Help troubleshooting a load center

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  #1  
Old 10-14-07, 05:13 PM
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Help troubleshooting a load center

Since this is my first post on this forum I'll make it an easy one for you guys!

I decided to add a 220 outlet to my garage to run my welders. My welders are wired for 3 wire dryer plugs.

I hired an electrician who charged $250 dollars and installed a 3/4" nipple, 50 amp dual pole square D breaker and a dryer outlet.

This setup worked fine but I decided I wanted to add a 30 amp 110 RV outlet to the mix. I pulled the 50 amp breaker from the main panel and opted to install a load center in my garage.

The load center mounted perfectly on the drywall right behind the main box so I utilized the same nipple to run the wires through.

I installed a 100 amp dual pole breaker and wired as you see here. One hot to each of the breakers and the 3rd wire to the grounding block in the main panel to the grounding block in the load center utilizing black 2 guage wire.

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In the load center I took each of the hots from the breakers and installed them to the two hot poles in the panel as you can see here:

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Like I mentioned I connected the grounding block in the main panel directly to the grounding block in the load center.

At this point in time I tested the voltage across the two main lugs in the load center and registered roughly 120 volts. so far so good I think.

I then wired the 3 wire dryer outlet to the 50 amp dual pole breaker which I installed in the 3rd and 4th position of the load center and the white wire on the top left to the grounding block as seen here:

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After that, I installed a 30 AMP RV outlet to a 30 amp 110 breaker installed in the 5th position. I wired a hot to the breaker, and a green and a white both side by side on the grounding block.

I buttoned it all up, and when I turned on the 100 amp breaker in the main panel I saw a spark, heard a loud pop which is when I shut the 100 amp breaker and this is where it stands now. I noticed a burn on the load center where the nipple enters as seen here:

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I looked all over for a short in a wire somewhere but this is all new wire and I was very careful not to leave anything exposed and there are no rough edges to rip the wire.

I am open to any and all suggestions.

Is the position of the breakers in the load center effecting anything?

Have I run the wires improperly?

How do I fix this???


Thank you one and all for your suggestions...

Steve
 
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  #2  
Old 10-14-07, 05:16 PM
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What size wire do you have feeding into that 100amp breaker for starters?
 
  #3  
Old 10-14-07, 05:21 PM
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2 guage wire to the 100 amp breaker and grounding strip.
 
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Old 10-14-07, 05:25 PM
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Try an ohmeter (analog) and take a reading from one hot lug to the other and each hot lug to ground. Both of these readings should show as open or infinite resistance.
 
  #5  
Old 10-14-07, 05:29 PM
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In your photos, I see that you used three black wires instead of two black and one white. Are you sure that you didnt mix one of the hots with what is supposed to be a neutral.
 
  #6  
Old 10-14-07, 05:30 PM
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I only have a digital meter. I have a Ideal Split Jaw smart meter. Can I test the resistance with this as you described? what reading am I looking for?

I assume I should take this resistance reading with the 100 amp breaker shut off?

Does the wiring configuration look correct from what you guys can tell from my photos?
 
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Old 10-14-07, 05:34 PM
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Subpanels require 4 wire cabling, and from what I can see, you only have two hots and a ground.

Ground buss and neutral buss need to be seperated and not bonded to each other in the subpanel.

I'm not an electrician, so hang in there for a some more knowledgable people to respond.
 
  #8  
Old 10-14-07, 05:35 PM
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Originally Posted by Rollie73 View Post
In your photos, I see that you used three black wires instead of two black and one white. Are you sure that you didnt mix one of the hots with what is supposed to be a neutral.

This is a possibility. I will go double check right now.
 
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Old 10-14-07, 05:38 PM
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Originally Posted by EscaladeSteve View Post
This is a possibility. I will go double check right now.
Ok I just used a tone generator to confirm I reversed one of the hots with the ground. Basically I connected the ground block on the load center to one of the hots on the 100 amp breaker. not cool!!!

One problem down, one more to go.

Do I need to add a 4th wire to the load center?

There is only one ground block and I dont see anywhere to put a neutral.

Can anyone clear up this mystery?
 
  #10  
Old 10-14-07, 05:39 PM
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Yes you can read resistance with the digital meter, as long as it has an ohm setting. You are looking for a reading of high resistance, numbers that wont stop jumping up or down, or a symbol like OL ( my fluke meter shows OL which is for something like open line).

The wiring configuration appears fine except for the fact that you may have crossed a hot with a neutral due to the fact that you used all black wires ( should have used at least white tape on the neutral )
 
  #11  
Old 10-14-07, 05:42 PM
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Originally Posted by Rollie73 View Post
Yes you can read resistance with the digital meter, as long as it has an ohm setting. You are looking for a reading of high resistance, numbers that wont stop jumping up or down, or a symbol like OL ( my fluke meter shows OL which is for something like open line).

The wiring configuration appears fine except for the fact that you may have crossed a hot with a neutral due to the fact that you used all black wires ( should have used at least white tape on the neutral )
Dwayne, you hit it on the head, I reversed two wires. Thank you guys for your assistance. Next time I'll mark my wires a bit better!
 
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Old 10-14-07, 05:46 PM
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Originally Posted by HotinOKC View Post
Subpanels require 4 wire cabling, and from what I can see, you only have two hots and a ground.

Ground buss and neutral buss need to be seperated and not bonded to each other in the subpanel.

I'm not an electrician, so hang in there for a some more knowledgable people to respond.
Correct, however this would not cause a short that would trip a breaker. The fourth wire is for equipment ground and must not be bonded to the neutral.

Yes you need to add a fourth wire. The block you are refferring to as a grounding block is actually a neutral bar. The neutral wires (white) should go to this.

You may need to add a grounding bar to the subpanel but be sure that the neutral and the ground bar are not bonded together. Do the same ohm/ resistance check and make sure you get an Open Line or similar reading.
 
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Old 10-14-07, 05:50 PM
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Glad I could help, but please see my previous reply and add the fourth wire, but make sure its green, mix ups could be very serious and cause bodily harm or even kill someone.
 
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Old 10-14-07, 06:11 PM
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Originally Posted by Rollie73 View Post
Glad I could help, but please see my previous reply and add the fourth wire, but make sure its green, mix ups could be very serious and cause bodily harm or even kill someone.
Ok so what I have in the load center now is a nuetral bar.

I need to order an add on ground bar, where do I wire that to?

In the main panel there is only one bar which is connected to copper which runs into the ground.
 
  #15  
Old 10-14-07, 08:08 PM
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If you measured 120 volts between your two hot wires then you found the problem yourself. You should have measured 240 volts between your two hot wires. You mixed up the wires.

Your installation is not legal in several ways. You should have used two black wires (or some other legal color for hot), one white wire for the neutral and a green or bare wire for the ground.

Further, you need a separate ground and neutral buss in your load center. The ground and neutral MUST be separated here.
 
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Old 10-14-07, 09:25 PM
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At this point in time I tested the voltage across the two main lugs in the load center and registered roughly 120 volts. so far so good I think.
Should have been 240v. Sounds like you have a neutral or ground where one of the hots should be.
 
  #17  
Old 10-14-07, 09:35 PM
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Ok so my question now is:

1. Why doesnt my load center have a neutral bar and a ground bar?

2. Why doesnt my main panel have a nuetral bar and a ground bar?

I'm not doubting that I need to seperate them but how do I do it?

Also I did reverse two of the wires and thanks to the assistance here I have corrected the problem and everything works now. I would like to add the 4th wire but need to know how to do it. Any assistance is appreciated.

As far as the wire coloring, it definately would have helped in this case, but my understanding is thicker than 6 guage color coding is not a requirement. Am I wrong on this?

Originally Posted by racraft View Post
If you measured 120 volts between your two hot wires then you found the problem yourself. You should have measured 240 volts between your two hot wires. You mixed up the wires.

Your installation is not legal in several ways. You should have used two black wires (or some other legal color for hot), one white wire for the neutral and a green or bare wire for the ground.

Further, you need a separate ground and neutral buss in your load center. The ground and neutral MUST be separated here.
 
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Old 10-14-07, 11:13 PM
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The black for neutral should have been re-designated with white tape on both ends.

In the subpanel the neutral must be isolated from the box and the ground bar bonded to the box. At the main panel is the only place ground and neutral or joined together. One wire bare or green goes from the main neutral (or ground bar if present) to the bonded ground bar of the subpanel. One wire white goes to the isolated neutral of the subpanel.

The sub panel neutral may have a screw or strap bonding it. This must be removed. Often you must add a ground bar. They make them specifically for the box you have. The panel should have threaded holes for fastening it.
 
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Old 10-15-07, 03:05 AM
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Originally Posted by EscaladeSteve View Post


As far as the wire coloring, it definately would have helped in this case, but my understanding is thicker than 6 guage color coding is not a requirement. Am I wrong on this?
Yes, the requirement states that no wire smaller than #6 can be re-identified, ie you must use the correct color insulation, not tape or paint.

Wire must always be identified to prevent the problem that you had.
 
  #20  
Old 10-15-07, 04:24 AM
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At one, and only one, place in your setup the neutral and ground are connected together. This is usually at the main panel. When this occurs at the main panel, the installed buss bars are used interchangeably, with grounds and neutrals connected to the same bars.

At sub panels and any other place (away from the main panel) the grou8nd and neutrals must remain separated. Most panels do not some with separate buss bars, to keep the cost down and because the panel may be used where the ground and neutral are the same. This means you must add a ground buss.

When you add a ground buss, the original neutral buss must NOT be bonded to the main panel, This usually involves removing and not using the green bonding screw that comes with the panel.
 
  #21  
Old 10-15-07, 07:32 AM
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Using a 3/4 nipple for three #2 conductors is very bad practice, possibly a reason for a Code violation if the work was inspecteed.

I notice there are reducing-washers behind the 3/4" lok-nuts, which suggests a 1" "KO" was punched out of the rear of the enclosure.

You will need a 1" nipple ( mininimum) between the two enclosures , because you will have to add an Equiptment Grounding Conductor to the three 100 amp conductors. I suggest you remove the 3/4 " nipple, and fit in a 1" nipple.

Also, be certain to thread 1" plastic bushings on the two ends on the 1" nipple to "cushion" the conductors from contact with the sharp ends of the nipple.

I always "over-size" boxes and nipples-- I would never reduce a 1" KO to 3/4" when fitting a nipple between two enclosures . Possibly the electrician who punched out the KO didn't have a 1" nipple "on hand"- if he did, he should have used it.
 
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