Throughout the plans there will be phrases such as “Contractor shall notify the engineer of any changes or modifications that differ from these construction drawings” or “Consult the electrical engineer before making any variations from these city approved construction drawings”.

A lot of thought goes into a final set of plans. Many things that the electrician might not even be thinking about have been considered and thought out as the plans are being prepared for submittal to the city for approval.

Whether its luminaire (light fixture) type/performance and the illumination level at the walking surface of the egress path, or the type of conduits and raceways that will be installed to maintain a fire rating; the best practice is to always stick to the approved plans.

When the inspector arrives for an inspection, the inspector is expecting to see electrical work that matches exactly what is on the city approved plans. Occasionally something in the plans will be incorrect and both the electrical engineer and the city plans examiner will have missed it but most of the time the plans will be drawn to comply with the codes.

Here is an example of a situation no electrician wants to be in:

Back in 2010 when I was an electrical inspector in one of the western states, I decided to lay my eyes on a recently approved set of plans from the senior plans examiner for the city. I wanted to familiarize myself with these plans since I would be the assigned electrical inspector for this specific project. The project was a hospital, and I knew it would be very technical.

I immediately noticed that the electrical engineer had specified the following for this project:

1. All electrical raceways and conduits to be ferrous metal (magnetic).
2. All electrical conduits to be installed overhead (above the ceiling), no electrical conduits to be installed underground other than site lighting and monument signs.
3. All electrical conduits and raceways installed overhead must follow the wall lines.

I immediately knew what the electrical engineer was trying to accomplish and since all conduits would be installed overhead, other than site lighting, I did not expect to be called out to inspect any underground conduit for many months until the site lighting was to be installed.

Interestingly enough, two weeks after the job began, the electrician scheduled an underground conduit inspection. When I arrived at the job site, I noticed immediately that there was miles of Schedule 40 PVC conduit installed, of every possible size between ¾ inch and 4 inch.

The electrician disregarded the notes in the plans from the engineer and figured he would do it faster and cheaper than what was specified. Unfortunately, before a single wall had been erected, this electrician had made a decision that would cost him his business.

When the plans were being drawn, the electrical engineer made the above specifications for several reasons:

Requiring all raceways to be magnetic, run overhead instead of underground, and to follow the wall lines accomplishes several things.

1. If installed per the approved plans, there would have been longer runs of conduit which equals more impedance at the end of a specified run of wire, resulting in a lower amount of available fault current at each downstream panelboard. A lower amount of available fault current at a panelboard means the AIC rating (ampere interrupting capacity) for the circuit breakers in the panelboard could be lower which is also cheaper.
2. Again, running the conduits overhead, above the ceiling, to follow the wall lines also results in longer runs of conduit, equaling more impedance at the end of a specified run of wire, resulting in a lower amount of available fault current at each downstream panelboard. A lower amount of available fault current at a panelboard means the AIC rating (ampere interrupting capacity) for the circuit breakers in the panelboard could be lower which is also cheaper. In addition, having the conduits above the ceiling following the wall lines means the ceilings above each patient room are wide open for the addition of future exam lighting upgrades or x-ray equipment.
3. Requiring all conduits to be ferrous (magnetic) means there is potential for induced current with the ferrous metal raceways enclosing the circuits (this doesn’t occur when using PVC raceways which aren’t magnetic) which equals less available fault current at each downstream panelboard. A lower amount of available fault current at a panelboard means the AIC rating (ampere interrupting capacity) for the circuit breakers in the panelboard could be lower which is also cheaper.
4. Reduction in incident energy at each panelboard. The engineer is required to perform a fault current analysis for each panelboard so the future hospital electricians will know what level of PPE to wear and what the distances are for the arc flash boundary. Changing from the original plan and installing shorter runs of nonmagnetic conduit results in completely different numbers at each panelboard which means the fault current analysis must now be recalculated for all panelboards and equipment in an entire hospital.
5. Selective coordination. The engineer is required to perform a selective coordination study for overcurrent devices serving specific branches of the hospital electrical system. Changing from the original plan and installing shorter runs of nonmagnetic conduit equals higher available fault current at each panelboard. This means the AIC rating (ampere interrupting capacity) for the circuit breakers in the panelboard needs to be higher to comply with NEC^® 110.9. Installing circuit breakers with a higher AIC rating changes the selective coordination that was originally planned out by the electrical engineer.
6. Mechanical protection. NEC^® Article 517 requires the wiring of the life safety and critical branches to be mechanically protected. The options for mechanical protection specified in NEC^® Section 517.31(C)(3) are mostly metal raceways, with an additional allowance to use Schedule 80 PVC, or even Schedule 40 PVC if encased in concrete.

If the electrician simply requested further information from the electrical engineer before placing the order and installing the underground PVC conduit, the engineer would have explained the importance of sticking to the plans and the electrician would still be in business.

Even if the electrician ignores the plans altogether and installs a different code compliant wiring method or fixture, there may still be a valid reason that the electrical engineer wanted the installation a certain way.