Download Interrupting ratings 6.6MB

Suggestion on How to Use
• Industry Trainers are encouraged to use this
material in their sessions
• Download the presentation file
• Print the Notes pages and read them as you
view the presentation in the “Slide Show”
view. In this way you see the slides in large
format and have animation (when available)
© 2015 Eaton. All Rights Reserved..
1
Interrupting Rating
© 2015 Eaton. All Rights Reserved..
Interrupting Rating
• NEC Article 100 defines interrupting rating:
• The highest current at rated voltage that a device is
identified to interrupt under standard test
conditions.
© 2015 Eaton. All Rights Reserved..
3
Interrupting Rating
• NEC 110.9
• Equipment intended to interrupt current at fault levels
shall have an interrupting rating at nominal circuit
voltage sufficient for the current that is available at the
line terminals of the equipment.
• Equipment intended to interrupt current at other than
fault levels shall have an interrupting rating at nominal
circuit voltage sufficient for the current that must be
interrupted.
• The interrupting rating of the OCPD must be equal to or
greater than the short-circuit current available or…
© 2015 Eaton. All Rights Reserved..
4
Interrupting Rating
• OCPD with improper Interrupting Rating
10,000A IR, 600V, Class H Fuse
50,000 Available
© 2015 Eaton. All Rights Reserved..
5
Interrupting Rating
• OCPD with improper Interrupting Rating
10,000A IR, 600V, Class H Fuse
50,000 Available
© 2015 Eaton. All Rights Reserved..
6
Interrupting Rating
• OCPD with improper Interrupting Rating
10,000A IR, 600V, Class H Fuse
50,000 Available
© 2015 Eaton. All Rights Reserved..
7
Interrupting Rating
• OCPD with improper Interrupting Rating
10,000A IR, 600V, Class H Fuse
50,000 Available
© 2015 Eaton. All Rights Reserved..
8
Interrupting Rating
• OCPD with improper Interrupting Rating
10,000A IR, 600V, Class H Fuse
50,000 Available
© 2015 Eaton. All Rights Reserved..
9
Interrupting Rating
• OCPD with improper Interrupting Rating
10,000A IR, 600V, Class H Fuse
50,000 Available
© 2015 Eaton. All Rights Reserved..
10
Interrupting Rating
• OCPD with improper Interrupting Rating
14,000A IR, 480V, Circuit Breaker
50,000 Available
© 2015 Eaton. All Rights Reserved..
11
Interrupting Rating
• OCPD with improper Interrupting Rating
14,000A IR, 480V, Circuit Breaker
50,000 Available
© 2015 Eaton. All Rights Reserved..
12
Interrupting Rating
• OCPD with improper Interrupting Rating
14,000A IR, 480V, Circuit Breaker
50,000 Available
© 2015 Eaton. All Rights Reserved..
13
Interrupting Rating
• OCPD with improper Interrupting Rating
14,000A IR, 480V, Circuit Breaker
50,000 Available
© 2015 Eaton. All Rights Reserved..
14
Interrupting Rating
• OCPD with improper Interrupting Rating
14,000A IR, 480V, Circuit Breaker
50,000 Available
© 2015 Eaton. All Rights Reserved..
15
Interrupting Rating
• OCPD with improper Interrupting Rating
14,000A IR, 480V, Circuit Breaker
50,000 Available
© 2015 Eaton. All Rights Reserved..
16
Interrupting Rating
• OCPD with improper Interrupting Rating
14,000A IR, 480V, Circuit Breaker
50,000 Available
© 2015 Eaton. All Rights Reserved..
17
Interrupting Rating
• OCPD with improper Interrupting Rating
14,000A IR, 480V, Circuit Breaker
50,000 Available
© 2015 Eaton. All Rights Reserved..
18
Interrupting Rating
• Marking the Interrupting Rating of OCPDs
• NEC 240.60(C) requires marking the interrupting
rating of branch-circuit cartridge fuses if other than
10,000A.
• NEC 240.83(C) requires marking the interrupting
rating of branch-circuit circuit breakers if other than
5,000A.
• Does not apply to supplemental protective devices
(glass tube fuses or supplementary protectors).
© 2015 Eaton. All Rights Reserved..
19
Interrupting Rating - Fuses
• Modern current-limiting fuses typically have a minimum
interrupting rating of 200,000A
© 2015 Eaton. All Rights Reserved..
20
Proper Application
50,000 Amperes
Class J, 20A
Time-Delay Fuse
300,000 A.I.R.
Fault
© 2015 Eaton. All Rights Reserved..
21
Proper Application
Before
After
Fuses: 300,000 A.I.R.
© 2015 Eaton. All Rights Reserved..
Isca = 50,000 A
22
Interrupting Rating - MCCB
• Circuit breakers can be rated in
various increments between
5,000A and 200,000A.
• Circuit breaker interrupting rating
is dependent upon voltage.
• Interrupting rating at 240V may
equal 65,000A. However, the same
circuit breaker may have an
interrupting rating at 480V of
35,000A.
© 2015 Eaton. All Rights Reserved..
23
Interrupting Rating - Example
• What Interrupting Rating must the fuse have?
• At least 50,000 amperes. (Class R, J, T, L and CC
fuses have an Interrupting Rating of at least
200,000 amperes.
• The short-circuit current rating of the switch may
also be 200,000 amperes.
© 2015 Eaton. All Rights Reserved..
24
Interrupting Rating - Example
• What Interrupting Rating must the CB have?
• Some value greater than or equal to 50,000 amperes.
• The interrupting rating for a circuit breaker is
dependent upon voltage.
• Circuit breakers come in a wide variety of interrupting
ratings – If the choices are 14,000A, 25,000A or
65,000A – a 65,000A circuit breaker would need to
be selected for the circuit shown.
© 2015 Eaton. All Rights Reserved..
25
Interrupting Rating
• The interrupting rating shown on the label for a 3pole circuit breaker is based upon the three phase
bolted fault test which has all three phase
conductors connected electrically together.
© 2015 Eaton. All Rights Reserved..
26
Single Pole Interrupting Capabilities
• A circuit breaker’s ability to safely open an overcurrent
at a specified voltage utilizing only one pole of the
circuit breaker is the single pole interrupting capability
• A circuit breaker’s single pole interrupting capability is
typically lower than its multi-pole interrupting rating.
© 2015 Eaton. All Rights Reserved..
27
UL 489 Table 7.1.7.2
Frame Rating
240V
480/277V
480V
600/347V
600V
100A Maximum
250V Maximum
4,330
--
--
--
--
100A Maximum
251-600V
--
10,000
8,660
10,000
8,660
101-800A
8,660
10,000
8,660
10,000
8,660
801-1200A
12,120
14,000
12,120
14,000
12,120
1201-2000A
14,000
14,000
14,000
14,000
14,000
2001-2500A
20,000
20,000
20,000
20,000
20,000
2501-3000A
25,000
25,000
25,000
25,000
25,000
3001-4000A
30,000
30,000
30,000
30,000
30,000
4001-5000A
40,000
40,000
40,000
40,000
40,000
5001-6000A
50,000
50,000
50,000
50,000
50,000 28
© 2015 Eaton. All Rights Reserved..
Single Pole Interrupting Capability
UL 489 Circuit Breaker Procedure
UL Single Pole Short-Circuit Test
CB Frame
Rating
100 A
Maximum
101 – 800 A.
480/277V
480V
10,000 Amps
8,660 Amps
10,000 Amps
8,660 Amps
© 2015 Eaton. All Rights Reserved..
29
Single Pole Interrupting Capability
UL 489 Circuit Breaker Procedure
UL Single Pole Short-Circuit Test
CB Frame
Rating
100 A
Maximum
101 – 800 A.
480/277V
480V
10,000 Amps
8,660 Amps
10,000 Amps
8,660 Amps
Example:
20 A, 480V CB having 65,000 A.I.R. (3 Pole Test).
Single pole tested at 8,660 Amps
© 2015 Eaton. All Rights Reserved..
30
2002 NEC® Change
240.85 FPN: Proper application of molded case
circuit breakers on 3-phase systems, other than
solidly grounded wye, particularly on corner
grounded delta systems, considers the circuit
breakers’ individual pole interrupting capability.
Reprinted from NEC® 2002
© 2015 Eaton. All Rights Reserved..
31
Ground Fault Current Path
277V
SERVICE
PANEL
A
BRANCH
PANEL
Fault to
Conduit
A
480V
B
C
B
480V
C
N
N
© 2015 Eaton. All Rights Reserved..
32
Solidly Grounded WYE System
SERVICE
PANEL
BRANCH
PANEL
277V
Steel Conduit
A
A
480V
B
C
B
480V
C
N
N
© 2015 Eaton. All Rights Reserved..
33
Solidly Grounded WYE System
Single Pole Must
SERVICE
BRANCH
Interrupt Fault Current
PANEL
PANEL
277V
Steel Conduit
A
A
480V
B
C
B
Fault to
Conduit
480V
C
N
N
© 2015 Eaton. All Rights Reserved..
34
Other System Types
• Corner Grounded Delta Systems (solidly
grounded)
• Resistance Grounded System
• Ungrounded System
© 2015 Eaton. All Rights Reserved..
35
Corner Grounded Delta System
SERVICE
PANEL
BRANCH
PANEL
Steel Conduit
A
A
B
C
480V
B
C
© 2015 Eaton. All Rights Reserved..
36
Corner Grounded Delta System
Single Pole Must
Interrupt Fault Current
SERVICE
BRANCH
PANEL
PANEL
Steel Conduit
A
A
B
C
480V
B
Fault to
Conduit
C
© 2015 Eaton. All Rights Reserved..
37
High Resistance Grounded System
SERVICE
PANEL
Resistor
BRANCH
PANEL
Steel Conduit
A
277V
A
480V
B
C
B
480V
C
© 2015 Eaton. All Rights Reserved..
38
High Resistance Grounded
System
Resistor Keeps First SERVICE
Fault Current Low: PANEL
5 Amps or So
A
BRANCH
PANEL
Steel Conduit
277V
A
480V
B
C
B
480V
C
© 2015 Eaton. All Rights Reserved..
First Fault
to Steel
Conduit
39
High Resistance Grounded System
Single Pole Must
SERVICE
BRANCH
Interrupt Fault Current
PANEL
PANEL
Steel Conduit
A
277V
A
480V
B
C
B
480V
C
High Value of Fault
Current Because
Ground Resistor No
Longer in Path
Second Fault
to Enclosure
© 2015 Eaton. All Rights Reserved..
First Fault
to Steel
Conduit
Takes Path of
Least Resistance
40
Ungrounded System
SERVICE
PANEL
BRANCH
PANEL
Steel Conduit
A
A
480V
C
B
B
480V
C
© 2015 Eaton. All Rights Reserved..
41
Ungrounded System
SERVICE
PANEL
BRANCH
PANEL
Steel Conduit
A
A
480V
C
B
B
480V
C
First Fault
to Steel
Conduit
Low Value of Fault Current
Because of Large Capacitively
Coupled Impedance to Ground
© 2015 Eaton. All Rights Reserved..
42
Ungrounded System
Single Pole Must
SERVICE
BRANCH
Interrupt Fault Current
PANEL
PANEL
Steel Conduit
A
A
480V
C
B
B
480V
C
High Value of Fault
Current Because
Large Impedance is
No Longer in Path
Second Fault
to Enclosure
© 2015 Eaton. All Rights Reserved..
First Fault
to Steel
Conduit
Takes Path of
Least Resistance
43
© 2015 Eaton. All Rights Reserved..
44