Thanks Guys,
Michael, your memory and/or your expert use of the archives clarified what I
should have remembered as Windy's comments. Thank you.
In related matters, what are the benefits / disadvantages / preferred
applications of a thermal-magnetic breaker over a thermal-hydraulic breaker.
Bill Loesch
Solar 1 - Saint Louis Solar
----- Original Message -----
From: Allan Sindelar
To: RE-wrenches
Sent: Thursday, May 13, 2010 9:22 PM
Subject: Re: [RE-wrenches] AC breakers used in DC applications
Wow, Michael, look at the monster you have created, Dr. Frankensolarbozo!
Yes, that's the thread. And I was about to post that Windy left today for
Costa Rica...just a trip, not a move.
William, there are certain perfectly appropriate applications - such as a
pressure switch controlling a DC pump, or an A/C disconnect (Square D CU200)
2-pole array disconnect for an array-direct pump. Historically there was
nothing DC-rated available, and conservative use of available AC equiipment
worked fine and lasted forever. Sometimes it just don' matter how it's Listed,
ya just gotta use it...ya know?
Allan
<![endif]-->
Allan Sindelar
al...@positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
EE98J Journeyman Electrician
Positive Energy, Inc.
3201 Calle Marie
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com
Michael Welch wrote:
Is this conversation what you were refering to? 7/22/01
Others offered caution to this approach, but clearly the subject was
switches, not breakers.
Allan at Positive Energy wrote:
2. ... I am using float switches to control 48V mercury displacement
relays for these DC pumps. Can anyone suggest a source of SPST, SPDT, and DPDT
bat (or any style) switches suitable for 48VDC nominal, low current loads?
These would be for a custom relay control enclosure with override and remote
low tank alarm signal circuits.
My frequent observation on DC ratings for mechanical switch contacts is
that it's amp rating at 125VAC equals its amp rating at 28VDC. This is
consistent in the specifications of a great many switches, relays, etc. If
there are higher voltage ratings, then if voltage is doubled, amps is half.
When 48V is not specifically listed (nor any higher DC voltage), I feel
safe following that rule if I apply a good safety margin, as long as the switch
has a rapid snap action like a toggle switch does. For the low current control
and alarm loads you describe, I would feel forevever safe using a switch with a
15A rating at 28VDC. If you need to get official approval, ask the manufacturer
of the switch you propose to use.
Windy
Bill Loesch wrote at 05:10 PM 5/13/2010:
Fellow Wrenches,
Some time ago, Windy Dankoff had a rule of thumb to substitute
(conservatively) an AC breaker for use in a DC application.
Is anybody's memory, or perhaps even the old dog himself; if he is
listening, better than mine?
TIA,
Bill Loesch
Solar 1 - Saint Louis Solar
314 631 1094
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