Pilz Safety Lockout System (PSLS) An alternative isolation method for LOTO By Doug Sten, Safety Consultant, Pilz Automation Safety
Objectives Challenges with manual, mechanical isolation disconnects Challenges with using a contactor as an isolator Solution: UL 6420 Equipment Used for System Isolation and Rated as a Single Unit OSHA acceptance for LOTO via System Isolation Equipment Filing for Variances; Federal and State
Traditional mechanical isolation devices Larger sizes rated only 2,000 operations, most are rated at 8,000 operations Frequent use AC23a rating provides 20,000 operations 1 isolation cycle = 2 operations Over a 20 year mission life = 1.3 operations per day Changing out disconnects is expensive and inherently an unsafe job
Traditional mechanical Disconnects can fail unsafe isolation devices The operator is required to stand next to the door to throw the lever, putting him in harms way if there is a fault Phases may remain energized even when locked out
Traditional mechanical isolation devices Clearance of 36 in front of the disconnect enclosure is required Series connected disconnects for multiple access points can lead to false zero voltage verification because a disconnect upstream may be off Wet cleaning in food-grade environments are especially dangerous when high voltage disconnects are accessible After a power failure, a manual disconnect stays on leaving the potential for hazardous energy to be present when power is reapplied
Contactor as an energy isolation device A contactor system is optimal for high cycle rates but is not an isolating device, unless AC-23a rated as a unit Normal contactor endurance testing per IEC60947-4-1 uses 6x rated current; AC23a requires 10x rated current and almost twice the cycle count Normal contactor testing per IEC60947-4-1 for SSCR (Short Circuit Current Rating) type 2 coordination with the protection device (fuse, CB) allows the contacts to tack weld closed if it can be broken free easily
Contactor as an energy isolation device Common cause failure In a dual contactor arrangement both contactors can weld on same phase when subjected to a fault current This inhibits motion in a typical guard door interlock but does not isolate energy To meet ISO13849, dual channel requires the system must be tested for this common cause failure to qualify for safety of energy isolation
UL 6420: Controls/contactor as an isolation device Equipment Used for System Isolation and Rated as a Single Unit Electromechanical contactors remotely controlled and monitored to provide remote isolation status indication with a defined integrity level Used both as a means for removal of power for prevention of unexpected start-up of a stopped machine and as an isolator to provide protection from electric shock by ensuring the removal of electrical energy This equipment is intended for installation in accordance with the National Electrical Code, NFPA 70 and the Electrical Standard for Industrial Machinery, NFPA 79: 2012
UL 6420: Controls/contactor as an isolation device Equipment Used for System Isolation and Rated as a Single Unit Principally intended for industrial machine applications where, isolation of power is so frequently required that the mechanical life of a typical disconnecting means is unacceptably short or where there are multiple entry points on the machine where disconnection is required, or both. Note Multiple entry points are a function of access needs and the layout of the machine. In 2015, OSHA added the ANSI/UL 6420 for product approvals by a Nationally Recognized Testing Laboratory (NRTL). Reference: OSHA 1910.7
Additional PSLS machine control interfaces UL 6420, 4.8.1: System isolation equipment can be configured to meet additional machine control interface applications such as: Safety related interface signal and feedback channels for Guard door locked status Release signal for guard locks Signal to and feedback from safety pneumatic control valve Signal from E-stop devices to and feedback from E-stop systems Run permissive to machine drive control system Zero speed signals from drive Signal to machine stop
Additional PSLS machine control interfaces UL 6420, 4.8.1: System isolation equipment can be configured to meet additional machine control interface applications such as: Information related interface channels Lockout switch positions (open or closed) Isolation system component status and troubleshooting aids Isolation system equipment status
Safety Lockout System Description A system to safely disconnect machines and facilities from electrical, hydraulic and pneumatic power, provide automatic zero energy verification in order to protect personnel and comply with industry standards to prevent unexpected start-up The power isolation is a control reliable design and uses dual channel circuitry in the disconnect path The concept is the same as a lockout tagout procedure with automatic verification (No light, No enter) UL 6420 System Isolation Equipment: the Pilz SLS system may be used as an isolation disconnect means for electrical servicing per NEC 430.109(A)(7) and NFPA79 2012 section 5.5.4(3)
Characteristics The energy isolation systems are modular in design Large complex systems require Pilz integration and can consist of: Multiple electrical power SLS Panel Optional Interface Panel or Remote Interface Subpanel PSS4000 Safety PLC Panel RLS Remote Lockout Switch Optional Pneumatic Exhaust Dump Valve Interface Optional Hydraulic Exhaust Dump Valve Interface Long Distance connections via SafetyNET and fiber optics
Characteristics For simple disconnect replacement, OEM/User installed systems consist of Main electrical SLS Panel w/ PNOZmulti Controller Optional Marshalling Boxes for expansion Optional Pneumatic Exhaust Dump Valve Interface Optional Hydraulic Exhaust Dump Valve Interface
Design principle RLS 1 OFF ON Pilz SLS RLS 2 RLS 3 OFF OFF ON ON PSS or PNOZmulti Controller Redundant Isolation Contactors and Voltage Monitor Optional C-Stop(s) or E-Stop(s) P P Redundant Valve(s) and Dual PS Feedback
Multi system More Marshalling Panels 8 more RLS Optional Marshalling Panel 480Vac Line Power 8 Remote Lockout Stations per main panel Power and Control Panel Hydraulic Isolation Panel Isolated 480Vac Load Power SRP/CS Interface E-Stop, Interlock Interface and Dual Contact System Isolated Feedback Ethernet Communication for fault and system status Pneumatic Isolation Panel
Systems Wall mount systems: 60A, 100A, 200A Floor mount systems: 200A, 400A, 600A
Adding fluid power Pneumatic isolation will be added to the standard end of 2018 Hydraulic Isolation to be added in 2019 A plug-in pneumatic panel with inlet pressure switch and dual, calibrated zero pressure, factory tested, verification switches is provided for isolation to ISO 13849-1 Category 4, PL e
System isolation equipment Advantages Safe disconnect (isolation) of machine or zone hazardous energy Prevention of unintended start-up Zero energy verification and visual acknowledgement of the safe state (no need to suit up for zero voltage verification) Long lifetime, compared to traditional disconnect switches designed for high cycle frequency and 20 year mission life Remote operation removes operator from power switching elements Electrical and fluid power isolation with a single remote lockout station (just 1 lock)
System isolation equipment Advantages Economical placement of lockout points at each access promotes using proper procedures Flexible configuration for large and diverse machines and facilities Clearance of 36 in front of the Remote Lockout Station is not needed because it is 24VDC low current Removes the operator from hazards associated with wash down environments by removing the presence of 480VAC at the access point
NEC accepts PSLS The National Electrical Code (NFPA 70:2005) System isolation equipment: A redundant monitored, remotely operated contactor isolation system, packaged to provide the disconnection/isolation function, capable of verifiable operation from multiple remote locations, each having the capability of being padlocked in the off (open) position System Isolation Equipment shall be listed for disconnection purposes SIE shall be installed on the load side of the current protection and the related disconnecting means
NFPA 70E allows PSLS and PU3Z The 2018 edition of NFPA 70E Standard for Electrical Safety has added an exception specifically to allow SLS use of permanently mounted voltage monitor for verification of absence of voltage for electrical servicing. Prior to the exception one had to suit up in arc flash gear and use a hand held instrument. Now not just the SLS but any electrical panel can use the PNOZ PU3Z in a LOTO procedure for un-expected startup OR electrical servicing. From clause 120.5(7):
NFPA79 accepts PSLS NFPA 79-2015 5.5.4 The following devices shall be permitted to fulfill the isolating function: (1) Devices described in 5.3.2 (2) A manual motor starter marked suitable for motor disconnect and compliance with UL 508 where located on the supply side of the last short circuit protection device (in the branch) (3) System isolation equipment that incorporates control lockout stations and is listed for disconnection purposes where located on the load side of the main supply circuit disconnecting means and over-current protection
ANSI Z244.1 2016 LOTO and alternative measures 3.12 Energy Isolating Device. A means of preventing the transmission or release of energy. NOTE 4: System isolation equipment that incorporates control lockout stations and is listed for disconnection purposes where located on the load side of the main supply circuit disconnecting means and over-current protection can be energy isolating devices. See NFPA 79. 8.4.4 Other Means of Hazardous Energy Isolation. Remotely activated electro-mechanical lockout systems are an acceptable alternative to be used in selected applications such as long machines and inaccessible or inconvenient locations of primary isolation devices. The user shall install and operate such systems (e.g., remote low voltage lockout system, pneumatics systems) in accordance with the manufacturer s directions. See Annex B for further details. See NFPA 79.
ANSI Z244.1 2016 5.4.1 Location. Energy isolating devices shall be accessible and, where practicable, be conveniently located to facilitate the application of isolating devices during necessary tasks. Energy isolating device should be located outside hazardous areas and at a convenient height from an adjacent walking area (i.e. not overhead or under machinery). If unable to position or install isolating device(s) at a convenient location, measures shall be taken to provide proper access to the devices. NOTE: As an example, a remote lockout or a system isolation equipment rated as a unit and listed for the purpose of isolating energy may be implemented as one such measure. See Annex B.
ANSI Z244.1 2016 Annex B Remote Lockout Systems Justification to use a remote lockout system instead of a manual disconnect for service disconnect isolation purposes includes: When frequency of the task exceeds the capability of a manual disconnect When environment is not acceptable to place a manual disconnect Large complicated machinery involving many lockout devices making the lockout procedure too cumbersome Reduce to a single lock point directly at the access point To prevent machine operators from standing in front of large disconnect switches in case of short circuit fault
ANSI Z244.1 2016 Annex B Remote Lockout Systems Justification to use a remote lockout system instead of a manual disconnect for service disconnect isolation purposes includes: Large disconnects can be physically hard to operate for some operators Required spaces not available (service access, electrical hazards, adequate ventilation, etc.) NOTE: Types of electrical lockout systems available include, but are not limited to remote low voltage system, and listed system isolation equipment.
PSLS in the US In 2015 OSHA accepted the standard into 1910.7 National Recognized testing Laboratory (NRTL) program as an acceptable standard a NRTL can certify product to and we are listed by UL By using UL6420 listed product the user meets NEC, NFPA79 and Z244.1 OSHA historically has moved slow in updating 1910.147 Prevention of unexpected startup which has not been updated since it was made law in 1989. OSHA currently has 1910.147 under review for an update
PSLS in the US OSHA deems electrical equipment acceptable for use if there is a standard for the product accepted and listed in the table in 1910.7 Our systems are proven in use since 1996 with no cases of a dangerous failure or OSHA citation for using it
OSHA 29 CFR Subpart S, Electrical 1910.399, Definitions applicable to this subpar Acceptable. An installation or equipment is acceptable to the Assistant Secretary of Labor, and approved within the meaning of this Subpart S: (1) If it is accepted, or certified, or listed, or labeled, or otherwise determined to be safe by a nationally recognized testing laboratory recognized pursuant to 1910.7 Accepted. An installation is "accepted" if it has been inspected and found by a nationally recognized testing laboratory (e.g. UL) to conform to specified plans or to procedures of applicable codes.
Variance: Federal / State OSHA Variance is an alternative procedure of compliance with some part of a safety and health standard granted by OSHA. Employer may not be able to comply fully and on time with a new safety or health standard because of a shortage of personnel, materials, or equipment. Employer may prefer to use methods, equipment, or facilities that they believe protect workers as well as or better than OSHA standards. See Title 29 of the Code of Federal Regulations (CFR), Part 1905, Rules of Practice
Types of variances Temporary Variance - Allows employers a short term (limited time) relief - Employer must implement an effective compliance program as quickly as possible - The employer must demonstrate to OSHA that all available steps are being taken to safeguard workers. - Inability to afford compliance costs is not a valid reason
Types of variances Interim order - Permits an employer to continue operating under existing conditions while OSHA considers the employer s request employers - Must inform workers by giving a copy of the order to authorized employee representatives and posting a copy prominently in the workplace
Types of variances Permanent variance Grants an alternative means of compliance with the requirements of a standard to employers who can prove that their methods, conditions, practices, operations, or processes provide workplaces that are as safe and healthful as those that follow the OSHA standards - machine specific Employers must let workers know they have filed the application and that the workers have the right to request a hearing OSHA reviews the employer s evidence and, if appropriate, visits the workplace to confirm the facts provided in the application
Types of variances Permanent variance Final variance orders detail the employer s specific responsibilities and requirements and explain exactly how the employer s method varies from the OSHA requirement Application for a permanent variance, see 29 CFR Part 1905.11 Subpart B Visit OSHA s website at www.osha.gov/dts/otpca/ variances /apply.html
Thank You Doug Sten, Safety Consultant Pilz Automation Safety, L.P. 7150 Commerce Blvd. Canton, MI 48487 Telephone: +1 (734) 354-0272 Email: info@pilzusa.com www.pilz.us