WBS: at which level should I put the E-P-C

Hello guys,

I'm currently developing the WBS concept, and generally the project has this EPC (Engineering Procurement and Construction) components under it's WBS. My question is at which level should I put the E-P-C ?

following are 2 options that I'm considering

Option 1 (put it on lvl 1)

lvl 0: Power plant
lvl 1: Engineering, Procurement, Construction

Lvl 2: E - basic engineering, detail engineering 

        P - transportation type

        C - Boiler, Turbine, Generator, BOP

Lvl 3: Boiler - civil, mechanical, electrical works

Option 2 (put it on the lowest level)

lvl 0: Power plant

lvl 1: Boiler, Turbine, Generator, BOP

Lvl 2: Boiler - Civil, Mechanical, Electrical works

lvl 3: Civil works - Engineering, Procurement, Construction

My concern with option 1 is that, you could only track the overall Construction progress. If you were asked to track Construction progress for Boiler, you definitely need option 2, am I right ?

So my point is, it seems like option 1 gives you a more high level control over the project while option 2, by putting EPC at the lowest level , you could track the E or P or C progress for each part of the power plant.

Please enlighten me...........  any thought/ ideas/ comments are welcome

Thank you in advanced.