trentw7231 Posted August 10, 2013 Report Posted August 10, 2013 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. Click to Enlarge 76.83 KB
Marc Posted August 10, 2013 Report Posted August 10, 2013 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
Jim Katen Posted August 10, 2013 Report Posted August 10, 2013 Marc summarized the issues well. I'll just add that those terminals are not ok for two wires unless there is some kind of marking on the equipment to indicate that. The real problem, though, is that the house has outgrown the panel.
Brandon Whitmore Posted August 10, 2013 Report Posted August 10, 2013 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"...
Jim Port Posted August 10, 2013 Report Posted August 10, 2013 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.
Marc Posted August 10, 2013 Report Posted August 10, 2013 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"... Yeah, I agree but I can't put a finger on it. How should I have said it? My mind works funny sometimes. Marc
Tom Raymond Posted August 10, 2013 Report Posted August 10, 2013 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.
Jerry Lozier Posted August 10, 2013 Report Posted August 10, 2013 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???
Brandon Whitmore Posted August 10, 2013 Report Posted August 10, 2013 Yeah, I agree but I can't put a finger on it. How should I have said it? My mind works funny sometimes. Marc Ampacity Chart
Marc Posted August 10, 2013 Report Posted August 10, 2013 Yeah, I agree but I can't put a finger on it. How should I have said it? My mind works funny sometimes. Marc Ampacity Chart Still 20 amps. See 240.4 (D) (5), though I did forget about that table. Marc
Jim Katen Posted August 10, 2013 Report Posted August 10, 2013 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.
Jim Katen Posted August 10, 2013 Report Posted August 10, 2013 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.
Jim Port Posted August 10, 2013 Report Posted August 10, 2013 If the detached structure is feed by a single circuit it does not require a grouding system. A MWBC is one circuit for this example.
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