What are the types of grounding (earthing) arrangements?

What are IT,

TT, TN-C, TN-S and TN-C-S grounding arrangements?

Alejandro Nava
Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta (Graduated 2021) · Author has 944
answers and 2.3M answer views · Updated Jan 5

The grounding (North-American/IEEE term) or earthing (European/IEC term) arrangements differ in the
existence (whether present or not) and location of the connections of neutral-to-case (neutral-to-case
bonding), of equipment-to-ground (equipment grounding), and of neutral-to-ground (system grounding).
These various terms regarding grounding/earthing and bonding, which I’ve previously explained in other
answers, are described below:

Casings: The normally-non-current-carrying conductive (metallic) parts and conductors.

This includes metallic raceways (EMT, IMC, RMC, flexible metal conduit, metallic wireways
and auxiliary gutters, etc.), cable trays, cable armors, cable sheath, metallic enclosures of
equipment (panelboards, control panels, switchgear, switchboards, service disconnects,
meters, etc.) and loads, metallic boxes, ground wires, grounding and bonding busbars and
terminal bars.

Equipment bonding: Connecting together all of the casings.

Neutral-to-case bonding: Connecting the casings to the neutral conductor of a system.

The neutral-to-case bonding can be classified as single-point or multi-point.

Equipment grounding: Connecting to earth ground, for the safety of personnel and equipment, the
casings.

System grounding: Connecting to earth ground, for the safety of personnel and equipment, one
normally-current-carrying conductor of a system.

Usually, it’s the neutral conductor of an AC system, or any-one conductor in a three-phase

three-wire delta AC system, or either the positive or negative conductors in a DC system
(negative usually or positive for telecom.)

System grounding can be classified according to the impedance between the grounded
conductor and the earth ground: solidly grounded (only a wire is used), resistance
grounded (a resistor is used), or reactance grounded (a reactor/choke is used). See this
answer for more details.

The grounding (whether the equipment/casings or the system/neutral) can be classified as

single-point or multi-point.

The grounding arrangements names are encoded with a nomenclature consisting of letters as follows,
per the IEC standard 60364–1 on section 312.2 (page 37):
 First letter: It indicates the system grounding, i.e. whether the neutral wire is grounded or not.

T : One normally-current-carrying conductor (usually the neutral wire for AC systems) is

solidly connected to the earth ground at the source.

I : No normally-current-carrying conductor is solidly connected to the earth ground. This

may be because no normally-current-conductor is grounded at all, or one is grounded
through a high impedance.

Second letter: It indicates the equipment grounding, i.e. how the equipment is grounded.

T : The casings are directly connected to the earth ground.

N : The casings are directly connected to the grounded conductor (usually the neutral
wire for AC systems).

Next letters, if present: These indicate the arrangement of the grounded (neutral, N) conductor
and the grounding (G; or protective earth, PE) conductor.

S : The neutral wire and ground wire are separated.

C : The neutral wire and ground wire functions are combined into one wire, called the PEN
conductor.

The types of grounding/earthing arrangements are the following, with the most common ones being TT,
TN-S and TN-C-S:

IT grounding arrangement: A system having the following characteristics:

no solid connection between current-carrying conductors and the earth ground (i.e. no
system grounding) or having only one at the source through a deliberately-introduced
high-impedance device,

one or more solid connections between normally-noncurrent-carrying conductive parts

and the earth ground (i.e. single-point or multi-point equipment grounding), and

no solid connection between normally-noncurrent-carrying conductive parts and a current-

carrying conductor (i.e. no neutral-to-case bonding).

TT grounding arrangement: A system having the following characteristics:

only one solid connection between one current-carrying conductor and the earth ground at
the source (i.e. single-point system grounding),

one or more solid connections between normally-noncurrent-carrying conductive parts

and the earth ground with a separate grounding electrode system (i.e. single-point or
multi-point equipment grounding), and

no solid connection between normally-noncurrent-carrying conductive parts and the

grounded current-carrying conductor (i.e. no neutral-to-case bonding).

TN grounding arrangement: A system having the following characteristics:

one or more solid connections between one current-carrying conductor and the earth
ground (i.e. single-point or multi-point system grounding),
 and one or more solid connections between normally-noncurrent-carrying conductive
parts and the grounded current-carrying conductor (i.e. single-point or multi-point neutral-
to-case bonding).

TN arrangements are further classified as:

TN-C grounding arrangement: A system having the neutral wire and ground wire
combined in a single conductor throughout the system; from the power source to the
equipment.

TN-S grounding arrangement: A system having the neutral wire and ground wire
separated in different conductors throughout the system; from the power source to the
equipment.

TN-C-S grounding arrangement: A system having the neutral wire and ground wire
combined in a single conductor in part of the system, and then separated for the rest of
the system. Usually, the separation point is at the origin of each customer’s electrical
installation; this means the grounding arrangement at the source and throughout the
distribution system is TN-C (neutral and ground wires combined), and throughout the
electrical installation of each customer is TN-S (neutral and ground wires separated).

I’ll illustrate them. For consistency across all types, three-phase four-wire closed-wye distribution
systems will be considered, although other common systems across the World are single-phase three-
wire systems (split-phase systems), as well as single-phase two-wire systems. Also, I’ll use the typical US
color code, which is black, red and blue for phases/lines A/1, B/2 and C/3, gray for neutral, and green for
ground; additionally, I’ll use purple for the PEN wire.

IT grounding arrangement

Main characteristics:

No separate ground wire (PE wire) is run by the utility company.

Regarding bonding:

The equipment is bonded together at each customer.

The neutral wire is not bonded to the equipment at each customer.

The neutral wire is not bonded to the equipment at the utility transformer.

Regarding grounding:

The equipment and the ground wire (PE wire) is solidly grounded at each customer.

The equipment and the ground wire (PE wire) may be single-point-grounded or may be
multi-point-grounded at each customer with various grounding electrode systems.

The system (neutral wire) is not grounded, or it is high-impedance-grounded, at the utility

transformer.
 The system (neutral wire) is not grounded at each customer.

If the system is high-impedance-grounded: The system (neutral wire) is single-point-

grounded at the transformer only, not throughout the secondary/low-voltage distribution
system.

Figure 1. Three-phase four-wire closed-wye system with IT grounding arrangement, with no system
grounding at the source, with single-point equipment grounding at each customer. Image source: own.

Figure 2. Same setup as figure 1, but instead with multi-point equipment grounding at each customer.
Image source: own.
Figure 3. Same setup as figure 2, but instead with high-impedance system grounding at the source. Image
source: own.

TT grounding arrangement

Main characteristics:

No separate ground wire (PE wire) is run by the utility company.

Regarding bonding:

The equipment is bonded together at each customer.

The neutral wire is not bonded to the equipment at each customer.

The neutral wire is not bonded to the equipment at the utility transformer.

Regarding grounding:

The equipment and the ground wire (PE wire) is solidly grounded at each customer.

The equipment and the ground wire (PE wire) may be single-point-grounded or may be
multi-point-grounded at each customer with various grounding electrode systems.

The system (neutral wire) is solidly grounded at the utility transformer.

The system (neutral wire) is not grounded at each customer.

The system (neutral wire) is single-point-grounded at the transformer only, not

throughout the secondary/low-voltage distribution system.
Figure 4. Three-phase four-wire closed-wye system with TT grounding arrangement, with single-point
equipment grounding at each customer. Image source: own.

Figure 5. Same setup as figure 4, but instead with multi-point equipment grounding at each customer.
Image source: own.

TN-C grounding arrangement

Main characteristics:

No separate ground wire (PE wire) is run by the utility company.

Regarding bonding:

The equipment is bonded together at each customer.

The neutral wire is bonded to the equipment at each customer. Therefore, the neutral wire
before the separation point (each equipment) is actually a PEN wire.
 The neutral wire is multi-point-bonded to the equipment at each customer, once at each
equipment and outlet per customer.

The neutral wire (actually PEN wire) may be or may not be bonded to the equipment at the
utility transformer.

Regarding grounding:

The equipment is solidly grounded at each customer.

The equipment may be single-point-grounded or may be multi-point-grounded at each

customer with various grounding electrode systems.

The system (PEN wire) is solidly grounded at the utility transformer.

The system (PEN wire) may be or may not be grounded at each customer.

The system (PEN wire) may be single-point-grounded at the transformer only, or may be
multi-point-grounded throughout the secondary/low-voltage distribution system with
various grounding electrodes, or it may be multi-point grounded by grounding it at each
customer once or multiple times.

Figure 6. Three-phase four-wire closed-wye system with TN-C grounding arrangement, with
system/equipment grounding at the source only. Image source: own.
Figure 7. Same setup as figure 6, additionally with single-point system/equipment grounding at each
customer. Image source: own.

Figure 8. Same setup as figure 7, but instead with multi-point system/equipment grounding at each
customer. Image source: own.
Figure 9. Same setup as figure 8, additionally with multi-point system/equipment grounding throughout the
distribution system. Image source: own.

TN-S grounding arrangement

Maim characteristics:

A separate ground wire (PE wire) is run by the utility company, which originates at the utility
transformer where it is connected to the neutral wire, and terminates at each customer where it is
connected to the equipment.

The ground wire (PE wire) may be single-point-grounded at the transformer only, or may be
multi-point-grounded throughout the secondary/low-voltage distribution system with various
grounding electrode systems, or it may be multi-point grounded by grounding it at each customer
once or multiple times.

Regarding bonding:

The equipment is bonded together at each customer.

The neutral wire is not bonded to the equipment at each customer.

The neutral wire is bonded to the equipment at the utility transformer.

Regarding grounding:

The equipment and the ground wire (PE wire) may be solidly grounded or may not be
grounded at each customer.

The equipment and the ground wire (PE wire) may be single-point-grounded or may be
multi-point-grounded at each customer with various grounding electrode systems.

The system (neutral wire) is solidly grounded at the utility transformer.

The system (neutral wire) is not grounded at each customer.

 The system (neutral wire) is single-point-grounded at the transformer only, not
throughout the secondary/low-voltage distribution system.

Figure 10. Three-phase four-wire closed-wye system with TN-S grounding arrangement, with
system/equipment grounding at the source only. Image source: own.

Figure 11. Same setup as figure 10, additionally with single-point equipment grounding at each customer.
Image source: own.
Figure 12. Same setup as figure 11, but instead with multi-point equipment grounding at each customer.
Image source: own.

Figure 13. Same setup as figure 12, additionally with multi-point equipment grounding throughout the
distribution system. Image source: own.

TN-C-S grounding arrangement

Main characteristics:

No separate ground wire (PE wire) is run by the utility company.

Regarding bonding:

The equipment is bonded together at each customer.

The neutral wire is bonded to the equipment at each customer. Therefore, the neutral wire
before the separation point (service disconnect of each customer) is actually a PEN wire;
 it carries the fault current during a line-to-case fault, like a normal ground wire but unlike a
normal neutral wire, and also it carries current under normal load conditions (no faults),
like a normal neutral wire but unlike a normal ground wire.

The neutral wire is single-point-bonded to the equipment at each customer, only once per
customer (at the service disconnect for countries that are governed by the NEC such as
the US).

The neutral wire (actually PEN wire) may be or may not be bonded to the equipment at the
utility transformer.

Regarding grounding:

The equipment and the ground wire (PE wire) is solidly grounded at each customer.

The equipment and the ground wire (PE wire) may be single-point-grounded or may be
multi-point-grounded at each customer with various grounding electrode systems.

The system (PEN wire) is solidly grounded at the utility transformer.

The system (PEN wire) may be or may not be grounded at each customer (it must be
grounded for countries that are governed by the NEC such as the US).

The system (PEN wire) may be single-point-grounded at the transformer only, or may be
multi-point-grounded throughout the secondary/low-voltage distribution system with
various grounding electrodes, or it may be multi-point grounded by grounding it at each
customer only once.

Figure 14. Three-phase four-wire closed-wye system with TN-C-S grounding arrangement, with
system/equipment grounding at the source only. Image source: own.
Figure 15. Same setup as figure 14, additionally with single-point system/equipment grounding at each
customer. Image source: own.

Figure 16. Same setup as figure 15, additionally with multi-point equipment grounding at each customer.
Image source: own.
Figure 17. Same setup as figure 16, additionally with multi-point system/equipment grounding throughout
the distribution system. Image source: own.

Besides the main characteristics described, there are other relevant ones, like:

Whether differential protection (GFCI/RCD) is required to clear ground faults (line-to-case faults
and line-to-ground faults).

Whether a grounding electrode system (usually ground rods) is required at each consumers’
installation.

Degree of impedance of the ground fault path (US term)/of the earth loop (UK term) for line-to-
case and line-to-ground faults.

Cost of installing the neutral, ground/PE, and/or PEN wires.

Hazards of broken neutral and/or PEN wires.

Degree of electromagnetic interference.

Other safety risks.

The following webpage has a table with those aspects: Earthing system - Wikipedia.
1.3K views · View upvotes · View 3 shares 1 of 2 answers

Comments

Comments Recommended

Nick Nicholas · 1y
Very detailed answer, thank you for the considerable effort put into this. A few observations for
consideration * The neutral wire (actually PEN wire) may be or may not be bonded to the equipment
at the utility transformer. 1> The “may not be” clause, in the context of a specification, is not
Read
the…
more
 Alejandro Nava · 1y
Hi Nick, thanks for your comments and feedback! —— 1> The “may not be” clause, in the context
of a specification, is not the opposite of “may be”. “May be” indicates an optional
implementation, “may not be” is prohibitive - there is no choice. Ups, true. I had forgotten
Readabout…
more
Nick Nicholas Thank you for the very thorough feedback Alejandro, I wish I had the time to go through it all. I’ve…
ki d f d f thi f EE l tb h ith it EMI/EMC dit I d t d h th l t

About the Author

Alejandro Nava
Electrical engineer
Electrical Engineer at Full Data Comunicaciones 2024–present

Bachelor’s degree in Electrical Engineering, Universidad Rafael Urdaneta Graduated 2021

Lives in Venezuela

2.5M content views 35.4K this month

Active in 4 Spaces

Knows Spanish

View 1 other answer to this question

About · Careers · Privacy · Terms · Contact · Languages · Your Ad Choices · Press · © Quora, Inc. 2025