240 wire questions...

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Old 03-14-17, 08:44 PM
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240 wire questions...

Hello, I'm new here and have a question about 240 wiring. Here's the situation: We recently had a building on our property demolished are in the process of building another one. We had the power run underground from our house breaker box to the old building. When I checked the lines coming from the conduit I saw that all three are black. My questions is how can I check these wires to determine which are the two hot wires? These are coming off a 100 amp breaker and will just power a few small tools in the building.

Thanks.
 
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Old 03-14-17, 08:58 PM
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Welcome to the forums.

You have three wires. Two are the hot legs and the third is neutral.

From each hot leg to neutral is 120vac.
From each hot leg to the other hot leg is 240vac.

CAREFULLY find the two that are the 240v legs. Mark them.
Check each one to neutral to confirm 120vac.

You will need to have a sub panel attached to those wires. The sub panel needs to be grounded via a ground rod and the circuits you connect need to be breaker and GFI protected.
 
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Old 03-15-17, 06:01 AM
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Is the conduit metal or PVC. You should also have a 4th wire (separate ground) going from the main panel to the sub-panel in the building. Grounds and neutrals in the sub-panel to be separated. Neutral bar isolated from the panel itself.

Not sure though if it is metal conduit if that counts as the separate ground.
 
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Old 03-15-17, 06:45 AM
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Depending on how the electrical code is enforced in your area you may need to add an equipment ground conductor (EGC) to that feed since you are putting up a new building. As said if the conduit is metal that may be used as the EGC.
 
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Old 03-15-17, 12:20 PM
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An existing 3 wire feeder is allowed to remain in use. I am not sure if the new building permit would change this. I would ask the inspector to clarify .
 
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Old 03-15-17, 07:11 PM
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Thanks for the replies. First of all the conduit is the approved for burial electrical PVC conduit. Also, I understand that the incoming wires are two hot and one neutral. My question is how do I test the wires to confirm which two are hot and which one is neutral? They are all black and I can't trace them back to the box. I have only a small voltage tester that you use to check if there is any current to a standard 110 base plug. My concern is I've never tested a 220 circuit and don't know what would happen if I touched the probes to the two hot wires simultaneously. Any suggestions?
 
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Old 03-15-17, 07:15 PM
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You should be using a meter to check them
OR
you can use your test light and check from each wire to ground.....one at a time.
Only the two hot legs will show a light when checked to ground.
The neutral will not show any light when checked to ground.
 
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Old 03-15-17, 07:23 PM
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First of all the conduit is the approved for burial electrical PVC conduit.
Which means you have no EGC. As PCBoss said you need to check with your AHJ (inspection department) if it is grand fathered.

To check the voltage a cheap, $8-$15 analog multimeter is all you need.
My concern is I've never tested a 220 circuit
It is a ~240v circuit.
and don't know what would happen if I touched the probes to the two hot wires
That is how you test. The meter would show 240 volts. If you're nervous about doing it live with the breaker off fasten the probes to two of the wires then turn the breaker on and observe the reading on the meter.
 
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Old 03-16-17, 12:37 PM
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Thanks for the extra info and the correction on the 240. Typing and thinking is not my long suit. Here's a picture of the meter I have:

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So by using this meter can I by process of elimination determine which two are hot and which is neutral? The two hot wires will combine for 240 and one hot and the neutral will indicate 120?
 
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Old 03-16-17, 02:34 PM
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Not a meter, a tester but you can use it.
 
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Old 03-16-17, 06:10 PM
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Well I used my tester today. One combination of two wires registered in the upper portion of the tester, in the 240 zone. While leaving one lead in place I switched the other lead to the other wire and it registered nothing, not even 120. Likewise when I switched other lead to the other wire. I then verified that the two original wires registering in the 240 zone. Is it normal for a hot wire and neutral wire to not register anything in this case?
 
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Old 03-16-17, 06:54 PM
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No, neutral should show ~120v to each hot. You need to see how it is connected at the other end.
 
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