I would first check that the original 12.47 kV standard was designed to 15 kV design class.
Also, check the as built clearances against the 13.8 kV standard.
If the spacing is less than the 13.8 kV standard and there is an incident, you may be held as contributing even though the incident had nothing to do with spacing.
In today's litigious world you have to CYA, (Cover Your ASSets)

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

Thanks Waross, good advise.
There is an interesting situation on most standards construction manual using normal and compact design for overhead MV designs. The compact design, use less clearance for voltage level. I having some difficulties to find standards for 13.8 kV but hoping that the 12.5 kV clearances may be technical satisfactory for using in the same environment conditions at 13.8 kV. However, I will follow your advise to prove it as soon get the 13.8 kV info.

cuky2000 (Electrical)(OP)31 Aug 24 19:32
'..It is safe to use a 12.47 kV design standard for a 13.8 kV overhead distribution system considering that both are within the traditional 15 kV ANSI class'
I have the following opinion for your consideration.
1. Consult the local authority for advice/approval.
2. Observe above roads clearance 5.5m, and above railway crossing 6.4m; would be adequate for up to 20kV.
Che Kuan Yau (Singapore)

If anything is different, you should verify you have the right arresters.

The US National Electrical Safety Code (NESC) does not distinguish between 750 V and 22 kV with respect to required clearances.

I have come across a few underground components with ratings that are OK at 12.5 kV but would be inadequate at 13.8 kV.

Many of the overhead clearance distances in the NESC are specified were originally based on a distance per kV plus a x foot buffer. At distribution voltage levels between 750 V and 22 kV, the 2 foot buffer portion dominates.

Does anybody has a typical pole design dimensions for 13.8 kV similar to the one show below?

Interesting that those dimensions add up to 10ft exactly, so it looks more like that is the max separation available from a 10 foot long plank(!)

The one below it is max separation for an 8ft plank

So not sure if these were actually "calculated"

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

How exact can you get on a wood plank?
That said, you only need an eight foot cross arm for three phases. The thing is the two outside insulators are on the ends. The middle phase can be on either side of the pole, usually with the pole ground on the other side of the pole.
It is likely easer to put the Middle phase on one side an keep it there, but I have heard it said it is better to change side on each pole.
Off the top of my head, I am thinking the spacing is about 18 inches from center to center for the conductors on the side with two phases.

Quote (cuky2000)

Does anybody has a typical pole design dimensions for 13.8 kV similar to the one show below?

The only change needed to the drawing is to change the voltage in the title block.

I agree with jghrist - those dimensions look fine for 13.8 kV (see NESC Section 235 for reference). However, the military overhead line construction specification has pretty good pole details similar to the detail you posted. See here, and look under Related Materials for "Pole Details."

xnuke
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REA standards are also a good reference. I don't have any of these as I don't design distribution.