Low voltage systems tend to be ungrounded; nevertheless, if the supply system is grounded, non-current-carrying metal portions of equipment linked with low voltage systems are needed to be grounded.
It is vital to understand the requirements for grounding low voltage systems under NEC regulations before grounding your low-voltage systems.
It is also vital to understand the difference between system and equipment grounding. One conductor from a supply system is purposely connected to the ground to connect to the earth. The other conductors supplied by the system establish a reference to earth.
When equipment is grounded, it is connected to the ground or to a conductive body that extends the connection. Equipment grounding is the process of placing equipment at or near the same potential (voltage) as the earth. The equipment grounding conductor, or another grounding conductor sizing, is a conductive body that extends the ground connection.
It would help if you were sure, you have the right NEC ground wire size no matter what you are grounding. To help here, in our guide, there is more information regarding grounding wire size, and for ease of reference, we have a grounding wire size chart.
By the end, you can quickly check the ground size chart and ensure your conductor size is sufficient as it won’t cause damage to any overcurrent device that trips your circuit breaker. (Read Light Bulb Socket Sizes Chart)
What Size of Ground Wire Is Needed?
The ground wire is copper in most homes and is #6 (6 AWG) or larger. Therefore, a #4 grounded electrode conductor is required for the 200-amp service.
The following definitions are found in Article 100 of the NEC 2008:
- The equipment grounding conductor is a conductive path used to connect specific non-current-carrying metal parts of your equipment to the system grounded conductor or your grounding electrode conductor.
- A grounded conductor is a system or a circuit conductor you have intentionally grounded.
- Grounding Electrode Conductor is a conductor that connects a grounding electrode or a point on the grounding electrode system to the system grounded conductor or equipment.
- Grounding Electrode will be a conducting object where a direct connection to earth is made.
The Code goes into great length about grounding because it is such a vital topic that, if done incorrectly, can cause problems in both low and high-voltage circuits.
Here you can see the NEC grounding recommendations for low-voltage systems. Again, 50 volts will be the threshold because that’s the level used in the Code.
Section 250.20 of NEC contains regulations on grounding systems at less than 50 volts (A) and the three conditions you need to meet for systems.
- When supplied by a transformer with a primary voltage higher than 150 volts, systems with less than 50 volts must be grounded.
- If the primary side of the transformer is not grounded, systems with less than 50 volts must be grounded when a transformer feeds them.
- Systems with less than 50 volts must also be grounded if feed conductors run outside as overhead conductors.
The NEC additionally specifies which low-voltage systems are not to be grounded. For example, low-voltage lighting systems are covered, as are transformer-supplied secondary circuits for these lighting systems. Low voltage landscape lighting systems and others are examples.
What is the definition of a grounded system? In a grounded system, one conductor is purposely grounded. No intentionally grounded conductor is supplied by the system that you connect or ground to earth).
The definitions of the terms ground, grounded, or grounding are:
“Ground. The earth.”
Being grounded (Grounding) is something connected to the ground directly or using a conductive body extending the ground connection.
Certain sections of the NEC provide grounding criteria for specific fixed equipment. Regardless of the voltage, the listed equipment must be grounded or linked to an equipment grounding conductor.
To put it another way, if the equipment, such as conduits, boxes, and devices, is placed for an ungrounded system, the equipment grounding criteria do not apply. (Read Allen Wrench Sizes Chart)
All the associated equipment must be grounded if the supply system is grounded. Conduit sleeves and back boxes used within interior walls for a communications circuit or a fire alarm circuit fed from a power supply with an ungrounded secondary illustrate this in typical applications.
| Rating or Setting of Automatic Overcurrent Device in Circuit Ahead of Equipment, Conduit, etc. Not Exceeding (Amperes) | Copper (AWG or kcmil) | Aluminum (AWG or kcmil) |
|---|---|---|
| 60 | 10 | 8 |
| 100 | 8 | 6 |
| 200 | 6 | 4 |
| 300 | 4 | 2 |
| 400 | 3 | 1 |
| 500 | 2 | 1/0 |
| 600 | 1 | 2/0 |
| 800 | 1/0 | 3/0 |
| 1000 | 2/0 | 4/0 |
| 1200 | 3/0 | 250 |
| 1600 | 4/0 | 350 |
| 2000 | 250 | 400 |
| 2500 | 350 | 600 |
| 3000 | 400 | 600 |
| 4000 | 500 | 800 |
| 5000 | 700 | 1200 |
| 6000 | 800 | 1200 |
Does Ground Wire Need To Be Same Size?
The earth must be about the same diameter as circuit conductors for house wiring. However, motors or heating equipment frequently employ one smaller diameter in manufacturing. This is because grounding may trip the circuit breaker or fuse if the wire is hot.
NEC Table 250.66 is used for sizing grounding electrode conductors for alternating current systems. An article called Grounding Electrode Conductor tells you how this piece of equipment is connected to a grounding electrode.
In prior editions of the NEC, the largest ungrounded service-entrance conductors were utilized to determine how prominent the grounding electrode conductor should be on alternating current systems.
In the 2020 NEC, the word “service-entrance” was omitted from the table since this table is also used to determine grounding electrode conductor size for buildings or structures supplied by feeders or branch circuits or at a separately derived system of a grounded or ungrounded AC system.
The grounding electrode conductor is not intended to carry current under normal conditions. Still, it provides a path to the grounding electrode to decrease voltage generated by lightning, power line surges, or unintended contact with higher-voltage lines.
As a result, the grounding electrode conductor is not the same size as conductors that are meant to carry current all the time.
When using the table, the size of a grounding electrode conductor depends on the size of the most prominent ungrounded conductor on alternating current systems.
For a service, occasionally, the utility company installs the service entrance conductors after the electrician is finished. Therefore, the electrician has no notion what size service entrance conductors will be installed until then. (Read 150 Amp Wire Size Guide)
Table 250.66 clarifies that if no service-entrance conductors are present, “the grounding electrode conductor size shall be determined by the equivalent size of the largest service-entrance conductor size necessary for the load to be served.”
Some grounding electrodes are not sized from Table 250.66. Under certain situations, ground rods, ground pipes, ground plates, concrete encased electrodes, and ground rings may be permitted to be smaller than the values in Table 250.66 according to Section 250.66(A) through (C).
Underground water pipe electrodes and metal in-ground support structures covered in 250.52 are consistently sized from Table 250.66.
What Size Ground Wire Do I Need For A 50 Amp Circuit?
Such a circuit would need 6 wwg conductors and ground of 10 w g as a minimum.
Equipment grounding conductors made of copper, aluminum, or copper-clad aluminum of the wire type must not be smaller than those listed in Table E3908.12. Still, they are not required to be larger than the circuit conductors that supply the equipment.
Section E3908.4 applies when a grounding raceway, cable armor, or sheath is used as the equipment grounding conductor, as specified in Section E3908.8.
When ungrounded conductors are extended beyond the smallest size that provides sufficient amp capacity for the intended installation, wire-type equipment grounding conductor sizing must be increased correspondingly to the largest ungrounded conductor circular mil area. (Learn How To Disconnect Hard Wired Smoke Alarm)
Here you can find tables that give the setting of automatic overcurrent device in AWG or kcmil.
| Size Of Largest Ungrounded Service-Entrance Conductor Or Equivalent Area For Parallel Conductors (AWG/kcmil) | Size Of Grounding Electrode Conductor (AWG/kcmil) | ||
|---|---|---|---|
| Copper | Aluminum or copper-clad aluminum | Copper | Aluminum or copper-clad aluminum |
| 2 or smaller | 1/0 or smaller | 8 | 6 |
| 1 or 1/0 | 2/0 or 3/0 | 6 | 4 |
| 2/0 or 3/0 | 4/0 or 250 | 4 | 2 |
| Over 3/0 through 350 | Over 250 through 500 | 2 | 1/0 |
| Over 350 through 600 | Over 500 through 900 | 1/0 | 3/0 |
Multiple Circuits
When a single equipment grounding conductor is used to connect multiple circuits in the same raceway or cable, it must be sized to protect the raceway or cable’s largest overcurrent device voltage drop.
What Size Ground Wire Is Required For A 200 Amp Service?
The minimum size of grounding conductors for 200 amp circuit protection should only be #6 copper or (4) aluminum, according to NEC Article 250. If you’re in the United States, you’ll probably stick to the National Electrical Code (NEC).
National Electrical Code – NEC 2008
- Main, Bonding Jumper is a connection between a grounded circuit conductor and the equipment grounding conductor at the service.
- Conductor for Grounding. A conductor is used to connect equipment or a wiring system’s grounded circuit to a grounding electrode or grounding electrodes.
- Equipment, Grounding Conductor (EGC). The conductive path between non–current carrying metal portions of equipment and the system grounded conductor, grounding electrode conductor, or both.
- Electrode for grounding. A conducting object that establishes a direct connection to the earth.
- Electrode Conductor for Grounding. A conductor connects a grounding electrode or a point on the grounding electrode conductors or to the system grounded conductor or equipment.
The size of the Main Bonding Jumper, Grounding Electrode Conductor, and Grounded Electrode is defined by table 250.66
Continuity and Attachment of Equipment Grounding Conductors to Boxes
If you look at the 200-ampere row, the 225-ampere rating row is more significant than the 300-ampere row. This is because the EGC must be 4 AWG for copper wire, and for aluminum or copper-clad copper, it must be 2 AWG.
Follow the same steps to determine what size conductor you need for any installation supply side. The minimum set out in the table isn’t enough for some installations.
The note below Table 250.122 says where it is necessary to meet requirements; the equipment grounding conductor shall be larger than given in this table, (250.122) which means the conductor should be sized larger.
Notes that are part of the NEC National Electrical code tables must be there (unlike Informational Notes). The reasoning for such notes is a high fault current on the supply side can damage or melt the equipment grounding conductor.
According to Section 250.122(B), wire-type equipment grounding lines must be sized larger in proportion to the circular mil area of ungrounded conductors.
This means that “if ungrounded conductors are increased in size for any reason other than as required in 310.15 (B) and 310.15 (C), wire-type equipment grounding lines must be made larger in proportion to the circular mil area.”
When there is a long branch circuit or feeder, the ungrounded conductors might get more significant to make up for voltage drop. (Read Can You Use A Junction Box To Extend Wiring)
Therefore, unless correction or adjustment factors are used, if a feeder or branch-circuit conductor is increased in size, the wire-type grounding conductor for this circuit would have to be increased at least as much as the feeder or circuit conductor size is increased.
Some examples:
There will be a 200-ampere rating feeder that goes through the middle of an extensive building. If the voltage dropped too much, this feeder would not work.
Table 310.16 says a 3/0 AWG copper conductor is needed for a 200-ampere rating. Instead, a 250-kcmil copper conductor was chosen for this job.
Table 250.122 usually says that the grounding conductor size for the 200-ampere rating of the automatic overcurrent device should be 6 AWG copper.
In size, to figure out how big an equipment grounding conductor size we need for this feeder, we would need to use the formula shown.
When the conductor size isn’t given in circular mils, we’ll need to use Table 8 of NEC Chapter 9 to figure out the area in circular mils (AWG).
