Clothes Dryer Circuits in Ontario

I just wanted to pass on some info I recently received in case there are some Ontario inspectors who may not already be aware of it.
Three of the last five homes I inspected, all 70’s and 80’s vintage, had dryer circuits comprised of 40A breakers and #10 copper wire. I called for further evaluation because a 40A breaker requires #8 wire, but I also thought this was too much of a coincidence so I contacted the ESA.
They advised that, over some period in the 70’s and 80’s, it was acceptable to the ESA to have a 40A breaker on #10 wire for this application. The reason - some very powerful dryers were being produced over that period causing nuisance tripping of 30A breakers.
Dryers now must consume 24A or less and therefore only 30A breakers are allowed for the #10 wire used today.
It still leaves me a little confused about what I should be writing when next I find a 40A breaker on #10 wire in an older house.

Since those dryers with nuisance tripping would be long gone now we could just note that it is recommended a 30 amp breaker be installed at some point when we see #10 wire. A short explanation, verbal and in the report as to why we comment on it this way. Good point to bring up.

Charles got it on the first try… definitely explain to the client they should change it for safety. Remember, if they don’t (and probably won’t) at least you have told them.

As this is not a code specific inspection, during the 1970 -1980’s the Electric safety Standards allowed the Branch circuit have 40amp on a #10 gauge wire. It’s reason as per ESA was the dryers then were less efficient and had a much heaver consumption. Todays dryers are " Energy Star" Compliant and inasmuch use less electricity. If your current dryer is an "energy Star " Compliant model it is recommended to have this circuit changed to todays electrical codes. Recommend electrician repair or replace as needed. This is for your information

This came into effect shortly it became a code requirement to install Clothes Dryer Receptacles.

Dryers were normally rated at 24 amps but some heavier clothes dryers had a 28 amp rating. the code had to be changed to accommodate these heavier clothes dryers.

Nuisance tripping was a small part of the reason for allowing 2 pole 40 amp circuit breakers on clothes dryer circuits wired with # 10 AWG copper wire. The main reason was due to overheating of the circuit protection that did cause a number of house fires. 30 amp circuit breakers would overheat if a clothes dryer was installed that had a current rating of 28 amps. Also the Ontario Code requires a de-rating to 80% of Fuses and circuit breakers capacity supplying electric heating and continuous loads. 80% of 30 amps is 24 amps; therefore you had to go to the next size of 2 pole 240 volt circuit which is 40 amps (80% of 40 amps is 32 amps) which accommodates a 28 amp clothes dryer. The TWH 90 degree C rating of the #10 AWG wire used to supply Clothes Dryers actually had a current rating of 35 to 40 amps. this fact is kept quiet but the code normally limits the load of #10 AWG copper wired circuits to 30 amps then, before and now.

There are still clothes dryers with the 28 amp load rating in use to-day. If the circuit breaker or fusing is changed to 30 amps for these 28 amp clothes dryers, it will create a definite fire hazard. I personally had to upgrade many fused and breaker circuits due to the fact that home owners purchased new clothes dryers rated at 28 amps.

40 plus years certified electrician in Ontario with Interprovincial Seal