Good day all

Does anyone have a simple formula for calculating the cal/cm3 required? or can you assist with what the requirement is for 400V and 11kV Indoor substations and for outdoor Units?

Kim

The most commonly used method globally for calculating the incident energy in terms of calories/centimeter-squared is IEEE 1584 known as: IEEE Guide for Performing Arc Flash Hazard Calculations. It is applicable for three phase arc flash calculations on systems with voltages from 208 V to 15,000 Volts. This is the method used by most major arc flash modeling software as well.

And here is the link to buy "1584-2002 - IEEE Guide for Performing Arc Flash Hazard Calculations" It is only $805 for PDF version
But if you are IEEE member, its available for $645.
http://www.techstreet.com/ieee/products/vendor_id/3111

check please http://arcadvisor.com/faq/ieee-1584-calculation-procedure for incident energy and arc flash boundary equations.

Much better to start a program using NFPA 70E Tables so you don't put off PPE selection waiting for a full engineering study. Make this a preliminary program to be improved after the engineering study is complete.

We recommend using common software with IEEE 1584 calculations built in so that you have a CAD update-able version of your system. Many systems do this. We use SKM and EasyPower and from time to time EDSA. There are several others but these are the most popular in the US.

Good luck. Jim Phillips classes online here are a great place to start or use the software company's classes.

Hugh Hoagland
e-Hazard.com

The problem with using the tables in NFPA 70E is that you need to know short circuit current and clearing time of the protective device for the equipment you are using the tables for. Without an engineering study, you don't know that.

Barry, I totally agree "technically" but "practically" we still recommend using the Tables rather than doing NOTHING. That's why I said "preliminary" until the engineering study is complete. But to ignore this because I don't have an engineering study is like the "chicken and the egg" story. Have to do good before you can get to the best. Does that make sense? I didn't say, "Just use the tables". Hopefully it is more clear now. You are definitely right but most lives would be saved by incorrectly using the tables (see our IEEE paper http://ieeexplore.ieee.org/xpl/login.js ... %3D6164450). This approach is why the tables were developed in the first place. Until a study could be done but the tables include limits as you correctly warn.

Hugh Hoagland

There are two methods to select the appropriate PPE.

1. Incident Energy Analysis OR
2. PPE Tables Method [130.7(c)(15)(A)(b) or 130.7(C)(15)(B) and 130.7(C)(16)]

An incident energy analysis shall be required in accordance with NFPA 70E 130.5 for the following:

1. Tasks not listed in Table 130.7(C)(15)(A)(a)
2. Power systems with greater than the estimated maximum available short circuit current
3. Power systems with longer than the maximum fault clearing times
4. Tasks with less than the minimum working distance

Hence, NFPA 70E prohibits using the PPE Table Method if short circuit fault current (2) and protection device operating time (3) is not know. Arcing current need be calculated in order to determine the upstream protection device operating time. Once, short circuit fault current, arcing current and arc duration have been calculated, incident energy and arc flash boundary for any tasks (1) and at any working distance (4) can easily be calculated using IEEE 1584 equations.

I sit in the NFPA 70E meetings and know very well what it says. Does your company tell people NOT to use the tables or PPE until you have fault current and clearing times in hand? I'd be happy to take that lawsuit.

NFPA 70E is clear, if you don't meet the tables, you can't officially use them BUT don't put off PPE waiting for anyone to complete your flash study. They take months in larger plants. Make a plan, select preliminary steps, write an ESP and get an arc flash assessment done (Tables or Calculations) but don't put off good work practices and PPE waiting for the engineers to finish a study. Most smaller plants with single utility feeds will meet the tables as long as the transformer isn't too large but some will not.

Hugh Hoagland
e-Hazard.com

Kim,
The simple answer is that is not a simple answer. There are a few things that need to known to get a basic but conservative answer. There are many more things to get a better answer. Both require some electrical knowledge and some sort of study.

Hugh is correct that doing something is better than doing nothing.