When this product (303018D or 303018C) is used as a splice bar, the ends of two rails are joined to form a continuous run of rail, with a gap ranging from 0” to 3/16”. The splice bar extends the effective continuous run of rail without affecting strength. For example, attaching two 168” rails end to end creates a structurally sound 336” rail length. The Unirac splice bar can be placed anywhere within the attachment span between two roof attachments.
When the Unirac product is used as an expansion joint, the ends of two rails are aligned in the same method, but the expansion joint is only attached to one of the two rails, and there must be at least a ½” gap between the rail ends. In this configuration, the expansion joint’s purpose is for the installation to comply with thermal expansion and contraction rules. Per Unirac’s design guidelines and installation manuals, an expansion joint is required to limit continuous rail lengths to under 40’ in length. For example, to create a rail 90’ long compliant with the expansion limits, two expansion joints would be needed. The expansion joint cannot be spanned by a PV module and cannot be placed in the middle third of the rail spanning between attachment points. Additional end clamps and grounding lugs are added for modules to end before the expansion joint, effectively adding (4) end clamps and (2) ground lugs per expansion joint.