Giving the 600MCM a Haircut

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Dean83169

Dean83169

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I had to comment on something I found upon opening up a 2500 split MDP. I found upon installing my feeders that the previous contractor, had pulled 600's and the lugs where only for 500 so they decided to cut the entire outer strands of the cable off. I raised this issue to the building owner who then called the contractor back and upon him looking at it he then tells us that this isnt the first time they have done this and that it was an engineering problem and that there isnt any code violation or safety hazard but if we felt better he would be highpress the 600 to 500 stud reducers on. I had one of my employers tell me to do the same thing years ago, I told him if he wants to he can do it himself, how many others have done this or encountered this? What are people thinking?
 
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Dean83169 said:
I found upon installing my feeders that the previous contractor . . . had pulled 600's and the lugs where only for 500 so they decided to cut the entire outer strands of the cable off.

. . . if we felt better he would be highpress the 600 to 500 stud reducers on.
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My first thought is what is the difference between the reduced diameter of the trimmed consuctor and the diameter of the reducers? Would the strands remaining not be equal to the stud because they're strands? Or because the missing strands are not terminated?

The strands certainly have intimate contact along the conductor length. Please understand, I'm not condoning, just postulating. If the reducer's stud is equivalent to 500 MCM, are the remaining strands also equivalent? Is the OCPD sized to protect the smaller resultant conductor size?
 
The most common reason to use high press reducers is because the wire size has been up sized for voltage drop reasons and the reduced size at the terminal still will have enough capacity to carry the load.

On the other hand if the load needs the 600s than reducing them down with a high press or a 'hair cut' is a problem.

The way to handle this is to order new lugs for the breaker that will handle 600s if the load needs the capacity of 600s.
 
Inspectors here will tag you for it.The wire is rated based on all of the strands and there simply is no way to rerate what you have left.Buy larger lugs or compress.
 
Since electrons move over the skin of the conductor, isn't a potential hot spot created at the trimmed outer strands?
 
chris kennedy said:
Since electrons move over the skin of the conductor, isn't a potential hot spot created at the trimmed outer strands?
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Electrons move throught the entire conductor. The current density in the conductor is not constant and is affected by the frequency of the current, the diameter of the cable (not the individual strands), and the proximity to similar electromagnetic fields.

Removing strands makes a smaller conductor. Smaller conductors can not carry the same amount of current without an increase in temperature.
 
Jim, isn't the path of least resistance on the skin because there are more free electrons present ? Do you have a link explaining how current is present in the whole conductor? Thanks for the help.
 
chris kennedy said:
Jim, isn't the path of least resistance on the skin because there are more free electrons present ? Do you have a link explaining how current is present in the whole conductor? Thanks for the help.
Click to expand...

Electricity does not take the path of least resistance - it takes all paths but in different amounts.

Skin Effect is primarily a function of frequency and has very little effect at 60hz. Proximity Effect should be of more concern but even it is not a big deal except in segregated phase systems.
 
As said above, trimming reduces the AWG to an undetermined size, and gets a red sticker.

With the reducer lugs. mfg info stated the amperage rating has to be reduced because of the use of the reducer. I had a similar situation with a 'new style' Sq D MCB that ONLY came with 500 lugs; after many phone calls, NO lugs larger than 500's were available for the 'new style' cb.

Luckly, the OCP was adjustable, and we reduced (crimps) down to 500's & all was good.

John
 
We see this ALL THE TIME, I have loads of pictures taken of this practice as part of our IR scans. I never understood why, when the correct parts are available, but it is done.


I won't do it, I do not condone my employees doing it.


As for the wire size reducers (Mac Adapts), these are one of the more common IR discrepancies we see. Not sure if the contractors utilize the wrong crimp tool, improperly install the reducers, or if this is just a problem product.
 
Only God can give 600mcm haircut's and even then the inspector would say "prove it to me" and God would reply "good call -just wanted to be sure you were looking" and he would make the appropriate correction [and assign that inspector an extra 5 in purgatory.]
 
I have seen conductors with a "haircuts" a couple of times. I have also seen just the opposite. Someone has a terminal lug thats a bit to large so they use excess copper wire, shove it into the lug for a tight fit, then crimp it. This is also poor workmanship in my mind although Im not sure that it will have any detrimental effects electrically speaking. Bottom line, use the right size lug for the cable.
 
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