Heat relief might be on everyone’s mind, but a record high use of electricity left many people in the dark Monday.

Air conditioners, fans and refrigerators were one of the reasons about 400 people lost power Monday, surpassing an all time high of electrical usage in 1988.

In 1988, electrical use peaked at 17,459,000 kilowatts. Between 3 p.m. and 4 p.m. Monday, customers in the DeKalb and Sycamore areas used 17,733,000 kilowatts of electricity, said Mario Fontana, Commonwealth Edison district manager.

Fontana said most of the blackouts were caused by over usage wearing out the transformers, but lightning blew a number of the fuses for a while.

The hotter it becomes, the harder it is for transformers to handle the load of increased use, Fontana explained. Electrical use was not only air conditioning, but fans and refrigerator use as well, he said.

Monday was the hottest day of this summer, 99 degrees, but the highest temperature on that day was 103 degrees, said NIU Weather Service Director Joel Veeneman. Nine days this summer have reached the 90s, he said.

In DeKalb, about 40 to 50 customers were without electricity from 5 p.m. to 2:30 a.m. About 200 customers in the DeKalb area had some power loss.

Another 200 customers in Sycamore had short spurts of power loss because of lightning and trees interfering with the power lines, Fontana said.

Fontana said the transformer for these customers was larger than his office was prepared to fix and an office from another district had to come in to repair it.

Some tips to cut back on electrical use include lowering the thermostat at night or when no one is at home and putting up shades. Windows act much like a greenhouse because the heat comes in but doesn’t leave, Fontana said.