FAULT CURRENT/ARC FLASH STUDIES

Per NFPA 70E - anything likely to be serviced or examined while energized. It's rare to apply labels below the 240 V or 208 V panel level. Most 480 V equipment should probably be labeled.
 
Please refrain from using ALL CAPITAL LETTERS! It is considered impolite, as though you were YELLING at us.
 
Arc flash issues are not the same as fault current issues.

Fault current is always an issue, in that it exists in any electrical system regardless of size or scope. All devices in an electrical circuit must always be rated and capable of handling whatever the available fault current (AFC) is at any point in a system. So does it apply to HVAC systems? Absolutely it does. If you get a packaged HVAC unit that has a label on it that says “5kA SCCR”, and you have even just 6kA AFC at that point, you cannot connect it!
 
Deltaforce said:
Summaries
No ask to read full
Please provide details those references would not allow a 5kA rated item to be used where 6kA is available.
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Pretty easy. if the unit has a fault that draws the full 6KA and it is only tested to withstand 5KA that can be a big boo-boo.
 
Strathead said:
Pretty easy. if the unit has a fault that draws the full 6KA and it is only tested to withstand 5KA that can be a big boo-boo.
But current limit device use upstream to raise panel effective sccr 5kA to 6kA accord 110.10 and UL 508A Supplement SB
Click to expand...
 
Jraef said:
Simple really, 5k > 6k. Not sure how you are interpreting that wrong…
Click to expand...
Scenario 5kA sccr panel, 6k AFC
110.10 Circuit Impedance, Short-Circuit Current Ratings, and Other Characteristics. The overcurrent protective devices, the total impedance, the equipment short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices used to clear a fault to do so without extensive damage to the electrical equipment of the circuit.
The above110.10 require select ocpd and sccr of equipment to avoid extensive to equipment.
UL 508A Supplement SB, SB4 Ratings show how do it
 
don_resqcapt19 said:
But nothing permits you to install equipment with a SCCR that is less than the available fault current on the line side terminations of the equipment.
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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.
 
Deltaforce said:
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.
Click to expand...
Interesting some of you here (who I respect and listen to) have clearly stated that you can't use a fuse to reduce the AFC at a piece of equipment. This seems to say that you can with clarifications. If I read it correctly, if non passive items such as fuses and circuit breakers are fully rated to the AFC on the line side of the fuse, then the fuse can be used to lower the AFC to non passive components.
 
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