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hhsting

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Glen bunie, md, us
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I have 3 sets of 500kcmil service conductors into main service disconnect MSB. The MSB main bonding jumper provided is #3/0 awg copper.

Engineer argument is table 250.66 note #2 applies and since their is no service entrance conductor the largest ungrounded conductor is 500 kcmil

Some how i think note #1 table 250.66 applies but their is no service entrance conductor.

Does anyone know in the above situation should MBJ be #3/0 awg or some other size? If other size then what and based on which code section table?
 
hhsting said:
I have 3 sets of 500kcmil service conductors into main service disconnect MSB. The MSB main bonding jumper provided is #3/0 awg copper.

Engineer argument is table 250.66 note #2 applies and since their is no service entrance conductor the largest ungrounded conductor is 500 kcmil

Some how i think note #1 table 250.66 applies but their is no service entrance conductor.

Does anyone know in the above situation should MBJ be #3/0 awg or some other size? If other size then what and based on which code section table?
Click to expand...
Note #1 is for "sets" which means each would feed a separate disconnect. Sounds like you have 3 conductors in parallel.

Can you be more specific about why there are - or you think there are - no service entrance conductors?
 
MBJs are sized by 250.102, not 250.66.
If you have parallel 500's,Cu, 3 per phase, then 3/0 would not be sufficient per Note 1 to Table 250.102(C)
 
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If the 3 sets of 500's are in parallel your largest service entrance conductor is 1500 kcmil.
 
electrofelon said:
Note #1 is for "sets" which means each would feed a separate disconnect. Sounds like you have 3 conductors in parallel.

Can you be more specific about why there are - or you think there are - no service entrance conductors?
Click to expand...

Service point is at the line side terminal of the main service disconnect
 
hhsting said:
Service point is at the line side terminal of the main service disconnect
Click to expand...
If you have 3 sets of 500 going into a main disconnect for the service then you have service conductors. The engineer is incorrect. Now a few code cycles ago the MBJ was sized the same as 250.66 but they moved the MBJ as well as other jumpers and grounded conductor to T250.102(C)(1)
 
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