By Dave Rongey Summary: Electrical Sub-Panel wiring considerations for the home complete with pictures. Careful planning for your Sub-Panel with immediate and future load considerations will help you understand how to size your Sub-Panel. This information will help as you consider a Sub-Panel and its size.
Check Out What Others Are Sharing at Ask the Electrician: Great website, especially if you don't think there's a need to pay an electrician for a potentially minor job. Garret from Shercock, UK
120 volt devices
Lighting
Electrical Convenience Outlets
GFCI Protected Outlets
240 volt equipment
Motor Loads:
Hot Tubs [see the Hot Tub Page]
Well Pumps
Air Conditioners
Sub-Panel Considerations-
Correct amperage for all existing loads and future requirements.
Considerations to help determine Sub-Panel Circuit Requirements:
Important Factor: Find out if the Main Service or the Panel that will supply the Sub-Panel Circuit have adequate Load Capacity and space for the needed circuit breaker.
How big should your Sub-Panel be ? (Watts and Amperage)
This will help you consider the circuits to be served by the Sub-Panel including general purpose electrical outlets and any special equipment which will be needed.
Special Considerations:
Large 220 Volt Loads such as Welders, Air Conditioners, Motors, Well Pumps and the like may require larger size wire and conduit to provide the necessary current this equipment requires. Be sure to list all the label requirements and manufacturers specifications. Long Distances from the power source will produce Voltage Drop, especially over 175 feet. A 2% Voltage drop factor and correction will most likely require an increased size of the wire and conduit.
How to Wire Grounds and Neutrals in Sub Panels – all the neutrals and ground wire and terminal bars must be separated from each other, and your sub feed should be a 4-wire cable that has a separated insulated neutral wire and a separate ground wire.
Understanding Grounding for Sub Panels: When you add a second electrical panel with separate neutral and common bars, do you ground the common to the box along with a ground rod connection?
Planning and Installing a Garage Sub Panel: Do This Before Installing a Garage Electrical Panel, Check the Main Panel, Select the Wire Type and Wiring Method, Check the Wiring Path, Outlets and GFCI Requirements, Electrical Code Compliance.
Planning for an Electric Sub Panel: Identifying Panel Circuits and Connected Loads. Sub Panels are installed and used for several reasons including expanding the circuit breaker capacity of the main electrical panel.
Learn more about How to Wire Circuit Breakers and Panels Perfect for Homeowners, Students and Electricians Includes: Home Electrical Circuit Breakers 120 Volt Circuits 240 Volt Circuits Multi-Wired Circuits Wiring Methods for Installing Electrical Circuit Wiring Electrical Codes for Home Electrical Wiring ....and much more. Be Sure to Get Your Copy!
Questions about Sub-Panels
Questions about Wiring Panels
Let Us Hear Your Question!
Roger in Virginia asks: Is the Wire Size to my Sub Panel Too Small?
I recently installed a sub panel in a storage building located about 150′ from my home. I fed this sub panel with #10 UF cable. From this sub panel, I am feeding 2 – 20 amp circuits with #14 wire. With nothing but the fluorescent lighting on, I pull about 2.7 amps of current with a measured voltage of 125 volts on this feed. When I turn on my shop vac however, I am pulling about 11 amps of current, and my measured voltage on this circuit drops to 118 volts. This causes my fluorescent light bulbs to cycle on and off. Is the voltage drop enough to cause this issue, or am I missing something?
Dave’s Reply: Wire Length and Voltage Drop
When planning the wire size for a sub panel, or any panel for that matter, it is important to factor in the length of the distance to the panel from the source, and the amperage of the sub panel. The circuit loads placed upon the sub panel will determine the size of the sub panel as well. So basically, everything starts with planning the load that will be placed on the sub panel, and then we calculate the wire size feeding the sub panel based upon the distance. It is also important to factor in any electric motors that may be used due to the starting load which will effect the amperage and the voltage.
Michael asks:
We bought a house with a detached shop.
The shop has a 200 amp service, it has it’s own pole and meter. With every breaker shut off, the lights and outlets still work. They still have power. Only when I shut the 200 amp breaker off does the lights and outlets quit working.
I can understand a possible bad breaker, but all defective. I highly doubt that. What do you think?
Additional Comments: The feedback I have read is very informative and professionally stated.
Dave’s Reply:
From what you have described, I think there is another panel somewhere. One way to know for sure is to open the panel and see if there is a spare set of lugs that are used to feed another panel.
200Amp Main Panel Circuits
Michael asks:
We bought a house with a detached shop.
The shop has a 200 amp service, it has it’s own pole and meter. With every breaker shut off, the lights and outlets still work. They still have power. Only when I shut the 200 amp breaker off does the lights and outlets quit working.
I can understand a possible bad breaker, but all defective. I highly doubt that. What do you think?
Additional Comments: The feedback I have read is very informative and professionally stated.
Dave’s Reply:
From what you have described, I think there is another panel somewhere. One way to know for sure is to open the panel and see if there is a spare set of lugs that are used to feed another panel.
More about Sub panel electrical
Why Is My Bathroom Light Fixture Not Working? How Can I Fix a Bathroom Light Fixture and a Bath Exhaust Fan that Stopped Working? The Most Common Problems with Bathroom Light Fixtures and How You Can Fix Them.
220 240 Volt Air Compressor Wiring How to Wire a 220 Volt Air Compressor and Control Switch: Wiring a standard 240 volt motor for equipment such as an air compressor there are only two insulated wires for the 220/240 volts and one separate wire for the ground.
How to Install an Electrical Sub Panel Thinking about installing a Sub Panel? Here is what must be considered first, and you may find that you really do not need a sub panel at all.
Electric Well Pump Circuits Can I power my shed with 120volt from the 240volt well circuit? Installing a 240volt 3wire Circuit for a Well Pump Panel, Dedicated Circuit for Well Pumps.
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.
Hot Tub Cable and Electrical Wiring How to Install Hot Tub Electrical Circuit Wiring: Can I run a regular 6AWG 3 conductor wire plus ground through a one inch conduit or do I need to run outdoor 6AWG wire?
Electrical Project Skill Level:
Intermediate to Advanced - Best performed by a Licensed Electrical Contractor.
Electrical Tools Required:
Basic Electricians Pouch Hand Tools and a Voltage Tester.
Estimated Time:
Depends on personal level experience, ability to work with tools, install electrical circuit wiring, and the available access to the project area. Electrical Safety:
Identify the panel circuit, turn it OFF and Tag it with a Note before working with the wiring. Working in an electric panel is dangerous due to arc flash hazards and the possibility of electric shock.
Electrical Wiring Parts and Materials:
Electrical parts and materials for circuit wiring projects should be approved for the specific project and compliant with local and national electrical codes.
Electrical Codes and Inspections:
Installing additional electrical circuit wiring should be done according to local and national electrical codes with a permit and be inspected.
This is a testing tool that 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.
This is great to troubleshoot a problem with outlet circuit wiring, is also used by most inspectors to test for power and check the polarity of circuit wiring.
It detects probable improper wiring conditions in standard 110-125 VAC outlets
Provides 6 probable wiring conditions that are quick and easy to read for ultimate efficiency
Lights indicate if wiring is correct and indicator light chart is included
Tests standard 3-wire outlets UL Listed Light indicates if wiring is incorrect, Very handy and easy to use.
A wire stripping tool used 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.
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