When it comes to DIY electrical projects, one of the favorite points inspectors look at is the proper use of wires for outdoor and indoor application. And when it comes to heavy duty wiring, Romex is well-known because of its cost-effectiveness, versatility, and utility.
The application of Romex wires is limitless, but most DIY-ers often find themselves confused about whether they can strip Romex and use it in a conduit outdoors.
The answer is generally yes. The National Electrical Code (NEC) calls for all non-metallic wires to be used in conduits to avoid protection from physical damage; especially if stripped. However, there are some other intricacies involved here as well, including the ANSI markings of stripped wires, which we’ll discuss in detail below.
Disclaimer: Electrical installations and modifications should only be carried out by a competent, trained person. If you are unsure about any steps in a DIY electrical project, it is always better to call in a qualified electrician.
Romex Wire – What Is It Really?
A bit about Romex; it is a brand – perhaps the most renowned brand – name for non-metallic wires. Romex company is the inventor of these non-metallic cables, rolling their first batch out in 1922. NEC found use of these wires in 1926, and in the 1960s, these wires became prevalent.
The wiring systems of most houses built or rewired after 1965 contain NM sheathed cables, or as they are more commonly known as, Romex cables. These wires are known for their cost-effectiveness and flexibility, featuring a plastic sheathing. There are two insulated wires – positive and negative – and one bare copper ground wire.
This copper wire is what gets exposed if the wire gets damaged, thus leading to other problems. This is why when stripping Romex wires and running them, it is best to use a weather-resistant conduit – especially outdoors or near utility lines.
The outer sheathing is made of woven rayon and the wires inside are bonded by paper, which is much better than the older plastic sheathing. This insulation is extremely flexible, which makes the wire much easier to use. The wire itself is inexpensive while offering good overall protection. Just remember, it’s not the most protective wire out there; just better than many.
The sheathing used to be white but today, these wires have a color-coded sheeting to help identify gauge of the cable. There are three gauges and colors you can find:
- 14-gauge wire. This wire has a white sheathing outside and is used mostly for 15-amp circuits – the standard circuits around the house for your appliances such as fans, lamps, your laptop, phone, and more.
- 12-gauge wire. This wire has a yellow sheathing outside and is used mostly for 20-amp circuits. These circuits can handle up to 2,500 Watts, thus making them suitable for heavier appliances such as air compressors, car charging, and more. These circuits are more common in commercial and industrial power distribution channels.
- 10-gauge wire. This wire has an orange sheathing outside and is used mostly for 30-amp circuits. These circuits can handle up to 7,200 Watts, and are therefore used for running power-hungry appliances such as space heaters, deep freezers, microwaves, and more.
Stripping a Romex
When you strip a Romex wire, you will find that there are three wires running within the protective PVC plastic sheathing.
- A white negative wire that is wrapped with paper. You can easily tear off the wrapper after stripping it.
- A black positive wire which is also wrapped with paper. Both, the white and black wires, are insulated inside the sheath.
- A bare copper grounding wire. There is also a paper wrapping around this wire.
The goal of paper winding throughout the interior is to ensure that the wires don’t stick together even after heating up. Furthermore, the paper provides the wires within the necessary flexibility during installation.
The PVC plastic sheathing surrounding the insulated conductors and copper ground wire is non-conductive and heat resistant. It is average when combating outdoor conditions, hence necessitating the use of a conduit. When using indoors, you have the freedom to choose.
A Warning About ANSI Markings
Wires, including Romex, will have various markings on them. These can refer to the size/guage of the individual wires, the sheathing material used, the number of wires inside the outer jacket, and more.
With Romex wire, the ANSI markings are usually only on the outside jacket (sheath) of the wire. However the NEC can require that these ANSI markings are displayed in an electrical installation, meaning that stripping the outer jacket off might not be up to NEC code.
Running Romex in a Conduit
When using any non metallic wire outdoor, including Romex, it is a good idea to run it through a conduit. Yes, they can be used outdoors, it is better to be safe than sorry. We recommend using a conduit when running the wire underground. Not only is it code, but also a good practice to ensure long life of the wire.
This is because the bare copper ground wire inside is relatively more exposed to the elements compared to the conductors. Furthermore, when you run the wire underground, it will be exposed to water, pests, pressure, weather, and most importantly, roots.
Roots have a way of growing into plumbing pipes, too, so how well do you think a soft, malleable, non-metallic wire would fare against them?
The need for a conduit becomes even direr if you’re using a stripped Romex. When the Romex wire comes in contact with water, gas, oil, or any other type of solvent, the bare copper ground wire can ruin the connection and trip the breaker again and again.
Electrical Code Requirements for Non-Metallic Cables
According to the National Electrical Code 2020, Article 334, Paragraph II (B), Protection From Physical Damage, it is stated that:
The cable shall be protected from physical damage where necessary by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, Type RTRC marked with the suffix –XW, or other approved means.
NEC 2020, Article 334
This shows the importance of a conduit, regardless of whether you use a metallic or a plastic one. This is why we mentioned that one of the favorite inspection points of electrical inspectors is to check whether Romex installed outdoors is in a conduit or not.
Furthermore, installing stripped Romex where the wire may be susceptible to damage is prohibited. This may include installation near sewage lines, bins, garage doors, and even those attached to the face of concrete walls!