Power outage in the office

Why is rotational load-shedding wicked?

Yep! Rotational load-shedding is wicked! It damages electronic devices, appliances and industrial electrical equipment, and worse is that your conventional surge protection does not protect your sensitive electronics from electrical power surges caused by rotational load-shedding.

This kind of sucks, you have paid good money for surge protectors, and now I'm telling you that the stuff does not protect your devices from load-shedding. Worse yet is that you are probably experiencing this currently at your office or home. Normally the first thing to fail from a load-shedding voltage surge is your mission critical TV, HiFi or Security System.

We also know that rotational load-shedding in South Africa is here to stay. Most energy experts say that load-shedding will be with South Africans until 2026. Load-shedding for a minimum of 5 years.

But most clients believe that their insurance cover will replace devices damaged by Eskom’s power outages. However, although most insurance cover provide clients with peace of mind against damage from lightning strikes this is not the case for load-shedding damages.

Why is it that your standard mains surge arrester does not protect equipment from scheduled power supply outages (what South Africans call load-shedding)?

Standard mains surge arresters make use of MOVs (Metal Oxide Varistors). These MOVs (Metal Oxide Varistors) are connected from line to Earth, that is from Live to Earth and from Neutral to Earth.

If you happen to have a more expensive mains surge arrester, then there will probably be a MOV between Live and Neutral. Have a look at the two circuit diagrams that detail this.

Surge arrester with a MOVs from Live to Earth and Neutral to Earth

Surge arrester with a MOVs from Live to Earth and Neutral to Earth.

Surge arrester with a MOVs from Live to Neutral, Live to Earth and Neutral to Earth

Surge arrester with a MOVs from Live to Neutral, Live to Earth and Neutral to Earth.

The MOVs (Metal Oxide Varistors) have a typical clamping voltage of about 275volts. While the voltage of the circuit remains below the Metal Oxide Varistors clamping voltage of 275volts, the Metal Oxide Varistor remains non-conductive (dormant). But when the clamping voltage is reached, the Metal Oxide Varistor starts to conduct. In this state, the MOV connects the live or neutral to the Electrical Earth to dispose of the electrical surge energy safely.

How surge clamping works and the high let-through surge voltage

How surge clamping works and the high let-through surge voltage.

What's the problem with rotational load-shedding then?

The problem with rotational load-shedding is that most surges from load-shedding remain below the Metal Oxide Varistors typical clamping voltage of 275volt. Because of this your electronics, appliances and industrial electrical equipment get fried by electrical surges before your surge arrester even starts working.

So, what do you need to protect your electronics, appliances and industrial electrical equipment from load-shedding?

What is needed is a device that tracks the mains sine-wave and provides a small window of operation that has a low transient let-through-voltage. This device comprises of an electronics circuit that is more than a single component. However, this electronic sine wave tracking circuit now protects only against rotational load-shedding. But what about transients from lightning?

How sine-wave-tracking surge arresters work and the let-through surge voltage

How sine-wave-tracking surge arresters work and the let-through surge voltage.

Can you get a surge arrester that works for lightning and rotational load-shedding?

For lightning, we need to add our trusted Metal Oxide Varistors (MOVs). Remember that Metal Oxide Varistors (MOVs) are designed to protect against transients from lightning (High-Voltage Spikes and Surges).

So, to have a surge arrester that works for both lightning and rotational load-shedding, both sine-wave tracking surge arresters and Metal Oxide Varistors (MOVs) need to be combined into a single surge arrester. This hybrid-type surge arrester is larger than a MOV-based surge arrester, but it is a load-shedding surge arrester and a lightning surge arrester in one.

Hybrid-type surge arrester circuit diagram

Hybrid-type surge arrester circuit diagram.


For BFR Digital's range of Mains Hybrid Surge Arresters, please follow these links.

Single-phase products:

20KA Single Phase Inline 220V AC Sine Wave Tracking Mains Surge Arrester.
20KA Single Phase 220V AC Sine Wave Tracking Mains Surge Arrester.
40KA Single Phase 220V AC Sine Wave Tracking Mains Surge Arrester.
60KA Single Phase 220V AC Sine Wave Tracking Mains Surge Arrester.

Three-phase products:

40KA Three Phase AC Sine Wave Tracking Mains Surge Arrester.
60KA Three Phase AC Sine Wave Tracking Mains Surge Arrester.

Who can install these surge arresters?

The only DIY product in our range is the BFR-20KA-INLINE. All the other units need to be installed by an electrician. But not to fear, we have negotiated a flat fee with our electrician.

So, if your home or office is in the greater Joburg area our electrician will charge R2200 for the installation of a single-phase arrester or R2800 for the wiring of a three-phase surge arrester. These prices exclude the surge arrester.

Please contact us for a detailed quote.


Cheers for now,

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