Author Topic: AC wiring and breaker sizing  (Read 1062 times)

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AC wiring and breaker sizing
« on: May 11, 2016, 12:10:35 PM »
As of May 5, 2016 the Ontario Electrical Safety Code 26th Edition has been adopted in Ontario.  There have been some changes regarding conductor sizing.

Most AC installers would follow Table 2 of the Electrical Code, and size the conductor according to the minimum circuit ampacity listed on the AC rating plate, as per Rules 4-006(2) & 8-104.  In my case, Lennox, no longer specifies the termination temperature, so we must use the 60C column in Table 2. 

The breaker is sized by following the maximum overcurrent protection listed on the AC rating plate. 

The allowable wiring length is determined by Table D3 and Rule 8-102 by calculating the voltage drop.

For example the Lennox 13ACX-18 lists a maximum overcurrent device of 20A.  We would install a 20A breaker.  The minimum circuit ampacity is listed at 12.4A.  Using Table 2 and the 60C column, we could use 14/2 wiring.  Factoring in the voltage drop we can use 14/2 wire up to 60', then we have to use 12/2 wire.

I attached a Lennox 13ACX wiring/breaker sizing chart and the OESC Table 2 below.

OESC Rule 4-006(3) says,

Quote
Notwithstanding Subrule (2), for high-voltage equipment where conductor termination temperatures are not marked, it shall be permitted to consult the manufacturer to establish the permitted termination temperature

I am hoping Lennox will say that their termination temperature rating is 75C, like on their older units.  This way we can use the 75C column in Table 2, which would allow smaller gauge wiring.

13ACX-18 - Max Overcurrent Device = 20A / Min Circuit Ampacity = 12.4A
13ACX-24 - 25A / 14.7A
13ACX-30 - 30A / 18.7A
13ACX-36 - 35A / 22A
13ACX-42 - 40A / 28.1A
13ACX-48 - 50A / 31.9A

Offline walker

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Re: AC wiring and breaker sizing
« Reply #1 on: November 16, 2017, 12:36:04 PM »
What type rating wire are you using on your installs?

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Re: AC wiring and breaker sizing
« Reply #2 on: November 16, 2017, 12:51:11 PM »
We use NMD90 wire, but follow the 60C column in Table 2 of the OESC 26th Edition for the wiring sizing.

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Re: AC wiring and breaker sizing
« Reply #3 on: November 16, 2017, 12:56:50 PM »
Okay that's what I've been using too. I think it's rated for up to 90C?  I just carry 10/2 and use it on pretty much everything.