employee safety. Questions regarding safety should be answered by the
facility's safety officer. The safety officer and ESD Coordinator should be
aware of this information
ANSI/ESD S20.20 states:
"Section 5. PERSONNEL SAFETY
The Procedures and equipment described in this document may expose personnel
to hazardous electrical conditions. Users of this document are responsible
for selecting equipment that complies with applicable laws, regulatory codes
and both external and internal policy. Users are cautioned that this
document cannot replace or supersede any requirements for personnel safety.
Ground fault circuit interrupters (GFCI) and other safety protection should
be considered wherever personnel might come into contact with electrical
sources. Electrical hazard reduction practices should be exercised and
proper grounding instructions for equipment must be followed."
There is always a safety concern when working around high voltage. All
electrical wiring and ground connections should adhere to the National
Electrical Code (NEC) as governed by OSHA. Per ESD Association ADV-2.0,
Safety rules for working with high voltages should dictate the design of the
workstation.
When equipment voltage exceeds 250 volts, guidance should be obtained from
the appropriate Safety Officer. Wrist Straps and Foot Grounders will
quickly and efficiently remove electrostatic charges to ground, however, if
there is a possibility that they may be exposed to voltages over 250 volts,
these personal grounding items should not be used. The Safety Officer has
to make the determination if the worker has any risk of being exposed to the
high voltage. If the Safety Officer determines that the high voltage is
adequately insulated and isolated, then personal grounding, which is more
effective and less expensive, can be used.
Many Wrist Straps and Foot Grounders] are Underwriter Laboratories listed.
UL cautions that these products are not recommended for use on equipment
with operating voltage exceeding 250 volts:
UL Marking for Wrist Straps and Foot Grounders:
"CAUTIONARY MARKING
This product is not recommended for use on equipment with operating voltage
exceeding 250 volts."
Gene Felder
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Drew meyer
Sent: 2010 - 03 - 19 7:31 AM
To: [log in to unmask]
Subject: Re: [TN] ESD protection / high voltage safety question
Graham,
I know how I managed a case like this several years ago for my company.
Now realize that ESD rules may have changed.
We were running HiPot test and there was concern for the operator should a
safety system fail. First step, no wriststrap. Second step, since
operators
were dissipative footwear, an insulative mat on the conductive floor to keep
the operator at a high resistance level. Third step an ionizing blower
mounted
above the station blowing down in front of the card cage and over the floor
mat. We never had an ESD event recorded at these stations over the course
of 3 years of operation.
Some ideas for you. Check the latest ESD Association standards for more.
At somewhere above 120VAC the wriststrap and footwear are not to be used.
Drew Meyer
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