Ever wondered why the electrical scope on some projects is so much more expensive than others?The primary reason is the requirements of the project or site electrical specification. In most cases these specifications are essential for standardisation and consistency in quality, but we’ve all run into situations where a consultant has ‘copy-pasted’ chunks from other projects with no thought for the practicality or impact on cost.
Here’s a quick rundown of the most common areas where costs can skyrocket.
The enclosure type and material can have a huge impact on cost. At the bottom end of the scale, an ‘off-the-shelf’ wall-mount powder-coated cabinet can cost a few hundred dollars, while a large free-standing cabinet with multiple cubicles – either custom-made or assembled using a modular system – can cost $5-10k or more.
The material used is also a big factor: stainless steel can cost twice as much as mild steel, while aluminium enclosures generally need to be custom made. Thicker material adds expense as well.
Finally, the cabinet finish can impact cost. Powder coating is the cheapest and most common, but some consultants specify a painted or baked enamel finish which are much more expensive. Polished stainless steel is also a very costly finish.
Segregation describes whether and how the functional units inside a switchboard are separated from each other – for example, by having each motor starter or power feed in its own cubicle.
Higher levels of segregation (e.g. Form 3 and Form 4) are important for high-current switchboards where the operator may be exposed to dangerous voltages and currents during maintenance, but may be overkill for smaller boards.
A Form 3 board can cost 2-4 times the cost of a Form 1 (single compartment) board.
This is where costs can really escalate. Take PLC’s for example.
An AB MicroLogix small PLC (with onboard I/O) sells at a list price of around $1600. You can add I/O cards if required and have a complete PLC rack for around $3k (list).
Meanwhile, for the ‘top of the range’ AB ControlLogix you’re looking at $24k – just for the CPU. After adding a chassis, power supply and a few I/O you can easily get to around the $35k mark (list) – more than 10 times the cost of a MicroLogix.
Obviously for larger systems, a small PLC won’t have the capacity or features required so a larger PLC is specified.
This is a common scenario in larger projects with multiple smaller equipment packages, all with their own PLC’s: the consultant expects the site PLC specification to apply to all packaged systems on the site as well.
For a small system with a few I/O, an over-specced PLC can add a huge amount of cost for virtually no benefit.
And the same can apply to variable speed drives, HMI’s, RTU’s, modems, switchgear and any other expensive components inside a switchboard.
Type testing describes the standardised test procedure conducted by testing authorities for a particular design of switchboard. It’s most common in power distribution and other high current boards, and provides assurance that the switchboard can remain safe in the event of a catastrophic fault.
In the context of smaller, low current (<100A) control panels and switchboards, it rapidly becomes overkill.
Adding the requirement for type testing to a small control panel can double, triple or quadruple the cost without delivering any discernible safety benefits to the end user.
That’s four of the biggest contributors to cost from electrical specifications; all the best with your future projects!
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