MEP Common Mistakes & How to Avoid Them

MEP installations can encounter many mistakes during project construction. This is in case the work is done by technicians who are not well-experienced or careless.

In this article, I focused on common mep mistakes made by electrical designers and execution teams during MEP installation in projects.

List of MEP Common Mistakes

Mistake number one

The electrical team will exceed the permitted maximum filling ratio for a conduit or tray, meaning more wires or cables are pulled into a conduit that exceeds 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 the designer or the installer or both of them forget or don’t take care of this point, so that the construction team will have a lot of wires or cables are pulled inside a conduit and take space inside the conduit more than the allowable fill ratio.

filling ratio of conduits — **Filling Ratio of a Conduit**

Mistake Number Two

The electrician forgot to install Junction boxes in the routing of exposed EMT conduits, even though we have more than 4 90-degree bends, because this affects cable or wire-pulling inside the conduit.

Also, later, for any maintenance purpose, pulling new wires/cables or re-pulling them will be very difficult. Please refer to photo no. 2, a screenshot from NEC article 358.26, which discusses the same matter.

Bend and number in one run — **Maximum Allowable Number of Bends**

Mistake number three

This mistake occurs when the electrical team fails to install an expansion coupler at the point where the electrical conduit crosses a structural expansion joint.

Is this conduit embedded in the concrete slab before casting, or is it installed exposed in the slab soffit?

Please refer to photo no. 3 & 4 show the expansion couplers from manufacturers’ catalogs for LSF conduit, which will be embedded in the concrete, and for EMT conduit, which will be installed as exposed in the slab soffit, respectively.

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Expansion Couplers Table - engalaxy.com — **LSF Expansion Coupler in Concrete Slab**

Rigid Expansion Coupler - engalaxy.com — **Rigid Expansion Coupling to be used with Exposed Conduits**

Mistake number Four

In this mistake, we will discuss not installing inspection bends at the routing of an exposed when it crosses a dropped concrete beam.

Usually, we see this mistake especially at the basement level because we may have many concrete drop beams there.

At the same time, if the electrical didn’t install the conduits of the different electrical/Low current systems (like BMS conduits, Electrical lighting & Power conduits, Data Conduits, Fire Alarm conduits…etc.) embedded in the concrete slab of the basement before its casting, so you will have many conduits shall be installed exposed, and in this case, there’s a high chance that these conduits may cross the concrete drop beams.

As you can see in the following photo, which I captured from one of our projects, you can notice that when the RGS exposed conduits try to cross the drop concrete beam, it needs 4 bends (90 degrees), which will make it very difficult to pull the wires/cables later.

That’s why we shall install inspection bends on both sides of the concrete drop beams. This is to make the wire-pulling process as easy as possible.

Moreover, without installing these inspection bends, it will be difficult to pull or perform maintenance on the wires or cables installed inside the conduit.

In this photo, we see two inspection bends: one before the drop concrete beam and the other after it. We installed a saddle between them to hold the RGS pipe with the beam.

Inspection Bend installation on-site - engalaxy.com

Mistake number Five

This mistake can be made by newbie electricians who pull a single wire through a metal conduit, which induces currents and, in the end, burns the wire. Please refer to photo no. 6 from the NEC article. 215.4, which describes the same.

Mistake number Six

This is a common mistake in construction projects. It can happen while installing the electrical conduit (uPVC or PVC) in the concrete slab before casting.

Due to poor coordination between electrical and mechanical teams, this coordination must be done first in the shop drawing stage before construction. However, a lack of proper coordination can cause electrical conduits to cross at the location of a mechanical penetration.

Mostly, this happens when the mechanical penetrations are not yet marked on the plywood formwork. The mechanical team’s delay in marking the slab’s mechanical openings/penetrations increases the risk of cutting electrical conduits that pass through the same locations as these penetrations and are not rerouted.

Also, the same problem can happen with the electrical team itself. This is when the electrical team doesn’t mark first the locations of their required openings for electrical cable trays, ICT cable trays, Busways…etc.

So, the delay in marking these electrical/ICT openings increases the risk of a clash between the electrical conduits on the slab and these openings.

In all cases, the best solution for this mistake is to mark and directly provide block-outs using plywood wooden boxes or (Sleeves) of all the mechanical & electrical penetrations in the slab. This is before installing the electrical conduits.

This is shown in photo no. 7

MEP penetrations in concrete slab - engalaxy.com

Mistake number Seven

This is a silly mistake. It happens due to confusion on the electrician’s side between the stud anchor bolt & unifix.

The confusion will come from the proper drill pit size which will be used for drilling the hole of the stud anchor bolt because, in most cases, the electrician is used to install the unifix, so when he has a unfix with a size 16mm (M16), he will need to use a concrete drill pit with a size 18mm (extra 2mm than the size of the unifix).

But when he needs to install a Stud Anchor Bolt with a size 16mm (M16), he needs to use a drill bit with a size 16mm.