**Arc Gap, Bus Gap, and Arc Length**Electric John wrote:

Hi everyone, I'm new in this forum. I'm hoping getting great infos on Arc Flash Analysis and also share my knowledge.

Here goes my first question.

In IEEE 1584-2002, one of the input values to perform Arc Flash Calculation is the Bus Gaps. The definition of this term is fairly clear (p.11) : Gap between conductors.

In NESC 2007, Table 410-1 (p. 247) states that their calculations are based on "Arc gaps as follow: 1 to 15 kV: 2 inch [...] See IEEE Std-4 1995.

Finally, in Electrical Safety Handbook edition 2, Flash Hazards calculations describing Heat Flux Calculations, states that an Arc Flash is proportional to Arc Length. (3.52)

Are all these values the same? What's the difference between Bus Gaps, Arc Gap and Arc Length .

Bus gaps can be found on the field or we can take default values proposed by IEEE 1584-2002. Where can we found Arc Length information?

Thanks

Welcome to the Forum,

I am going to assume that, since you mentioned the NESC, you are concerned with overhead outdoor construction at 1 to 15 kV for the purposes of my response.

We use ArcPro for our calculations and "bus gap" is not an issue since two basic assumptions are that the arcs will all be single phase to ground and will not in a box.

As you stated from NESC 410-1, the "arc gap" is 2", 4", or 6" depending on the system voltage level (15, 25, or 35 kV). For utility "primary" systems, I do not get concerned with the other publications.....just the NESC. I must assume that the physics and/or other dynamics of the arc are modelled properly in the software. I expect this is the case since, as I have noted in previous posts, the energy levels of the table match the ArcPro outputs to within .1 or less.

For the low voltage portions of the systems (480 and 208), ie..padmounts, transclosures, meterbases, etc. have not decided whether to use the factors recommended with ArcPro, revert to some of the other pubs for arc in a box type calcs, or just use the NESC minimum of 4 cal.

Hope it helps,

Alan