[RE-wrenches] Cable Sizing

[Bill Brooks]

Peter,

No--is that short enough.

Imax is defined by 690.8(A). Imax is the value used for doing all conditions
of use calculations including temperature corrections, conduit fill, and
sunlight impact.

The overcurrent protection device (OCPD) must be sized to 125% of Imax for
continuous operation of the OCPD. In other cases in the NEC, conditions of
use are not considered in the sizing of OCPD, so it follows that 690.8(B)
should not either. There is a proposal to the 2011 NEC to clarify this in
690.8(B).

How's that.

Bill.



-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Peter
Parrish
Sent: Thursday, January 08, 2009 1:20 PM
To: 'RE-wrenches'
Subject: [RE-wrenches] Cable Sizing

Boy did I light one off. Can I steer an enlightened soul back to my specific
question:

"In specific: if we have two DC PV circuits (4 wires: 2 positive, 2
negative) in EMT and we have taken into account the "PV 125% circuit current
calculation", "cable sizing of 125% for proper operation of overcurrent
devices", and cable derating for temperature -- do we now apply the derating
from B.310.11 for 4-6 wires?"

Peter T. Parrish, President
California Solar Engineering, Inc.
820 Cynthia Ave., Los Angeles, CA 90065
Ph 323-258-8883, Mobile 323-839-6108, Fax 323-258-8885
CA Lic. 854779, NABCEP Cert. 031806-26
peter.parrish at calsolareng.com 


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