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Kevin, Licensed Electrical Contractor
Category: Electrical
Satisfied Customers: 3590
Experience:  30 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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I need to wire up a Double Pole Double Throw (DPDT) Switch

Customer Question

Customer: My name is***** need to wire up a Double Pole Double Throw (DPDT) Switch and I don't understand what A1 A2 and B1 B2 refer to.
JA: Thanks. Can you give me any more details about your issue?
Customer: There are 6 terminals: LEFT SIDE TOP TO BOTTOM: L2(black) B2(silver) A2(gold) and RIGHT SIDE TOP TO BOTTOM: B1(Silver) A1(Gold) L1(Black)
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Submitted: 1 year ago.
Category: Electrical
Expert:  Kevin replied 1 year ago.

Hello and welcome to Just Answer. My name is ***** ***** I will be happy to assist you with your electrical question.

1) A DPDT switch can switch between (2) two separate loads using (1) one power source.

2) Based on your description of the 6 terminals, most likely the L1 & L2 terminals are for the power circuit. L1 & L2 indicate LINE side voltage

A1& A2 would be the 2 terminals for LOAD "A"

B1 & B2 would be the 2 terminals for LOAD "B".

3) If you have a continuity meter or an Ohm meter, the terminals can be confirmed.

4) What is the application for the Double Pole Double Throw switch?

Customer: replied 1 year ago.
It is to route power to EITHER 12amp balcony whirlpool bathtub (air only, no heat), OR existing general power socket on the balcony. Seems easier than running an additional separate line from an additional breaker in the main panel..
Expert:  Kevin replied 1 year ago.

Thanks for the confirmation and replies.

1) DPDT switches are often used for a 240 voltage source and switching between 2 separate 240 volt loads.

DPDT's are not used for switching 120 volt circuits since only the hot conductor is switched on a 120 volt circuit and the neutral conductor is never switched.

Expert:  Kevin replied 1 year ago.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.


Customer: replied 1 year ago.
Your reply makes no sense to me. --- You say A1 & A2 would be the 2 terminals for LOAD "A2, but A1 and A2 are both GOLD terminals. --- You also say B1 & B2 would be the 2 terminals for LOAD "B" but B1 & B2 are both SILVER terminals. --- And why can L1 & L2 (both BLACK terminals) be the power source?? The DPDT only has one power source!
Expert:  Kevin replied 1 year ago.

1) Because a DPDT switch is only used on a 240 volt circuit which contains 2 hot conductors and 240 volt loads which also contain 2 hot conductors.

2) It is against electrical codes to switch a neutral conductor on a 120 volt circuit. Take a look at all of your wall switches wired in your home and all of them are only switching the hot conductors. A 120 volt circuit contains 1 hot and 1 neutral conductor and only the hot conductor is switched.

3) Without having a manufacturer wiring diagram of the switch, I assume that L1 & L2 are for the LINE side connections as L1 & L2 is often used in the electrical industry to designate LINE side connections. LINE side = the power source or incoming voltage. Some DPDT switches will designate the power source as the "Common" or "COM" terminals. Once again, a continuity tester or an Ohm meter can confirm the terminals.

Expert:  Kevin replied 1 year ago.

1) What is the voltage of the whirlpool tub? 120 or 240 volts?

Customer: replied 1 year ago.
120V, as is the line itself.
Customer: replied 1 year ago.
You can find hundreds of 120V DPDT switches on the web, for North America and UK, eg:
Customer: replied 1 year ago.
Sorry, I don't trust you any more and don't trust your advice.
Please refund the fee I paid under "Satisfaction guaranteed" warranty.
Expert:  Kevin replied 1 year ago.

Get yourself a SPDT switch for your application.

I've opted out of the question.

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