Elevator Controller SCCR

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petersonra said:
UL 508a allows for this but it has to be marked on the control panel by the manufacturer. And there are serious limitations.
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Yep. It has to be done by the manufacturer, it cannot be done simply by field installing a fusible disconnect, unlike what I routinely saw.
 
jim dungar said:
Option 2 is valid only if the elevator controls and fuses have been tested and listed as a combination. It makes no difference if they have an integral OCP or not.

Fuses do not really lower the fault current until the fault current reaches their current limiting threshold.
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augie47 said:
110.22 & 240.86 require the method of reduction must be thru a LISTED combination or designed by a professional engineer.
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Ok you guys know my stance on this. The tested combination is for OCPD's and does not apply to SCCR. See the definition of "current limiting fuse" right in the NEC. Considering that I am seeing nothing prohibiting this.

Current-Limiting Overcurrent Protective Device. A device that, when interrupting currents in its current-limiting range, reduces the current flowing in the faulted circuit to a magnitude substantially less than that obtainable in the same circuit if the device were replaced with a solid conductor having comparable impedance
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Until the NEC has a statement saying that this is not an acceptable method to reduce AFC, I will not be able to accept that it is prohibited.
 
electrofelon said:
Ok you guys know my stance on this. The tested combination is for OCPD's and does not apply to SCCR. See the definition of "current limiting fuse" right in the NEC. Considering that I am seeing nothing prohibiting this.



Until the NEC has a statement saying that this is not an acceptable method to reduce AFC, I will not be able to accept that it is prohibited.
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The protective device must be in its current limiting range before it has any current limiting effect. While it is easy to hit this threshold for relatively small fuses, it can often exceed 22kA for devices 800A and larger.

The NEC definition of current limiting is not the same as the UL definition, which includes a time element as well as a current magnitude. Many modern molded case breakers meet the NEC definition but not the UL, partly this is why series combination ratings are relatively easy to obtain using existing equipment designs.
 
jim dungar said:
The protective device must be in its current limiting range before it has any current limiting effect. While it is easy to hit this threshold for relatively small fuses, it can often exceed 22kA for devices 800A and larger.

The NEC definition of current limiting is not the same as the UL definition, which includes a time element as well as a current magnitude. Many modern molded case breakers meet the NEC definition but not the UL, partly this is why series combination ratings are relatively easy to obtain using existing equipment designs.
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I haven't seen many HVAC units or elevators, 800 amps and over, let alone other equipment. It seems to me that this discussion is getting in to the weeds like we (I am including myself) often do here on MH. Correct me if I am wrong, but you aren't disputing that a J or R type fuse on a 5000A SCCR elevator that has an overcurrent protection of 70 - 110 amps which is typical for my installations is code compliant.
 
see the discussion at

HVAC Short Circuit Withstand Rating

So I have a chiller, and like almost all HVAC Equipment, it has a short circuit withstand rating of 5KA. It has a MCA of about 500 amps, so I'm obviously going to supply it with a system that has a much greater available fault current than 5KA, which is a code violation. I can add a fused...
forums.mikeholt.com
 
Strathead said:
I haven't seen many HVAC units or elevators, 800 amps and over, let alone other equipment. It seems to me that this discussion is getting in to the weeds like we (I am including myself) often do here on MH. Correct me if I am wrong, but you aren't disputing that a J or R type fuse on a 5000A SCCR elevator that has an overcurrent protection of 70 - 110 amps which is typical for my installations is code compliant.
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I don't recall any of my fuse training courses, not seminars, through Mersen and Bussmann ever claiming a current limiting fuse could be assumed to lower the available fault current for untested equipment like contactors, relays, and VFDs.
 
jim dungar said:
I don't recall any of my fuse training courses, not seminars, through Mersen and Bussmann ever claiming a current limiting fuse could be assumed to lower the available fault current for untested equipment like contactors, relays, and VFDs.
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Yeah. The sure-fire solution is to use only series-rated combinations! Why do people have to crack their heads on these problems?
 
jim dungar said:
I don't recall any of my fuse training courses, not seminars, through Mersen and Bussmann ever claiming a current limiting fuse could be assumed to lower the available fault current for untested equipment like contactors, relays, and VFDs.
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I don’t have enough knowledge to debate, so I am actually questioning not arguing. Doesn’t this document from Bussman indicate that fuses limit the available fault current.
 
Strathead said:
I don’t have enough knowledge to debate, so I am actually questioning not arguing. Doesn’t this document from Bussman indicate that fuses limit the available fault current.
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I don't know what document you are referring to, but in my old copies of their SPD Bussmann doesn't include fuses when performing their Short Circuit calculations.

In their current limiting fuse section they do use address bus bars and conductors as examples but not control panels.
 
That is a good publication for OEMs looking to build and list equipment, particularly control panels to UL508A. I dont see it as much help in the majority of field applications

This 2016 Eaton publication never talks about taking fuse current limitation into account when performing available fault current calculations and general compliance with the NEC.
 
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jim dungar said:
That is a good publication for OEMs looking to build and list equipment, particularly control panels to UL508A. I dont see it as much help in the majority of field applications

This 2016 Eaton publication never talks about taking fuse current limitation into account when performing available fault current calculations and general compliance with the NEC.
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And I think it is a little irresponsible for Bussman (Eaton) to keep ignoring that issue. I see this document trotted out almost every time contractors, who don’t fully understand the context it was intended for, but have to deal with low SCCR values on equipment from lazy suppliers. All Eaton needs to do is add a preamble explaining the purpose of this paper and point out that the methods can’t be used in the field by users and contractors.
 
Jraef said:
And I think it is a little irresponsible for Bussman (Eaton) to keep ignoring that issue. I see this document trotted out almost every time contractors, who don’t fully understand the context it was intended for, but have to deal with low SCCR values on equipment from lazy suppliers. All Eaton needs to do is add a preamble explaining the purpose of this paper and point out that the methods can’t be used in the field by users and contractors.
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Please educate me. I see Eaton stating the let through current of their fuses. If the let through current is, SYS 3800 amps peak, then why isn’t the sccr also 3800 on the load side of the fuses.
 
Strathead said:
Please educate me. I see Eaton stating the let through current of their fuses. If the let through current is, SYS 3800 amps peak, then why isn’t the sccr also 3800 on the load side of the fuses.
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Let me help. Though Eaton says it is, it doesn't mean it actually is!
As 240.86 provides, you are given 2 options and a prohibition:
One, it is a selection of a fuse/ breaker combination done by a licensed PE, the documentation available for others to those authorized to design, install, inspect, maintain, and operate the system; the PE ensures that the downstream protective device remains passive during the interruption (by the upstream protective device); signs, and seals/ stamps the correctness of the selection, etc.
Two, and the easier way, is to get tested series-rated combinations from manufacturers of these protective devices.

Prohibition is to never use a series-rated combination if motor circuits are connected between the higher-rated overcurrent device and the lower-rated device and the motor full-load currents exceed 1% of the interrupting rating of the lower-rated protective device.
 
topgone said:
Let me help. Though Eaton says it is, it doesn't mean it actually is!
As 240.86 provides, you are given 2 options and a prohibition:
One, it is a selection of a fuse/ breaker combination done by a licensed PE, the documentation available for others to those authorized to design, install, inspect, maintain, and operate the system; the PE ensures that the downstream protective device remains passive during the interruption (by the upstream protective device); signs, and seals/ stamps the correctness of the selection, etc.
Two, and the easier way, is to get tested series-rated combinations from manufacturers of these protective devices.

Prohibition is to never use a series-rated combination if motor circuits are connected between the higher-rated overcurrent device and the lower-rated device and the motor full-load currents exceed 1% of the interrupting rating of the lower-rated protective device.
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But we are not talking about 2 OCPDs in series, we are talking SCCR, 240.86 does not apply.
 
I agree. That 240.86, and seems to bolster the argument that fuses can be used. Since it doesn’t say you can’t use fuses.
 
Strathead said:
I agree. That 240.86, and seems to bolster the argument that fuses can be used. Since it doesn’t say you can’t use fuses.
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Did you read the Eaton article about complying with the 2017 NEC? The article does not address article 240. They do mention fuses as part of a control panels listing process and for bus bars.
Eaton never includes fuse current limitation in any of their SCCR calculation methods.
 
electrofelon said:
But we are not talking about 2 OCPDs in series, we are talking SCCR, 240.86 does not apply.
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Quite circuitous but those terms are related, IMO. You are required to choose an OCPD that will protect/ will never subject the electrical component to conditions beyond its withstand ratings (SCCR). When we talk about SCCRs, we are also looking at OCPD settings/ ratings. I never doubted what I posted especially when the OP mentioned fuse's (a protective device) let-through levels.
 
topgone said:
Quite circuitous but those terms are related, IMO. You are required to choose an OCPD that will protect/ will never subject the electrical component to conditions beyond its withstand ratings (SCCR). When we talk about SCCRs, we are also looking at OCPD settings/ ratings. I never doubted what I posted especially when the OP mentioned fuse's (a protective device) let-through levels.
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My point is 240.86 does NOT require a tested combination for SCCR of a downstream device. That section is for two OCOD's in series.

As it is, I see no NEC prohibition against using a properly selected CL fuse (no PE required) to reduce the fault current for SCCR purposes. I actually don't have a dog in the fight - If this isn't an "accepted" method, then the NEC needs to tell me it's not.
 
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