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
Voltage Rating
© 2015 Eaton. All Rights Reserved..
Voltage Rating
• Voltage rating of the OCPD must be equal to or greater
than the system voltage.
• Voltage rating determines the ability of the OCPD
extinguish the arc during an overcurrent condition.
© 2015 Eaton. All Rights Reserved..
3
Voltage Rating
• NEC 240.60(A) permits 300V cartridge fuses to
be used on circuits not exceeding 300V
between conductors or single-phase line-toneutral loads not exceeding 300V.
• NEC 240.60(B) requires fuseholders to reject
fuses with lower voltage ratings.
• NEC 240.60(C) requires the voltage rating to be
marked on the fuse barrel or label.
• NEC 240.61 allows fuses rated 600V or less to
be used for voltages below their rating.
© 2015 Eaton. All Rights Reserved..
4
Voltage Rating
• NEC 240.83(E) requires circuit
breakers to be marked with a
voltage rating that indicates the
circuit breaker’s capability to
interrupt overcurrents between
phases or phase to ground.
• Voltage rating can be “straight”
or “slash” rated.
© 2015 Eaton. All Rights Reserved..
5
Voltage Rating
• NEC 240.85 covers the requirements for straight
rated and slash rated circuit breakers.
• A straight rated CB (480V) can be applied on systems
that no more than 480 volts between any two
conductors.
• A two-pole circuit breaker applied on a 3-phase,
corner-grounded delta system must be marked 1Φ3Φ.
© 2015 Eaton. All Rights Reserved..
6
Voltage Rating
• NEC 240.85 (Cont)
• A slash rated circuit breaker, such as 480Y/277V, can
only be applied in a solidly grounded circuit where the
nominal phase to ground voltage does not exceed the
lower number (277V) and the phase to phase voltage
does not exceed the larger number (480V).
© 2015 Eaton. All Rights Reserved..
7
© 2015 Eaton. All Rights Reserved..
8
Voltage Rating
3-Pole, 480/277V CB
Three Phase
C
Corner Grounded
Delta system
B
A
Equipment Bonded to Ground
© 2015 Eaton. All Rights Reserved..
9
Slash Rated CB Application
480 volts
line to line
Circuit breaker
480Y/277 slash voltage rating
A
480Y/277 Volt
Three phase
Four wire
Solidly grounded
wye system
B
C
N
G
277 volts
line to ground
© 2015 Eaton. All Rights Reserved..
10
Is Slash Rated 480Y/277V Device Permissible?
A
277V
Solidly Grounded
480Y/277V
480V
Click on Answer
B
Yes
OR
480V
No
C
N
© 2015 Eaton. All Rights Reserved..
11
Is Slash Rated 480Y/277V Device Permissible?
A
277V
Solidly Grounded
480Y/277V
480V
B
Yes
OR
480V
No
C
N
© 2015 Eaton. All Rights Reserved..
12
Is Slash Rated 480Y/277V Device Permissible?
A
277V
Solidly Grounded
480Y/277V
480V
B
Yes
OR
480V
No
C
N
© 2015 Eaton. All Rights Reserved..
13
Is Slash Rated 480Y/277V Device Permissible?
A
277V
Solidly Grounded
480Y/277V
480V
B
Yes
OR
480V
No
C
N
© 2015 Eaton. All Rights Reserved..
14
Is Slash Rated 480Y/277V Device Permissible?
Corner Grounded
Delta
A
Click on Answer
Yes
B
480V
OR
No
C
© 2015 Eaton. All Rights Reserved..
15
Is Slash Rated 480Y/277V Device Permissible?
Corner Grounded
Delta
Yes
A
B
480V
OR
No
C
© 2015 Eaton. All Rights Reserved..
16
Is Slash Rated 480Y/277V Device Permissible?
Corner Grounded
Delta
Yes
A
B
480V
OR
No
C
© 2015 Eaton. All Rights Reserved..
17
Is Slash Rated 480Y/277V Device Permissible?
Corner Grounded
Delta
Yes
A
B
480V
OR
No
C
© 2015 Eaton. All Rights Reserved..
18
Slash Rated Exercise
System
Secondary
L-L
L-G
Can 480Y/277
Voltage
System Type
Volt
Volt
CB Be Used?
480Y/277
Solidly
Grounded WYE
480
277
Yes
No
480
277
Yes
No
480
480
Yes
No
480
*
Yes
No
480
480
Resistance
Grounded WYE
Delta Corner
Grounded
B Phase
480
Delta
Ungrounded
* Ungrounded delta systems - phase conductors
are capacitively coupled to ground
© 2015 Eaton. All Rights Reserved..
19
Slash Rated Exercise
System
Secondary
L-L
L-G
Can 480Y/277
Voltage
System Type
Volt
Volt
CB Be Used?
480Y/277
Solidly
Grounded WYE
480
277
Yes
No
480
277
Yes
No
480
480
Yes
No
480
*
Yes
No
480
480
Resistance
Grounded WYE
Delta Corner
Grounded
B Phase
480
Delta
Ungrounded
* Ungrounded delta systems - phase conductors
are capacitively coupled to ground
© 2015 Eaton. All Rights Reserved..
20
Slash Rated Exercise
System
Secondary
L-L
L-G
Can 480Y/277
Voltage
System Type
Volt
Volt
CB Be Used?
480Y/277
Solidly
Grounded WYE
480
277
Yes
No
480
277
Yes
No
480
480
Yes
No
480
*
Yes
No
480
480
Resistance
Grounded WYE
Delta Corner
Grounded
B Phase
480
Delta
Ungrounded
* Ungrounded delta systems - phase conductors
are capacitively coupled to ground
© 2015 Eaton. All Rights Reserved..
21
Slash Rated Exercise
System
Secondary
L-L
L-G
Can 480Y/277
Voltage
System Type
Volt
Volt
CB Be Used?
480Y/277
Solidly
Grounded WYE
480
277
Yes
No
480
277
Yes
No
480
480
Yes
No
480
*
Yes
No
480
480
Resistance
Grounded WYE
Delta Corner
Grounded
B Phase
480
Delta
Ungrounded
* Ungrounded delta systems - phase conductors
are capacitively coupled to ground
© 2015 Eaton. All Rights Reserved..
22
Slash Rated Exercise
System
Secondary
L-L
L-G
Can 480Y/277
Voltage
System Type
Volt
Volt
CB Be Used?
480Y/277
Solidly
Grounded WYE
480
277
Yes
No
480
277
Yes
No
480
480
Yes
No
480
*
Yes
No
480
480
Resistance
Grounded WYE
Delta Corner
Grounded
B Phase
480
Delta
Ungrounded
* Ungrounded delta systems - phase conductors
are capacitively coupled to ground
© 2015 Eaton. All Rights Reserved..
23
© 2015 Eaton. All Rights Reserved..
24