when CAN a #14 be used for 25 amps?

[basicbill]

Hi all,
First off, I'm from Canada. Our Code ampacity tables have been harmonized with the NEC ampacity tables.
Of course, we're surprised with the possibility of the new, higher ampacities.

But I have searched high and low and I haven't been able to find a single example of where a #14 awg conductor would be allowed to have an ampacity of 25 amps. #14, #12 and #10 have the restriction to 15, 20 and 30 amp O/C device except 'where otherwise provided in the code'.

Since these ampacities have been in your code for some time, would you be able to give me a (or perhaps a couple) of examples where the #14 awg conductor could have these higher ampacities?

Many thanks.

 

[suemarkp]

Don't think you're ever going to get 25A on #14, as I know of no 90C rated terminations. Our 240.4(D) rule generally limits #14 overcurrent to 15A. However, there are exceptions in 240.4(G) where you can violate that. Typical applications are motors, HVAC units, and welders. You get a double bonus with these -- you can use the HVAC MCA, motor * 1.25, or welder duty cycle table value of up to 20A on a #14 wire assuming these have 75C terminations. Then, the overcurrent can be even larger because of the specific rules (generally up to 250% of the motor amp rating).

Generally, the 30A value can only be used for thermal derating issues (ambient temperature and conductor bundling). You take the lower of the termination ampacity or the thermal derated ampacity.

 

[basicbill]

Thanks Mark. That's a great place for me to start. I'll check our rules on HVAC and welders and put it together here.
I think most of our rules and coming into sync.

 

[Sierrasparky]

In simple terms you use the higher ampere rating as the starting point for Derating purposes.

 

[infinity]

Depending on the wiring method an AC unit with a minimum circuit ampacity of up to 20 amps can be protected by an OCPD of 25 amps or possibly even 30 amps if the conductors are #14.

 

[augie47]

I think some clarification is in order. The HVAC/motor/welder situations don't affect the conductors ampacity, but simply allow it to be protected at a value higher than it's ampacity.
A 14 gauge conductor could carry 30 amps indefinitely, the limiting factor is normally the insulation. Some appliance wiring, using different materials for the conductor itself, or different insulation, use a #14 for currents in excess of 30 amps.
Table 400,5(B) is an example of this.

 

[iwire]

I think some clarification is in order. The HVAC/motor/welder situations don't affect the conductors ampacity, but simply allow it to be protected at a value higher than it's ampacity.

Very good point.

 

[kwired]

Some quick motor examples taken from Square slide motor calculator

Motor HP - volts - AWG (@75C) - suggested breaker (all three phase)

3.0 - 208 or 240 - 14 - 20

5.0 - 208 - 12 - 35

5.0 - 240 - 12 - 30

7.5 - 208 - 10 - 50

7.5 - 240 - 10 -45

7.5 - 480 - 14 - 20

10.0 - 240 - 10 - 60

10.0 - 480 - 14 - 25

15.0 - 480 - 10 - 40

20.0 - 480 - 10 - 60

The breakers listed are just Square D's suggested breakers and generally will work in most cases. Most are not even up to the allowed 250% of FLC level. If you still have trouble starting the motor without tripping the breaker there are exceptions that allow to go even higher.