Short Circuit Rating for a Control Panel
Short Circuit Rating for a Control Panel
(OP)
A requirement of UL508A is to establish the "short circuit current (kA symetrical" of a control panel. Their procedure to accomplish this is pretty detailed. My question is if I have a disconnect - short circuit rated at 200kA - with class CC fuses rated at 100kA, would the short circuit rating of my panel simply be 100kA irregardless of the components on the load side? Or am I making a poor assumption here?






RE: Short Circuit Rating for a Control Panel
RE: Short Circuit Rating for a Control Panel
RE: Short Circuit Rating for a Control Panel
RE: Short Circuit Rating for a Control Panel
strictly on the basis of voltage, current, and interrupting
rating alone will not assure component protection from
short-circuit currents. High interrupting capacity
electro-mechanical overcurrent protective devices,
especially those that are not current-limiting, may not
be capable of protecting wire, cable or other
components within high short-circuit ranges. The
interrupting rating of a protective device pertains only
to that device and has absolutely no bearing on its
ability to protect connected downstream components.
Quite often, an improperly protected component is
completely destroyed under short-circuit conditions
while the protective device is opening the faulted
circuit.
If both the let-thru currents (IRMS and Ip) of the
current limiting fuse and the time it takes to clear the
fault are less than the short circuit withstand rating of the electrical component, then that component will be protected from short-circuit damage.
Often overlooked is the short circuit withstand rating of the wiring itself. Thus, in your illustration, you must go back and look at the disconnect and the load side wiring maximum short-circuit withstand current in amps to see if the fuses will clear the fault in one cycle or less before these values are reached.
David Baird
mrbaird@hotmail.com
Sr Controls Engineer
EET degree.
Journeyman Electrician.
RE: Short Circuit Rating for a Control Panel
This is not to encourage or endorse non-listed equipment but just a fact, in most of the USA. It is not uncommon to find installed control systems which are 'made up' using UL listed or UL recongnized (or equivalent) components but not listed as an assembly.
RE: Short Circuit Rating for a Control Panel
A requirement of UL508A is to establish the "short circuit current (kA symetrical" of a control panel. Their procedure to accomplish this is pretty detailed. My question is if I have a disconnect - short circuit rated at 200kA - with class CC fuses rated at 100kA, would the short circuit rating of my panel simply be 100kA irregardless of the components on the load side? Or am I making a poor assumption here?
///The component inside the panel will have to withstand 100kA which is very high fault level for most control panels. A current limiting fuse, e.g. Ferraz Shawmut A2Y/A6Y 30A, should be used instead bringing 200kA fault level way down to about 9000A. Visit
http://www.ferrazshawmut.com
for more info.\\\
RE: Short Circuit Rating for a Control Panel
http://www.ferrazshawmut.com/products/pdf_107/ATMR.pdf
RE: Short Circuit Rating for a Control Panel
Get out that calculator at start cipherin Jethro. Doesn't seem to be any way around it if you want that UL508A rating.
Have fun.