Jump to content

10 guage run to 100 amp fused subpanel


Recommended Posts

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
tn_20138921814_102.jpg

76.83 KB

Link to post
Share on other sites

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

Link to post
Share on other sites

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

Link to post
Share on other sites

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.

Link to post
Share on other sites

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???

Link to post
Share on other sites

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.

Link to post
Share on other sites

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.

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...