Bonding all metallic systems for better lightning safety

By Dave Burke

 

Lightning is a highly destructive force. Even a nearby lightning strike that does not strike a structure directly can cause systems in the structure to become electrically energized. Lightning strikes vary in strength from 1,000 amps at the low end to 200,000 amps peak; a typical strike contains 10,000 - 20,000 amps.

 

Despite the damaging nature of lightning, lightning protection systems are generally not required. The National Electric Code (NEC) and the National Fuel Gas Code do not consider lightning protection within their scope and, instead, rely on the electrical grounding system, which is not designed to handle current from lightning strikes.

 

Differences in potential between systems may cause the charge to arc between systems. In fact, all metallic systems (the electrical, plumbing and heating and air conditioning, for example) can be affected by lightning strikes. Safety isn’t just about how each system is installed; it’s about how each installation relates to other metallic systems.

 

Such arcing can cause damage to corrugated stainless steel tubing (CSST) and other systems. Bonding and grounding should reduce the risk of arcing and related damage. NEC Section 250.104b note states that “bonding all piping and metal air ducts within the premises will provide additional safety.”

 

All continuous metallic systems in a multi-unit home or commercial building should be bonded and grounded for additional lightning safety. The owner should confirm with an electrical or construction specialist that each continuous metallic system in a structure has been bonded and grounded by an electrical professional, in accordance with local building codes. This should include, but is not limited to, metallic chimney liners, metallic chimney liners, metallic appliance vents, metallic ducting and piping, electrical cables and structural steel.

 

Care should be taken when installing any type of fuel gas piping (including CSST, iron or copper) to maintain as much separation as reasonably possible from other electrically conductive systems in the building. Refer to section 4.3, Routing, in the Gastite Design and Installation Guide for proper installation techniques.

 

Consult local building codes

 

Local building codes are controlling. As a general practice, however, fuel gas piping, including CSST, should not be installed within a chase or enclosure that houses a metallic chimney liner or appliance vent that protrudes through the roof. In the event that such an installation is necessary and conforms to the local building codes, the metallic chimney liner or vent must be bonded and grounded by a qualified electrical professional. A separation distance, as specifically permitted by the applicable local building code between the CSST and the metallic chimney liner or vent is required. Physical contact between the metallic chimney liner and/or the vent is prohibited. If this physical separation cannot be specifically identified in the local building code and achieved or if any local building code requirements cannot be met along the entire length, the rerouting of the CSST is required, unless such installation is specifically permitted by the local building inspector.

 

Bonding and grounding should reduce the risk of arcing and related damage. The builder owner should confirm that a qualified contractor has properly bonded the CSST gas system to the grounding electrode system of the premises.

 

Ensuring lightning safety is very important for engineers and designers of a HVAC and electrical systems. It is essential to understand that all metallic systems within a home can be affected by lightning strikes. Looking at all the systems and how they relate to each other is the only way to ensure lightning safety.

 

Dave Burke is applications engineering manager for  Gastite.