240 wiring at both ends

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  #1  
Old 10-15-00, 06:53 AM
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I am providing power from Bld. A to Bld B. I'd like to provide 240 from a 2-pole, 60-Amp breaker at Bld. A. I'll use both leads (I'm using 2/2/4, so they're both black)into each respective breaker with the ground to ground. The question is at the receiving panel at Bld. B. I am unclear whether I am taking one of the leads to the "hot" pole, one to the "neutral" and the other to the ground. Or, whether I should somehow have another "main" 2-pole breaker at the panel B. Panel B is simply going to be used for lights (120) at this point, therefore, I intend to simply use 15A breakers there.
 
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  #2  
Old 10-15-00, 07:56 AM
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Yes, you will need a 2-pole main breaker in the new box. What you are setting up a is sub-panel. You should carry the 2 hot leads, the neutral, and the ground out to the new panel and keep them all separate.
You'll connect the two hot leads to the two poles on the main. The neutral will connect to a neutral bus, and finally the ground will go to a ground bus separate from the neutral.

What you will end up with will be a series of 15A breakers on 2 alternating poles.
 
  #3  
Old 10-15-00, 01:49 PM
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<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by ranck:
Yes, you will need a 2-pole main breaker in the new box. What you are setting up a is sub-panel. You should carry the 2 hot leads, the neutral, and the ground out to the new panel and keep them all separate.
You'll connect the two hot leads to the two poles on the main. The neutral will connect to a neutral bus, and finally the ground will go to a ground bus separate from the neutral.

What you will end up with will be a series of 15A breakers on 2 alternating poles.
<HR></BLOCKQUOTE>

You mention 4 leads. I've only got 3. The two large #2s and one #4. The idea was connect the two large leads to the breaker. This leaves the smaller lead as the ground. With that in mind, and if I'm to have a 2-pole main at the sub-panel, how then do I configure it? I'm a bit more puzzled now.

 
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Old 10-15-00, 02:11 PM
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Hi Cbrandkamp,

Two things. First you do not need a main in bldg B. You can use a main lug only panel.
Secondly, ranck indicated 4 wires because you need a neutral. Your wiring scheme does not provide for a neutral and thus you won't have 120 volts available in your new panel.
Your neutral will be the same size as the hot, you need to clearly mark it with white tape.
You also will not bond the neutral bar to the equipment (panel) in building B. You will have a separate grounding bar for grounds.
I presume you have the larger size wire because of voltage drop which you have already calculated.
 
  #5  
Old 10-15-00, 07:48 PM
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The other replys are good, but they don't have the right answer for your installation. Let's go over this from the start.

#1: run 2/2/4 from Bldg A to Bldg B. This is ok if you don't have any metallic paths, such as gas or water, run between the two buildings. If you do, then you have to do it another way. for now, say you don't. Attach the larger wires to the two termination on the 60amp, 2-pole breaker. The other wire (a #4) you need to mark white, and connect to the neutral bar in your panel. This will be your neutral wire, not a ground wire.

#2: At the 2nd building, you can, but don't have to, run this wiring to a main breaker. Either way, your #2 will land on either the main breaker lugs, or just the buss lugs. The #4, which is marked white here also, is attached to the neutral bar. Don't stop there tho. You also have to install a grounding electrode system (usually an 8' ground rod) and run a #6 copper wire from it to the same neutral bar. You are also required to install the box bond screw or strap. Look at the lable inside the panel for the location of this.

#3: Now that you have all this done, you can install your 15amp branch breakers to feed your loads. You use one breaker for 120v loads, and if needed, you can run a 240v load out of this box, in much the same way you did to run the 240v to Bldg B (use a 2-pole breaker, correct wire size, etc...)

This is a code approved method of wiring two buildings. It is not the preferred method, which would be to run 4-wires, and float the neutral at Bldg b, but you can do it this way and still meet code.

Hope this clears it up for you.

Rick
 
  #6  
Old 10-17-00, 03:51 PM
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RickM is right in his wiring design for you three wire feeder going to the outbuilding.

The only thing that I disagree is the main breaker and when it is required. If you only have a 6 circuit panel then a main is not required. If you have more than a 6 circuit panel in the outbuilding then you must have a main breaker. The reason for the main being required if more than 6 circuit designed in you panel is that you are limited to 6 main disconnects to a structure. When you install the three wire service then you must install the ground rod to provide the fourth wire as a grounding wire. This new grounding source at the out building makes that panel a main service rated panel and the neutrals and ground must be married in a main service panel and the 6 main disconnect rule must apply. If the panel only has 6 breakers you are within the maximum allowed for main breakers and all those breakers would be considered main breakers. If more than six circuit in that main service rated panel you would exceed the maximum of 6 main disconnects requiring the one main breaker bolted in the panel serving the number of breakers if over the maximum of 6 breakers.

Hope this clearifies the main breaker requirement.

Wg
 
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Old 10-17-00, 04:05 PM
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Thought I would clearify the main versus the sub panel in a detached structure served from the main dwelling.

If you run a four wire cable from the main bldng to the detached structure, this detached structure becomes the same as a part of the main structure because you are using the grounding source from the main structure. This makes the panel in the detached structure a sub panel of the main panel in the main building, requiring the neutrals and the ground to be separated in the second sturcture that has become the same entity as the main structure. No ground rod is allowed because you would then have two grounding sources to the same structure.

If you run only three wires from the main building to the detached structure, then you have a separate detached structure and this panel is considered a main panel with its own grounding source [ground rod] supplying this structure seperate from the grounding source at the main building. The main service panel in the detached structure must have a ground rod supplied at the detached structure and the neutrals and grouding conductors must be married together because you now have a main service rated pane. This panel in the detached structure is a main service rated panel with the neutrals and grounding conductors married together because you only have the two hots and a neutral coming from the main structure requiring you to supply a new grounding source at the detached structure.

HOpe this helps

Wg
 
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Old 10-18-00, 07:14 AM
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Yes, it helps tremendously. I thought I was on the right track while mapping this thing out, but it became a bit foggy between the books, the local hardware store comments, and the neighbor's barking dog. Thanks all for your professional assistance. This is a great service.

Chris Brandkamp
 
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Old 10-18-00, 10:34 AM
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I hope someone will comment on this a little further. I note in the original question that the neutral line is a lighter gage than the two hot leads. Isn't that a problem when the load is going to be divided like this? If it was going to a 240V load, OK, but he intends to split this up into two or more 120V circuits. Seems like that neutral should be the same size as the hots. Or am I remembering this wrong?
 
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Old 10-20-00, 02:19 PM
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The 93 NEC allowed the neutral on a dwelling to be reduced two wire sizes automatically without question. In 96 NEC they code panels decided to treat a dwelling the same as an industrial design. I have a concern for that decision. I question that the majority of the electricians installing wiring in dwellings have the knowledge required to size a neutral.

All along we were allowed to reduce the neutral demand load to 80% for any service 200 amp or larger. We also were allowed to apply a reduction on our demand load to 70% on the range load in our calcualtion above the original 80% on the total load.

A neutral would not be even needed if both line 1 and line 2 had the same load. This would be called a balanced circuit. An unbalanced circuit would be like the following; line 1 = 10 amp and line 2 = 25 amp the neutral load would be 15 amp. The neutral load is sized by the difference in amps between the two hot conductors. In a multiwire circuit it is impossible, with all good connections to have a neutral load carrying more amps than any one hot conductor of a multiwire circuit. If we had a multi wire circuit feeding a house with a perfect amp load of 100 amps on line one and a matching load of 100 amps on line two then the neutral load would be 0 amps on this service even though the service is loaded to maximum. This would be considered a balanced load. Most cables approved by UL are approved with a neutral reduced two sizes smaller than the ungrounded conductors.

Hope this clears up neutrals and multi wire feeders or circuits a little.

Good Luck

Wg
 
  #11  
Old 10-22-00, 12:34 PM
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In the area that I'm in, reducing the neutral wire size is not allowed. This done simply to ensure a large enough neutral wire without proving balanced circuits. This can cost a little more money, but provides simplicity for the panel installation. If memory serves me, to install a sub-panel in a garage powered from my main panel in the house, I would have to run 3 insulated conductors (2 power and 1 neutral) all having the same wire guage size. The 4th wire, the ground wire, would also have to be the same size as the power and neutral conductors, if I was going to use the main panel for grounding. To eliminate having to run a #2 ground wire I can run #6 ground wire from my sub-panel to TWO ground rods at least 8 ft. in the ground and at least 10ft. apart at the garage. Although installing ground rods can be some work, it eliminates me from having to run #2 ground wire. To answer your question, the two black power conductors that are connected to the breaker in your main panel will connect to the two power buses (bars) in your sub-panel. One wire to each. These power buses are what your breakers attach to. The 3rd main feeder line (should be coloured white) is for your neutral line. This is connected to the neutral bus in your main panel and then connected to the neutral bus at your sub-panel. Then comes the ground wire. This can be an uninsulated wire which can be run back to the main panel and then connected to the grounding buses or run to grounding rods at the sub-panel. The breaker at the main panel is sufficient to break the sub-panel. No main breaker is required at the sub-panel.

[This message has been edited by sheetmet (edited October 22, 2000).]
 
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