Dynamic vs. Static Load Shedding

EVCI.tech EV Charger Installations
From the van — an electrician’s take

At EVCI, the guy you talk to is the guy who does the work — no contractors – and 40+ years of trade experience

Why “throttling” power (smart charger) isn’t the same as “cutting off” (static load management)

A geyser going from 4kW to 0kW (static) – and a charger going from 7.4kW to 3.6kW (dynamic) – Same idea but SANS only certifies one of them.

EVCI.tech · Field notes from an EV charger installer

STATIC (CT + CONTACTOR) 4kW 0kW instant cut Geyser: full load → zero, no in-between DYNAMIC (CHARGER DLM) 7.4kW 3.6kW 0kW EV charger: steps down, car keeps charging
Same goal — stay under the limit — completely different mechanism underneath.

Static power shedding and dynamic charger throttling (same objective) are two completely different things

“Load shedding” gets used loosely on site (i.e. static or smart charging throttling). These are two very different things – and it matters, because only one of them is a SANS certified safety mechanism.

A current transformer (CT) clamp on your main incomer measuring total household draw and tripping a contactor is a hard, physical, binary event. An EV charger’s dynamic load management (DLM) reading that same kind of signal and softening its own output is a soft, negotiated, proportional one. They both respond to “too much current,” but that’s where the similarity ends.

The two mechanisms, side by side

⚠ Static — CT + contactor
  • Binary: fully on or fully off
  • Physical contacts open the circuit
  • No cooperation needed from the load
  • Deterministic — fails to the open (safe) state
  • Classic use: geyser, pool pump, underfloor heating
⌛ Dynamic — charger throttling
  • Proportional: current is stepped down, not cut
  • A signal tells the car to draw less
  • Relies on the vehicle obeying that signal
  • Software/firmware dependent, not hardwired
  • Classic use: EV charger dynamic load management
Worth repeating: a contactor doesn’t ask the geyser’s permission to switch off. A charger’s DLM asks the car nicely to draw less, over a communication link, and trusts it to comply. Wiring code covers compliant wiring and safety – a smart charger can be helpful but a seperate matter.

Working the numbers on your example

You used 50A as the threshold and 3.6kW as the throttled charging figure. Both check out — here’s the arithmetic behind them.

50A threshold, single phase
WORKING 01
Calculation50A × 230V
Result11,500W = 11.5kW
Typical SA contextStandard single-phase supply: 60A or 80A
Smart-meter load-limiting floor10A ≈ 2.3kW
At a 10A load-limit — the level Eskom’s smart-meter trials drop supply to during a limiting event — a geyser element (typically 3–4kW) simply cannot fit under the ceiling. It has to be hard cut, not throttled, because there’s no smaller “geyser mode.”
Charger throttle steps, single phase
WORKING 02
32A (typical ceiling)7.36kW
16A (throttled)3.68kW
6A (minimum useful current)1.38kW
Your “3.6kW” figure lines up almost exactly with a charger stepping itself down to 16A. Unlike the geyser, the car doesn’t switch off — it just charges slower. That’s the whole point of dynamic throttling: it tries to avoid the hard cut, not replace it.

Where SANS actually draws the line

SANS 10142-1 is the standard every registered electrician works to, and it’s been covering EV charging installations since its 2017 edition. What it requires of me, as the person issuing the Certificate of Compliance, is a proper maximum demand calculation with diversity factors applied — sizing the main switch, breakers, and cabling so the fixed installation stays safe under both normal and fault conditions.

That protection scheme — breakers, main switch, a contactor-based shedding setup if one’s installed — is certified. It’s tested, it’s inspected, and critically, it works whether or not anything downstream cooperates.

Here’s the fundamental difference: (Dymanic Load Mnagement) DLM throttling is not a certified protective device – because it depends on the CT reading being accurate, the charger’s firmware doing its job, the comms link staying up, and the vehicle correctly obeying the control pilot signal. Any one of those can fail quietly – Vs. SANS compliance is to make sure your installation is safe assuming none of that works — because on the day it doesn’t, the breaker is the only thing left standing between a fault and a problem.

The bottom line

Dynamic charger throttling is a genuinely useful feature — it means your geyser is less likely to get hard-cut just because the car’s plugged in. It makes better use of the capacity you’ve already got. But it’s a convenience layer sitting on top of your electrical safety system, not a replacement for it. The breaker doesn’t care what the charger’s app says. That’s not a flaw in EV chargers — it’s just what “certified” actually means, and it’s exactly why the two mechanisms shouldn’t be sold, or understood, as the same thing.

Wiring in an EV charger with load management?

I’ll size your protection correctly under SANS first, then, if necessary, help you configure dynamic throttling as the bonus it is — not the safety plan.

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EVCI.tech — EV Charger Installations · General principles only, not a substitute for a site-specific electrical assessment and Certificate of Compliance.

By Older W.

I'm a senior licensed electrician. I do electric vehicle charger installations in and around Cape Town, Western Cape (only).