Disconnects

J

Jimmy7

Senior Member
Location
Boston, MA
Occupation
Electrician
I have a question about disconnect switches. In the past I have used a double pole switch for a 240 V pool pump or a 15 amp 240 V air handler. When do you switch to a traditional disconnect switch ( Side Arm for example) does it depend on the amperage?
 
Jimmy7 said:
When do you switch to a traditional disconnect switch ( Side Arm for example) does it depend on the amperage?
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Of course, in that the switch should be sized for at least the load's current and HP ratings.

You could even use a 2p toggle switch if adequately rated.
 
Jimmy7 said:
I have a question about disconnect switches. In the past I have used a double pole switch for a 240 V pool pump or a 15 amp 240 V air handler. When do you switch to a traditional disconnect switch ( Side Arm for example) does it depend on the amperage?
Click to expand...
Well there aren't any traditional snap switches that will handle 40 amps, that I know about, and there are 30 amp DP switches but they can be a bear to install in one gang boxes with #10 wire. I used to used DP 30 amp snap switches for water heaters because they look neater but we basically went over to the small air conditioner type disconnects.
 
Well according to this is is not necessary

(A) Alternating-Current General-Use Snap Switch.

This form of switch shall only be used on ac circuits and used for controlling the following:
  • (1)
    Resistive and inductive loads not exceeding the ampere rating of the switch at the voltage applied
  • (2)
    Tungsten-filament lamp loads not exceeding the ampere rating of the switch at 120 volts
  • (3)
    Electric discharge lamp loads not exceeding the marked ampere and voltage rating of the switch
  • (4)
    Motor loads not exceeding 80 percent of the ampere rating of the switch at its rated voltage
  • (5)
    Electronic ballasts, self-ballasted lamps, compact fluorescent lamps, and LED lamp loads with their associated drivers, not exceeding 20 amperes and not exceeding the ampere rating of the switch at the voltage applied
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If a dp switch is rated 30 amps and it is hp rated then if the load of the motor is 24 amps without the 125% added then it can be used because that 125% of 24 is 30 and 80% of 30 is 24. I think that is where this rule comes from
 
This makes it interesting

430.110 Current Rating and Interrupting Capacity.

(A) General.

The disconnecting means for motor circuits rated 1000 volts, nominal, or less shall have a current rating not less than 115 percent of the full-load current rating of the motor.
Exception:
A listed unfused motor-circuit switch having a horsepower rating not less than the motor horsepower shall be permitted to have a current rating less than 115 percent of the full-load current rating of the motor.
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Dennis Alwon said:
If a dp switch is rated 30 amps and it is hp rated then if the load of the motor is 24 amps without the 125% added then it can be used because that 125% of 24 is 30 and 80% of 30 is 24. I think that is where this rule comes from
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Going from memory I thought that there were HP rated switches where the HP rating exceeded the 80%.
 
Can you help me with this example. The circuit is 120 volts for this motor. Can I run a 20 amp circuit with a 20 amp switch (The owner wanted a switch by the motor).
1732639438982.png
 
Jimmy7 said:
Can you help me with this example. The circuit is 120 volts for this motor. Can I run a 20 amp circuit with a 20 amp switch (The owner wanted a switch by the motor).
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According to what Dennis posted in post #9 the 20 amp switch would be operating at less than 80% of it's rating so it would be code complaint.
 
Jimmy7 said:
Can you help me with this example. The circuit is 120 volts for this motor. Can I run a 20 amp circuit with a 20 amp switch (The owner wanted a switch by the motor).
View attachment 2574539
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The switch should be hp rated. The ones I see online do not have hp rating written on the switch so I am not sure if the paperwork, if shown, would be acceptable. IMO, it should be fine.
 
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