General use snap switch

[alaskan JW]

I am wondering if i can use a 120/277 volt rated, double pole single throw snap switch as a disconnect for a single phase 240v 2hp motor. the switch is rated at 30 amps.

The real question i had is if that rating-120/277 is a line to neutral rating and not a line to line rating so can it still be used as a disconnect even though the motor is 240v line to line load. I am thinking no but i am not sure. Does a line to line fault have more short circuit current then a line to neutral fault? I am thinking yes but i do not know the theory behind it.

thanks

 

[Dennis Alwon]

I use dp switches all the time for well pumps. I do not see a problem with your install. I believe a DP switch is meant for exactly the purpose you propose.

 

[iwire]

In the 2002 NEC it would be 430.109(C) that you want to look at.

A general use snap switch can be used for stationary motors 2 HP and less but the switch must be rated two times the full load amp of the motor as determined by table 430.138.

Table 430.138 shows a single phase 2 HP motor @ 240 has an FLA of 13.8 so a 30 amp rated switch is OK.

 

[benmin]

You can use that switch as a disconnect for that application. That is what I would use

 

[iwire]

The real question i had is if that rating-120/277 is a line to neutral rating and not a line to line rating so can it still be used as a disconnect even though the motor is 240v line to line load. I am thinking no but i am not sure.

A 30 amp switch is 30 amps per pole regardless of the voltage.

Are you sure you have a two pole and not a 4 way?

It strikes me that a 2 pole would be rated 250 volt but I can definitely be mistaken here.

 

[don_resqcapt19]

From the UL guide for Snap Switches (WJQR)

AC general-use snap switches are tested for the control of resistive, inductive (including electric discharge lamp) and tungsten-filament lamp loads at 120 V up to the full current rating of the switch, and for motor loads up to 80% of the amp rating of the switch, but not exceeding 2 hp. ... Snap switches having voltage ratings other than 240 or 250 V are tested on circuits involving full rated potential to ground.

Don

 

[Dennis Alwon]

From the UL guide for Snap Switches (WJQR)

AC general-use snap switches are tested for the control of resistive, inductive (including electric discharge lamp) and tungsten-filament lamp loads at 120 V up to the full current rating of the switch, and for motor loads up to 80% of the amp rating of the switch, but not exceeding 2 hp. ... Snap switches having voltage ratings other than 240 or 250 V are tested on circuits involving full rated potential to ground.

Don

Don are you saying that a 120/277 volt switch cannot be used for a 240 volt motor load or for any 240 volt load?

 

[don_resqcapt19]

Dennis,

Don are you saying that a 120/277 volt switch cannot be used for a 240 volt motor load or for any 240 volt load?

I am saying it can be used on circuits of up 277 volts to ground, and up to a maximum of 2 hp.
Don

 

[John Valdes]

Does the motor have any overcurrent protection? Either in the motor or in the circuit? The switch is okay. But I would have some concern regarding overload protection.
Switches designed for motor use usually have a trip function built in.

 

[LarryFine]

Heck-fire, I've even used the same switch for a water-heater disconnect, where the home was just too pretty for a surface-mounted switch or pull-out.

 

[cadpoint]

Where'd that Go ...

Where'd that Go ...

In the 2002 NEC it would be 430.109(C) that you want to look at.

A general use snap switch can be used for stationary motors 2 HP and less but the switch must be rated two times the full load amp of the motor as determined by table 430.138.

Table 430.138 shows a single phase 2 HP motor @ 240 has an FLA of 13.8 so a 30 amp rated switch is OK.

Ouch, 2007 NEC no 430.138 quote, charts or graphs ... DOH
2007 I assume your stating the same as 430.83 (C)

 

[suemarkp]

See also subparts (1) and (2) of that same section. Part (2) allows a switch to only be 125% of the motor FLA if it is labeled "AC Only". Most switches that don't make a loud CLICK are labeled AC Only nowdays.

 

[iwire]

Ouch, 2007 NEC no 430.138 quote, charts or graphs ... DOH
2007 I assume your stating the same as 430.83 (C)

No.

Using the 2005 NEC 430.83(C) has to do with motor controllers.

I quoted 430.109(C) of the 2002 which is the same in the 2005 NEC.

430.109(C) deals with motor disconnects which is what we are talking about in this thread.

 

[Dennis Alwon]

I think cadpoint was talking about your comment on Table 430.138. I think you meant Table 430.248. Also at 230 volts single phase it is 12 amps.

 

[iwire]

I think cadpoint was talking about your comment on Table 430.138. I think you meant Table 430.248.

No, I said I was working from the 2002 NEC in my post. In the 2002 it is Table 430.138.

Also at 230 volts single phase it is 12 amps.

Yes, I read the 208 column.:roll:

I guess you missed the part about 430.83(C) and 430.109(C).

 

[alaskan JW]

Does the motor have any overcurrent protection? Either in the motor or in the circuit? The switch is okay. But I would have some concern regarding overload protection.
Switches designed for motor use usually have a trip function built in.

yes the motor is thermally protected internally.

 

[John Valdes]

Dennis.....Excellent choices for your profile pics. I love everyone except JJ.

 

[spsnyder]

Dennis,

What was your old pic. of?

 

[Dennis Alwon]

Dennis,

What was your old pic. of?

Nobody other than the great Robert Zimmerman aka Bob Dylan

Dennis.....Excellent choices for your profile pics. I love everyone except JJ.

Thankl you--- I was wondering if anyone could tell who they all were. I figured most wouldn't know Frank Zappa.

 

[LarryFine]

Dennis.....Excellent choices for your profile pics. I love everyone except JJ.

What's wrong with Janis? :-?

I figured most wouldn't know Frank Zappa.

"Watch out where the huskies go, and don't you eat that yellow snow!" :smile: