Transcript NEC Article 409 & UL508A “Industrial Control Panels” 1

NEC Article 409 & UL508A
“Industrial Control Panels”
Troy Miesse/ IE Business Development
Industrial Control Panels
Miesse/ IE / 3-1-07
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Industrial Control Panels
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Agenda
• NFPA 70: National Electric Code (NEC®)
• Short Circuit Current Ratings
• Article 409 “Industrial Control Panels”
• UL508A (Supplement SB)
• Arc Flash and NFPA 70E
• Personnel Protection Equipment
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National Electric Code
• NFPA 70: National Electric Code (NEC®)
• Most states and Authorities Having Jurisdiction (AHJ)
have adopted the 2005 NEC.
• NEC® is updated approximately every 3 years
• Article 409 “Industrial Control Panels” was added to
the NEC® in 2005
• Article 409 requires all industrial control panels to be
marked with an SCCR.
• Empty enclosures do not have a SCCR
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What is a SCCR ?
• A Short Circuit Current Rating is the maximum
current a device or panel can safely withstand for
3 AC electrical cycles (50 msec.) or while an
over-current protective device operates.
• SCCR is usually expressed in RMS kA at the
system voltage. Example: 18 kA at 480 VAC
• RMS is the Root Mean Squared AC current.
• The SCCR of a fuse or circuit breaker is the
same as its Interrupting Rating (IR).
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NEC Article 409
• Industrial Control Panel - An assembly of two or more
components such as motor controllers, relays, CB’s,
etc…..and related control devices
• Industrial Control Panels do not include the controlled
equipment.
• Requires all industrial control panels to be marked
with SCCR – This is a major addition!
• This addition will impact control panel builders, OEMs
and end users in numerous ways:
- How control panel are designed and marked
- The selection of power circuit components.
- The specification of preferred manufacturers.
- How control panels are installed and modified.
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Before the NEC 2005…
• Only Industrial Machinery required marking for
interrupting rating or SCCR of main over-current
protective device
• Industrial control panels, HVAC control panels,
motor controllers, and meter disconnects were not
required to be marked with SCCR
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2005 NEC
• The 2005 NEC requires SCCR markings on all:
• Industrial Control Panels -NEC Article 409
• Motor controllers -NEC Article 430.8
• HVAC controllers -NEC Article 440.4(B)
• Industrial machinery -NEC Article 670.3
• Meter disconnects -NEC Article 230.82(3)
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How do I Determine the Panel SCCR ?
NEC Article 409.110 states that the SCCR of an industrial
control panel is based on one of the following:
• SCCR of a Listed and labeled assembly
• SCCR based on the use of an “approved” method
• UL 508A Supplement SB is given as an example of an approved
method
• Method approved by local electrical inspector (AHJ)
• Engineer (PE) approved apparent RMS method.
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How do I Determine the Panel SCCR ?
NEC Article 409.110 states that the SCCR of an industrial
control panel is based on one of the following:
• SCCR of a Listed and labeled assembly
• Easy enough if you just buying the control panel
• Not an option if you are building or specifying a control panel
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How do I Determine the Panel SCCR ?
NEC Article 409.110 states that the SCCR of an industrial
control panel is based on one of the following:
• SCCR of a Listed and labeled assembly
• SCCR based on the use of an “approved” method
• UL 508A Supplement SB is given as an example of an approved
method
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UL 508A Standard
• UL 508A standard is “Industrial Control Panels”
• The standard covers industrial control panels
intended for general industrial use, operating at a
voltage of 600 volts or less
• This equipment is intended for installation in ordinary
locations, in accordance with the National Electrical
Code, ANSI/NFPA 70
• Supplement SB is included to help determine SCCR
for Industrial Control panels by providing, among
other things, default SCCR ratings for common
components
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UL 508A Supplement SB
UL 508A Supplement SB describes three steps to
determine the SCCR of industrial control panels:
1) Determine the SCCR of all individual power components
by one of the following methods:
- SCCR rating marked on the component
- Use assumed SCCRs in table SB 4.1 of Supplement SB
- Use the tested SCCR from component combinations per UL508
2) Modify the SCCR of certain series combinations if
current-limiting devices are used in the feeder circuit.
3) Determine the overall panel SCCR according to charts in
SB4.4
- Flow chart that help understanding and assignment of SCCR
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UL 508A Standard – Supplement SB
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UL 508A Supplement SB – (review)
UL 508A Supplement SB describes three steps to
determine the SCCR of industrial control panels:
1) Determine the SCCR of all individual power components
by one of the following methods:
- SCCR rating marked on the component
- Use assumed SCCRs in table SB 4.1 of Supplement SB
- Use the tested SCCR from component combinations per UL508
2) Modify the SCCR of certain series combinations if
current-limiting devices are used in the feeder circuit.
3) Determine the overall panel SCCR according to charts in
SB4.4
- Flow chart that help understanding and assignment of SCCR
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UL 508A Supplement SB4.4 Chart
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SCCR Calculation Example – Individual SCCR’s
Control Trans
W/ fuses
Control Relay
Terminal Blocks
Main CB
Power Circuit
SCCR at 480V
 Main CB
30kA
 Contactor
5kA
 Overload Relay
5kA
 Fuses on C-Trans 200kA
Control Circuit
 Control Trans
 Control Relay
 Terminal Blocks
-------
Contactor
W/ Overload
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SCCR Calculation Example – Individual SCCR’s
Control Trans
W/ fuses
Control Relay
Terminal Blocks
Main CB
Power Circuit
SCCR at 480V
 Main CB
30kA
 Contactor
5kA
 Overload Relay
5kA
 Fuses on C-Trans 200kA
If no additional information is
available the the Industrial Control
Panel must be rated at the lowest
rating of any component: 5kA
Contactor
W/ Overload
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SCCR Calculation Example – Tested Combinations
Control Trans
W/ fuses
Control Relay
Terminal Blocks
Main CB
Power Circuit
SCCR at 480V
 Main CB
30kA
 Contactor
5kA
 Overload Relay
5kA
 Fuses on C-Trans 200kA
Control Circuit
 Control Trans
 Control Relay
 Terminal Blocks
-------
Contactor
W/ Overload
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SCCR Calculation Example – Tested Combinations
Control Trans
W/ fuses
Control Relay
Terminal Blocks
Main CB
Power Circuit
SCCR at 480V
 Main CB
 Contactor
30kA
 Overload Relay
 Fuses on C-Trans 200kA
UL508 component combination test
results show that the CB and starter
combination can be rated at 30kA.
The Industrial Control Panel can now
be rated at a higher SCCR: 30kA
Contactor
W/ Overload
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How to Increase SCCR
• Use components and approved combinations with
higher rated SCCRs.
• Use current limiting over-current protective devices
(CB/ fuses) whenever possible.
• Replace low interrupting rated over-current protection
with higher rated ones (retrofit).
– According to UL 508A Articles SB3.2 and SB4.4, the SCCR
of the panel cannot be greater than the interrupting rating of
any over-current protective device in branch circuits or in the
primary of control circuits.
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Industrial Control Panel Marking
Per NEC an industrial control panel shall be marked with the
following information that is plainly visible after installation:
• Manufacturer’s name, trademark, etc.
• Supply voltage, phase, frequency and full-load current
• SCCR
• Identify as service equipment (if applicable)
• Electrical wiring diagram or the index number
• Enclosure type (rating) number
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Panel Marking
Paper Converting Machine
Serial Number
Current
Largest Motor H.P.
Max OCP Device
Voltage
Phase & Freq..
Short Circuit Current Rating
Diagram Number
RC2356YUP77
125 Amperes
20 Horsepower
60 Ampere
460 - 480 volts
3ph., 60 Hz
100,000 Amperes RMS
RT-1982
Ri-Machine
Goodold, USA
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On-site Compliance
• On-site engineer provides the following information
– Available short circuit current at installation point
– Planned SCCR of the equipment or panel
• Inspector compares actual marked SCCR to the
provided data
• If SCCR data is accurate then approval is give
• Inaccurate or incomplete data can result in “red-tag”
and may require additional analysis
• Engineers and inspectors must work together
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Industrial Control Panel Marking
Why are Marked SCCR’s Important?
• Needed to ensure compliance with NEC® and
UL508A
• Helps to eliminate hazards where components and
equipment could be applied above their ratings
• Simplifies inspection approval process for
engineers and inspectors
– New installations
– Machinery relocation
• Contributes to a safe electrical system
– Guards against arc-flash hazards
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What is Arc Flash?
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What is an Arc-Flash?
• A flow of current through the air between phase
conductors or phase conductors and neutral or ground
• Usually unintentional
• Causes include:
– Human error
– Insulation failure
– Animal interference
•
5-10 times per day in U.S. - arc flash accidents injure or kill a worker
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Arc-Flash Hazard Standards
•
•
•
•
OSHA Standards 29-CFR, Part 1910 – Work safety
NFPA 70 (NEC) – Warning label requirements
NFPA 70E 2004 – Appropriate work practices
IEEE 1584 – 2002 – Arc flash hazard calculations
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Arc-Flash Hazard
• An arc flash hazard is defined in NFPA 70E as a
dangerous condition associated with the release of
energy caused by an electric arc
• The NEC requires a label that states the existence
of an arc flash hazard
• OSHA regulations state the employers shall protect
employees from recognized hazards
• NFPA 70E tells employers how to protect
employees from recognized hazards
• IEEE 1584 shows the math to calculate the
hazards
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Arc-Flash Panel Marking
Flash Protection Boundary: 2.9 ft
• Boundary where person could receive 2nd
degree burns from arc flash - 1.2 cal/cm2
Incident Energy: 2.3 Cal/ cm2
•Amount of energy produced during an arc flash
Working Distance: 18 in.
•The distance between worker and arc source
Required PPE Level: 1
•Protective clothing and apparatus to
protect against arc flash injury
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Arc-Flash Panel Marking
Shock Hazard Voltage: 3450 VAC
• Potential voltage levels that can be delivered
Limited Approach: 10.0 ft.
•Shock protection boundary – Qualified
personnel only unless escorted
Restricted Approach: 2.2 ft.
•Shock protection boundary – Qualified
personnel only with PPE
Prohibited Approach: 0.6 ft.
•Shock protection boundary – Qualified
personnel only with PPE (contact is possible)
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Arc-Flash Hazard
• Arc Flash Hazard boundaries are based on
voltage, available short-circuit current and
predicted fault duration
• Different levels mean different protective gear
required when servicing a panel ( i.e opening
the panel door)
• This applies to all personnel that may need to
access the panel or be exposed to live
equipment
• May need an Arc Flash analysis performed
– Determine arc flash protection boundaries
– Personnel Protection Equipment (PPE) and training
is a must
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What Does OHSA Say?
• OSHA regulations state in 1910.333 (a) that workers
should not work on or near exposed live equipment
(greater than 50 volts) except for one of two reasons:
1. De-energizing introduces additional or increased
hazards such as cutting ventilation to a hazardous
location.
2. Infeasible due to equipment design or operational
limitations such as when voltage testing is required
for diagnostics. When it is necessary to work on
energized equipment you should follow safe work
practices including assessing the risks, wearing
proper PPE, and using the proper tools
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Personnel Protection Equipment - PPE
• PPE is designed to minimize injuries
• NFPA 70E requires any body part that is within the
flash protection boundary be protected by using
appropriate PPE (OSHA say basically the same
thing)
–
–
–
–
–
–
Hard hat
Safety glasses or goggles (Arc-rated face shield)
Hearing protection
Gloves (leather, rubber)
Flash suit (multi-layer clothes)
Leather work shoes
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Personnel Protection Equipment - PPE
Notes:
 1 cal/ cm2 equates to holding ones finger over the tip of a flame of a cigarette lighter for 1 sec.
 1.2 cal/ cm2 is considered the threshold for a curable burn (second-degree)
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PPE Protection From Arc-Flash!
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How to Avoid Arc-Flash Hazards
• Build control panels within the properly rated
enclosures
• Minimize exposure to energized equipment
• Follow proper lockout/ tag-out procedures
• Design into control cabinets access options that
will allow programming, data acquisition and
system adjustment without having to open the
panel door
• Maintain and update equipment and
documentation
• Conduct safety training for all personnel
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Industrial Control Panel Access Options
• Properly applied they can reduce arc-flash
hazards
• Save time and money - No PPE required
• Maintains enclosure type ratings
• Many options available:
–
–
–
–
–
RJ 45, SUB-D9, USB, etc.
Eternal shelves
Document enclosures
Operator panels
Viewing windows
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Updated Industrial Control Panel
Paper Converting Machine 7A
345RTT-04
480V, 3-phase, 60 Hz, FLC 60A
SCCR 18kA
Diagram-RTT-06
RiMachine – Spfld, OH
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Industrial Control Panels
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NEC Article 409 & UL508A
“Industrial Control Panels”
Troy Miesse/ IE Business Development
Industrial Control Panels
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41