NM (Non-Metallic) and NM-B are two of the commonly used cable types which do not have either a metallic sheath or a spacing layer, however there are several differences that are present in the structures, the intended use, their operational temperature range and also their the electrical characteristics. Below are the key differences between NM and NM-B:
Temperature Rating:
- The permissible operating temperature of NM-B cable increments to 90°C which allows the cable to work efficiently under high operating temperature.
- Standard NM cables are often rated at 60 °C and 75 °C.
Insulation:
- The insulation of NM-B cables is preferably made to be more robust as it is necessary for high temperature application use.
- NM cable insulation materials might be of low heat tolerable hence supplementary treatments might have to use in case of high temperatures.
Environment of Use:
- NM-B cable is acceptable in dry and wet weather conditions in both residential and commercial constructions since it provides better charge against moisture and water.
- NM cables are mainly applicable in dry conditions in residential as well as light commercial use and have less scope of application in wet conditions compared to NM-B.
Voltage Rating:
- Considering the wire’s construction and application flexibility, it is able to carry higher rated voltages; thus type NM-B cables may have 600V voltage ratings.
- NM cables tend to be rated at a lower voltage which may restrict their application in some non standard high voltage requirements.
Installation flexibility:
- Owing to NM-B cables’ unique design, they may be more flexible and pliable than NM cables, making installation less complicated, especially in tight and intricate places.
- The NM cables may have some restrictions concerning the bend radius and installation flexibility especially in situations where there is a need to bend it often.
Cost:
- Because NM-B cables usually have a higher temperature rating and improved mechanical protection, the cables may be more expensive than other standard NM cables.
- This is because NM cables have a lower upper temperature rating and downsized construction hence making them cheaper.
It is clear that type nm-b cables offer outstanding advantages. Selection of NM or NM – B cables is still dependent upon the application, the installation conditions and the local electrical code.
