FAQ - 2011

[Dennis Alwon]

Am I required to Run an EGC to a Separate Structure?

In the 2005 NEC we had options , however, since the 2008 code cycle those options were taken away and we must run an egc or we must have a raceway that is suitable as an egc. Many are confused on what to do with the grounded conductor and the egc at the panel located at the separate structure. The egc must be kept isolated from the grounded conductor. This panel in the detached structure is a subpanel and it is wired the same way as any other subpanel except that we have a GEC to install. This GEC connects to the ground bar, NOT the neutral bar, of the panel

[Dennis Alwon]

The Six-Handle Rule
Services, Feeders to detached structures, etc.

The rules for the number of switches allowed to disconnect all ungrounded conductors of a structure are given in different locations depending on the application.

For services, 230.71(A) dictates that no more than six handles shall disconnect a service from the structure served. Throughout all of Part V of Article 230 are several rules dictating how large the disconnecting means must be, how to determine how large the service is, where it must be located and what may be attached to the line and load sides of a service disconnect.

For detached buildings that are fed from another building, the rules are given in Part II of Article 225. Section 225.33(A) also requires no more than six handles to a structure. Article 225.36 requires the disconnecting means to be marked as suitable for service equipment unless it is a MWBC feeding the structure. The exception allows a snap switch to be used.

Please note that the key to both 230.71(A) and 225.33(A) is the number of handles present, not the number of spaces available. Therefore, based on this fact, you can install a 40-circuit panelboard, install a single 100A breaker to feed an interior panelboard inside a structure, and comply with these rules. This is widely considered a practice that may be legal but should be avoided. However, by the NEC such an installation should be approved.

Grounding requirements for services are found in Article 250, Parts I and III.

Bonding and Grounding requirements for detached structures are found in 250.32, and are discussed in detail in this FAQ.

Related threads:

[Dennis Alwon]

Wire Insulation Types and Letter Designations

"T" stands for thermoplastic insulated cable.

"H" means the insulation is heat resistant.

"HH" means that the insulation is heat resistant and can withstand a higher temperature. This insulation can withstand heat up to 194 degrees Fahrenheit.

"W" means that the insulation is approved for damp and wet locations. This wire is also suitable for dry locations.

"X" means the insulation is made of a synthetic polymer that is flame-retardant.

"N" is for the nylon coating that covers the wire insulation.

Thhn- thermoplastic high heat resistant nylon
Thwn- thermoplastic heat and water resistant nylon
Thw- thermoplastic heat and water resistant
Thhw- thermoplastic high heat and water resistant
Tw- thermoplastic water resistant
UF- Underground feeder
Rhw- Rubber insulated heat and water resistant
Rhh- rubber insulated and high heat resistant
Mtw- machine tool wiring
USE- underground service entrance cable
SE- service entrance
SEU- Service entrance unarmored. I have also heard it as -- uninsulated (neutral)
SER- service entrance round
Xhhw- Cross-Linked Polymer High Heat Water Resistant

It is important to note that many insulation types, such as Thhw, are listed for wet and dry location but when used in wet location the temperature rating is 75C. When used in a dry location the same wire is rated 90C. Some wires have a designation of -2, eg. Thwn-2. This means that the wire is listed for 90C in both wet and dry locations.