Is there an electrician in the house?

[Rollie Meyers]

25 ampere breakers are not allowed for general purpose branch circuits, 15 or 20 ampere breakers must be used.....

The OP did not specify if they were single or 2 pole breakers, which are they?

[Mark Boyette]

breakers are about 4 bucks a piece so get rid of those 25's . Just buy some 20a breakers and run 12/2 wire. simple.

[david a graham]

Unless you are very comfortable with the source of your used panel you should look it over for signs of damage. Sometimes used electrical items have been removed from flood or other damage situations.

[Roger Frazee]

Hi Kevin

First thing that takes precedent is the instructions from the manufacturer.
For example a 3 hp unisaw model 36-L336 or 36-L352. The branch circuit should be no less than 12 awg protected by a 20 amp time delay fuse. Notice it specifies "fuse" and not circuit breaker.

http://www.dewaltservicenet.com/docu...94,36-L336.pdf

So the model number of your saw would help or any information from an instruction manual.

Now taking the example above and considering this is a individual (dedicated circuit) to the unisaw and considering this is motor circuit. I decide I want to use cord and plug using a 6-15P (this is the plug stated for the 3 hp model). The ampacity of 12 awg 60C is 25 amps. The saw apparently has the need only for a 230 volt 6-15P so its running amps (FLA) must be 15 amps or less at 230 volts or they would specifiy a 6-20P. Now 12 awg has an ampacity of 25 amps. So I could use a 25 amp double pole breaker on that 12 awg if I am serving that saw with a dedicated branch circuit....but....I must enter a "fused" disconnect that has 20 amp time delay fuses installed in each hot leg before the receptacle where the saw is plugged in. Or you could hardwire the saw ..which is probably best because it requires fuses in the branch circuit and that would limit where it could be plugged in. Plus cabinet saws are not easily mobile anyway.


You could also wire a motor feeder circuit from which you tap to each 230 volt power tool and place a disconnect with over current protection device (circuit breaker or fuse ..could be your 25 amp breakers) in the tap conductors specific to each tool. The feeder would be sized to carry the load of all the tools and would have a circuit breaker at the breaker panel.

Barring any manufacturer instructions then you would size your branch circuit conductors and ocpd for the power tools off the hp and nameplate data of the motor. One of the most important aspects when doing this is to determine if the motor has internal overload protection...usually indictive by a red reset button on the motor and stated thermally protected on the nameplate.

This is very commonly done when the owner doesn't have manuals or information from the manufacturer.

However if you have 12 awg and that is acceptable for the branch circuit amps to serve the motor then you most certainly can use a 25 amp breaker. This is not the same as branch circuits like Rollie mentioned earlier where you are limited to 20 amps for the breakers on 12 awg conductors.

[David Prince]

Would a person want to also take into consideration that you really do not want to "oversize" your breakers for load? 25 amp breakers normally carry a load for 20 amp draw. What kind of tools are you running that are drawing 20 amps? If your tool is only taking 15 amps or so, a 20 amp breaker is the recommendation. Correct?

[Roger Frazee]

Residential Load Center Breakers are rated to carry their amperage listing for non continuous loads... if they serve a continuous load then you should not load them more than 80% of their listing. Motors are not continuous loads unless they are in an application where they are running continuously for more than 3 hours. A continuous duty motor does not mean it is a continuous load.

Upsizing breakers is a necessary need in many cases for motors so that they will start due to the initial start up currents, however for most woodworking power equipment this is not necessary.

Anyway in this case Kevin has some double pole 25 amp breakers and 12 awg he would like to use for his 230 volt woodworking equipment. So long as there are no objections in the instructions for the electrical supply to the tool and considering that the branch circuit serves that tool and no others (dedicated) then he can use 25 amp breakers on 12 awg in accordance with art. 430 of the NEC.

For example a 230 volt unisaw 3 hp motor under article 430 has an flc of 17 amps in table 430.248. The ampacity of the branch circuit conductors must be 1.25 x 17 = 21.25 amps. The circuit breaker must be sized to carry the load so the next size up from 21.25 amps is a 25 amp breaker. Looking at the wire ampacity chart in 310.16 you see that 14 awg at 60C can carry 20 amps so this is too small but 12 awg is 25 amps. So 12 awg is the minimum wire size I can use to serve the motor for that unisaw. The inverse time breaker is allowed to be upsized as much 250% as long as the motor has thermal overload protection either internal or external. Starting current is generally the locked rotor current of the motor which is considered to be 6 times the flc of 17 amps. Looking at table 430.251(A) locked rotor current is 102 amps. So you need a breaker that will hold that momentary inrush current at startup without tripping. Generally speaking an inverse time circuit breaker will hold 6 times its handle rating for around 3 seconds. This generally is plenty of time to start the motor if it is not under load at time of start up. The ampacity of 12 awg is 25 amps and if the wire ampacity falls on a standard size breaker in accordance with NEC 240.6 (A) and we are serving a motor load with a dedicated branch circuit then I am allowed to use that 25 amp breaker.

You need to remember load requirements dictate the size of the wire and the breaker is then chosen to protect the branch circuit from ground faults and short circuit and overheating of the wire not the equipment utilizing the branch circuit. Faulty equipment may trip the circuit breaker but it is the circuit breakers purpose to protect the branch circuit from the faulty equipment.

Where you need to be careful is if your going to plug the motor to a receptacle and btw the receptacle for a dedicated branch circuit must be simplex not duplex, the receptacle must be rated not less than the rating of the branch circuit. The rating of the circuit breaker determines the rating of the branch circuit. In the example case the dedicated branch circuit is rated 25 amps and a 30 amp simplex (single) receptacle must be used.

As mentioned earlier you follow the manufacturers instructions, that not being available then you are allowed to wire the power equipment in accordance with art. 430 of the nec.

Clear as mud ...eh?

[Ken Harris]

In regard to 25 amp breakers due consideration has to be applied to amp draw of your machines.Example my powermatic 66 draws 15 or 16 amps dust collector 23 amps planer 16 amps.#12 20 amp circuit # 10 30 amp circuit.You do not want to have a 25 amp breaker for # 12 wire and risk possibibity of fire due to wire over heating.When you try to apply # 10 wire to a 20 amp oulet you will then realize what a mistake you made using # 10.If need be check with your local electrical inspector they can be a wealth of information if they are approached in the right manner,just my 2 cents.

[Chris Damm]

I don't believe you can use the quick connect for 12ga either. They are only available for 14ga. So moot point really.

Some quick advise for people that use the quick connect.........DON'T!

[Rollie Meyers]

In regard to 25 amp breakers due consideration has to be applied to amp draw of your machines.Example my powermatic 66 draws 15 or 16 amps dust collector 23 amps planer 16 amps.#12 20 amp circuit # 10 30 amp circuit.You do not want to have a 25 amp breaker for # 12 wire and risk possibibity of fire due to wire over heating.When you try to apply # 10 wire to a 20 amp oulet you will then realize what a mistake you made using # 10.If need be check with your local electrical inspector they can be a wealth of information if they are approached in the right manner,just my 2 cents.

For a motor load, 12 AWG is rated for 25 amperes as long as it is not NM cable. If a cord & plug connected load, I would not use the values allowed by article 430 + in order to use those higher values , overload protection for the motor is required, then the circuit breaker is for short circuit protection only.


BTW if you upsize your ungrounded (hot) conductors, you are also required to upsize the grounding conductor.



Here is something from the 2008 NEC section 250.122(B)

"(B) Increased in Size. Where ungrounded conductors are
increased in size, equipment grounding conductors, where
installed, shall be increased in size proportionately according
to the circular mil area of the ungrounded conductors."

This is unchanged from the 2002 & 2005 editions.