240 v neutral vs. ground

[mmouse]

Another 240 question here. Please help me understand the difference between the neutral and ground when only using a 3 prong/wire cord. For example, my welder and compressor only have 3 wire hookup. Do you use the neutral, or ground? My sub panel has separate neutral and ground. I know either one will make them work, but what is the correct way?

At a previous house, I got quite a shock from a neutral wire on a light circuit, that still baffles me. I know that neutral and ground go to the same place, but are separated. Does 240v carry a load back to the panel via ground? Or only 120v? So on my 240v compressor that has 2 hots and a ground, why don't I get a "neutral shock" if I touch it, or the metal conduit while the motor is running, yet I got zapped from a neutral on a 120v light circuit?

Thanks for clearing this up.

 

[Gary S]

120v uses neutral to complete the circuit. 240v uses the two hots to complete the circuit.

If you are truly getting a shock off the neutral, you have something wired on that circuit that is backfeeding when you open the circuit.

 

[ezzzzzzz]

In the main feed panel the neutral and ground are both tied to the panel. In a subpanel the neutral is 'floating' while the ground to tied to the subpanel. By 'floating' I mean that the neutral is not connected to the ground in any way. Separate neutral and ground wires run back to the main panel where they are bonded together. Assuming you are installing receptacles for your welder and compressor, connect the neutral lead of the receptacle to the 'floating' neutral in the subpanel. Your shock experience may have been related to a white lead that was actually a 'hot' feed from a switch and not properly marked as such.

 

[ddawg16]

The ground is ONLY connected to neutral at the load center. Actually, we should neutral is connected to earth ground. This sets up your 'reference' for the rest of the voltages. Without that connection, if the neutral was not connected to earth ground anywhere else, you 'could' have a 240VAC supply that is several thousand volts above ground.

With that said....3 prong vs 4.

With 3 prong 240 vac... You have 240 plus ground. All the current that comes in one hot leg goes out the other. There should be no current flow through ground.

On 4 prong you also have a neutral. Typically ovens are like this. The neutral also gives you 120 which is used for the oven controls.

If you measure from neut to either hot you get 120. But hot to hot is 240. The neut is nothing more than the center tap of the load side of the supply transformer.

To give you an idea about current flow....

Using our oven, say the controls pull 1a and the heating elements 30a. Under operation, the hot that has the controls on it will have 31a of current. The other hot will have 30a and the neut will have 1a of current

 

[mmouse]

Thank you, it makes sense now. 3 wire = use ground. 4 wire = use neutral and ground.

 

[wyliesdiesels]

Another 240 question here. Please help me understand the difference between the neutral and ground when only using a 3 prong/wire cord. For example, my welder and compressor only have 3 wire hookup. Do you use the neutral, or ground? My sub panel has separate neutral and ground. I know either one will make them work, but what is the correct way?

At a previous house, I got quite a shock from a neutral wire on a light circuit, that still baffles me. I know that neutral and ground go to the same place, but are separated. Does 240v carry a load back to the panel via ground? Or only 120v? So on my 240v compressor that has 2 hots and a ground, why don't I get a "neutral shock" if I touch it, or the metal conduit while the motor is running, yet I got zapped from a neutral on a 120v light circuit?

Thanks for clearing this up.

For a 240v ONLY device, neutral is NOT needed because the device ONLY needs 240v. If the device was rated 120v/240v, then u would need 2 hots AND a neutral, to provide 120v. Under normal cicumstances, current should NEVER be present on EGCs/ground wires, metal conduit, panel enclosures, etc. Current only flows on EGCs when there is a ground fault!

The only way to get shocked by a neutral is either A: there was a load/current returning on the neutral and u opened the circuit while touching both splices of the neutral and thus the neutral return current of the circuit was completed through your body and the electricity flowed through u, or B) somewhere on your body you were touching a hot leg AT THE SAME TIME as you were touching the neutral, thus completing the circuit.

 

[mod9]

basic rule of thumb . the ground is for people protection. the neutral is for equipment protection. all extra current not used travels back on the neutral . that's why if you ever get shocked off of a neutral ....hang on cause its gonna hurt. you are not protected by the trip of a breaker.....

 

[Milton Shaw]

Regardless of the color of a wire, the neutral is only neutral (shock free) when it is connected to the neutral/ground bar in the main box or connected in a sub panel that is connected correctly. The color of the wire--white-- is just to identify it that it is supposed to be neutral. Don't trust it to be shock free until you test it with a meter/ voltage sensor.

 

[wyliesdiesels]

basic rule of thumb . the ground is for people protection. the neutral is for equipment protection. all extra current not used travels back on the neutral . that's why if you ever get shocked off of a neutral ....hang on cause its gonna hurt. you are not protected by the trip of a breaker.....

Huh? Just how does a neutral provide equipment protection?

And in a 120v circuit, there wouldnt be any "extra current". Youre thinking of an MWBC where the neutral carries the imbalance between the hot legs!

And in no circumstance would a regular breaker protect a person from shock no matter what wire a person touches.

Regardless of the color of a wire, the neutral is only neutral (shock free) when it is connected to the neutral/ground bar in the main box or connected in a sub panel that is connected correctly. The color of the wire--white-- is just to identify it that it is supposed to be neutral. Don't trust it to be shock free until you test it with a meter/ voltage sensor.

A neutral thats part of a live circuit can still be shocking if u disconnect it, grab it with one hand and touch a grounded panel with the other hand!