The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Safety at heights?
by gfretwell
Today at 02:19 AM
Looking for older post
by Trumpy
Today at 01:04 AM
Last time to chat here
by Trumpy
Yesterday at 11:41 PM
Unsafe Situations
by Trumpy
Yesterday at 09:46 PM
Webmaster > Admin
by Trumpy
Yesterday at 08:29 PM
New in the Gallery:
Desk-mounted "power-board"
Shout Box

Top Posters (30 Days)
Admin 35
HotLine1 20
Trumpy 19
Ruben Rocha 17
gfretwell 16
Who's Online
0 registered (), 164 Guests and 12 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#97095 - 01/19/06 05:32 PM Conductor Size
Sparky_1 Offline
Member

Registered: 11/20/04
Posts: 14
What is the smallest size feeder and neutral that I can use in this situation?

I have a fat storage tank that has a Control panel that feeds a 4500 watt / 240 volt heating element,
7 1/2 HP 3 phase motor 240 V (20.5 amps), fractional hp circulating pump 1/2 amp,
convenience outlet and light. Roughly 40 amps, with the nameplate of the fat tank control panel at 65 amps. ( The tank company stated that the 125% of FLA was listed on the FLA
sticker) The control circuit is fused down to 15 amps 120 volt.

We have 480 Volt 3 phase, so I set a 30 kva transformer feeding a 100 amp 240 Volt disconnect.
Can I feed this control panel with # 6 THHN fused at 70 amps and reduce the neutral to a # 12,or does it have to be a # 6?. Or do I have to run # 4s THHN to this unit?

[This message has been edited by Sparky_1 (edited 01-19-2006).]

Top
2017 / 2014 NEC & Related Books and Study Guides
#97096 - 01/19/06 09:22 PM Re: Conductor Size
gfretwell Offline


Member

Registered: 07/20/04
Posts: 9066
Loc: Estero,Fl,usa
If I was answering a question on a test I would say the #6 THHN fused at 70a (using the round up rule) with a #12 neutral serving 1 or 2 single pole 20a breakers on different phases is the minimum. I can't say that is the best design decision.
_________________________
Greg Fretwell

Top
#97097 - 01/20/06 02:51 PM Re: Conductor Size
Sparky_1 Offline
Member

Registered: 11/20/04
Posts: 14
Everything worked out today, we ran # 6s with a separate 15 amp control circuit.
I threw a amp meter on the unit, the FLA was 41.
The inspector wants a sticker stating that is has two separate disconnects.

Top


ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals