If you are looking at shielded cable options for your electrical wiring, you will usually have a choice between NM cable and UF electric wire cable for your project. Although there are some similarities in the two types of electrical wiring, there are some significant differences as well. Therefore, this article will describe some of those differences and why you should know about them.
NM or NM-B cables stand for "non-metallic" which aids in flexibility. The "B" denotes a heat rating of 194 degrees Fahrenheit. UF cables stand for "underground feeder" and may look similar to NM cables.
1. Sheathing Protection
The most significant difference between NM cable and UF electric wire is the type of sheathing that is used. Although NM cable is covered with a flexible thermoplastic covering on the outside of the wiring, the strands of wire themselves are usually protected with little more than a paper wrapper. On the other hand, UF cable utilizes solid thermoplastic exterior covering, and each individual wire is also enclosed in a protective sheath.
This is an addition to the regular insulation that is installed on the thin gauge electrical wire. Therefore, UF electrical wiring offers much better sheathing protection than the NM type and is rated for outdoor, in-ground, and damp-area installation.
2. Indoor and Outdoor Usage
Almost all municipalities and local building inspectors restrict the use of NM wire cable to interior projects. That means that the NM cable cannot be used to wire outdoor outlets, fixtures, or other items that are used on the exterior of the home. On the other hand, UF electrical wire is approved for use in most areas as outdoor fixture and electrical wire.
UF cable can even be buried underground without a need for electrical conduit or any other type of protective covering. This is because of the thick rubber sheathing that is used as well as individuals sheathing for each electrical wire. Of course, UF cable can also be used inside the home. With that in mind, if you have a simple DIY project inside the home, NM cable is fine. If you need to wire something on the outside of your home, you need to choose the UF cable wire.
3. Need for Conduit
As mentioned above, UF electrical wire does not require the use of conduit or any other type of protective covering. In most cases, this also applies to interior wiring projects as well, except where subject to physical damage, such as where the cable exits the ground. Then conduit, normally electrical PVC, is required.
While NM wiring may be used without conduit in many areas, there are some parts of the country where the local building inspector will require that you place an NM wiring inside a piece of conduit. So, if you want to avoid conduit altogether you should choose UF electrical cable. In fact, if you consider the cost of the conduit as well as NM cable, purchasing UF wire makes a better choice when trying to save some money.
4. Cost Difference
Generally speaking, there is about a 15 to 20 percent price difference between the cost of NM cable and more expensive UF electrical wire. However, if you consider that UF cable has better shielding, doesn't require conduit, and is much more readily accepted by local building inspectors, the small price difference could be considered negligible.
UF and Romex Cable FAQ
What is UF cable used for?
Typically, UF-B cable is used as an underground wire that brings power to outside lights and fixtures, such as sewer pumps, electric gates, and any other appliance or device outside the home.
Is it against code to run Romex in conduit?
Violating electrical codes is not a huge criminal offense in most cases and in many cases, there are no specific coding laws about Romex in particular. However, Romex does not need to be run through conduit and it is inadvisable to do so.
Romex is sheathed in durable, flexible plastic material and individually coated wires. You can run Romex through conduit if you are determined to do so but you shouldn't.
The National Electric Code, which is not a set of laws or regulations but more like a series of suggestions, recommends running only non-metallic wires through conduit. Romex is mostly made with copper covered over with plastic.
Does UF cable need conduit?
UF cable should be in conduit sometimes and sometimes not. When UF cable is buried 24 inches deep or more, you can skip the conduit.
But when UF cable is running vertically or it's less than 24 inches below ground, conduit is a good idea.
Why can't you use Romex outside?
Romex cable can become damaged if it comes into contact with water, oil, gas, or other very common solvents. If the protective outer shell becomes damaged and bare copper wire is exposed, this could cause a great deal of damage.
Which areas are not permitted to have Romex wire used?
Romex wire is used quite often in small buildings and in residential homes. However, it is not designed to be used in buildings that have more than three stories.
Because of this, you will not often find Romex in apartment or housing developments.