MainPower continuously monitors and controls the load on the network to ensure a secure, reliable supply of electricity for our region.


Sometimes, during periods of peak electricity consumption, MainPower switches off electricity supplied to hot water cylinders for a short time to make sure the network is not overloaded.


In New Zealand, most hot water cylinders are controlled in this way by the regional electricity distribution business. Customers who allow their hot water to be controlled will typically pay lower rates on their power bills. To learn more about your electricity billing, contact your electricity retailer.

Load Control

Why does MainPower control load on the network?

MainPower continuously monitors the load across the electricity distribution network of North Canterbury. When necessary, adjustments are made to ensure a continuous supply of electricity for the region. Load control helps to keep the cost of distributing electricity as low as possible.

When does MainPower control electricity delivered to hot water cylinders?

Like roading networks, electricity networks experience peak times when demand is high and capacity is near the limit. On a roading network, this would look like a rush hour traffic jam.

Peak times on the MainPower network typically occur on cold winter mornings and evenings (when most customers are running heaters, lights, and other appliances at once), or in summer when irrigators and air conditioning are running at full capacity. Hot water cylinders are remotely controlled when the electricity network is experiencing high load.

How does load control work?

Electrical load on the network is continuously monitored through our network control system. When areas of the network approach peak load, signals are sent out through the network to switch off the hot water cylinders in the affected area.


These signals are call ‘ripples’ and reach ‘ripple receivers’ fitted to the meter board at each house or business, signalling them to switch off the hot water cylinder. Hot water cylinders are switched back on as soon as the load on the network starts to reduce.


MainPower limits the amount of load control to four-hours within any eight-hour period. In most cases, the effects of load control aren’t noticed by customers. Hot water cylinders store enough heat to stay hot throughout the four-hour window, as well as meeting an average household’s hot water needs.

What appliances are affected by load control?

In New Zealand, electricity supply to most hot water cylinders can be controlled through ripple signals.


In some rare, emergency situations, MainPower may also turn off electricity supply to irrigators through the same ripple control system.

Does load control affect the whole network at once?

Only the part of the network that is nearing peak load will be controlled.

Does MainPower control irrigator load?

Irrigators use a large amount of electricity. Irrigators on the MainPower network may be connected to our emergency load control system. Houses, sheds etc. are not connected to the emergency load control system. Irrigation load is not controlled to manage load on a seasonal basis, unlike hot water.


In emergency situations where MainPower needs to urgently decrease the load on the network, we may turn off the electricity supply to irrigators. This is to ensure continued supply across the region and only happens in extremely rare, emergency situations. If it is necessary to turn off irrigators, MainPower will try to contact affected customers, however this may not always be possible in short-notice, emergency situations.