Common mistakes by MEP team to be avoided in projects

Hello everybody, today I will talk about some common mistakes done by some electrical designers and execution teams while installing the electrical conduits (embedded in the slab or exposed) in projects.

   1- the First mistake is: more wires or cables are pulled inside a conduit which is exceeding the accepted fill ratio. As per NEC table 1 in photo no.1, the maximum allowable fill ratio for more than 2 cables inside a conduit is 40%, but sometimes a designer or installer or both of them forget or doesn’t take care about this point, so we will have a lot of wires or cables are pulled inside a conduit and take a space inside the conduit more than the allowable fill ratio.

2- the Second mistake is: Junction boxes are not provided in the routing of electrical exposed EMT conduits, while we have more than four 90-degree bends, because this affecting on cable or wire-pulling inside the conduit. Also, later for any maintenance purpose, it will be very difficult to pull new wires/cables or re-pull them. Please refer to photo no. 2 which is a screenshot from NEC article number 358.26 which is talking about the same matter.

3- the Third mistake is: not installing an expansion coupler where the electrical conduit is crossing a structural expansion joint, this is either this conduit is embedded in the concrete before casting the slab or installed exposed in the slab soffit. Please refer to photos no. 3 &4 which show the expansion couplers from manufacturers’ catalogs for LSF conduit which will be embedded in the concrete and also EMT conduit which will be exposed in soffit respectively.

4- the Fourth mistake is: not installing inspection bends at the routing of an exposed while it’s crossing a dropped concrete beam, it happens especially in the basement level, without installing these inspection bends, it will be difficult for pulling or do maintenance for the wires or cables which are inside the conduit. Please refer to photo no. 5 which shows the proper installation in the site.

5- the Fifth mistake is: pulling a single wire carries a voltage inside a metal conduit, which will cause induction currents and at the end will cause burning of the wire. Please refer to photo no. 6 from NEC article no. 215.4 which is describing the same.

7- Sixth mistake is: while installing the electrical conduit in concrete slab before casting, no proper coordination between electrical and mechanical teams, so may these electrical conduits will cross a mechanical penetration which may is not yet marked on the plywood of formwork, so later the opening will be marked and may the mechanical team will not inform the electrical, which will cause later to cut these electrical conduits if they are not rerouted. The best thing that lockouts (Sleeves) of all mechanical penetrations in the slab to be installed before installation of electrical conduits. This is as shown in photo no. 7

Thank you for your time for reading this article, see you later with other explanations in MEP division.