Multiple conductors under one lug

Status
Not open for further replies.
T

Titus

Member
I have an existing main lug panel 225a that also has a #4 wire under each phase (lug) feeding a subpanel. Is this permissable? I've been unable to find in the NEC>:confused:
 
There are two issues here.

The first is whether it is acceptable to put more than one conductor under a lug. All the NEC will tell you is that you must do what the manufacturer says to do. So it boils down to whether the manufacturer has said that the equipment is good for multiple conductors under one lug.

The second issue is whether it is acceptable to use #4 wire (rated 85 amps) to feed the sub-panel, given that the feeder to the larger panel is protected by a 225 amp breaker. The answer depends on whether you satisfy the tap rules in 240.21B. We would need more information about the installation, before we can tell for certain.
 
Probably not permissible. The lugs needs to be rated for more than one conductor which I would guess that they're not. Look at 110.14(A).
 
What size breaker feeds mlo panel.That may be your first problem, over fusing the #4. The next question would be what does the #4 wire feed ? If its a tap then the question would be how far?
 
Last edited:
charlie b said:
There are two issues here.

The second issue is whether it is acceptable to use #4 wire (rated 85 amps) to feed the sub-panel, .
Click to expand...

Off topic here Charlie. Just trying to get my head around something. When it's said that #4 is good for 85 amps based on 75deg, doesn't 110.14(a) say 4awg should be used for only the 60deg column or does the 3rd point in that article where it says "conductors with higher temp rating if the equiptment is listed and identified for use with such conductors" mean as long as a subpanel (in this case) lugs are identified for 75deg column that 85amps is ok?

Thanks
 
Dexie123 said:
Off topic here Charlie. Just trying to get my head around something. When it's said that #4 is good for 85 amps based on 75deg, doesn't 110.14(a) say 4awg should be used for only the 60deg column or does the 3rd point in that article where it says "conductors with higher temp rating if the equiptment is listed and identified for use with such conductors" mean as long as a subpanel (in this case) lugs are identified for 75deg column that 85amps is ok?

Thanks
Click to expand...


Almost all lugs are now rated for 75 degrees C. 110.14(C)(1)(a)(3) would allow you to use the 75 degree rating for a #4 lug.
 
infinity said:
Almost all lugs are now rated for 75 degrees C. 110.14(C)(1)(a)(3) would allow you to use the 75 degree rating for a #4 lug.
Click to expand...

Except that the panel is existing and we have no idea how old it is.
 
Dexie123 said:
. . . or does the 3rd point in that article where it says "conductors with higher temp rating if the equiptment is listed and identified for use with such conductors" mean as long as a subpanel (in this case) lugs are identified for 75deg column that 85amps is ok?
Click to expand...
I agree with Trevor's answer:
infinity said:
Almost all lugs are now rated for 75 degrees C. 110.14(C)(1)(a)(3) would allow you to use the 75 degree rating for a #4 lug.
Click to expand...
 
The 225A panel in question is an old Sq D which is fed with rag wire.
The #4 to the sub panel is THW and falls within the 10' tap rule.

However, based on the requirements of the lugs in the panel, and as per NEC 110.14 for dissimilar conductors I think I have some leverage. I know the THW contains copper conductors but I think the rag wire is copper-clad. If so per 110.14 it will not work. I'll need to investigate further.
 
infinity said:
Almost all lugs are now rated for 75 degrees C. 110.14(C)(1)(a)(3) would allow you to use the 75 degree rating for a #4 lug.
Click to expand...

Actually the temperature rating of the lug itself is not important (today most lugs are rated 90?C). What is important is the rating of the termination point which includes the lug and the equipment it is connect to. Many people wrongly believe they can simply change lugs in order to achieve a higher temperature rating.
 
OK so what abot lugs in older panels or breakers in older panels marked with40c . so how do you calculate the wire ampacity for 40c. I have often wondered about this when working in older panels. also if there is no temp marking on the panel,lugs or breakers would you then use the 60c rating for calulation purposes?
 
Forget temperature. How do you get around 110.14(A)? I don't believe that older panels had there lugs identified for use with more than 1 conductor. If you change lugs wouldn't violate the U.L. listing of the panel? My suggestion would be install a new breaker to feed the the load that the number 4 's are going to.
 
Riograndeelectric said:
OK so what abot lugs in older panels or breakers in older panels marked with40c . so how do you calculate the wire ampacity for 40c. I have often wondered about this when working in older panels. also if there is no temp marking on the panel,lugs or breakers would you then use the 60c rating for calulation purposes?
Click to expand...

I have never seen terminations rated 40?C. Maybe you are confusing the ambient air rating of circuit breaker and enclosures with that of the termination/conductor rating?
 
Status
Not open for further replies.
Top