Why NRTL ?

[augie47]

Had an interesting situation on an installation.
The State of TN requires NRTL certification on equipment.
On a recent install the facility has a SCA of 45k not counting motor contribution.
A new piece of equipment for controlling (30) 25 hp motors was installed. The control cabinet did not meet the requirements of 409.110 ('08). In complying, the manufacturer supplied a nameplate indicating a SCCR rating of 65k.
To meet the State requirement, they had a UL field evaluation performed and as a result the new, UL certified nameplate shows a withstand raring of 5k.
Obvioulsy a potential danger that would have remained unchecked were it not for the NRTL requirement.

 

[jumper]

Good catch Gus.:thumbsup:

 

[shortcircuit2]

How are they going to protect the equipment now?

 

[augie47]

How are they going to protect the equipment now?

A couple of interesting inputs from the cabinet manufacturer...
(a) "we don't understand UL limiting the SCCR to 5k as the 800 amp main breaker is
rated 65k"
(b) "the way we see it, it's a feeder problem, not a cabinet problem"
(he has a point if the customer would only increase his feeder (parallel 500s) by 1500 ft, problem solved)

The scary part is their stating this is the "standard cabinet" and they have never had this problem. From earlier conversions it appears they have never had a one NRTL listed.
That's one of the reasons for my post.... cabinets like these are out there, folks !

 

[shortcircuit2]

Can't they protect the equipment with current limiting fuses?

 

[augie47]

Can't they protect the equipment with current limiting fuses?

I'll leave that up to the engineer's to decide, but I have not found a fuse that will
reduce 43k to 5 k.
The equipment has Class J fuses on each starter. Apparently those did not satisfy the evaluators. (The IEC starters have a 5k rating which seems to be the weak link in the chain)

 

[petersonra]

I'll leave that up to the engineer's to decide, but I have not found a fuse that will
reduce 43k to 5 k.
The equipment has Class J fuses on each starter. Apparently those did not satisfy the evaluators. (The IEC starters have a 5k rating which seems to be the weak link in the chain)

my guess might be that the evaluators did not look real close. most iec contactors are rated at 65k with class j fuses.

 

[augie47]

my guess might be that the evaluators did not look real close. most iec contactors are rated at 65k with class j fuses.

lets hope that's the case...
I have not seen the UL report..there may well be some other limiting factor.

 

[Jraef]

Had an interesting situation on an installation.
The State of TN requires NRTL certification on equipment.
On a recent install the facility has a SCA of 45k not counting motor contribution.
A new piece of equipment for controlling (30) 25 hp motors was installed. The control cabinet did not meet the requirements of 409.110 ('08). In complying, the manufacturer supplied a nameplate indicating a SCCR rating of 65k.
To meet the State requirement, they had a UL field evaluation performed and as a result the new, UL certified nameplate shows a withstand raring of 5k.
Obvioulsy a potential danger that would have remained unchecked were it not for the NRTL requirement.

Maybe, maybe not. 5kA is basically the "courtesy" SCCR rating level that can be applied to just about anything that has not been tested or listed higher. The process of determining the SCCR rating is not terribly difficult, but it is easy to miss a detail or two, leaving you with a default down to that lower level. Example:
Let's say the power components are a bunch of starters, assembled from components of the same mfr, like Siemens (because I know some numbers there to use in this). If you look at the contactor alone, it will say 10kA SCCR, then the overload relay says 5kA SCCR, and the MCP is rated 65kAIC. But Siemens will have a "series combination" of those three devices, with specific part numbers, that has been separately tested and listed by UL to have an overall SCCR rating of 65kA. If every starter inside the box was assembled of the correct components in a listed series combination, and there were no other power components in the box, then they can put a label on it that says it is rated at 65kA SCCR. But if even one component in the power circuit was not on the list of series combination devices, and it was unevaluated on its own or the mfr blew it off and just used 5kA, it invalidates everything else that may have been done and everything defaults down to that 5kA level.

But if the panel had no NRTL label on it in the first place, that means the supplier was NOT a UL508A listed shop, so the documentation would not be there to determine any series combination listings. In calling for UL to do a field inspection, if they did not specifically ask UL to perform the necessary tasks to do an SCCR determination and provide them with the information, they wouldn't do it (UL charges extra for that). Bottom line, it comes down to that panel supplier living in the past and from the comments you posted later, has no clue they are... No can do any more, they need to catch up or fold up.

 

[jim dungar]

But if even one component in the power circuit was not on the list of series combination devices, and it was unevaluated on its own or the mfr blew it off and just used 5kA, it invalidates everything else that may have been done and everything defaults down to that 5kA level.

In my experience, the most common component is a power distribution block.

 

[Jraef]

In my experience, the most common component is a power distribution block.

Yeah, that's often a killer. AB 1492 PDL distribution blocks have been listed as 100kA SCCR since 2008, but hardly anyone noticed or cared. Now that inspectors in more states have been trained on what to look for regarding SCCR ratings, they have been flying off the shelf.

 

[petersonra]

In my experience, the most common component is a power distribution block.

many of them have pretty decent ratings though when protected by fuses.