Home Electrical Wiring 101
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Every modern home needs enough juice to run all of our modern day gadgets. Electrical wiring, along with plumbing, are important systems to your home where not enough attention is given since they are mostly hidden behind walls. The older the home, the more likely it may have older wiring that is not up to today’s building codes and is potentially dangerous. Rewiring an entire house can run in the thousands of dollars, so it is important to know what you are buying. As always, it is a good idea to have a general home inspection which may also recommend a more through look at the electrical components by a certified electrician.
Common Types of Wiring in the U.S.
| Wiring Type | Dates Commonly Used |
| Knob and Tube | 1890s to 1910s |
| Flex Armored Cable (often called BX) | 1920s to 1950s |
| Nonmetallic-sheathed cable (often called Romex) | 1950s to today |
- Metal Conduit (BX) added benefits to Knob and Tube since the wires were encased by metal and the system could be grounded. BX wiring is still commonly found in houses built in the 40’s and 50’s. Sometimes homes of this age have a mix of BX and the newer Romex-style wiring. Hendersonville homes built between 1940 and the late 1960’s probably have this type of wiring.
- Modern NM (Romex) wiring was introduced in the late 60’s and incorporated the use of a bare copper grounding wire along with the hot and neutrals. It is the most common in homes from 1970’s to today.
- Knob and Tube is typically found in older homes dating to the early 1900s which makes it more common in the Northeast part of the country. Knob and Tube wiring is a form of wiring where wires are protected by a rubberized cloth fabric and installed in walls and studs using ceramic tube insulators. The protective cloth is usually brittle as it was rated for a 25-year life expectancy. Electricians recommend upgrading all knob-and-tube, especially since it is ungrounded. Historic homes in Hendersonville, North Carolina my still have remnants of this type of wiring.
How much Electrical Service do you Need?
The amount of electrical service needed coming into the house from the power company is a function of how many things need to be powered which also relates to the size of the house. Older homes may have 100 or 150-amp service which could power a stove, water heater, lighting, and outlets but is not sufficient for electric heating/cooling systems. Buyers should pay close attention to homes with 100-amp service as these homes will often have fewer outlets per room and may require an upgrade. Newer homes will likely have at least 200-amp service which is enough power for the average size home with modern appliances (many have gotten more efficient over the years and require far less power like the switch from console to flat-panel TVs). Larger homes, say over 3,500 sq. ft., or items that require heavy power loads may need even more power and require a 400-amp service.
All home inspections should indicate the level of service entering the home. If you locate the circuit breaker, you can usually find the main circuit for the entire panel that will say 60, 100, 150, 200, etc. If the panel uses fuses, it is 30 or 60-amp service and is recommended to be upgraded.
[panel picture]
Untangling the Questions about Wiring
Modern wiring commonly has at least one hot, one neutral, and one ground (bare copper) wire. Older wiring systems drop the ground wire.
- Neutral is the return conductor of a circuit and usually colored white.
- Hot is the conductor (what will zap you) and usually colored red.
- Ground is a safety conductor with a path back to earth and usually colored green or bare copper wire.
The type of wiring is also important based on the power consumption of the device being supported. An LED lightbulb draws very little power, but hair dryers and toaster ovens might need 1,500 or more watts. To reduce the risk of problems, devices that require more power should use heavier-duty wiring which is ranked by the gauge (thickness).
Below are examples of electrical devices and services in relation to the recommended wire gauge.
| Device/Use | Rated Ampacity | Wire Gauge |
| Low-voltage lighting and lamp cords | 10 amps | 18-gauge |
| Extension cords | 13 amps | 16-gauge |
| Light fixtures, lamps, lighting runs | 15 amps | 14-gauge |
| Receptacles, 120-volt air conditioners, built-in ovens, electric water heaters | 20 amps | 12-gauge |
| Electric clothes dryers, 220-volt window air conditioners, built-in ovens, electric water heaters | 30 amps | 10-gauge |
| Cooktops | 45 amps | 8-gauge |
| Electric furnaces, large electric heaters | 60 amps | 6-gauge |
| Electric furnaces, large electric water heaters, sub panels | 80 amps | 4-gauge |
| Service panels, sub panels | 100 amps | 2-gauge |
| Service entrance | 150 amps | 1/0-gauge |
| Service entrance | 200 amps | 2/0-gauge |
The Bottom Line
Make sure your home inspection uncovers the basics of the home’s electrical systems. If the home was built prior to 1960’s, be sure to take note of the amount of service coming into the home. If the home was built before 1940, ensure the system is not using knob and tube wiring. Hiring an electrician to perform additional inspections could uncover items that must be fixed and provide you with additional negotiating power with the seller.