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 Post subject: Underrated Equipment Label
PostPosted: Fri Jan 12, 2018 12:18 pm 
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Joined: Mon Jan 08, 2018 12:47 pm
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Has anyone seen this type of label being utilized........ANY WHERE?
Attachment:
Underrated Label.pdf

What would be a good alternative?


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 Post subject: Re: Underrated Equipment Label
PostPosted: Mon Jan 15, 2018 7:51 am 
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Joined: Fri Nov 06, 2015 1:05 am
Posts: 21
Location: Evansville IN
Never have witnessed these labels but what an idea. I could use these right now!(SCCR of various equipment)


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 Post subject: Re: Underrated Equipment Label
PostPosted: Mon Jan 15, 2018 8:10 am 
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Joined: Wed Dec 21, 2011 5:00 pm
Posts: 9
Seems like it is missing some information or is a danger.

Why would you want to energize a circuit if you don't want to operate the equipment. If you didn't then the signage should state not to energize and the potential to energize locked out.

If you did need to energize but not use certain equipment then danger from scenario should be protected by other means such as removing fuses and that information included in the label.

Is there a conflict in that facility between electrical maintenance (or engineering) and production (or others)? For example, maintenance stating the circuit is unsafe and production stating that we will use the equipment if we feel the need to do so? In which case the former feels that they have protected themselves from liability? If so, the owner of the facility needs know the liability now rests with him and they would be the "designated felon".


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 Post subject: Re: Underrated Equipment Label
PostPosted: Mon Jan 15, 2018 1:53 pm 
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Posts: 11
Has the equipment been locked out (not just tagged out) to prevent inadvertent energisation? Or alternatively, the supply isolated, cabling disconnected and bagged & tagged?

If so, only adding the engineer/technician responsible for deeming the equipment unsuitable for operation and dated, plus equipment identification if deemed necessary.

If not, no its not sufficient. The label on its own is only an administrative control and easily circumvented.


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 Post subject: Re: Underrated Equipment Label
PostPosted: Mon Jan 15, 2018 2:15 pm 
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Here is an example of what I have been using; see attached

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underrated example.pdf


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 Post subject: Re: Underrated Equipment Label
PostPosted: Tue Jan 16, 2018 4:24 am 
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Location: North Carolina
I'm still in the camp that "underrated" need not always apply just as arc flash may generate some crazy result once in a while that we know that we can ignore because it might be true from a pure mathematical point of view but that doesn't mean that it's "true".

Take for instance the medium voltage expulsion fuse mounted in a cutout. If it's rated correctly and it trips, what does it do? It blows in half and the cutout falls open. So what happens if it's underrated? If it trips, it blows in half and the cutout holder is also damaged and falls open so when we go to reset it, we have to replace more than just the fuse. The practical effect is kind of moot.

Another example that commonly occurs is if we have several turbine generators on a common intermediate bus. Some of the scenarios may predict that under some extreme combination of conditions such as running all turbine generators at the same time in a plant that is steam limited to running some number less than that or say running with both mains and a tie closed in a main-tie-main switchgear that we exceed short circuit ratings but that has never been done in 20+ years and operationally there is no scenario under which that would be done. See, the math gives a "correct" result but it doesn't match reality.

Another real example I've seen is a plant where some areas ran 2x500 MCM per phase and others ran a single 500 MCM cable per phase for feeders to switchgear. Under ANSI ratings it is mildly under-rated for the single cable case. The plant has been operating for 50 years and has NEVER had a failure. Rerunning under the IEC short circuit model shows that ANSI overpredicts, which we know it will do because of some of the simplifications of the simplified ANSI model that was developed at a time when we still did these things with slide rules as opposed to just using the actual impedances and solving the sparse matrix with a computer like we do today. But in the US we use the ANSI standard. Does that mean that we rip out hundreds of feeders, duct banks, cable trays, and conduit, and spend millions of dollars "fixing" a problem of using a standard that is known to give conservative (overpredict) results? Or stick a bunch of crazy labels out there and scare people needlessly?

This is obviously vastly different from when purchasing starts buying 100 A, 10 kA breakers because they are way cheaper than 100 A, 35 kA breakers because they are cheaper or wanting to standardize on one breaker when the 35 kA's won't fit in the 10 kA hardware and the 10 kA's are obviously undersized. That's just stupidity and something maintenance has to watch out for but something that frequently occurs, particularly when stuff becomes obsolete and you end up out in the secondary/surplus/EBay market for parts.


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 Post subject: Re: Underrated Equipment Label
PostPosted: Thu Jan 18, 2018 8:17 am 
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This label is being utilized through out our company on equipment that is being utilized and interacted with on a day to day basis's. I have one location that had 777 label placed on equipment. It is causing a HUGE misconception of how the equipment will react if operated. I have reviewed the studies and some equipment is underrated and we identify those device's and remediate ASAP. A lot of the equipment has marginal results, IF conductor impedance is utilized and motor contributions along with realistic settings in the model the equipment becomes cat 4 or in some cases lower.
In a nut shell this type of sticker is crippling the facilities from a operations stand point, even if the equipment is underrated it can be interacted with safely.
Example: MCC has bus that is underrated BUT the buckets are not and are cat 2 or lower, the buckets can be opened and motor overloads reset with proper PPE. The bus is not going to explode if you turn a bucket off and open the door to reset an overload. If you have to remove the bucket from the MCC that is a whole different scenario! I appreciate all of the responses...This is huge topic right now for us!


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 Post subject: Re: Underrated Equipment Label
PostPosted: Fri Jan 19, 2018 7:02 am 
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Location: North Carolina
Griff8966 wrote:
This label is being utilized through out our company on equipment that is being utilized and interacted with on a day to day basis's. I have one location that had 777 label placed on equipment. It is causing a HUGE misconception of how the equipment will react if operated. I have reviewed the studies and some equipment is underrated and we identify those device's and remediate ASAP. A lot of the equipment has marginal results, IF conductor impedance is utilized and motor contributions along with realistic settings in the model the equipment becomes cat 4 or in some cases lower.
In a nut shell this type of sticker is crippling the facilities from a operations stand point, even if the equipment is underrated it can be interacted with safely.
Example: MCC has bus that is underrated BUT the buckets are not and are cat 2 or lower, the buckets can be opened and motor overloads reset with proper PPE. The bus is not going to explode if you turn a bucket off and open the door to reset an overload. If you have to remove the bucket from the MCC that is a whole different scenario! I appreciate all of the responses...This is huge topic right now for us!


This is a complete but common misunderstanding. You are mixing apples, oranges, and everything else.

In an overload and indeed most of the time during switching we are at most at 2-7 times FLA at most.

In an arcing fault the current is 40-85% of the bolted fault current. Typically again it's not a problem. There is also the principal of dynamic impedance which current limits even that but I'm digressing into details here. Suffice to say that arc flash has absolutely NOTHING to do with "underrated" equipment.

Bolted faults are what this problem is...during a short circuit the possibility of things flying apart. This is where we get to 10-100 times the normal operating current or more. Since magnetic force is porportional to the square of current, even modest underratings are really, really bad. You won't get much of an arc flash with these...just a boom and everything is torn to shreds. Biggest danger is shrapnel as things come flying apart under extremely high force, or the tendency for breakers to NOT open or explode if they do.


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