Available fault current ratings
Available fault current ratings
(OP)
We have a new machine that came in. It has a 5ka rating. My available fault current is higher than that. I assume I need to install a disconnect and fuses to get it lower than the 5000. Anyone know what style or type of fuse I can use?
RE: Available fault current ratings
Nope. No can do in a Code compliant way. This was a failure of whomever bought the machine to tell the machine supplier that this was a requirement. If the tender document stated that it was the SUPPLIER'S responsibility to ensure that the "SCCR" (Short Circuit Current Rating) meet or exceeded your Available Fault Current, it would have triggered a set of conversations about your needs and the supplier COULD HAVE very simply designed and listed their control panel to meet that requirement. But unfortunately there is no simple or low cost way to fix this after the fact.
Your options are:
1. Remove the control panel and find a local UL-508A listed panel shop willing to gut and rebuild that panel, putting their OWN new UL listing on it with the proper SCCR.
2. Send the machine back to the manufacturer and tell them to do it.
3. Hire a registered PE in your area to do a deep dive evaluation of ALL of the components in the power circuit of the machine, then come up with a STAMPED drawing or document stating that they have done a thorough evaluation and approved the use of a SPECIFIC current limiting fuse ahead of this. Good luck on finding that PE by the way (I know, I've tried). They would be staking their professional license on this, so they are not going to do so inexpensively, if at all.
Take note of that initial statement I made for any and all future machinery purchases. IF YOU DON'T SPECIFY WHAT YOU NEED, SUPPLIERS WILL OFTN IGNORE THIS ISSUE. It's easy to just put a "default" rating of 5kA on a panel, because you do NOT do any of the relatively simple and inexpensive steps that it takes to get a decent SCCR. One of those simple steps is to use devices that are ALREADY listed in series with each other, so that you do not have to do the expensive testing. That however means the component MANUFACTURERS have had to do that expensive testing, and one mfr is not going to do testing of their components in series with a competitor's components. That then means that if you use Siemens breakers, you have to use Siemens Contactors and Siemens Overload Relays etc. etc. Cheap panel builders and OEMs want to use the cheapest parts they can find for every component, i.e. Siemens breaker, Schneider contactor, ABB terminal block etc., but that then means they cannot get more than the "courtesy" 5kA SCCR. If YOU, the buyer, tell them that it MUST have an SCCR of 65kA (or whatever you need), then they CAN just spend a little extra for the parts that all match up.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Available fault current ratings
RE: Available fault current ratings
You should be able to verify the let-through current of selected fuses.
RE: Available fault current ratings
RE: Available fault current ratings
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Available fault current ratings
I wasn't speaking about UL listed panels in my post and I am not that much conversant with American practice.
Thanks again.
RE: Available fault current ratings
RE: Available fault current ratings
RE: Available fault current ratings
RE: Available fault current ratings
RE: Available fault current ratings
RE: Available fault current ratings
Provided an AHJ accepts that as an "approved method", and then you have to live with the losses of that transformer forever.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Available fault current ratings
RE: Available fault current ratings
RE: Available fault current ratings
240.86(A) is the only possible exception in terms of getting a "series rating" with a current limiting device, and that is where the Code establishes the requirement for it to be done and stamped by a registered PE.
" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
RE: Available fault current ratings
jraef - sure the code may say that, doesn't mean the inspector won't work with you and allow something else. The inspector always has final say.
RE: Available fault current ratings
This should be good enough.
RE: Available fault current ratings
RE: Available fault current ratings
RE: Available fault current ratings
RE: Available fault current ratings
Why do you suggest an AHJ would need to approve this in regards to the acceptability of installing the panel at this location? It is simply lowering the "available fault current" as mentioned in 409.22.