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 Post subject: ArcPro parameters for calculating values in 1910.269 Table 7Posted: Wed Nov 26, 2014 9:43 am

Joined: Wed Jun 24, 2009 4:45 pm
Posts: 41
Location: WA State
I have not been able to duplicate the values in OSHA 1910.269 Table 7 using ARCPRO. I would appreciate receiving some feedback from others on selecting the correct parameters. I've started with the first value in Table 7; 4.0 to 15.0 kV, fault current of 5 kA, duration of 197 cycles. For this scenario, what should my ARCPRO parameters be to duplicate the Table 7 calculations?

Current (kA): 5
Source Voltage (V): 8660
Duration (cycles): 197
Electrode Material: Copper
Arc Gap (cm): ?
Distance to Arc (cm): MAD - 2*arc length = 65cm - 2*? = ?

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 Post subject: Re: ArcPro parameters for calculating values in 1910.269 TabPosted: Wed Nov 26, 2014 10:39 am
 Arc Level

Joined: Tue Jan 13, 2009 5:00 pm
Posts: 566
I used inches so Arcpro would give me calories per sq cm.

The gap is 1 inch per 10kV line to ground, but ArcPro will not let this value go below 1 in. MAD=2.14 ft *12 in/ft= 25.68. Less twice the 1 in arc length yields 23.68 in distance. I get 3.5 cal/cm^2.

At 4 kv your MAD reduces to 2.07 ft, and I get 3.8 cal/cm^2.

I saw no difference on this one changing the electrode, but when doing this in the past for the NESC, I believe I got closer results using SS electrodes.

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 Post subject: Re: ArcPro parameters for calculating values in 1910.269 TabPosted: Wed Nov 26, 2014 11:27 am

Joined: Wed Jun 24, 2009 4:45 pm
Posts: 41
Location: WA State
stevenal wrote:
The gap is 1 inch per 10kV line to ground, but ArcPro will not let this value go below 1 in. MAD=2.14 ft *12 in/ft= 25.68. Less twice the 1 in arc length yields 23.68 in distance. I get 3.5 cal/cm^2.

Okay, so Table 7 appears to use an arc gap of 1 inch for 4-15 kV, due to the input limitations of ArcPro. That would have been a good addition to the footnote! Table 5 "Selecting a reasonable arc gap" would have me use 2.0, which would lead to 6.5 cal/cm^2 instead of 3.5 cal/cm^2. That's a big difference from what is recommended for calculation and what is provided in the table. I would think that table values would typically be more conservative than calculations. Seems odd that it is the opposite in this case.

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 Post subject: Re: ArcPro parameters for calculating values in 1910.269 TabPosted: Wed Nov 26, 2014 2:02 pm

Joined: Wed Jun 24, 2009 4:45 pm
Posts: 41
Location: WA State
stevenal wrote:
I saw no difference on this one changing the electrode, but when doing this in the past for the NESC, I believe I got closer results using SS electrodes.

I did find a difference when selecting stainless steel. Calculation changed from 3.5 to 4.0 cal/cm^2, which is exactly the value that I expected based on the table. I'm going to use stainless steel.

Strange thing is that it did not change after simply changing the drop down from copper to stainless steel and running the analysis again. It only updated the calculated value after changing another parameter. Seems like a bug in the software to me. Check for yourself by running one way, then existing completely and running the other way.

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 Post subject: Re: ArcPro parameters for calculating values in 1910.269 TabPosted: Wed Nov 26, 2014 3:41 pm
 Arc Level

Joined: Tue Jan 13, 2009 5:00 pm
Posts: 566
That explains why nothing changed when I went to SS this time.

I see now that table 7 parameters are based on the maximum voltage in each range, so ignore the 4 kV stuff above.

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