1. Keeping the Customer
Safe
Socket Safety Clips, Hot Sockets &
Other Recent Research & Development
at TESCO
10/02/2012 Slide 1
Prepared by Tom Lawton
TESCO – The Eastern Specialty Company
for EEI Fall Transmission, Distribution and Metering Conference 2014
2. The Issue
• Hot Sockets are not a new phenomenon. Virtually every meter man has pulled a meter with a
portion of the meter base around a blade melted and virtually every utility has been called to
assist in the investigation of a fire at a meter box.
• From 2007 to 2011 the four years before the start of the majority of AMI deployments there were
590 reported fires in the United States that originated in the meter or the meter box. An average
of 125 per year and an incidence rate of less than one in a million meters each year.
• Since that time the number has increased dramatically to the point where meter fires have
dominated the news locally, nationally and internationally at various times over the past three
years.
– Utilities going through a full AMI deployment are seeing
incident rates one and two orders of magnitude greater
than normal, leading to a media frenzy and a public focus
on the safety of the meter on the side of their house.
Slide 2
3. The Issue
Utilities need to understand this phenomenon and be proactive in identifying and responding to
consumer and commission questions related to the safety of a meter installation. Questions that
each utility should be able to answer going forward;
– What causes a hot socket?
– Are the meters ever the cause of a meter box failure?
– Are some meters or some meter enclosures more susceptible to fires than others?
– Why are there suddenly so many meter related fires?
– Have we done enough testing before deploying new meters and new technology to ensure
that what we are doing is safe and will make the customer safer?
– What are the things to look for when inspecting an
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existing meter installation?
– What are the best practices for handling potential hot
sockets?
This presentation will cover the results of our lab investigation, our conclusions and our answers
to these questions. Each Utility in the room will have to answer these questions for themselves.
If successful this presentation will spark a conversation on updating our “best practices”.
4. Why do we know anything about hot sockets?
• TESCO has been fortunate enough to be involved in several meter deployments where we
supplied full time and part time meter engineers and project managers to our customer’s AMI
deployment teams. In this capacity we have been involved in evaluating hot socket issues and
helping to determine an appropriate response to actual or potential hot sockets.
• TESCO’s meter lab has been contracted to develop a laboratory fixture that would simulate the
various features common to most hot sockets found in the field.
• TESCO developed and refined a fixture since the 2013 Fall EEI running tests and gathering data
on the effect of hot sockets on meters.
• TESCO has access to a large number of
meters which have been exposed to hot
sockets both before and after catastrophic
failure.
• We have access to a limited number of
sockets that were hot sockets and did not yet
fail catastrophically.
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5. Hot Socket Simulator (Catalog No. 3100-L)
The TESCO Hot Socket Simulator is a piece of meter lab equipment
to assist in the investigation of meter failure issues related to hot
socket phenomenon. The Simulator is equipped with one 2S meter
socket with four jaws, one of which is the heated jaw. The
arcing/heating apparatus can be moved to any of the four jaws (jaw 1
is the standard). Additional arcing/heating elements can be provided
as an option for multiple hot jaws on the existing socket.
• Ability to Simulate a hot socket in line and load jaws through
controlled arcing (frequency, gap size) or cartridge heater
(temperature control)
• Easily replaceable jaw and socket parts
• Temperature recorded at stab with non-contact pyrometer
with a digital display and thermocouple signal output
• Selectable loads (5A, 10A, 15A, 20A, 25A)
• Adjustable arcing gap size, 0.03” (0.8mm) and 0.015”
(0.4mm) cams provided (other sizes available)
• Screw adjustment of gap size for non-vibration arcing
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6. Expected & Unexpected Results
Expected:
• Hot Sockets are exactly that – hot sockets. The hot sockets are the source of the
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problem and not hot meters.
• Electromechanical meters withstand hot sockets better than solid state meters
Unexpected:
• Current plays only a small role in how
quickly a meter will burn up. Meters were
burned up nearly as quickly at 3 amps, 30
amps, and 130 amps.
• Relatively small amounts of vibration can
be the catalyst in the beginning and
eventual catastrophic failure of a hot
socket. Note: Other catalysts include but
are not limited to power surges, debris,
humidity, salt water.
• Contact resistance plays no role in
creating a hot socket
And some newer solid state meters are
better than electromechanical meters.
8. What are the necessary ingredients
for a hot socket?
There are three necessary ingredients to create a hot socket (Note: We are
not suggesting that we have simulated or even understand all causes for all
hot sockets and meter related fires, but rather that we have simulated and
understand the causes behind most hot sockets and meter related fires);
• Loss of jaw tension in at least
one of the socket jaws.
• Vibration (or other catalyst
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to initiate arcing)
• Minimal load present
9. What to look for in the field
Common Features and Common Sources of Concern
• Pitted and discolored meter blades
• Melted plastic around one or more of the
meter stabs (typically the plastic around
one stab is where the deformation starts)
• Pitted and discolored socket jaws
• Loss of spring tension in the socket jaws
Slide 9
11. Jaw to Blade Arcing
Jaws with intermittent
connections will arc to the
meter blade resulting in
pitting on the blade.
Blade shows early signs
of arcing.
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12. 12
Severe Arcing Jaw to Blade
Tin burned off
Blade hole due to arcing
to jaw – Copper melts at
1040ºC (1900ºF)
AX-SD base thermoset
plastic melts at 960ºC
(1760ºF)
13. Base Line Data Electro Mechanical meters vs solid state vs the latest
generation of meters designed with hot sockets in mind
• At the start of our laboratory investigation the oldest electro mechanical meters
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withstood hot sockets the best
• The latest vintage solid state meters withstood hot sockets the least.
• Over the course of the past twelve months some meter manufacturers have begun to
release 2S meters designed to withstand hot sockets and some have even begun to
put temperature sensing closer to the meter blades instead of only on the metrology
boards.
• One meter vendor’s service switch meter has used high temperature base plate
plastic since it was launched in 2008.)
14. Conclusions from the Research Data that shed
additional light on the subject
• Repeated meter insertions degrades the tension in the socket jaws (see graph), but
Slide 14
not to dangerous levels
• Exposure to elevated temperatures rapidly degrades the socket jaw tension to
dangerous levels (see graph)
• Visual inspection will catch some but not all dangerous socket jaws
• Arcing creates the heat
• Exposure to elevated temperatures has a cumulative effect on the meter socket jaw
• Relatively small vibration can initiate arcing
16. Service Degradation
• Calipers show a .01” gap,
with that size gap between
jaws and stabs we were
able to heat meter stabs
over 1000 degrees
Fahrenheit in a few
minutes.
• The rough spots you see
on the post-test jaw next to
the calipers are over .005”
high. This surface
degradation appears on the
stab as well.
• Between the two surfaces
you can have large gaps,
along with insulating by-product
of the arcing, that
can sustain heavy arcing in
a solid state.
Slide 16
17. Field Inspection of Sockets
Best Practices
Slide 17
• Example field check list
– Gaps in meter socket jaws
– Discoloration of one jaw vs. the other three
– Signs of melted or deformed plastic on meter base
– Pitting of either meter blade or socket jaw
– Loss of tension in meter socket jaws
– Check condition of wire insulation and connections
to meter jaws
– Check the overall condition of the box, socket,
meter and how they attach to each other and the
building.
– Look for signs of tampering
– Look for signs of water or debris inside of the
meter can
18. Hot Socket Gap Indicator (Catalog No. 300)
The new TESCO Hot Socket Gap Indicator is used to determine if a meter socket jaw has become
worn-out and unsafe for continued use. The Gap Indicator determines unsafe holding force on meter
socket jaws based on laboratory testing. The TESCO Hot Socket Gap Indicator is available in two
versions:
•Thin-Blade (Catalog No. 300-1) - The "original" Hot Socket Gap Indicator provides a large safety margin for the utility
user. It is not designed for use with jaw styles that have a designed-in gap. These style jaws are designed to provide
greater contact area between meter blades and socket jaws. The thinner blade is also not designed for use with freshly
lubricated socket jaws.
•Wide-Blade (Catalog No. 300-2) - The newly designed Wide-Blade Hot Socket Gap Indicator is better suited for
newer style meter socket jaws with designed-in gaps, and socket jaws which have fresh lubricant. This version will
work with all sockets, but has a smaller built-in safety margin than the original Hot Socket Gap Indicator.
Slide 18
19. What can be done once a hot socket is
identified?
• Easiest resolution is to replace the damaged jaw.
• Never try and repair a damaged jaw. The tension in the damaged
jaw will not return simply by taking a pair of pliers and closing the
jaw tighter.
• Either the entire box should be replaced or the damaged jaw
(assuming the wiring and other jaws are deemed safe through the
rest of the inspection.)
• A Socket Safety Clip can be used to leave the service in a safer
condition than when discovered and provide a “spare tire” that can
buy the customer or the utility time to address the unsafe condition.
The alternatives are to either shut the customer’s power off or
knowingly leave the unsafe condition behind.
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20. Socket Safety Clip (Catalog No. 301)
TESCO's Socket Safety Clip has been designed to give meter technicians a
way to temporarily reassure that a hot socket will not affect a faulty meter
socket jaw.
•Improves the Holding Force to 20 lbs. per socket
•Temporary solution to alleviate disconnecting service
Slide 20
21. • Most AMI deployments utilize third party contractors to handle residential and
some self contained non-2S services.
• After to or prior to AMI deployments, Utility personnel typically see these
Slide 21
sockets
• Transformer rated meters typically handled by the meter service department
of the utility.
• Hot socket concerns with lever by-pass sockets used on 3-phase meters are
extremely rare.
Who Sees Hot Sockets?
22. Summary of the Issues
• Hot sockets start with a loss of tension in at least one of the meter socket jaws. This
loss of tension can be from a variety of sources that start as early as improper
installation or even “tight sockets”.
• Loss of tension is necessary to create the initial micro-arcing conditions.
• Sockets with repeated meter exchanges observed to have higher incidence of hot
socket issues and “booting” a meter may spring jaws even more.
• Vibration appears to be the most common catalyst to the micro-arcing that creates the
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initial heat in a “hot socket”.
• The meter must have some power, but current is not a significant factor in how quickly
or dramatically a hot socket occurs
• The effects of vibration and weakened jaw are cumulative
• Meter Manufacturers have all been working on the design of their meters to better
withstand a hot socket. These new meters have better baseline performance than
even the older electro mechanical meters, but a hot socket will eventually burn up
even the most robust meter.
23. Recap of the Questions
Can we respond adequately to;
– What causes a hot socket?
– Are the meters ever the cause of a meter box failure?
– Are some meters or some meter enclosures more susceptible to fires than others?
– Why are there suddenly so many meter related fires?
– Have we done enough testing before deploying new meters and new technology to ensure
that what we are doing is safe and will make the customer safer?
– What are the things to look for when inspecting an
Slide 23
existing meter installation?
– What are the best practices for handling potential hot
sockets?
Some of these questions are more factual in nature and easier to answer. For others every Utility
will have to answer these questions for themselves, their personnel and their customers. There
is no one size fits all response given the different rules in the different service territories.
24. Questions and Discussion
Tom Lawton
TESCO – The Eastern Specialty Company
Bristol, PA
215-688-0298 (cell) - 1-800-762-8211
This presentation can also be found under Meter
Conferences and Schools on the TESCO web site:
www.tesco-advent.com
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