How to Size a Control Panel for Your Borehole or Booster Pump
An oversized control panel means you've paid for protection and capacity you'll never use. An undersized one trips constantly, runs hot, or simply can't do the job — and either mistake usually only becomes obvious after it's installed. Sizing a panel correctly comes down to a handful of concrete numbers and decisions, not guesswork. Here's what actually goes into it.
Start with the motor and pump data
Everything else follows from this. Before anything can be sized, you need:
- Motor rating (kW) and rated current (A) — from the motor's own nameplate, not an estimate
- Supply voltage and phase — single-phase 220V or three-phase 380/400V, and what's actually available at the site
- Number of pumps — a single borehole pump is a different job to a three-pump booster station that needs to alternate and stage pumps against demand
- Duty cycle — does it run continuously, cycle on pressure/level, or start and stop frequently through the day?
If you're requesting a quote, these four points are the fastest way to get an accurate one back.
Choose the control method
This is usually the first real decision point, and it drives most of the rest of the panel's cost and complexity:
Direct-on-line (DOL) — the motor connects straight to mains through a contactor and overload, full speed only. Cheapest option, but no speed control, no soft start, and the hardest on the motor and pipework at every start.
Soft starter — ramps the motor up and down to reduce mechanical and electrical shock at start/stop, without ongoing speed control once running.
VSD/VFD — full variable speed control throughout the run, not just at start-up. Lets the pump match actual demand rather than running flat-out or cycling on/off, with the added benefit of built-in protection (over-current, over/under-voltage, overload, phase-loss) that a DOL setup doesn't have on its own.
For most borehole, booster and irrigation applications we build panels for, a VSD is the right call — the energy savings and reduced wear tend to pay back the extra cost over a DOL setup, and it gives you speed control you can't add later without rebuilding the panel.
Protection and control components
Beyond the drive itself, every panel needs a baseline of protection hardware: a main isolator (so the panel can be safely de-energised for maintenance), contactors and overloads sized to the motor's rated current, and — depending on the site — surge protection where lightning or unstable supply is a known risk. This is the part of the panel that doesn't show up in a spec sheet comparison but is exactly what separates a panel built to last from one that fails at the first surge.
Decide how much automation you need
A single pump with straightforward speed control is often just a VSD, its protection components, and a pressure or level sensor feeding the drive's built-in PID control — no separate controller required. A multi-pump booster station, or any system that needs to alternate pumps, log data, or run interlocked logic between multiple devices, generally needs a PLC to coordinate it and an HMI so an operator can see status and adjust setpoints without opening the panel. (We've covered what a PLC actually does and when you need one in a separate guide if you're not sure which camp your project falls into.)
Enclosure rating and site conditions
Where the panel lives matters as much as what's inside it. Outdoor or exposed installations need a higher IP-rated enclosure against dust and water ingress than an indoor plant room panel does, and ambient temperature range matters for continuous-duty applications in direct sun. Tell us where the panel will actually be mounted and we'll spec the enclosure to match — this is one of the more common oversights in a self-specified panel.
How we build it
Every panel is designed, assembled and tested in-house at our Pretoria East workshop or at one of our partnered panel builders before dispatch, so you're not left troubleshooting wiring or configuration issues on-site. That applies whether it's a single-pump borehole panel or a multi-pump booster station with full PLC-based automation.
Quick FAQ
Can one VSD run multiple pumps? Not directly for independent speed control — each pump generally needs its own drive. A PLC coordinates multiple VSDs so they alternate and stage together, which is where a multi-pump panel differs from simply wiring several single-pump setups side by side.
Do I need a PLC for a simple borehole pump? Usually not. A single pump with a VSD and a pressure or level sensor can often run on the drive's own built-in PID control, with no separate PLC required.
What information do you need to quote a panel? Motor kW and rated current, supply voltage/phase, number of pumps, duty cycle, and where the panel will be installed (indoor/outdoor, ambient conditions). Send those through and we'll come back with a sized quote and build timeline.
Ready to spec a panel? Contact us with your motor and site details for a tailored quote, or read more about our Custom Control Panel Building Services. Browse the VSD/VFD range that goes into most of our panels while you're at it.