When constructing a reinforced concrete slab, one of the most critical yet often overlooked rules in MEP (Mechanical, Electrical & Plumbing) coordination is this: electrical conduits must never be laid in a straight line within the slab.

The Structural Reason:

A concrete slab behaves as a single, unified structural unit — what engineers call a monolithic element. When a conduit pipe runs in a perfectly straight line through the slab, it creates a continuous weak plane along that line. Under load, the slab tends to crack exactly along that path, much like how a piece of glass breaks along a scratch.

The Risk It Creates:

A straight conduit effectively acts as a pre-cut line inside the slab. When live loads, dead loads, or thermal stress are applied, crack propagation follows the path of least resistance — and that path becomes the conduit line. In severe cases, this can compromise the structural integrity of the entire slab.

The Correct Practice:

Engineers and site supervisors follow these guidelines to prevent the issue:
Conduits must be offset or routed diagonally to avoid forming a continuous straight weak plane.
• The diameter of the conduit should not exceed one-third of the slab thickness.
• A minimum spacing of 3D (three times the conduit diameter) must be maintained between parallel conduits.
• Conduits should be positioned at mid-depth of the slab, between the top and bottom reinforcement layers.
• Where two conduits cross, one must be bent to avoid stacking at the same level.

The Code Perspective:

According to ACI 318 and the Bangladesh National Building Code (BNBC), embedded conduits must not reduce the effective structural depth of the slab or interrupt the continuity of the concrete mass. These provisions exist specifically to protect slab performance under load.

The Simple Takeaway:

A straight conduit a straight crack waiting to happen. Proper routing of electrical conduits is not just an electrical concern it is a structural safety requirement that every civil engineer, contractor, and site supervisor must enforce during slab casting.