Hi all

I am reviewing UL508a and some graphs of fuses to figure out the SCCR of a control panel. My issue is i feel that most of the graphs, charts, data blablabla are geared toward 480vac. My supply voltage in the feeder circuit is 240vac, so do i need to take this into consideration when i am pulling numbers from graphs such as peak let through current for example, or the SCCR of a fuse? nothing i find is dependent on feeder voltage.

Thanks

 

Why is any of this in the automotive section? Maybe we can get it moved to the power section.

The applicable documents have a focus on NEC (National Electric Code) article 409 and UL (Underwriters Laboratories) UL 508a. and involve or provide acceptable guidelines for industrial control panels and power distribution. This includes Short-circuit current rating (SCCR) of industrial control panels and protection circuits.

My supply voltage in the feeder circuit is 240vac, so do i need to take this into consideration when i am pulling numbers from graphs such as peak let through current for example, or the SCCR of a fuse? nothing i find is dependent on feeder voltage.

Yes as it's about the load currents the panel feeds out being protected, short circuit protection. Once we get this out of automotive and into a power section one of th industrial power guys can help better than I can.

Ron

 

Circuit protection devices that are adequate for 480 volt service will certainly be adequate for 240 volt service. The 480 volt devices just open to larger gaps to extinguish the longer arcs that the higher voltage can produce. The only downside to the 480 volt items for 240 volt use is the higher cost, Insulation for 480 volt use costs more than that only rated for 240 volt use.

 

Hi all

I am reviewing UL508a and some graphs of fuses to figure out the SCCR of a control panel. My issue is i feel that most of the graphs, charts, data blablabla are geared toward 480vac. My supply voltage in the feeder circuit is 240vac, so do i need to take this into consideration when i am pulling numbers from graphs such as peak let through current for example, or the SCCR of a fuse? nothing i find is dependent on feeder voltage.

Thanks

HRC (high rupture capacity)/HBC (high breaking capacity) fuses for use in mains circuits normally have a maximum breaking capacity of 1500A. This reflects the fault current that could flow in the event of a short circuit or earth fault.

Bear in mind that it is not always necessary to specify HRC/HBC fuses within mains circuits – where circuit impedance limits the maximum possible fault current (to say <100A), then a lower maximum breaking capacity fuse could be used.

Designers – who only see the fuse rating, often overlook the maximum breaking capacity rating of a fuse. Many fuses have a specified maximum breaking capacity of 35A, or 10x fuse rating (whichever is greater), but are used in circuits where a significantly greater fault current could flow.

 

Regarding the breaking capacity of the fuse, this means that you need to know, at least roughly, the current capability of your power source. That should be possible to calculate if you know what is upstream of your control panel.