Terminating oversized motor leads.

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J. Hofstetter

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Berne, Indiana, USA
I am putting together a sand and gravel plant that is stretched out over a pretty long distance. A couple of the conveyor motors are reaching out to 1500' from the MCC. We've done all the calculations to compensate for voltage drop which has increased the wire significantly from what it would be if the motors were within any reasonable distance. Now it's time for terminating the motor leads. I was taught a long time ago that the first few feet from the motor starter and the last few feet to the motor that I could size the wire to the load without concern for voltage drop, which is pretty handy because most generally you can't fit the oversized motor leads in the motor starter lugs without cutting few stands off. This has always worked with no issues, but what is the actual code rule that allows this (if any)?

Thanks,
 
J. Hofstetter said:
I am putting together a sand and gravel plant that is stretched out over a pretty long distance. A couple of the conveyor motors are reaching out to 1500' from the MCC. We've done all the calculations to compensate for voltage drop which has increased the wire significantly from what it would be if the motors were within any reasonable distance. Now it's time for terminating the motor leads. I was taught a long time ago that the first few feet from the motor starter and the last few feet to the motor that I could size the wire to the load without concern for voltage drop, which is pretty handy because most generally you can't fit the oversized motor leads in the motor starter lugs without cutting few stands off. This has always worked with no issues, but what is the actual code rule that allows this (if any)?

Thanks,
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The code rule is that the wire simply needs to be sized for the ampacity requirements. Voltage drop isn't required to be controlled in the NEC, although the NEC does contain recommendations and equipment or job specs might have specific requirements.


The voltage drop of a heterogeneous conductor assembly is simply calculated through the total resistance of the circuit. Each resistance of each constituent run of conductor adds up directly as resistances in series, to get the total resistance. Since 6 ft of a small local conductor is insignificant compared to 300 ft of the main conductor run, it will not contribute significantly to the voltage drop. You can calculate it if you desire, and see how it affects overall voltage drop.
 
just the cowboy said:
If you look at a MCC bucket the conductors from the starter to the term strip are just load sized not VD sized.
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Yes, that is why the bucket is listed as a assembly.
But I do find it interesdting as tyo why the OP has changed included that the motor manufacturer arbitrarily oversized the conductor though. Oversize is a ambiguous reference with no basis..
 
J. Hofstetter said:
I am putting together a sand and gravel plant that is stretched out over a pretty long distance. A couple of the conveyor motors are reaching out to 1500' from the MCC. We've done all the calculations to compensate for voltage drop which has increased the wire significantly from what it would be if the motors were within any reasonable distance. Now it's time for terminating the motor leads. I was taught a long time ago that the first few feet from the motor starter and the last few feet to the motor that I could size the wire to the load without concern for voltage drop, which is pretty handy because most generally you can't fit the oversized motor leads in the motor starter lugs without cutting few stands off. This has always worked with no issues, but what is the actual code rule that allows this (if any)?

Thanks,
Click to expand...
cutting a few strands off to fit the terminals is not an option that is code compliant. If conductor is too large for the terminal you need to reduce it by approved methods, you may need additional splice box to do this in if there is not room in the enclosure you are terminating in.
 
templdl said:
Yes, that is why the bucket is listed as a assembly.
But I do find it interesdting as tyo why the OP has changed included that the motor manufacturer arbitrarily oversized the conductor though. Oversize is a ambiguous reference with no basis..
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The word "oversize" to me, means that the conductor is sized larger than the minimum size it needs to be, for ampacity reasons alone.
 
Carultch said:
The word "oversize" to me, means that the conductor is sized larger than the minimum size it needs to be, for ampacity reasons alone.
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That would be an assumption. Isn't interesting that the motor manufacturer "oversized" the wire? It is as interesting that the OP has avoided providing any actual information regarding what specifically the wire size was and what he thought it should be.
 
templdl said:
That would be an assumption. Isn't interesting that the motor manufacturer "oversized" the wire? It is as interesting that the OP has avoided providing any actual information regarding what specifically the wire size was and what he thought it should be.
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OP said the run was in the 1500 foot range and the supply conductors were "oversized" for voltage drop reasons. I don't see anything in OP about the motor manufacturer oversizing leads on the motor.
 
kwired said:
OP said the run was in the 1500 foot range and the supply conductors were "oversized" for voltage drop reasons. I don't see anything in OP about the motor manufacturer oversizing leads on the motor.
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I was going by "Terminating oversized motor leads" not branch circuits conductor size. But I agree with you.
 
Carultch said:
The code rule is that the wire simply needs to be sized for the ampacity requirements. Voltage drop isn't required to be controlled in the NEC, although the NEC does contain recommendations and equipment or job specs might have specific requirements.


The voltage drop of a heterogeneous conductor assembly is simply calculated through the total resistance of the circuit. Each resistance of each constituent run of conductor adds up directly as resistances in series, to get the total resistance. Since 6 ft of a small local conductor is insignificant compared to 300 ft of the main conductor run, it will not contribute significantly to the voltage drop. You can calculate it if you desire, and see how it affects overall voltage drop.
Click to expand...
As further evidence of this concept, look at the size of the conductors used in the WINDINGS of the motors next time you get a chance! Yet no matter what you do OUTSIDE of the motor, those never change.
 
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