Circuit integrity

Circuit integrity refers to the operability of electrical circuits during a fire. It is a form of fire-resistance rating. Circuit integrity is achieved via passive fire protection means, which are subject to stringent listing and approval use and compliance.

Providing fireproofing for cables, cable trays, or electrical conduit, is meant to keep cables operational during a specified fire exposure and time. This can be done in two different ways:

In Canada, testing is run in accordance with ULC-S101, as required by the local building code. Unfortunately, S101 is ill equipped to deal realistically with circuit integrity, particularly for enclosures. For circuit integrity cables, one simply uses a full scale wall panel test, loops the cables through the fire, energises the cables and quantifies the current carrying capacity of the cables during the fire.

There are two ways of achieving circuit integrity. One may either choose mineral insulated or otherwise fire-resistant (tested for that purpose) cables, or one may use an enclosure that was tested for that purpose. This is where "grandfathered" systems still find acceptance in certain parts in North America. A prime example of this is Canada, where the code indicates that 2" of concrete coverage over or around electrical circuits is sufficient to obtain an unquantified duration of circuit integrity. No testing documentation exists to qualify this measure, according to the Institute for Research in Construction, a part of the National Research Council of Canada. 2" of concrete, regardless of the conductor configuration, percentage fill, etc. is of course a judgment call.

Inherently fire resistive cables can be tested to UL 2196, Tests for Fire Resistive Cables, whereas enclosures for cables that are not inherently fire resistive can be tested to UL 1724 or USNRC Generic Letter 86-10, Supplement 1 in North America, or BS476 in the United Kingdom or DIN4102 in Germany.

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