[TR] Ruining rheostats

[Anthony Rhodes]

Tim, thanks for adding this info.  Until I knew about this difference between
Lucas and US fuses, I always thought of US fuses as blowing instantly at
anything above the rated current value.  I suppose that one could think of the
US fuses as somewhat "slow-blow" compared to the Lucas versions.

Once I realized that there was a difference, I just use the factor of 2 as an
approximation of the conversion of one to the other.

I guess I would find the US rating system as making more sense.  It follows
the pattern that your wiring harness will melt in an overload situation.  A
little overload will only slowly fry the wires, so you do not need the fuse to
blow instantly.  A major overload (2X?) will heat the harness fast and needs
to have the fuse let go PDQ.

-Tony

P.S.  The English wire sizes (by # of strands) is helpful for calculating the
current capacity.  It is generally about 0.5A per strand.
__________________________________________________________________________
Original message:

>Date: Sat, 10 May 2008 09:53:10 -0500
>From: "Ann and Tim Buja" <thebujas at comcast.net>
>Subject: Re: [TR] Ruining rheostats
>To: <triumphs at autox.team.net>
>Message-ID: <AAENINAHPDGILMLPMKDIKELOCLAA.thebujas at comcast.net>
>Content-Type: text/plain; charset="us-ascii"
>
>John Mitchell <jmitch at snet.net> wrote:
>
>> I used a 10 amp acg for the inline which
>> should go before the 35 amp Lucas.   John Mitchell  76 TR6
>
>This should be about the right size.  Remember, Lucas and AGC fuses are
>rated in different methods:
>
>The number usually found on Lucas fuses is the continuous fusing current
>which is twice the continuous amp rating that the system should be using.
>The Lucas "35A" fuse will carry 17.5 amps continuously and is supposed to
>blow at 35 amps continuous and 40 amps instantaneous.  This is an IEC
>standard.
>
>3AG fuses are rated to a UL/CSA standard.
>>From the Bussman catalog:
>3AG ELECTRICAL CHARACTERISTICS:
>% of Ampere Ampere Opening
>Rating Rating Time
>110% 1/32-35 4 hours, Minimum
>135% 1/32-35 1 hour, Maximum
>200% 1/32-10 5 sec., Maximum
>12-30 10 sec., Maximum
>35 20 sec., Maximum
>
>>From the chart, the 10 AGC fuse will take 4 hours to blow at 11 amps, 1
hour
>at 13.5 amps, and five seconds at 20 amps.  This should give you good fuse
>coordination with the 35A Lucas fuse rated for 17.5 amps that is controlling
>the circuit.
>
>Tim Buja - Rockford, IL - 80 TR8, 73 Stag, 72 TR6