A closely related issue: In class (E3), They flogged us pretty good with the notion of "Pyrophoric Carbonization"(sp?). This is the stuff that has cause electrical fires in vacant buildings W/ disconnected power service (because of a high resistance neutral/ ground bond in the building next door). It seems even very small sustained arcs (AC or DC) over time has caused the flash point of building materials to drop significantly. I also agree that most metal conduit is not significant protection from a sustained low current arc. In fact, I'm hearing more and more rumblings that some folks object to grounds altogether because they provide an unnecessary unprotected current path.
Merry Mud Season Y'all.
db
Dan Brown
Foxfire Energy Corp.
Renewable Energy Systems
(802)-483-2564
www.Foxfire-Energy.com
NABCEP #092907-44
-------- Original Message --------
Subject: Re: [RE-wrenches] Starting fires for fun with string wiring
From: Chris Mason <[email protected]>
Date: Mon, March 12, 2012 8:25 am
To: RE-wrenches <[email protected]>
Jeff,In my limited knowledge of this issue, there is no doubt DC arcs have the capacity to burn and are difficult to extinguish, and good wiring practices are essential at these elevated voltages. However, you need to distinguish between high temperature arcs which can burn, and Arc-Flash risks which require special PPE and procedures. In order for the there to be a serious risk of Arc-Flash, there has to be both a high voltage such as 480V and a very high source current, in the order of 65,000 Symmetrical Amperes, such as you find near a HT/LT transformer. The extremely high current is what creates the explosive heating of the air. Solar PV, being current limited, has high enough DC voltages but does not have anywhere near the current capacity and cannot cause arc flash.Chris
_______________________________________________
List sponsored by Home Power magazine
List Address: [email protected]
Options & settings:
http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org
List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org
List rules & etiquette:
www.re-wrenches.org/etiquette.htm
Check out participant bios:
www.members.re-wrenches.org
_______________________________________________ List sponsored by Home Power magazine
List Address: [email protected] Options & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out participant bios: www.members.re-wrenches.org
