OCPD

[voltron666]

Hello! First post.

I'm looking to protect a circuit that is powered by one phase of a three-phase WYE, the circuit is powered between hot and neutral on a 415V (phase-phase), 240V (phase-neutral) WYE where the neutral is solidly grounded.

240.60 (A)(2) makes it clear I can use a 300V fuse. But I want to use a 240V (non-slash rated circuit breaker).

From an Eaton document
-----------------
"
A straight rated OCPD (whether a fuse or circuit breaker) that protects
a single pole can be used to protect single-phase, line-to-neutral
loads when supplied from a three-phase, solidly grounded circuit. For
example, a 300 V rated fuse can be used to protect single-phase, line-
to-neutral loads when supplied from a three-phase, solidly grounded,
480/277 V circuit, where the single-phase, line-to-neutral voltage is 277
V. This is allowed in this application because a 300 V fuse will not have
to interrupt a voltage greater than its 300 V rating."
---------------

The NEC seems ambiguous; it doesn't seem to have the equivalent of 240.60 (A)(2) under the circuit breaker section.

So is it OK to use a 240V straight rated circuit breaker to protect a Single-phase line-to-neutral circuits supplied from a 3-phase, 4-wire, solidly grounded neutral source where the line-to-neutral voltage doesn't exceed 240V?

 

[Besoeker3]

"the circuit is powered between hot and neutral on a 415V (phase-phase), 240V"
If it is 415/240i s it possibly 50Hz?

 

[bwat]

Interesting. I think you're right. I don't see an applicable 240.60 (A)(2) for breakers. And I can't tell whether the sections below permit or prohibit what you're proposing. I think I want to say that they prohibit though because of the words "nominal system voltage".

240.83 Marking.
(E) Voltage Marking. Circuit breakers shall be marked with a
voltage rating not less than the nominal system voltage that is
indicative of their capability to interrupt fault currents between
phases or phase to ground.

240.85 Applications. A circuit breaker with a straight voltage
rating, such as 240V or 480V, shall be permitted to be applied
in a circuit in which the nominal voltage between any two
conductors does not exceed the circuit breaker’s voltage rating.
A two-pole circuit breaker shall not be used for protecting a
3-phase, corner-grounded delta circuit unless the circuit
breaker is marked 1φ–3φ to indicate such suitability.

A circuit breaker with a slash rating, such as 120/240V or
480Y/277V, shall be permitted to be applied in a solidly grounded
circuit where the nominal voltage of any conductor to
ground does not exceed the lower of the two values of the
circuit breaker’s voltage rating and the nominal voltage
between any two conductors does not exceed the higher value
of the circuit breaker’s voltage rating.

Informational Note: 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.

 

[don_resqcapt19]

The 480/277 or a straight 480 volt rated breaker is what you need.