OT: Short Circuit Current Calculation To Satisfy EN60204

[kamenges]

We have a machine we are supplying to a European customer. From what I can tell, according to EN60204 we are required to specify the short circuit current withstand capacity of the main enclosure we are supplying. However, I can't seem to find any information concerning how to determine this value. I have found all sorts of information about how to calculate available fault current from the supply but not much about how to determine a completed enclosures withstand capability. I have to assume it is done similarly to a UL SCCR calculation but I don't know. If anyone has a source of information on this I would love to know about it.

Keith

 

[kamenges]

Bump

 

[Gil47]

My guess is that you look at all components in the enclosure that are mains powered,
finding the one with the lowest rating, and its the winner for your rating

 

[Manglemender]

I've only ever done this the other way around by calculating/specifying the fault current and selecting components to meet that requirment.

As Gil47 says. To assess a control panel that is already built you would need to look at the fault current rating of the power facing components to first determine which has the lowest rating i.e. if your main breaker can only handle 10KA then that is the fault level.

Each power breaker / fuse that you add will alter the maximum fault current downstream and many manufacturers produce tables for what is called "type 2 co-ordination" that specify what downstream components are acceptable below a primary device to ensure that the right breaker trips in the event of a fault.

Nick

 

[Badger]

Is it not the withstand capability of the earth wire that is connected to said enclosure, it would make sense. Suppose the enclosure was made of plastic? The actual enclosure should never be an integral part of the earthing system.

 

[kamenges]

Thanks for the replies. That definitely helps.

Functionally, in my case does it make more sense to start at the "end" and work backward toward the enclosure supply? That is, should I determine the withstand capability of my power components (drives, contactors, etc) then work upstream toward my supply, determining a new withstand value based on the peak let-through current of my circuit protection devices or the withstand of the circuit protection device, whichever is lower? Or can't the available fault current be modified by the peak let-through value? Also, there seem to be several current ratings listed for a specific device. Which rating do I use to determine the short circuit rating?

Thanks,
Keith

 

[James Mcquade]

since you are building a machine for a european company, please note the following:

1. the power frequency may be 50 hz.
2. the three phase power will more than likely be 380 volts
(sqrt of 3 times 220). 220 volts is the single phase
voltage level.

3 there are three documents that you must comply with.
the eu directive, the safety directive, and i cannot remember the third. it has been to long since i worked with the requirements.

regards,
james

 

[kamenges]

Interestingly enough we have supplied equipment into Europe before. So we have a pretty reasonable handle on the basic design side stuff. But to the best of my knowledge we haven't supplied a short circuit rating before; only a rated current value. Since we have always supplied equipment through another manufacturer I suspect they handled the short circuit current calculation for us.

Keith

 

[osmanmom]

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/shb900-rm001_-en-p.pdf

 

[kamenges]

osmanmom, can you tell me where in that document I can find a short circuit rating calculation? That document looks more related to general equipment safety than overcurrent protection specifically.

Keith

 

[osmanmom]

apps.geindustrial.com/publibrary/checkout/Short%20Circuit?TNR=White%20Papers|Short%20Circuit|generic

www.cooperindustries.com/content/da...ch_Lib_Short_Circuit_Current_Calculations.pdf

ecmweb.com/design/short-circuit-fault-calculations

w3.siemens.com/powerdistribution/global/EN/consultant-support/electrical-planning-software/service-support/documents-publications/tabcardpages/Documents/Publications/Short_Circuit_Calculations_with_SIMARIS_design.pdf

 

[osmanmom]

Google

 

[osmanmom]

stevenengineering.com/tech_support/PDFs/06FUSA.pdf

www.centralmat.com.br/artigos/mais/mvamethodexample_sc_lf.pdf

www2.schneider-electric.com/documents/technical-publications/en/shared/electrical-engineering/electrical-know-how/low-voltage-minus-1kv/ect158.pdf

 

[osmanmom]

www.theseus.fi/bitstream/handle/100...Circuit Current Calculation and Solutions.pdf

 

[kamenges]

I think I must be missing something. The links posted above tell me how to calculate the prospective fault current at various locations in the circuit. So is the idea that I just use the withstand current of the devices at the end of the string (a drive or contactor, for example) and run the calculation backward to determine the withstand capability of the complete enclosure?
In the end, assuming that this is similar to a North American installation, I have to put a number on the enclosure that indicates the maximum current allowed to the enclosure if a fault occurs inside the enclosure. Depending on component selection that may be higher than the actual fault current that will flow. Since I have no control over the supply to the enclosure I can't use the enclosure feeder lines or transformers to help determine the prospective fault current. All I have is the published withstand capability of the components I have in the enclosure. So all I can definitively state is the fault current limit that the installer needs to stay under in order to safely install the enclosure.

Keith