EV Charging Site Power and Load Assessment

Measure rather than assume

Assessment starts with recorded load data across a representative period, not with a design calculation. Buildings rarely draw what their documentation predicts, and the gap runs in both directions.

Where no data exists, a temporary logger at the supply point over a period covering the seasonal and weekly peak is the first step. Skipping it means designing against a guess.

Find the real peak

• Seasonal peak, which for most buildings is cooling or heating driven
• Weekly pattern, including whether the peak is occupancy or plant driven
• Coincidence between the existing peak and the expected charging window
• Any contracted demand limit, which may bind before the physical rating does

The coincidence question matters most. Overnight charging at a commercial site sits outside the peak and is nearly free capacity. Daytime workplace charging lands directly on it.

Diversity, honestly applied

Not every bay draws full current simultaneously, and designing as though they do wastes the site. But diversity assumptions must be defensible, and they change with fleet composition, dwell time and whether charging is managed.

An unmanaged site has to be designed for the worst case, because nothing prevents it. A managed site can design against a controlled allowance, which is the entire commercial argument for management.

Phase balance and protection

Single-phase chargers should be distributed across phases rather than clustered. Protection coordination, earthing arrangement and the suitability of existing distribution boards are assessed alongside capacity, because a site with headroom and unsuitable protection is not ready.

Design the expansion path now

The second phase of a deployment is usually harder than the first, because the easy capacity was spent. Establishing at the outset what the site supports at full build, and what triggers a supply upgrade, prevents an expansion that requires redoing the first installation.

What the assessment produces

• Measured headroom against the real peak, not the nameplate
• Supportable bay count, unmanaged and under each management level
• Phase allocation and protection findings
• The trigger point at which a supply upgrade becomes necessary
• An expansion sequence that does not strand the first installation

Moving the load is usually cheaper than raising it

A load assessment that ends in a recommendation to upgrade the supply has answered only the easiest version of the question. The harder and usually cheaper question is whether the load has to arrive when everyone assumes it does.

Apartments make this concrete. They show the highest utilisation of any AC site we operate, and it concentrates overnight, which is exactly the window the building is least able to absorb. The instinct is a transformer upgrade. The alternative is to hold charging out of the evening peak, run reduced current through it, and complete across the hours afterwards. A resident who plugs in at seven and leaves at seven does not care which of those twelve hours the energy arrived in.

So the assessment should produce two numbers rather than one, and the gap between them is often the entire business case.

• Unmanaged: the capacity the site needs if every vehicle charges at full rate simultaneously
• Scheduled: the capacity it needs if charging is spread across the hours the vehicles are parked anyway