Install Current Limiting Fuse to Reduce KAIC

You need to
electrofelon said:
So what about something like a typical automatic transfer switch?
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You need to look at the listing procedures for these devices and see what steps must be followed to get the SCCR and withstand ratings.

I know that ATS manufacturers have several choices when determining their fault handling labels which are then confirmed through actual testing.
 
electrofelon said:
Ok, yes, maybe we are on the same page then. I agree UL508A not only likely contains non passive devices, but the listing process / rules have specific requirements for SCCR and upstream OCPD's that you can't ignore.

So what about something like a typical automatic transfer switch?

What about something like a package HVAC unit, do essentially all of those have a UL 508 panel inside of them?
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The ATS manufacturers have tested combinations allowing you to use specific fuses or breakers to support higher withstand ratings.

 
ron said:
The ATS manufacturers have tested combinations allowing you to use specific fuses or breakers to support higher withstand ratings.

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Yes that is a bad example. I have seen and applied the charts provided with ATS's for various protection types and sizes.

Although, IMO, I do not see language in the NEC prohibiting the use of a CL fuse for SCCR purposes, most things seem to have their own manufacturer tested combinations in the instructions that must be followed. I guess as far as equipment goes, you would need something that doesnt have a UL508 control panel or any provided SCCR vs OCPD information.
 
One reason you can't just apply a cl fuse to a circuit and claim to lower the AFC is you have no way to know what is installed on that circuit.

If you used a cl fuse to reduce the AFC to say 10k on a circuit, that would allow you to use 10 kaic CBs downstream, but they might not have been tested to work with a cl fuse.
 
petersonra said:
One reason you can't just apply a cl fuse to a circuit and claim to lower the AFC is you have no way to know what is installed on that circuit.

If you used a cl fuse to reduce the AFC to say 10k on a circuit, that would allow you to use 10 kaic CBs downstream, but they might not have been tested to work with a cl fuse.
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I don't buy that argument. I mean sure if there is a locked door and for national security reasons Joe Byron (and he is actually awake) and won't let you in so you can't see what is passed it then yeah you say no I can't install a CL fuse because I need to look at the rest of the circuit to see if there are circuit elements that are compatible with this method and since I can't look then I can't do it...
 
electrofelon said:
I don't buy that argument. I mean sure if there is a locked door and for national security reasons Joe Byron (and he is actually awake) and won't let you in so you can't see what is passed it then yeah you say no I can't install a CL fuse because I need to look at the rest of the circuit to see if there are circuit elements that are compatible with this method and since I can't look then I can't do it...
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It does not work that way.

You have to be able to trust that the AFC labeled on the box you are wiring from is not conditional because it might not be you doing the install down the road
 
petersonra said:
It does not work that way.

You have to be able to trust that the AFC labeled on the box you are wiring from is not conditional because it might not be you doing the install down the road
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Sorry, absurd argument. It's no different than anything else: we do things all the time where we need to confirm that an existing component or aspect of an electrical system is compatible with what we are doing. And no I am not concerned about someone coming in the future and doing something wrong.
 
There is nothing in the NEC directly saying that you can’t do it. I believe the term that INDIRECTLY says it is the the SCCR of the equipment must be determined by an “approved method” (words to that effect, I don’t have my NEC here). Then somewhere else they list the approved methods, being testing, or the series listing process in UL508A Supplement SB, or a PE letter attesting to the validity of the series combination.

So that is what stops contractors and end users from doing it on their own in the field when some buyer slacks off and fails to include a PROPER level of SCCR in the call for bids on the equipment. Because really, it’s NOT DIFFICULT to attain a decent workable SCCR, it just requires selecting combinations of parts that have ALREADY BEEN SERIES TESTED AND LISTED TOGETHER, instead of buying the cheapest part you can find for any component and kicking the can down the road.

And circling back to the CL fuse issue, they CAN AND ARE used in this process all the time, but they must be TESTED AND LISTED with the components involved for it to be valid (other than the PE option). Most UL/ETL/CSA listed components will have gone though that process already, so the people building the panel just have to find that data and document it when applying their UL label. But it does mean that the list of components they can use TOGETHER is more restricted because, for example, a Square D or Eaton or AB contactor will not be listed in series with a cheap Overload relay that they got from some Chinese supplier that is technically UL listed, but never series tested. Simple little rules like that.
 
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