Available Fault Current - Electrician Talk - Professional Electrical Contractors Forum
Go Back   Electrician Talk - Professional Electrical Contractors Forum > Electrical Forum > General Electrical Discussion

Like Tree4Likes
  • 1 Post By FaultCurrent
  • 2 Post By micromind
  • 1 Post By telsa
Thread Tools Display Modes
Old 09-25-2017, 08:59 AM   #1
Junior Member
Join Date: Apr 2014
Location: FL
Posts: 23
Rewards Points: 14
Default Available Fault Current

Need help ASAP. With the situation in south Florida, FLP NOT able to compute a AFC letter and I need to build a commercial service quick. My question: I'm building a small 3ph service for irrigation. Feed from open Delta two transformer system. I'm going to compute the primary at infinite since FPL is on hurricane duty. How do I input the transformer data since the 3ph two transformer delta system nameplates are 1ph 120/240. Oh yes, if you are not familure with AFC calcs please don't answer. And don't need any advise on building the service. Thanks in advance
pfactor2 is offline   Reply With Quote
Join Contractor Talk

Join the #1 Electrician Forum Today - It's Totally Free!

ElectricianTalk.com - Are you a Professional Electrical Contractor? If so we invite you to join our community and see what it has to offer. Our site is specifically designed for you and it's the leading place for electricians to meet online. No homeowners asking DIY questions. Just fellow tradesmen who enjoy talking about their business, their trade, and anything else that comes up. No matter what your specialty is you'll find that ElectricianTalk.com is a great community to join. Best of all it's totally free!

Join ElectricianTalk.com - Click Here JOIN FOR FREE

Warning: The topics covered on this site include activities in which there exists the potential for serious injury or death. ElectricianTalk.com DOES NOT guarantee the accuracy or completeness of any information contained on this site. Always use proper safety precaution and reference reliable outside sources before attempting any construction or remodeling task!

Sponsored Links
Old 09-25-2017, 10:45 AM   #2
Senior Member
FaultCurrent's Avatar
Join Date: May 2014
Location: California
Posts: 496
Rewards Points: 931

Most utilities use the infinite bus as the basis for the primary FC. Since you say you have an open delta setup - many utilities use this rule - Open Delta services have maximum fault currents equal to or less than single-phase services with the same transformer size and voltage. Use the single-phase table and the larger of the two transformers to identify the maximum secondary fault current.

This table works well. Answers are close enough.
This is the one I have bookmarked, I'm sure there are others:

brian john likes this.
At it since 1971 and still going....kind of.
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Grandpa was old, and he was slow. But he got there.
FaultCurrent is offline   Reply With Quote
Old 09-25-2017, 11:12 AM   #3
Bilge Rat
Join Date: Aug 2007
Location: Fernley, Nevada (near Reno)
Posts: 6,913
Rewards Points: 3,434

With an open ∆, each transformers contribution is independent of the other because they are connected to each other at only one end, not both. Therefore, the maximum available fault current will be the larger of the 2 transformers.

Divide the impedance by the full-load current and you'll have fault current.

Example, suppose the largest transformer is 50KVA, 240 volts and the impedance is 5.2%

50,000 240 = 208. 208 .052 = 4000 amps.
brian john and telsa like this.
micromind is online now   Reply With Quote
Sponsored Links
Old 09-25-2017, 03:57 PM   #4
Senior Member
Join Date: May 2015
Location: Sacramento, California
Posts: 14,337
Rewards Points: 26,920

This stuff is also to be found in Ugly's.

Pages 58-61.

All of the formulas are right there.
brian john likes this.
telsa is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
can anyone explain what is neutral grounding devces and its using? mike883 General Electrical Discussion 11 08-11-2017 01:35 AM
Fault current Dash Dingo General Electrical Discussion 4 07-25-2017 11:53 PM
Fault Current Protective device 6KA/10KA johnegan General Electrical Discussion 0 09-21-2016 04:38 AM
Converting Fault Current Into Calories Lone Crapshooter Workplace Safety 4 04-17-2016 07:33 PM
Average Primary Fault Current RePhase277 General Electrical Discussion 21 02-10-2016 07:26 AM

All times are GMT -4. The time now is 12:51 PM.

Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.1
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Our Pro Sites Network
ContractorTalk.com | DrywallTalk.com | HVACSite.com | PaintTalk.com | PlumbingZone.com | RoofingTalk.com