FAULT CURRENT/ARC FLASH STUDIES

Strathead said:
Interesting some of you here (who I respect and listen to) have clearly stated that you can't use a fuse to reduce the AFC at a piece of equipment. This seems to say that you can with clarifications. If I read it correctly, if non passive items such as fuses and circuit breakers are fully rated to the AFC on the line side of the fuse, then the fuse can be used to lower the AFC to non passive components.
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The Bussmann literature has always vaguely hinted at the ability of fuses to be used to lower fault current, however I have never seen product (UL) standards that do. But they discuss this topic in several different areas.
The closest I have seen is is UL 508A which has some blanket acceptance for fuses <30A, but all larger sizes need to be tested.

This is where internet searches, especially AI, falls down. It finds popular citations which may actually be taken out of context.
 
jim dungar said:
The Bussmann literature has always vaguely hinted at the ability of fuses to be used to lower fault current, however I have never seen product (UL) standards that do. But they discuss this topic in several different areas.
The closest I have seen is is UL 508A which has some blanket acceptance for fuses <30A, but all larger sizes need to be tested.

This is where internet searches, especially AI, falls down. It finds popular citations which may actually be taken out of context.
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Do you think that quoted section directly from Eaton was taken out of context? I don't. My pea brain has always thought it makes sense that a quick blowing fuse could limit the damage to acceptable levels.
 
Strathead said:
Do you think that quoted section directly from Eaton was taken out of context? I don't. My pea brain has always thought it makes sense that a quick blowing fuse could limit the damage to acceptable levels.
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Yes, I do. In the old Bussmann SPD books they had sections on electricians meeting 110.10 rules and OEM building control panels which led to different conclusions on using let-through currents.
Ask the Eaton power systems engineers (the ones that do Short Circuit and Arc Flash studies) what they think about using fuse let through curves to protect equipment like HVAC. Check with an equipment manufacturers as to why they offer both 65k and 5K rated distribution blocks.
 
jim dungar said:
Yes, I do. In the old Bussmann SPD books they had sections on electricians meeting 110.10 rules and OEM building control panels which led to different conclusions on using let-through currents.
Ask the Eaton power systems engineers (the ones that do Short Circuit and Arc Flash studies) what they think about using fuse let through curves to protect equipment like HVAC. Check with an equipment manufacturers as to why they offer both 65k and 5K rated distribution blocks.
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I hope you know, I am not pretending to understand the nuance of this. What I do know is there are certainly thousands, if not millions of jobs out there where this is violated. Not aware of many design teams or inspectors focused on this. Kind of concerning when I read form knowledgeable people like you.
 
Strathead said:
Not aware of many design teams or inspectors focused on this.
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I spent 15 years on the Schneider Electric team doing this work. We competed with every other manufacturer like Eaton and Siemens.
These are the groups that perform the Short Circuit studies often required in job specifications.
 
This topic comes up quite a bit. The theory makes sense, but this is another one of those issues that comes to a combination of manufacturer instructions, listings and practical installation.

It is quite a deep rabbit hole but it was really affirmed by busman and UL at a recent conference that trying to do so is just not feasible. All of the UL, busman, littlefuse, etc. reps said that literature is meant for people who make the control panels / industrial control panels. And installed inside of the panel. Not exterior to the panel.

Meaning, trying to reduce peak let through by exterior means, like fuses, acknowledges you are installing it knowing that the available fault current is higher. Tested / listed series rating combinations is the only way I know of that manufacturers allow to protect their panel.

Strathead said:
I hope you know, I am not pretending to understand the nuance of this. What I do know is there are certainly thousands, if not millions of jobs out there where this is violated. Not aware of many design teams or inspectors focused on this. Kind of concerning when I read form knowledgeable people like you.
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This is true and is a combination of factors.

1) available fault current is a maximum value and is almost never that high. Meaning equipment failure by means of too much fault current is not always probable. But, if it does occur, can be catastrophic to the building, equipment, people nearby, etc.

2) Because newer equipment has a different failure life cycle. Mainly the controls or programing are the primary reason for replacement, removal, etc. It is rarely a fault that marks the end of life for industrial control panels.

3) Multi hat inspectors are a jack of all trades and seldomly recognize the nuance issues. Not all plan reviews require AFC on the plan check. So by the time the field inspection takes place, the electrician / contractor is just installing it per plans. The engineer of record might not even know the SCCR of the equipment purchased by the owner when he is drafting the plans for plan review. Or the general contractor / electrical contractor doesn't coordinate with the engineer for AFC when buying the industrial control panels thinking they know what they are buying. There are a lot of messed up ways this can get lost in translation between involved parties.
 
Deltaforce said:
4) Install a current-limiting overcurrent device,
such as a Class RK1 or J fuse, that reduces the
calculated available fault current to a value equal
to or less than the equipment SCCR. When using
the specific manufacturer let-through data, it is
suggested to mark the specific fuse required on
the equipment. For instance, “Replace with only
Eaton Bussmann series LPJ 60 A fuses.” This
method is only suitable for protecting “passive”
components in the equipment. It is NOT suitable
for non-passive devices such as circuit breakers
and fuses. Circuit breakers or fuses must have an
interrupting rating adequate for the calculated
available fault current. This limitation is based
on NEC 240.86(A), which indicates that using an
engineered series combination rating is only per-
mitted for existing systems, and is not permitted
where the circuit breakers are non-passive. Circuit
breaker manufacturers state that all modern circuit
breaker designs are non-passive, so an engineered
method is generally not permitted.
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Yet I have set in on a number of classes given by a power engineer from Eaton who is a PE and every time he says we cannot do that. He is currently the director of Codes and Standards for Eaton.

Appears that there is a difference of opinion on this issue among electrical professionals, even those from the same organization.
 
don_resqcapt19 said:
Yet I have set in on a number of classes given by a power engineer from Eaton who is a PE and every time he says we cannot do that. He is currently the director of Codes and Standards for Eaton.

Appears that there is a difference of opinion on this issue among electrical professionals, even those from the same organization.
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For metod 4, no downstream fuse or circuit breaker, it can used straightaway, otherwise no possible use
Complexity of method 4 thus
Other methods like method1 viable
 
Deltaforce said:
For metod 4, no downstream fuse or circuit breaker, it can used straightaway, otherwise no possible use
Complexity of method 4 thus
Other methods like method1 viable
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No.
No.
No.
There is no industry accepted methodology for applying current limiting fuses except as a piece of equipment. I don't care how many AI generated summaries can be produced from internet sources that rely on sales and marketing literature.

Post #27 cites the Codes and Standards director from Eaton, while post #26 mentions a conference on this topic. Back in 1999 I attended a week long course taught by Bussmann where we were taught that current limiting fuses are not the answer to all problems other than cables and bus bars. Primarily because components rarely have their Peak current (Ip) values provided for field evaluation.

If an item carries a label from a testing agency, such as UL, you cannot simply put fuses in front of it if the available fault current is too high. If it was this simple why didn't the company do that when they submitted the item for testing?
 
jim dungar said:
No.
No.
No.
There is no industry accepted methodology for applying current limiting fuses except as a piece of equipment. I don't care how many AI generated summaries can be produced from internet sources that rely on sales and marketing literature.

Post #27 cites the Codes and Standards director from Eaton, while post #26 mentions a conference on this topic. Back in 1999 I attended a week long course taught by Bussmann where we were taught that current limiting fuses are not the answer to all problems other than cables and bus bars. Primarily because components rarely have their Peak current (Ip) values provided for field evaluation.

If an item carries a label from a testing agency, such as UL, you cannot simply put fuses in front of it if the available fault current is too high. If it was this simple why didn't the company do that when they submitted the item for testing?
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Drop method 4 ( for separate thread?)
But method 1, method 2 and method 3 viable
 
I know some of you have direct access with Mr. Holt. It would be really helpful to have a video lecture by him and possibly an industry expert to discuss SCCR and having AFC's that are too high. This is a good thread and we have had this discussion previously as well. But a firm comprehensive video we could point to would be helpful.

This actually reminds me a little of derating for the # of current carrying conductors. back in the early 90's and before, it was not enforced with any vigor. Box fill another one. Today both seem to be on the top of minds.
 
Deltaforce said:
But method 1, method 2 and method 3 viable
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Yes, methods one and two make changes in the circuit that actually results in a reduction of the available fault current, and method 3 changes the components in the equipment so that the equipment has a higher SCCR. .
 
Strathead said:
Not aware of many design teams or inspectors focused on this. Kind of concerning when I read form knowledgeable people like you.
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There have been many threads on this site over the years from electrical contractors asking how to solve the issue of equipment, mostly HVAC equipment, that is marked with a SCCR of 5kA where the supply circuit has an available fault current that far exceeds the marked SCCR.
 
don_resqcapt19 said:
Eaton's director of codes and standards says you cannot use method 4. No exceptions.
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This para 'Circuit
breaker manufacturers state that all modern circuit
breaker designs are non-passive, so an engineered
method is generally not permitted.' also present in method 4 under #18.
But opinions differ as in
240.86(A) Series Rated Systems. Selected Under Engineering Supervision in Existing Installations. https://www.electricallicenserenewa...ucation-Courses/NEC-Content.php?sectionID=424
 
Deltaforce said:
Drop method 4 ( for separate thread?)
But method 1, method 2 and method 3 viable
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Those other methods are not in question, as they actually reduce the amount of available fault current. Item 4 is the one that frequently gets misapplied.
 
T
Deltaforce said:
This para 'Circuit
breaker manufacturers state that all modern circuit
breaker designs are non-passive, so an engineered
method is generally not permitted.' also present in method 4 under #18.
But opinions differ as in
240.86(A) Series Rated Systems. Selected Under Engineering Supervision in Existing Installations. https://www.electricallicenserenewa...ucation-Courses/NEC-Content.php?sectionID=424
Click to expand...
The term 'modern' is misleading as circuit breakers have had non-passive construction for close to 100 years now. All molded case breakers are non-passive regardless of their age. The engineering option is really only applicable to the old open style construction found in power circuit breakers or the filled breakers common in utility equipment as UL now requires most breakers to have an instantaneous 'self protection' trip point beyond its normal Time Current Curve.

It has been more than 40 years since I have heard of any engineer actually applying this exception.
 
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jim dungar said:
UL now requires most breakers to have an instantaneous 'self protection' trip point beyond its normal Time Current Curve.
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If series rated system under engineered Supervision not possible, why 240.86(A) there still, it be removed but till date not proposed. not done, because it still useful for existing old installations

QUOTE="jim dungar, post: 3020018, member: 56314"]
It has been more than 40 years since I have heard of any engineer actually applying this exception.
[/QUOTE]
Professional liability, proprietary details not made public, I think
 
I
jim dungar said:
Those other methods are not in question, as they actually reduce the amount of available fault current. Item 4 is the one that frequently gets misapplied.
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Method 3 not reduce AFC, it like method 4 increase effective sccr of equipment
 
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