Some methods by Eaton in article EQUIPMENT
SCCR
AND
AVAILABLE
FAULT CURRENT
EQUIPMENT
SCCR
AND
AVAILABLE
FAULT CURRENT
HOW TO SATISFY YOUR CUSTOMER NEEDS
What if the SCCR is not adequate?
Responsibility for SCCR can be a challenge for all
parties involved. Ideally, the electrical design engi-
neer will determine the anticipated available fault
current and communicate this requirement to all oth-
er parties and the equipment manufacturers. During
the equipment approval stage, the design engineer
responsible for the specific equipment will verify
that adequate equipment SCCR has been provided
prior to releasing the equipment for production.
However, some equipment manufacturers design to
the minimum 5 kA and do not offer a design with
a higher SCCR. This leads to situations where the
SCCR of the equipment is inadequate, such as in
where the HVAC equipment marked with
a 5 kA SCCR was installed in a location with 13.7 kA
available fault current.
If a situation like this occurs, there are a few options
to bring the equipment into compliance with the
NEC, subject to approval by the AHJ:
1) Install an isolation transformer ahead of the
equipment that reduces the fault current (such as a
480-480 V transformer with a kVA adequate for the
load). The resulting available fault current can be de-
termined via Eaton’s Bussmann series FC2
mobile app
(which also produces labels and documentation).
2) Install additional conductor length to reduce
fault current. The additional conductor length can be
added in Eaton’s Bussmann series FC2
mobile app to
determine the fault current.
3) Modify the equipment as needed and recer-
tify the equipment through field evaluation so the
resulting equipment SCCR (relabeled) is adequate
for the fault current. The equipment manufacturer
is not permitted to make any changes to the equip-
ment after it leaves their manufacturing facility
and retain the original listing. The modification
can be done by a qualified person, however rela-
beling must be provided by a third party Nation-
ally Recognized Testing Laboratory (NRTL).
The NRTL will not provide guidance on how to
modify the equipment; they only evaluate the
equipment as installed. A list of current NRTLs
can be found on the OSHA website.
4) Install a current-limiting overcurrent device,
such as a Class RK1 or J fuse, that reduces the
calculated available fault current to a value equal
to or less than the equipment SCCR. When using
the specific manufacturer let-through data, it is
suggested to mark the specific fuse required on
the equipment. For instance, “Replace with only
Eaton Bussmann series LPJ 60 A fuses.” This
method is only suitable for protecting “passive”
components in the equipment. It is NOT suitable
for non-passive devices such as circuit breakers
and fuses. Circuit breakers or fuses must have an
interrupting rating adequate for the calculated
available fault current. This limitation is based
on NEC 240.86(A), which indicates that using an
engineered series combination rating is only per-
mitted for existing systems, and is not permitted
where the circuit breakers are non-passive. Circuit
breaker manufacturers state that all modern circuit
breaker designs are non-passive, so an engineered
method is generally not permitted.
