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Re: [Amps] 240V Outlet

To: Carl <km1h@jeremy.mv.com>, AMPS List <amps@contesting.com>
Subject: Re: [Amps] 240V Outlet
From: Martin A Flynn <maflynn@att.net>
Reply-to: maflynn@att.net
Date: Sun, 09 Aug 2009 21:00:01 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Martin Wrote:
>> Paul,
>> The breaker and  device are the same rating.  My comment was to state
>> that his recommendation was to make the conductors and ground one wire
>> gauge larger then NFPA 70 states it should be.
>>
>> Martin
> That only makes sense if the I*R drop is excessive. Since the Invader 
> 2000 is only going to draw about half the ratings of #12 wire, then 
> going to #10 makes little sense on a basement long run. Going to #10 
> requires all different plugs and outlets and the cost about goes thru 
> the roof compared to a 20A feed.
The FPN notes in  NFPA 70 (which is not part of the actual document) 
suggests no more then a 5% total drop between feeder and branch 
circuits.  Here's the quote:  (fair use excerpt)

Art 210-19(A)(1), FPN No. 4: "Conductors for branch circuits as defined 
in Article 100, sized to prevent a voltage drop exceeding 3 percent at 
the farthest outlet of power, heating, and lighting loads, or 
combinations of such loads, and where the maximum voltage drop on both 
feeders and branch circuits to the farthest outlet does not exceed 5 
percent, provide reasonable efficiency of operation.

In the original case I commented on the run is ~50 feet, straight line 
distance.  Service is 120/208 3 phase   A licensed electrician made the 
calculations, presented them to the electrical inspector, and both 
agreed that the oversize wire was appropriate. 

I did the same at home.  The difference in cost between #12 THHN and #10 
THHN was negligible.  I used Square D breakers and Hubbell  connectors.  
Since the  wire clamp range on a Hubbell HBL2410 -  20 Amp twist lock is 
18-10 AWG,  and the 20 amp 2 pole QOB Square D breaker  is 14-8 AWG, it 
fit together fine with no difference in cost other then the wire.

Martin


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