How much electricity does an electrified fence consume per month?

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

25 December 2022

Gitau Ndung’u wants to know “How much electricity does an electric fence installed on 50×100 feet (1/8th acre) plot consume in a month if it's on continuously?” The answer is somewhere between zero and negligible! This is because the system only consumes significantly when an intruder touches the wires.

Electricity flows only when a circuit from live to neutral is completed. In the normal situation, the live and neutral wires in an electric fence do not touch one another – that would be a short circuit! So, no electric current flows. Hence no electricity is being consumed; the only consumption is for keeping the control unit on.

Electric fence controllers typically consume less than 10W when on standby. Thus, in one day, the total energy consumed is about 240 watt-hours (10 x 24); and in one month (30 days), the consumption is 7,200 watt-hours (240 x 30).

But electricity is sold in kilowatt-hours (kWh) and 1kWh = 1,000 watt-hours; thus, they typical electric fence might consume about 7.2kWh. The net cost of electricity in Kenya today is about sh25 per kWh so, the bill for the fence comes to about Sh180 per month.

Is Sh180 per month a lot of money? Well, it depends on how you look at it. It is definitely cheaper than employing a security guard!

When an intruder makes contact with the fence, he completes the circuit. The electric fences operate at around 500 volts and this can inject a current of about 0.1 amps through the body. This quite a strong shock which will send him away in a fraction of a second – perhaps, half a second!

During that short time of contact, the power consumption of the system shoots up from 10W to 50W (0.05kW); but it lasts for only 0.5s and the intrude retreats from the wires. Thus, the additional electricity consumption is also extremely small.

One hour has 3600 seconds, therefore half a second is 0.05/3,600 = 1/7,200 of an hour. So, in the time that the intruder is touching the wires, the electricity consumed will be 0.5kW x 1/7,200 = 0.0000069kWh. At Sh25 per kWh, this will cost Sh0.00017, or 0.017 Kenyan cents! Even if there was an intruder every day, the electricity cost of the electric fence will remain under Sh200.

The only significant cost in an electric fence is the price of installation. I have seen installers advertising at under Sh100,000 for a “50 x 100” (one-eighth acre) plot.