2007 Mariani Tierra

Sistemas de puesta a tierra
para instalaciones de baja
tensión.

1
Ing. Eduardo Mariani

Resistividad – Definición y unidades

l
R = ρ×
s

 m2 
Ω  = [Ωm]
 m

1

2
Ing. Eduardo Mariani

Medición de la resistencia de
puesta a tierra
G
V

3
Ing. Eduardo Mariani

La tierra como conductor

Resistividad del terreno
ITEM
1
2
3
4
5
6
7
8
9
10

TIPO DE TERRENO
Terreno de humus húmedo
Terreno decultivo
Terreno arcilloso y arenoso
Terreno arenoso y húmedo
Terreno arenoso y seco
Argamasa 1:5
Grava húmeda
Grava seca
Terreno pedregoso
Roca

RESISTIVIDAD
[Ohm x metro]
30
100
150
300
1000
400
500
1000
30000
107
4

Ing. Eduardo Mariani

La tierra como conductor

Resistividad del terreno
Variación con la temperatura para un suelo
arenoso con una humedad del 15,2%
Temperatura
(ºC)

Resistividad(Ωm)

20

72

10

99

0 (agua)

138

0 (hielo)

300

-5

790

-15

3300

Ing. Eduardo Mariani

5

Conclusiones sobre la tierra

• No posee potencial 0
• Posee resistividad elevada y
no es lineal
• Por lo tanto la tierra es un mal
conductor y no debe ser
utilizado como tal
6
Ing. Eduardo Mariani

NFPA
IEC
NFC
VDE
NACE

ANSI/IEEE C62
IEC99.1
ANSI /
IEEE 80
NFPA

F(s)
H(s)

OSHA
7
Ing. EduardoMariani

Los tres sistemas de conexión a
tierra normalizados.
Breve descripción.

8
Ing. Eduardo Mariani

Tierra para seguridad electrica
• Tres grupos; TN(TN-S, TN-C, TN-CS) TT e IT.
• 1ª letra. Situacion de la conexión a tierra
• T- Conexión directa a tierra
• I- Aislado de tierra

• 2ª letra. Conexión de las masas (a N o a T)
• 3ª Letra. Unión entre neutro y protección.
• S- Conductores separados
•C- Conductor común

9
Ing. Eduardo Mariani

TN-C
L

N

E
Generación

Acometida

Punto de uso
10

Ing. Eduardo Mariani

TN-S
L

N

E
Generación

Acometida

Punto de uso
11

Ing. Eduardo Mariani

TN-C-S
L

N

E
Generación

Acometida

Punto de uso
12

Ing. Eduardo Mariani

TN-C-S (EE.UU)
L

N

E
Generación

Acometida

Punto de uso
13

Ing. Eduardo Mariani

TT
L

N

E
Generación

Acometida

Puntode uso
14

Ing. Eduardo Mariani

IT
L

N

E
Generación

Acometida

Punto de uso
15

Ing. Eduardo Mariani

Tierra y masas

PAT

Masa
16
Ing. Eduardo Mariani

Tolerancia a corriente.

17
Ing. Eduardo Mariani

Disyuntor diferencial

PAT

Masa
18
Ing. Eduardo Mariani

Norma ANSI / IEEE 142.

19
Ing. Eduardo Mariani

20
Ing. Eduardo Mariani

Abstract: The problems of system grounding, that is,connection to ground of
neutral, of the corner of the delta, or of the midtap of one phase, are covered.
The advantages and disadvantages of grounded versus ungrounded systems
are discussed. Information is given on how to ground the system, where the
system should be grounded, and how to select equipment for the grounding of
the neutral circuits.
Connecting the frames and enclosures of electricapparatus, such as motors, switchgear, transformers, buses, cables conduits,
building frames, and portable equipment, to a ground system is addressed.
The fundamentals of making the interconnection or ground-conductor
system between electric equipment and the ground rods, water pipes, etc. are
outlined.
The problems of static electricity-how it is generated, what
processes may produce it, how it ismeasured, and what should be done to
prevent its generation or t o drain the static charges to earth t o prevent
sparking-are treated.
Methods of protecting structures against the effects of
lightning are also covered.
Obtaining a low-resistance connection to the
earth, use of ground rods, connections to water pipes, etc. is discussed. A
separate chapter on sensitive electronic equipment isincluded.
21
Ing. Eduardo Mariani

Abstract: The problems of system grounding,
that is, connection to ground of neutral, of the
corner of the delta, or of the mid tap of one
phase, are covered.

22
Ing. Eduardo Mariani

The advantages and disadvantages of grounded
versus ungrounded systems are discussed.

23
Ing. Eduardo Mariani

Information is given on how to ground the system,
where the system...