Download Impact of Bonding Requirements for CSST on LP

Impact of Bonding Requirements
for CSST on
LP-Gas Piping Systems
April 2009
Lightning Statistics
• Ave. number lightning flashes/year in US: 25,000,000
• Average annual number of U.S. home fires* by cause:
- Fires caused by lightning: 4,800
- Fires caused by natural gas: 2,100
- Fires caused by lightning/fuel gas: 180
- Fires caused by lightning/wires: 260
- Fires caused by electric distribution: 24,000
Lightning damage to gas piping is an uncommon event
compared to other causes of fires.
* NFPA data
Energizing Metallic Piping Systems
• Direct lightning strike on the structure
• Lightning that branches from nearby strike
• Lightning energy conducted through the soil and
underground metallic systems or through overhead
power lines
• Lightning current takes all pathways of electrical
resistance to ground and not just the path of “least
resistance”.
Lightning Induced Piping Damage
• Lightning does not discriminate. It will damage all piping
materials and systems.
• Damage is attributed to arcing caused by a difference in
voltage build-up between the grounded electrical system
and any other electrically conductive pathway.
• Gas system components typically damaged:
– Perforations of PE pipe with copper tracer wire
– Perforations of CSST wall
– Flow/loss of pipe dope between threaded joints
– Failure of flexible connectors on steel pipe system
– Failure of copper tubing/pipe
– Failure of gas burning equipment components
Lightning Induced Damage
Arcing damage possible
to all gas piping materials
Copper tracer wire will be
energized and arc to PE
Increase and maintain
minimum physical
separation distance
Grounding verses Bonding
• A conducting connection between an electrical circuit
or equipment and the earth that limits the voltage
imposed upon it. Only the premise wiring system is
grounded.
• The permanent joining of metallic parts to form an
effective electrical path that ensures continuity and
the capacity to safely conduct any current likely to be
imposed. Gas piping is bonded.
Grounding Requirements
Grounding system limits
power surge and lightning
energy
Grounding required at
transformer as well as
house
NEC requirement
Grounding Requirements
Grounding not required for LP storage containers.
Grounding Electrode System
Various types of
electrodes permitted
Grounding electrode
conductor and bonding
conductor are different
Do not install separate
electrode for LP-gas
service
Lightning Protection System
Protects structure
LPS effective against indirect
strikes through its grounding
electrode system
Lightning activity varies
around country
Bonding of underground
metallic piping required by
NFPA 780
Lightning Induced CSST Damage
Arcing damage impacts
all gas piping materials
CSST does not fail due
to lightning induced
voltage levels
Thinner pipe wall is a
contributing factor
CSST Solution
• Increase robustness of bonding connection beyond
minimum required by NEC.
• Bonding at service entrance to divert energy off gas
piping system and lower voltage level.
• Increase jumper size to reduce the difference in
voltage build-up between other electrically conductive
pathways and minimize potential for arcing.
• Equi-potential bonding of all metallic systems will
further reduce the chances for arcing by balancing the
voltage levels in all connected systems.
• Maintain physical separation as much as practical
Applicable Codes and Standards
NFPA 58/54/70/780 Requirements
6.9.3.15 LP-Gas piping shall not be used as a grounding
electrode. (also NFPA 54 and 70)
6.22.1.3 Grounding and bonding shall not be required on
LP-Gas systems.
7.13.4 Lightning Protection Systems. Where a
lightning protection system is installed, the bonding of
the gas piping shall be in accordance with NFPA 780.
NFPA 780 requires the bonding of any underground
conductive piping to the grounding electrode system at
or near the entry point into the structure.
2009 Bonding Requirements*
CSST gas piping systems shall be bonded to the electrical
service grounding electrode system at the point where the
gas service enters the building. The bonding jumper shall
not be smaller than 6 AWG copper wire or equivalent.
* 2009 NFPA 54, IFGC and UPC
Equipment Grounding Conductor
EGC sized to protect
against ground faults
12 AWG wire not able to
carry electrical energy
from lightning
12 AWG wire not able to
respond to lightning
frequencies
2009 IFGC Electrical Isolation
404.8.1 Isolation. Metallic piping and metallic
tubing that conveys fuel gas from an LP-gas
storage container shall be provided with an
approved dielectric fitting to electrically isolate
the underground portion of the pipe or tube from
the above ground portion that enters a building.
Such dielectric fitting shall be installed above
ground and outdoors.
Same proposal submitted for 2011 NFPA 58.
Dielectric Fittings
Commercially available
- Union
- Shut-Off Valve Combo
Installed upstream of
pressure regulator and
above ground
Only required if underground
piping is metallic
Impact on CSST Piping Systems
Complete Piping System
- Tubing
- Fittings
- Strike Plates
Update ANSI Standard
Installed in accordance with
manufacturer’s instructions
Uniform bonding practices
Six Manufacturers: One Approach
Ward Mfg - Wardflex
Parker - ParFlex
Omegaflex - TracPipe
Titeflex - Gastite
Truflex - Pro-Flex
MetalFab - Diamondback
CSST Bonding Instructions
• Direct bonding of CSST to the grounding system is now
required
• All new CSST installations for all gas appliances
• One-size-fits-all for most residential applications
• Installation and sizing requirements consistent with NEC
Section 250 for metallic piping and current edition of
NFGC
• Installed by person recognized by AHJ as qualified to
perform such work
• Do not bond any underground metallic piping upstream
of second stage regulator (at service entrance)
KISS Principle
• One simple, universal
bonding approach
• Effective and low cost
• Consistent with NEC/NFGC
requirements
• Applies to all single family
and low-rise multi-family
• Commercial applications
may require an engineered
solution
Direct Bond Connection
• Electrical service
equipment enclosure
• Grounded conductor at
the electrical service
• Grounding electrode
conductor
• Grounding electrode
Bond Near the Gas Service
• Customer side of meter
• Downstream of 2nd
stage LP regulator
• Indoors or outdoors
• Upstream of first CSST
fitting
Bonding Jumper
• At least a 6 AWG copper
wire or equivalent
• Installed in accordance
with NEC
• Jacketed or bare
• Above or below grade
• Keep as short as possible
Attachment Points
Between meter and first
CSST fitting
Attached to pipe or pipe
component per the clamp
listing
Never attach to corrugated
tubing itself
Insure metal-to-metal
contact between clamp
and sub-surface
Bonding Clamp
• Listed to national
standard
• UL 467
• Attached in accordance
with NEC 250.70 and
listing
• Always accessible
Avoid Physical Contact
• Avoid using other
metallic systems for
support
• Avoid direct contact
with other metallic
systems
• Avoid co-locating
CSST with metallic
appliance vents
Summary
• Direct bonding of gas piping will:
– Lower voltage levels
– Reduce differences in electrical potential
– Minimize the possibility of arcing
• Maintain physical separation where practical
• Bonding together of all metallic systems
• All CSST products require the same type of
bonding in accordance with current edition of
NFPA 54 or IFGC or UPC
Conclusions
• No code or standards requirements mandating lightning
resistance, protection or mitigation.
• New bonding requirements above minimum of NEC.
• Direct bonding will reduce impact of lightning strikes on
gas piping system without effecting ground-fault
protection.
• New CSST bonding requires dielectric isolation
• CSST industry requiring direct bonding on all new CSST
installations with a “keep-it-simple” approach.
• National model code change proposals are being
developed.
• CSST product standard being updated.
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