Welcome back to lucky number 13 in this series about fostering a better understanding of Article 250 on grounding and bonding in the National Electrical Code. Let’s wrap up our discussion on the equipment grounding conductor (EGC), focusing on some unique situations that apply in Part VII of Article 250.

Editor's Note: Read part 12 of this series, or catch up starting with part 1.

Part VII deals specifically with making the connection to the EGC. At the service end of the EGC, Section 250.130(A) states that the EGC must be connected to the grounding electrode conductor (GEC) and the grounded service conductor for grounded systems. This is done through the main bonding jumper. For ungrounded systems, the only difference is that there is no grounded conductor to connect to the EGC, but there is still the GEC connection.

Section 250.130 specifies where to connect an EGC to a system when replacing nongrounding devices with grounding devices or when making an extension of a circuit that adds grounding-type devices. We can use a list of six items for running a separate EGC to make this connection. This allows us to run an EGC separately from the circuit conductors if the existing circuit didn’t contain an EGC. 

Where we make the connection will depend on what is available and accessible. The first two items listed are any accessible point on the GEC or on the grounding electrode system. If there is no accessible point on the grounding electrode system or GEC, we will need a connection method in the enclosure where the circuit supplying the new devices or another GEC originates. If we need to take it all the way back to the enclosure where the circuit originates, we have a couple options, such as the equipment grounding terminal bar, the grounded service conductor or, for ungrounded systems, the enclosure’s grounding terminal bar.

Next, look at methods of connecting fixed or fastened-in-place electrical equipment by a permanent wiring method. The general concept here is simple: either the wiring method needs to qualify as an EGC, or there must be a wire-type EGC installed in the wiring method. However, if the equipment is mounted to a metal rack or structure connected to an EGC, that EGC can serve as the EGC to interconnect all mounted equipment.

If the equipment is cord-and-plug-connected, the equipment’s normally non-current-carrying metal parts must connect to the EGC. This can happen in one of two ways. The most common scenario is that the cord used to connect this equipment contains an EGC within the cable assembly or a flexible cord connected to a fixed grounding contact will connect to the receptacle device’s equipment grounding contact. The other method is a strap or flexible wire connected to the EGC. 

But what if the receptacle doesn’t have an EGC? Well, one such situation covered in Article 250 applies to using the grounded conductor to ground the frame of equipment, such as a clothes dryer. Generally, if we install new circuits, we can install ones with an EGC, and using the grounded conductor is not an option. So, this rule is for existing circuits only, specifically existing circuits without an EGC and grounding terminal on the receptacle. 

However, some conditions come with this permission, since it is different from having a dedicated EGC.

The first condition that must be satisfied is that this permission is limited to circuits supplied by 120/240V, single-phase system, or the circuit is derived from a 120/208V, three-phase, wye-connected system. 

The next limitation is that the grounded circuit conductor must be at least a 10 AWG copper conductor or 8 AWG aluminum or copper-clad aluminum conductor. This ensures the grounded conductor will have a low enough impedance to facilitate the operation of the circuit breaker or fuse. 

Finally, if the equipment contains an internal grounding-type receptacle, the equipment grounding terminal on the internal receptacle must be bonded to the equipment frame.

Two more items in Section 250.1140(B) center around whether the grounded conductor is insulated or bare. If the grounded conductor is insulated, you are all set. But a decision arises when using wiring methods such as SE cable, which might have an uninsulated grounded conductor. If the circuit originates in the service equipment, the uninsulated grounded conductor is not required to have a field-installed covering. If the circuit originates in other than service equipment, the grounded conductor needs covering to maintain separation between the EGC and the grounded conductor downstream from the service equipment. 

Part VII of Article 250 specifies requirements for the EGC’s continuity and connection to the equipment grounding terminal of grounding-type receptacles. Several options exist to make this connection. In general, an equipment bonding jumper is used to connect the receptacle’s grounding screw to a metal box connected to the circuit EGC. A few exceptions allow this connection to be made by direct contact to the device yoke or strap or by using a self-grounding device yoke. For isolated ground receptacles, the device’s grounding terminal is permitted to be connected to a separate and isolated EGC to reduce electromagnetic interference. 

This brings the series on Article 250 to a close. Stay safe and remember to always test before you touch!

Benjamin Clapp / stock.adobe.com