AboutMaster Bob Expertise Master Electrician / Owner RKO Electric (USA Only) - can answer most of the typical residential, commercial and industrial electrical questions regarding new installations, wiring additions, lighting, switches and receptacle outlets and electrical upgrades of any nature.I will make every effort to respond to your questions as soon as possible at the end of the work day...very busy electrical company - your patience is appreciated. Stop by and see us at: www.rkoelectric.com
Experience Licensed Master Electrician with over 32 years licensed experience - updated with the latest NEC Codes every 3 years. Over see the daily electrical operations of two electrical companies. Also serve as a judge (for Electrical Contracting Products Magazine) to help select which new products are fit and safe for electricians and the electrical market.
Question hello master bob
I am trying to figure out the correct wire size to feed a 125A sub panel from a 100 A breaker in the main panel. The one way distance to the sub panel is approx. 70 ft. The entire run will be in 1 1/4" pvc conduit, with about 25 ft. buried.
The rest will be either in crawlspace or in a metal building. The ambient temperature here can be as high as 100 F in summer. The ampacity tables are at best very confusing to a lay person. Is #4 THHN acceptable, or should I use #3 THHN. I plan to run four wires, two hot, one neutral, and one ground. There will be no connection of the neutral and the ground in the sub panel or building. Can you reccommend the correct wire sizes for this application?
Thanks in advance, Dave
Answer Hi Dave,
Sorry....but we are fixing to leave here shortly for our Holiday vacation...so I do not have time to answer your question in detail.
For a 100 amp feed - you will need 3 runs of #2 copper (not #3 or #4) ....although the ground can be a #4.
Your local inspector will be able to provide more detail when you pick up the permit.
About Electrical Wiring in the Home
This site answers questions related to home electrical wiring, home wiring, general electrical help,and other electrical questions related to aleternating current (AC). You can find help on the National Electical Code, home electrical issues, wiring electrical outlets, installing lighting, electrical grounding, and general electrical help for do-it-yourself projects not require an electrician. If you do not see your home electrical wiring question answered in this area then please ask your electrical wiring question here
