LA Rating Calculation

<...LA...>

Luton Airport? Los Angeles? Lightning Arrester?......

http://www.acronymfinder.com/LA.html

Any competent, local electrician can help you.

SInce you give no useful information in your post, it is impossible to answer the question.

LA?

Location?

Regulations in effect?

Knowlegable electrician on-site?

Safety officer on-site?

Any reputable manufacturer of lightning / surge arresters will have an application guide or table to help you choose the correct arrester rating for your system configuration (voltage level, delta or wye, grounded or not, etc.). For example, look at this guide from ABB:

ABB Surge Arresters Buyers Guide

Check the web for manufacturers' info, and you will see that they all use pretty much the same ratings.

The rating calculation for Lance Armstrong just recently went deeply into negative numbers. The sad part is that Livestrong is a noble organization that might not exist without those temporary yellow jerseys.

I'm not going to give this an OT because I feel like being a CRIMINAL today.

The application guide linked below should answer most of your questions.

http://www.geindustrial.com/Newsletter/lightning_arresters_guide.pdf

Surge arrester selection will depend not only on line voltage, but also the system being protected (transformer, line, static VAR compensator, etc.) and the type of earthing associated with the system. Feel free to return with additional questions once you are familiar with the basics.