Type T will clear in less than 1/2 cycle but listed for non inductive loads.
Type LPS-RK a dual element will clear in less than 1/2 cycle and is designed
for protection ahead of motor controlers with heavy inrush currents. would
probably be better for a transformer primary if they make it in the proper
amperage. the rub is $65 a clatter. There has been major changes in the
industry in the last ten years mandated by government. And prices reflect
it.
Jim
N7FCF
Jim
N7FCF
----- Original Message -----
From: "Jim Thomson" <jim.thom@telus.net>
To: <amps@contesting.com>
Sent: Sunday, January 09, 2011 5:03 AM
Subject: [Amps] Fuses
> Date: Sat, 8 Jan 2011 16:21:22 -0800
> From: "James R Carr" <n7fcf@hctc.com>
> Subject: Re: [Amps] Fuses
>
>
> Down in prosser, WA about 30 years ago they had a problem with a potato
> processing plant and a mechanic came running into the panel room and
> before
> anyone could stop him threw the main 480v 3 phase breaker. The plant was
> under full load with motors up the cazoo. When the back emf hit it blew
> the
> breaker out of the panel. The guy was lucky he wasn't hurt.
> I retired in 2000 and there is a whole raft of devices that have come on
> line since.
> Jim
> N7FCF
>
> ### This is why you want monster size movs across the load itself. Here
> is a case, where
> the up-stream .... 'whole house breaker' won't do much good..... it's
> on the line side of the
> breaker, instead of the load side. If you want to see the effects of
> back emf.... try running
> a 10 kva pole pig flat out... key down cxr....then reach over, and shut
> the main contactor OFF !
> [ typ 240 in - 4800 v out, then FWB = +6700 vdc no load.... ham supply
> for a YC-156, etc]
> Now you can see why you want the voltage rating on any 208/240/360/480/600
> vac breaker on the
> high side of the actual normal V.
>
> ## After a rude awakening trying the above stunt, it's also why I use
> parallel, bolt down MOV's [ 277 v rated]
> directly across the 240 vac primary of the plate xfmr. I also use
> similar parallel 130 v rated movs [ bolt down type]
> between each hot leg of the xfmr..and neutral. I also use more big
> movs, directly across the contacts of the contactor
> I use for the main on/off. Then any mag-hydraulic breaker/ fuses
> upstream won't get blasted with the mother of all
> back emf. It's also why I use contactor's instead of relay's.
> Contactor's are just 2 x sets of contacts in series... with a huge
> solenoid spring. This breaks the arc into 2 x arcs. I use contactor's
> rated for way in excess of normal average current
> being drawn on the 240v primary. [ both to minimize V-drop..and also to
> handle the typ 3-5 x normal current... caused by the
> high C filter].
>
> ## I'm wading through Buss's eng notes. Apparently they have a new
> style fuse out, [dual ele] that will clear a hard fault super
> fast, yet allow for 500% overload for 4 x seconds... for typ motor
> start up. They are sized at 130% of the motor's normal run current.
> They have new ones out.. for non motor start.. that will clear faster than
> their old line of fuses..[ again, a hard fault]. They mention 'current
> limiting
> fuses'... [even in their old literature].. which is a bit of a
> mis-nomer. I see no mention of 1/2 cycle clear times [ 8.3 msec]
> ...yet. I'm still looking.
> Buss's idea of .....'current limiting' is really reduced..... 'let
> through max peak current' compared to their older series of fuses. You
> still end up
> with a high fault current.... but a lot lower than their old style fuses..
> plus they will clear faster ! This is all being driven by recent
> changes in
> arc suppression requirements by most gov'ts.
>
> Jim VE7RF
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|