10/02/2012 Slide 1

Keeping the Customer Safe

Socket Safety Clips, Hot Sockets & Other Recent Research & Development

at TESCO

Prepared by Tom LawtonTESCO – The Eastern Specialty Company

for EEI Fall Transmission, Distribution and Metering Conference 2014

Slide 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 seeingincident 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 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 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”.

Slide 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.

Slide 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

Slide 6

Expected & Unexpected Results Expected:• Hot Sockets are exactly that – hot sockets. The hot sockets are the source of the

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.

Slide 7

Temperature Rise Data

Slide 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 to initiate arcing)

• Minimal load present

Slide 9

What to look for in the field

• 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

Common Features and Common Sources of Concern

Slide 10

Jaws with intermittent connections will arc to the meter blade resulting in pitting on the blade.

Blade shows early signs of arcing.

Slide 11

Jaw to Blade Arcing

12

Tin burned off

Blade hole due to arcing to jaw – Copper melts at 1040ºC (1900ºF)

AX-SD base thermoset plastic melts at 960ºC (1760ºF)

Severe Arcing Jaw to Blade

Slide 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 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.)

Slide 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 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

Slide 15

• 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.

Service Degradation

Slide 16

Slide 17

Field Inspection of SocketsBest Practices

• 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

Slide 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 19

• 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.

What can be done once a hot socket is identified?

Slide 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 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 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?

Slide 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 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.

Slide 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 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.

Slide 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