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Help with Sevice Entrance Cable size


Bryan
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I need help confirming my findings regarding the service entrance cable on today's inspection. The breaker is 100 amps being fed by number 4 TWH copper. My understanding, per code check, a number 4 service conductor wire size should be protected a 100 AMPS, and therefore, this set up should be adequate. Is my thinking along the correct path.

Thanks in advance Bryan

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Hi Bryan,

From Table 10 in 5th Edition of electrical code check, #4 Cu THW (not TWH) is rated for 100 Amps. The other Tables, 11-14, take into account allowable ampacities, ambient temperature correction, adjustments for conduit exposed to sunlight, and derating for condutor proximity.

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Thank you for the quick responses.

Bryan

Hi Bryan,

Just food for thought...per your post, how does the 100-amp breaker protect those #4 service entrance cables?

Jerry,

The breaker limits the amount of current that can be drawn through the service cables by the system, no matter which side it is on.

It won't do anything for a short on those cables before the breaker, no matter how improbable but at that point the transformers limit protection should take over.

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