Short Circuit Rating for a Control Panel 1

[rdub]

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?

 

[rbulsara]

I would say your assumption is safe from engineering point of view. Getting an actual UL listing (Lable) is a different matter.

 

[alehman]

Class CC fuses will adequately protect most control components. You will need to have a UL certified shop build it if it must be UL listed and labeled. There will be an extra (possibly significant) cost for that service.

 

[advidana]

No, the short circuit for your panel is not rated. have a cerified lab run a test on your panel for rating.

 

[dbaird]

CAUTION: Choosing overcurrent protective devices
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.

 

[rbulsara]

Just aside having a UL or equivalent listing is not necessarily a Code requirement as the AHJ ( authority having jurisdiction) can accept or reject any installtion.

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.

 

[jbartos]

Comment on (Electrical) Apr 5, 2004 marked ///\\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.\\

 

[alehman]

Class CC fuses are also very good at current limiting.

http://www.ferrazshawmut.com/products/pdf_107/ATMR.pdf

 

[skiier]

How detailed can these calculations be? Do you not have a finite number of cct's in your panel? Is it that you don't want to do the calculations?
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.