Tunnels - Disconnecting, Grounding, & Bonding

OSHA outlines requirements for disconnecting, grounding, and bonding in tunnels.

Disconnecting

A disconnecting means that can simultaneously open all ungrounded conductors must be installed at each transformer or motor location.

Grounding and Bonding

All non-energized metal parts of electric equipment, metal raceways, and cable sheaths must be grounded and bonded to all metal pipes and rails at the portal and at intervals of no more than 1,000 feet throughout the tunnel.

Class 2 and Class 3 power supply units cannot be used in tunnels unless durably marked to indicate the class of supply and electrical rating where plainly visible. Other specific voltage requirements apply to circuits based on class divisions. These requirements are outlined in detail in CFR 1926.408.

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