The message of this blog is directed to any residential or small business customer who is considering installing new energy-intensive devices. Please inform your local electric utility. I am not referring to regular appliances like fridges, stoves and air conditioners. These are all no issue. I am referring to more energy-intensive devices such as heat pumps, driveway heaters, level 2 car chargers or crypto-mining servers (especially). Letting us know could prevent a major outage for you and your neighbours and also prevent a potentially dangerous situation.
A few weeks ago, we had an unusual event. One of our pole-mounted transformers blew up. This was a small transformer, only 10 kW, and it only served one residence. It had operated without any issues for decades. It was also located in a rural area so no damage was caused by the event other than to the hydro equipment.
What we discovered is that the owner of the residence had installed a number of energy-intensive devices, including crypto-mining servers, without telling us. This transformer had been operating with up to 40 kW of power running through it. It was amazing it performed as long as it did but eventually the power load was too much. NOTL Hydro has since installed a much larger transformer.
The average house does not use very much electricity. Power usage at any point in time is usually 3-4 kW. As a result, utilities will typically size a transformer assuming this and may have 8-10 residences on a 50 kW transformer.
In fact, the average monthly usage of electricity by residences has been falling over time. This is happening for two reasons. First, the average occupancy is declining with smaller family sizes and more seniors staying in their residences for longer. Second, the energy efficiency of most appliances and of lighting has improved substantially.
There is, though, a countervailing force and that is that some residences are installing much more energy intensive devices such as heat pumps, level 2 electric car chargers or crypto-mining servers. A heat pump can require up to 7 kW on a very cold day while a level 2 electric car charger can require up to 10 kW. An individual crypto-mining server can use 1.5 kW and some users will install multiple servers.
These could lead to the transformer becoming overloaded and, as in the dramatic example above, failing. NOTL Hydro has for decades used 100 kW rather than 50 kW transformers as its standard for pad-mounted transformers serving residential customers. It is also using 167 kW transformers occasionally as well. NOTL Hydro also periodically reviews the loading on transformers and will make adjustments if needed.
However, these reviews will not capture sudden changes in loading. That is why we are asking customers to call in with any major changes. We can check to assess the loading on the local transformer and determine if any action is needed or not.
It should be noted that residential customers will not be charged if we need to upgrade our transformers. That is a NOTL Hydro responsibility. However, depending on the nature of the new equipment, the customer may need to upgrade their service from 200 Amps to 400 Amps. That is the responsibility of the customer and should be discussed with an electrician.