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10 guage run to 100 amp fused subpanel


trentw7231

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Check out the picture. Here is the scenario. The subpanel has a 30 amp breaker in the main panel and 10 AWG run to the fused Subpanel rated at 100 AMP. The neutrals are not isolated and there is 12 AWG going to 25 AMP fuses. Some are double tapped. Questions: What is the minimum size wire that should be run to the subpanel and what about the double taps. Am I correct that there is overfusing and the neutrals are not isolated? Hope someone can advise.

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The feeder supplying the sub with power should be sized to meet the electrical loads connected to that sub. The breaker on the main panel that serves the feeder which goes to the sub should be sized to protect that feeder from damage. The sub should be rated no less than the breaker supplying it with power.

A 25 amp breaker is too large to protect a 12 gauge conductor. It should be no more than 20 unless it's for an appliance having motor loads and the nameplate allows those ampacity and breaker values.

A 120/240 sub-panel should be served by 4 conductors.

Neutrals should be kept separate from EGC's in a sub-panel.

I don't know if those terminals are listed for double tapping.

Marc

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A three wire feeder installed before the adoption of the 2008 NEC was allowed provided no other metallic path was between the buildings. The neutrals were again re-bonded like a service panel.

Yes, but:

1. That assumes separate structures, and

2. It requires it's own GEC. The OP doesn't have one.

It's wired incorrectly. It's too small. It's obsolete. Three strikes, call for replacement.

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A three wire feeder installed before the adoption of the 2008 NEC was allowed provided no other metallic path was between the buildings. The neutrals were again re-bonded like a service panel.

The 100 amp rating is the maximum that it can be supplied by.

Jim:

aren't 3 wire subpanels also limited to no more than one branch circuit???

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A 25 amp breaker is too large to protect a 12 gauge conductor.

Marc,

I don't think this is what you meant to "say"...

Actually, I think it's correct. While #12 wire might have a higher ampacity, it should always be "protected" at 20 amps. Even in the case of some motor loads, where the motor provides some of that protection.

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A three wire feeder installed before the adoption of the 2008 NEC was allowed provided no other metallic path was between the buildings. The neutrals were again re-bonded like a service panel.

The 100 amp rating is the maximum that it can be supplied by.

Jim:

aren't 3 wire subpanels also limited to no more than one branch circuit???

No. You're thinking of the rules that allow a single branch circuit in a detached building to have no grounding electrode system and be served by only a single snap switch.

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