[RE-wrenches] Cable Sizing

[Mark Frye]

In any case,I believe "load diversity" refers to the duty cycle of the
various circuits with constant load levels, as opposed to the instant
current flowing in the conductors to any given load.

 
Mark Frye
Berkeley Solar Electric Systems
303 Redbud Way
Nevada City,  CA 95959
(530) 401-8024
www.berkeleysolar.com 

-----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 11:01 AM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] Cable Sizing

NEC 2005 Handbook, Annex B, page 1204, Table B.310.11

I see now that 100% diversity applies to 4-6 and 7-9 ccc's but 50% above
that. Sorry. 

- Peter

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 


-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Bill Brooks
Sent: Thursday, January 08, 2009 10:19 AM
To: 'RE-wrenches'; exeltech at yahoo.com
Cc: 'Will Logan'
Subject: Re: [RE-wrenches] Cable Sizing

Peter,

Where do you read the 50% diversity? My 2005 NEC handbook clearly says that
the raceway adjustment table is based on NO diversity--all conductors loaded
at maximum.

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 9:47 AM
To: exeltech at yahoo.com; 'RE-wrenches'
Cc: 'Will Logan'
Subject: [RE-wrenches] Cable Sizing

Here is an issue that has been bothering me for some time and I finally was
asked to explain it to a junior member of our Company and had to admit
ignorance...

I am referring to the issue of derating the ampacity of wire in a raceway or
conduit with other current carrying wires. I refer to Table B.310.11, Annex
B of the 2005 NEC Handbook, but the same information occurs elsewhere in the
HB as Table 310.15(B)(2)(a) and the CB.

Table B.310.11 requires a 20% derating for four to six current carrying
conductors. There is a note that this derating includes the effects of a
"load diversity" of 50%. Am I to assume that 50% load diversity means that
each current carrying wire is operating at 50% of its temperature-corrected
ampacity (or less)?

Does this table apply equally well to DC and AC circuits? What about
3-phase/3-conductor wiring?

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?

This is what we have been doing, and I'm looking for confirmation.

- Peter

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 

-----Original Message-----
From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Exeltech
Sent: Wednesday, January 07, 2009 7:37 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] fire safety vs. fire hysteria?

Yes, it's made the rounds (13 total hits using the link Michael provided),
but the entire list of 13 is actually comprised of only six websites.

The originating site has two hits on the list, leaving five sites for the
other 11 hits.  One site is a BBS, similar to this one and would likely
require a refuting post -- perhaps a copy/paste of the superb response
posted earlier.  The four remaining sites may respond and remove the
inaccurate material and/or links if contacted in a similar positive tone.

The sooner it's addressed, the fewer the links there will be for the
crawlers to find...

I've assembled a summary list of the sites if anyone wants to contact me off
list for a copy.


Dan



--- On Wed, 1/7/09, Michael Welch <michael.welch at re-wrenches.org> wrote:
> Right, but this piece has made the rounds on the internet. 
> 
> Check out this Google search
> http://tinyurl.com/7amhk4



      
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