I got a new air compressor that says 240 volt only but it only has a black and white wire please help.
Electrical – How to connect a 240v compressor with only black and white wires
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Yes this is bad/dangerous because you now have current running on the ground wire at all times. This type of timer requires a seperate neutral (whereas most switches just interrupt the hot) so that the timer can be powered when the switch is in the off position.
In your configuration, the line (power) comes in at the fixture and there is likely a 14/2 cable running to the switch for the sole purpose of interrupting the hot. The other configuration is where the line comes in at the switch which then sends power to the fixture when the switch is closed.
In order for you to use this type of timer, you need a dedicated neutral in the box with the switch. You would need to replace the 14/2 cable with a 14/3 cable (extra conductor) so that you can have a dedicated neutral from the line, and then still switch the hot to control the light.
Depending on the position of the switch and fixture it may be easy enough to pull a new 14/3 cable.
The picture helps a lot. The second white wire is coming from the switch, and it should have been wrapped with black electrical tape to indicate it was actually playing the role of a black wire. Determine which white comes from the switch, and that's the "black" wire.
Then the problem is as simple as connecting the new whites to the white wire, and new blacks to the black.
The following picture is what you have except on the light side, they have connected the black wires together and both whites are going to the lamp.
In order to determine which wire goes to the switch, you'll need a voltage tester. Turn off the breaker to the circuit and the light switch, and carefully remove the wire nut from the black wires in the lamp box. Be sure the wires are not touching anything, and turn the breaker back on. Using your voltage meter, touch the twisted black wires with one probe and each white wire going to the lamp. The white wire that shows 120v is the actual white wire coming from the breaker box. The other white wire will be the "black" wire coming from the switch. Turn the breaker back off and twist the wire nut back on. Be super careful when measuring the voltage with the breaker on.
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Best Answer
Get some red electrical tape and wrap it around the white wire, this will make the wiring more obvious to you. It is not properly color-coded because they are using common off-the-shelf 3-wire cordage, which is manufactured as black/white/green. It's legal to omit the marking on machinery, but it's required in wiring that's part of your house (often omitted there too).
You will need 240V electrical service. If you connect it via cord and plug, you will need a NEMA 6 plug and a NEMA 6 receptacle. You can also use a NEMA 14 plug and receptacle; in that case you will not hook up neutral on the plug.
If you are doing brand-new wiring for this, it may be best to use /3 cable and bring along a neutral in the wiring to the outlet point. You would not use the neutral, but it would be installed and ready for use for some future application.