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Electrical Wire and Cable

Understanding Sub-Panels and Neutral Wires

Is it true that an uninsulated neutral is not allowed to be used with the power feed cable for a sub-panel? Electrical Panels with Neutral Wires and Ground Wires.

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Sub-Panels Require a 4-Wire Cable with an Insulated Neutral
Electrical Question: Is it true that an uninsulated neutral is not allowed to be used with the power feed cable for a sub-panel?

The main line coming into my home and my fathers home from the power company transformer to my main box is not insulated. There are 3 wires from the pole twisted 2 insulated and one that is not. So is this a Double Standard where the power company can do whatever they want?

This electrical question came from: Greg, a Homeowner from Durham, North Carolina.

Dave’s Reply:
Thanks for your electrical wiring question Greg.

Wiring a Sub Panel with an Insulated Neutral and Separate Ground

Application: Wiring a Sub Panel.
Skill Level: Intermediate to Advanced. This electrical wiring project is best performed by a Licensed Electrical Contractor, and is not recommended for Homeowners.
Tools Required: Electricians pouch of hand tools and the various power tools necessary for installing the sub-panel.
Estimated Time: Depends on the type and size of the panel and available access to the project area.
Precaution: Any existing electrical wiring within the immediate area that may interfere with the installation of the sub panel should be identified and turned OFF and Tagged if necessary. Working in an electric panel is dangerous due to arc flash hazards and the possibility of electric shock.
Notice: Installing additional electrical wiring and a sub-panel should be done according to local and national electrical codes with a permit and be inspected.

Understanding Electrical Panels with Neutral Wires and Ground Wires

Greg, the panel that you are referring to is a Sub-Panel, not a Main Panel, and there is a Big Difference which I will explain with the following example:

  • All single phase 240 volt Sub-Panels MUST have a 4-wire cable feed which must have a separate insulated neutral wire and a separate ground wire, which may be uninsulated.
  • The neutral wire used with the Main Panel overhead service feed from the electrical utility company is most always un insulated as you and your father observed. If the Main Service feed was underground then the neutral wire would be required to be insulated.
  • There is no Double Standard, and the power company cannot do whatever they want because they have electrical codes to follow as well. The only difference would be in some third world countries where they do not have established codes like we do here in the USA.

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This is a testing tool that I have had in my personal electrical tool pouch for years, and is the first test tool I grab to help identify electrical wiring. It is a Non-contact tester that I use to easily Detect Voltage in Cables, Cords, Circuit Breakers, Lighting Fixtures, Switches, Outlets and Wires. Simply insert the end of the tester into an outlet, lamp socket, or hold the end of the tester against the wire you wish to test. Very handy and easy to use.

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This is the first tool I grab to troubleshoot a problem with outlet circuit wiring. This popular tester is also used by most inspectors to test for power and check the polarity of circuit wiring.
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Strip Off Wire Insulation without Nicking and Damaging the Electric Wire!

The Wire Stripper and Wire Cutter
My absolute favorite wire stripping tool that I have had in my personal electrical tool pouch for years, and this is the tool I use to safely strip electrical wires.
This handy tool has multiple uses:
The wire gauges are shown on the side of the tool so you know which slot to use for stripping insulation.
The end of the tool can be used to grip and bend wire which is handy for attaching wire onto the screw terminals of switches and outlets..

The wire stripper will work on both solid and stranded wire. This tool is Very Handy and Easy to Use.

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FAQs Frequently Asked Questions and Comments

6 Responses to “Understanding Sub-Panels and Neutral Wires”
  1. Floyd Wickie says:

    I have a main panel that feeds a sub panel. On my subpanel I have a 220 volt 30 AMP ganged breaker feeding a Hot water tank. I am taking the hot water tank out and replacing with a gas hot water on demand. I want to use the this 220 as two 120 15 AMP circuits however cannot access my neutral from my sub panel BUT CAN access a neutral wire from my main panel. Can I have the two 120 power from Sub and neutral from Main panel. Alternative is to take one of the power lines from 220 in sub and put it on neutral in Sub to give me one 120 VAC 15 AMP circuit but would like to have two. Thanks in advance Floyd Wickie

  2. sean says:

    Kind of off topic but why does Electrical Sub-Panels Require a a Neutral wire if the loads are all 240 volts. Can you show the code article that requires neutral wire in all feeders? Thanks.

  3. Dave Rongey says:

    Hi Sean,
    Sub-panels may provide both 120/240 volt circuits, so a separate neutral and a separate ground conductor and their terminal strips are required.
    If the you are referring to a single 240 volt disconnect then a ground wire of the circuit is required but a separate neutral is not required unless the equipment requires a neutral.
    As for electrical codes, please see the following section of the website: Home Electrical Codes

  4. Rudy says:

    My main panel, the one with meter installed has a 100 AMP main breaker feeding a sub panel located in the garage. The info stamped on the wire from Main breaker to sub panel is kind of hard to read so having trouble finding its current carry capacity. I did find this on the inside of the sub panel door:

    Main Ckt Breaker
    1-1/0 CU-Al

    This sub panel has 16 places for single breakers it currently had 3 double pole and 8 combo 15 & 20 breakers installed. This leaves only 2 single or 1 double pole addition available.

    How do I determine the size of a replacement sub panel? My requirements for kitchen upgrade calls for 6 dedicated circuits. Worried if I expand the existing sub panel to include the needed circuits the main will be under rated for my new sub panel.

  5. Dave Rongey says:

    Hi Rudy,
    The information about the sub panel that you have described is the maximum amperage rating allowed for that panel, however you have discovered that the panel is being supplied with 100 amps, so that is the maximum capacity of the sub panel. Next, you will need to determine how much ampacity is available from the sub panel by determining what the existing circuits are being used for. It would be helpful to measure the amperage load of the panel using a clamp on amp meter, however the load will fluctuate depending on what the circuits are being used for. Even though there will be 6 dedicated circuits for the kitchen project all of these circuits will not be at maximum capacity at the same time. Depending on the project, some of these new circuits may be replacing existing circuits, so you should keep this in mind. Much will need to be considered to really understand if an additional panel may be installed, or if the main panel will need to be upgraded to a larger size. Evaluating the existing panel and circuit loads, the additional circuits to be added for the kitchen, and the size of the home and any future circuits to be installed will reveal what your electrical service size should be.
    I hope this helps,

  6. Stan says:

    I work for an electric utility and we go by the NESC (National Electrical Safety Code) which does NOT specify minimum wire sizes as NEC requires. It’s not a double standard as we wore to demand and not maximum demand. Hope this clears up any confusion.