Table 250.122

mbrooke

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*
If they ever adopt what is in that table, current cables with 6 AWG conductors and 10 AWG EGC's would have to be made with 8 AWG EGC's. Then we are possibly stuck with needing to change out anything existing that had 10 AWG in some situations.

Might be other larger cables with similar issues.

You bring up a good point- I noticed that as well.

In Canada #6 is typically accompanied with number 8 if my interpretation of their code is correct.

Being honest (I know I'll get roasted for this) I personally have always felt that some EGCs were undersized like #6 for a 200 amp OCPD.
 

kwired

Electron manager
Location
NE Nebraska
You bring up a good point- I noticed that as well.

In Canada #6 is typically accompanied with number 8 if my interpretation of their code is correct.

Being honest (I know I'll get roasted for this) I personally have always felt that some EGCs were undersized like #6 for a 200 amp OCPD.
Without some studies I really couldn't tell if that is sufficient or not. For shorter circuit lengths I would guess it is sufficient, but have no clue on how long it must be to start becoming a problem.
 

infinity

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New Jersey
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Journeyman Electrician
For large services the minimum neutral size is 12.5% same would apply to the main bonding jumper. Also for a large transformer the system bonding jumper minimum size of 12.5% so somewhere along the way they figured out that this number would be enough to handle the fault current.
 

mbrooke

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For large services the minimum neutral size is 12.5% same would apply to the main bonding jumper. Also for a large transformer the system bonding jumper minimum size of 12.5% so somewhere along the way they figured out that this number would be enough to handle the fault current.
Yes, but remember length plays a role.
 

mbrooke

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Without some studies I really couldn't tell if that is sufficient or not. For shorter circuit lengths I would guess it is sufficient, but have no clue on how long it must be to start becoming a problem.
Anything beyond a 1 second disconnection time under 150 volts but over 60 volts to ground is a no go in my book, and anything over 35 cycles above 150 volts to ground but not over 250 volts to ground should be limited. No more than 15 cycles for 300 volts to 500 volts to ground.
 

kwired

Electron manager
Location
NE Nebraska
Anything beyond a 1 second disconnection time under 150 volts but over 60 volts to ground is a no go in my book, and anything over 35 cycles above 150 volts to ground but not over 250 volts to ground should be limited. No more than 15 cycles for 300 volts to 500 volts to ground.
Ungrounded conductor size and length also factors into overcurrent device clearing time you possibly still could have longer clearing time even with a EGC that is larger than ungrounded conductors on a long run.
 

mbrooke

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Ungrounded conductor size and length also factors into overcurrent device clearing time you possibly still could have longer clearing time even with a EGC that is larger than ungrounded conductors on a long run.
Very true.

I think what the code ultimately needs to do is implement distance restrictions for any particular wire size.
 
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