Ultimately it comes down to the project requirements and electrical specifications. While these specifications are, in most cases, vital for consistency and standardisation, too often consultants simply copy and paste information from other projects without taking into account practicalities or cost factors.
These are the areas where costs are most likely to blow out.
Enclosures
Enclosure type can have a significant impact on cost. At the lower end of the scale are wall-mounted and powder-coated cabinets which cost under a thousand dollars. At the other end are big free-standing cabinets with cubicles. These can range from $25k – 100k or higher, including custom-made enclosures or those assembled with a modular system.
Another important factor is the material. Stainless steel can be twice as expensive as mild steel. Aluminium enclosures usually have to be custom made. Thicker material also costs more.
Lastly, the cabinet finish can add to the cost. Power coating is the most popular and cost-effective option but some jobs specify using a baked enamel or painted finish, and this will add substantially to the cost. Polished steel is also very expensive.
Segregation
Segregation refers to the ways functional units are separated from each other inside a switchboard – for example, placing every motor starter and power feed in a separate cubicle.
Form 3 and Form 4 levels of segregation are needed with high-current switchboards where an operator is at risk of being exposed to dangerous currents and voltages during maintenance, but these higher levels may not be necessary for smaller boards.
A Form 1 board (single compartment) can be 2-4 times cheaper than a Form 3 board.
Equipment
The brand of equipment specified can greatly add to cost. For example, the AB MicroLogix small PLC is under $2K. Add I/O cards if needed and you can have a full PLC rack for less than $5k.
In contrast, you’re looking at more than $20k just for the CPU for the AB ControlLogix, considered ‘top of the range.’
Add power supply, a chassis and a few I/O and you’re easily looking at more you can the $35k, which is over 7 times the price of a MicroLogix.
For large systems, a smaller PLC lacks the required capacity or features, which is why a larger PLC is needed. When used with a small system with just a few I/O, an unnecessarily large PLC can add a massive amount to the cost for no benefit.
The same can also said of variable speed drives, RTU’s, HMI’s, switchgear, modems and other expensive switchboard components.
Testing and Quality Assurance
Undertaking full Factory Acceptance Testing, which includes energising the switchboard, adds considerable cost to the switchboard. The trade-off is fault finding the switchboard once installed on site where costs are higher and time pressure is increased.
Using an assembler with an externally certified Quality Assurance system will give added piece of mind but will also add cost when compared to an assembler that has a lesser or no system.
Certification
RPEQ Certification is a requirement in cases when professional engineering services are needed. This means engineering principles and data are applied to a design, or added to a production or construction activity, related to engineering, and does not include cases where an engineering service is applied only in keeping with a prescriptive standard.
Prescriptive standard refers to a document stating procedures and criteria:
"for carrying out a design, or a construction or production activity, relating to engineering; and
the application of which, to the carrying out of the design, or the construction or production activity, does not require advanced scientifically based calculations."
Most switchboards have no RPEQ requirement. This unnecessary addition adds $5 - $20k to the overall cost, for no obvious or discernible benefit to the end user.
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