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Actual gap measuring your 480VAC equipment.
https://brainfiller.com/arcflashforum/viewtopic.php?f=23&t=5145		 Page 1 of 1
Author:  CLL [ Wed Jul 24, 2019 7:35 am ]
Post subject:  Actual gap measuring your 480VAC equipment.
My office uses ETAP software for Incident Energy calculations on 480VAC single phase (240 L-N) lighting systems. With regards to Arc gaps, I was informed to select "Other" for the bus type and to put the actual measured gap values of installed equipment (Eaton 100A fused and non fused disconnects, molded case panel mounted circuit breakers, etc.).

I have not used my actual measured values before and I am looking to get some confidence for this approach.
Is it as simple as is seems or does someone have some insight, pointers, lessons learn that they can pass on?

Thanks!
Author:  JBD [ Thu Jul 25, 2019 6:41 am ]
Post subject:  Re: Actual gap measuring your 480VAC equipment.
Except for padmount transformers and other open busbars, I don't think I have ever deviated from the 'default' values for the equipment type.
I have used SKM, Etap, and Easypower.
Author:  SteveA [ Mon Jul 29, 2019 6:42 am ]
Post subject:  Re: Actual gap measuring your 480VAC equipment.
who informed you to do so?

Generally gap distances used by manufacturers are based on the recognized minimum gap distances for specific voltages (Line to Line and Line to ground). Some manufacturers may choose to increase those to some extent or the other. Larger than minimum required gap distances should only lead to lower risk potential and lower calculated incident energy levels. Use of these recognized minimums as default values will then provide for a "worst case" for that equipment.

If for a specific piece of a equipment you, or your customer has a reason to want to take measurements for use in the calculations there is no reason not to make that extra effort. Just be cognizant of exactly where you are measuring the gap distance and that the distance may vary within a piece of a equipment, which will affect your calculations depending on how you are modeling the equipment exactly.

Personally, I would be hesitant to use measured values without good reason. Then if I were to use measured values I would only use the smallest measured gap distance for a piece of equipment, or for the bounded working area of that equipment (ie within an individual MCC bucket).

Otherwise, yes, entering your own gap distance is fairly simple. It is an input into the formulas used for calculating incident energy and as such can be made whatever the Engineer decides it should be. Again, I would be hesitant to deviate from the default value without good reason.

Remember, the calculations will determine PPE worn, and PPE is the last line of defense a person working on energized equipment has to prevent bodily harm. As an Engineer I want to make sure that person is wearing the appropriate level of PPE that will both allow them to perform the required task in a safe manner and be protected if an arc fault were to occur.
Author:  Robertefuhr [ Mon Jul 29, 2019 8:29 am ]
Post subject:  Re: Actual gap measuring your 480VAC equipment.
Please refer to viewtopic.php?f=33&t=4842&hilit=Gap You will notice that most consultants will be using default values for the equipment gaps. It is very time consuming to measure the gaps. To do it correctly, you need to de-energize the equipment and then make the measurements.
Author:  CLL [ Mon Aug 26, 2019 8:43 am ]
Post subject:  Re: Actual gap measuring your 480VAC equipment.
Regarding "who informed you to do so?"

Someone with the software company made the suggestion as a response to my request for information.
Author:  CLL [ Mon Aug 26, 2019 10:24 am ]
Post subject:  Re: Actual gap measuring your 480VAC equipment.
With regards to low voltage (208 to 480V, 1 or 3 phase) individual pieces of equipment, Is there a document indicating which of the 3 (of 5) gap distance categories they belong to?

13 mm – cable/junction box
25 mm - Low Voltage Distribution – panels, MCCs etc.
32 mm – Low Voltage Power – Switchgear

Equipment of interest are:
- Safety Switches (non-fused, fused, circuit breaker)
- Molded case circuit breakers
- Motor starters
- Lighting contactors
- Power distributions blocks
- General purposes relays
Author:  JBD [ Mon Aug 26, 2019 11:16 am ]
Post subject:  Re: Actual gap measuring your 480VAC equipment.
CLL wrote:
Regarding "who informed you to do so?"

Someone with the software company made the suggestion as a response to my request for information.


Over the years I have learned that software company "support" are not NFPA 70E interpretation experts.
Author:  Raghu [ Fri Oct 11, 2019 11:51 am ]
Post subject:  Re: Actual gap measuring your 480VAC equipment.
With the power of software calculations. We can look in to this input data collection such as gap, electrode configuration, box dimensions etc using a simplified arc-flash technique that allows for determination of the settings of over current device or selection of arc-rated PPE based on a reference incident energy boundary area. It is useful to play with multiple variations in the input data to determine a incident energy curve in a TCC that can allow you to coordinate the protective device to a desired incident energy value.

Please refer to this paper for more details

"Application of Incident energy reference boundary area plots in TCCs considering IEEE 1584-2018 input parameter variability" Paper no. PCIC-2019-10
Author:  arcad [ Sat Oct 12, 2019 6:20 am ]
Post subject:  Re: Actual gap measuring your 480VAC equipment.
CLL wrote:
My office uses ETAP software for Incident Energy calculations on 480VAC single phase (240 L-N) lighting systems. With regards to Arc gaps, I was informed to select "Other" for the bus type and to put the actual measured gap values of installed equipment (Eaton 100A fused and non fused disconnects, molded case panel mounted circuit breakers, etc.).

I have not used my actual measured values before and I am looking to get some confidence for this approach.
Is it as simple as is seems or does someone have some insight, pointers, lessons learn that they can pass on?

Thanks!


What's the problem using actual instead of typical values? Anyone can use 'typical' values for anything starting with fault current, gap between conductors, electrode configuration, arc duration and so on but surprisingly the outcome is as good as the assumptions are. yes it takes time and effort to collect accurate information and do your home work but that's what people ultimately I paid for.
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