Documenting and testing overcurrent devices for series rating 240.86(A)

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Tainted

Tainted

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Engineer (PE)
How do you document and test overcurrent devices for series rating?

For example, 240.86(A) allows a professional engineer to stamp and document his own series rated combination and use it in his/her free will.

I am a professional engineer, and I am willing to take the liability of doing this but I would really like to know how this is done the correct way. Does anyone know anybody that did this?

I'm assuming that I need a lab and some testing equipment. But what are the steps?
 
Keep in mind this only applies to existing systems. While I'm not a PE, I would guess this is pretty treacherous territory as far as professional responsivity goes.
I have had situations in the past where, say, you have something like a chiller rated at 5K but the available fault current is, say, 50K and the PE says, OK, no problem, we'll just put current limiting fuses ahead of it and all will be good. I don't think so.
I'll let the PEs who have experience with this make further comments as I'm not qualified to make such calculations.
 
texie said:
Keep in mind this only applies to existing systems. While I'm not a PE, I would guess this is pretty treacherous territory as far as professional responsivity goes.
I have had situations in the past where, say, you have something like a chiller rated at 5K but the available fault current is, say, 50K and the PE says, OK, no problem, we'll just put current limiting fuses ahead of it and all will be good. I don't think so.
I'll let the PEs who have experience with this make further comments as I'm not qualified to make such calculations.
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Oh I didn't even realize it was for existing installations... But still I'm curious to know how this can even be tested and documented.

Yea you are right, some engineers with more experience than me think current limiting fuses limit faults completely but they do not take into account the dynamic impedances.
 
Tainted said:
Oh I didn't even realize it was for existing installations... But still I'm curious to know how this can even be tested and documented.

Yea you are right, some engineers with more experience than me think current limiting fuses limit faults completely but they do not take into account the dynamic impedances.
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They actually run fault current through the combination and see what happens. There are a couple of testing labs that can source 200kA and at least one that can source 300kA.
 
don_resqcapt19 said:
They actually run fault current through the combination and see what happens. There are a couple of testing labs that can source 200kA and at least one that can source 300kA.
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Simple as that? I would imagine there's much more to it than just running fault current to it and seeing what happens? Do these labs have their own professional engineer to do these test per 240.86(A)
 
Tainted said:
Simple as that? I would imagine there's much more to it than just running fault current to it and seeing what happens? Do these labs have their own professional engineer to do these test per 240.86(A)
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No PE is required if the combination is listed. They no doubt follow some procedure made up by UL to do the testing. My understanding is Allen Bradley has one of the few labs that can do this kind of testing and at one time they were booked for 7 years what with testing their own equipment and other peoples.
 
petersonra said:
No PE is required if the combination is listed. They no doubt follow some procedure made up by UL to do the testing. My understanding is Allen Bradley has one of the few labs that can do this kind of testing and at one time they were booked for 7 years what with testing their own equipment and other peoples.
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Bussmann has such a lab near St. Louis. They do all of the Eaton and Bussmann testing. They could do 200kA about 20 years ago, when I had a chance to visit it. I think they have since upgraded to 300kA. S&C has a 100kA test lab in the Chicago area. KEMA has a 50kA lab in Pennsylvania that can source 230KA at lower voltages. I am sure there are others too.
 
electrofelon said:
Which I never quite understood. If it's existing, who is saying or requiring that it be "brought up to code"?
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I think anything that is infringes life safety is required to be up to code. Maybe some jurisdiction have it in their code books, I think NY has it somewhere but I forget where it's burried.

Some are just not comfortable working with anything that affects life safety. I was working on bringing the fire pump circuitry up to code and I've encountered instances of electricians turning down jobs because of liability issues. Their words were "if I touch it I own it".
 
electrofelon said:
Which I never quite understood. If it's existing, who is saying or requiring that it be "brought up to code"?
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And also, what exactly is meant by "existing installations"? The wording goes on to say, "the series rated combination devices shall be selected by a licensed professional engineer......". So the existing part would be say a switchboard or panel board and you can add new breakers or fuses to them? Do both the upstream and downstream switchboard/ panel board need to be existing or can one add a downstream device that didn't exist before?
 
Tainted said:
I think anything that is infringes life safety is required to be up to code. Maybe some jurisdiction have it in their code books, I think NY has it somewhere but I forget where it's burried.

Some are just not comfortable working with anything that affects life safety. I was working on bringing the fire pump circuitry up to code and I've encountered instances of electricians turning down jobs because of liability issues. Their words were "if I touch it I own it".
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I am not aware of any such requirement, and
besides who decides when a no longer code compliant installation affects life safety?
 
electrofelon said:
And also, what exactly is meant by "existing installations"? The wording goes on to say, "the series rated combination devices shall be selected by a licensed professional engineer......". So the existing part would be say a switchboard or panel board and you can add new breakers or fuses to them? Do both the upstream and downstream switchboard/ panel board need to be existing or can one add a downstream device that didn't exist before?
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I had the same question in my head, it's not specific as to what it means by "existing installation"
 
Tainted said:
Did he actually stamp and document an existing series combination?
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It seems unlikely that he would have been able to actually take it out and test it since that would require removing the equipment and sending it to a testing lab. He probably just made some kind of determination that it was acceptable to him and wrote that down and put his seal on a piece of paper.

I have never understood this provision of the code. It appears there's no way to know if a series combination of modern circuit breakers and fuses will work correctly, so how could anybody possibly know that some ancient combination of fuses and circuit breakers would actually work.

On the other hand, I'm not sure there's any cases where this is actually been a problem.
 
There was a fire some years ago at a Seatttle ice plant due to utility replacing transformers which had more fault current. Existing gear was not able to interrupt fault current.
 
petersonra said:
It seems unlikely that he would have been able to actually take it out and test it since that would require removing the equipment and sending it to a testing lab. He probably just made some kind of determination that it was acceptable to him and wrote that down and put his seal on a piece of paper.

I have never understood this provision of the code. It appears there's no way to know if a series combination of modern circuit breakers and fuses will work correctly, so how could anybody possibly know that some ancient combination of fuses and circuit breakers would actually work.

On the other hand, I'm not sure there's any cases where this is actually been a problem.
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Again, I could be misremembering, but in some cases can't one look at the trip curves and establish that one device will remain passive during a fault event? (That's what 240.86(A) says, so I assume it is possible in some cases).
 
electrofelon said:
Again, I could be misremembering, but in some cases can't one look at the trip curves and establish that one device will remain passive during a fault event? (That's what 240.86(A) says, so I assume it is possible in some cases).
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Trip curves rarely display actual overcurrent device performance during faults much larger than 10-20kA with timing of at least .01sec. This is one reason why the code requires actual testing. For the past twenty years or so even large breakers are capable of beginning to open in times not shown on trip curves.

Engineered ratings made sense decades ago when devices were built to stay closed during a fault, like ANSI power breakers without Instantaneous trip elements, but they definitely are not applicable to molded/insulated case breakers which have a self protection override point even when their Instantaneous function is not enabled.
 
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jim dungar said:
Trip curves rarely display actual overcurrent device performance during faults much larger than 10-20kA with timing of at least .01sec. This is one reason why the code requires actual testing. For the past twenty years or so even large breakers are capable of beginning to open in times not shown on trip curves.

Engineered ratings made sense decades ago when devices were built to stay closed during a fault, like ANSI power breakers without Instantaneous trip elements, but they definitely are not applicable to molded/insulated case breakers which have a self protection override point even when their Instantaneous function is not enabled.
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Thanks jim, good info. So can you provide an example of when 240.86(A) would be used? Would this be say some 70s era equipment where something is being added downstream and for some reason it's not practical to fully rate it?
 
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