[RE-wrenches] Third Radian ---> Class T Fuse With/Without Fuse Holder

[Jerry Shafer]

Wrenches
In the event you or some else installed a Class T fuse and you want to
protect it a little more from cable stress, installing it inside a PVC C
conduit body and cover and fastening the cables to the fuse inside that,
this will protect the fuse from stress and metallic contact and you can put
a label on it stating size and type.
Jerry

On Wed, Apr 26, 2017 at 6:05 PM, Matthew Sirum <matthewsirum at gmail.com>
wrote:

> Greetings William,
>
> Good point.  This is something I always take into consideration.  I
> have used Class T Fuses in many situations with and without their fuse
> holders.  In the case of the installation shown in my custom DC Bus
> System pictures the wire/cable type and wire management avoid putting
> too much physical stress on the Class T Fuses.  The #4 AWG conductors
> are supported from above and apply very little stress on the fuses
> they connect to.  The 4/0 AWG cabling is Cobra X-Flex (fine stand,
> very flexible) and each of these conductors is secured a few inches
> from where they connect to their fuses.  Care was taken in making up
> these connection and they were all carefully adjusted and inspected to
> ensure they would not stress the fuses.  I feel really good about how
> it all came together.  The same care and attention will be needed
> whenever these connections are serviced and the fasteners are
> torqued/tightened.  When well planned and carefully assembled I do not
> have concern there will be any issues related to not using the fuse
> holder.  I also think about this another way as well...  Using the
> Class T Fuse Holder adds another 2 connections to the circuit.  I try
> to remind myself that more connections can equal more chance of
> issues...  Although, if a manufacturer of a Class T Fuse states the
> fuse holder must be used with their fuse there could be an NEC
> violation by not using it.
>
> One thing to note about the use of these fuses in this installation is
> that they are supplemental over current protection (OCP).  Each
> positive (ungrounded) conductor connecting to this DC Bus System has a
> means of primary over current protection and disconnect on its
> opposite end.  The battery systems, the charge controllers, and the
> inverter/chargers all have circuit breaker disconnects on their
> respective positive circuit conductors connecting to this DC Bus
> System.  I have seen other folks build without having the needed
> appropriate means of disconnect and OCP; although most folk are
> probably more likely to include the primary OCP, but not consider the
> supplemental OCP.  The supplemental OCP (Class T Fuses) provide
> protection in the event of a fault or short in a circuit between the
> Bus System and the other OCP at the other equipment.
>
> Like many folks I have installed and worked on battery systems where
> we install a Class T Fuse directly onto the positive terminal of the
> battery bank or via some form of busbar or connector etc.  In these
> cases not only do we need to take care not to stress the fuse, but the
> fuse itself (and added busbar/connector etc) can act like a lever and
> along with the mating cable lug(s) create too much stress on the
> battery terminal...  Potentially damaging the terminal, the inner
> battery connection to the terminal, and/or the seal between the
> battery case and the terminal.  Carelessly tightening the
> hardware/fasteners to assemble these items to the battery terminal is
> a common way of inflicting damage on the battery as well.  I know I
> have been involved in some service situations where there was more
> stress on the Class T Fuse than I would like to see, but as best I
> know there have not been any fuse failures because of it.
>
> Thanks for bringing up this question!
>
> Best regards,
>
> ----MATT
>
> Matthew Sirum
> P.O. Box 1227
> Greenfield, MA 01302-1227  USA
> phone: +1.413.773.0611
> email: MatthewSirum at gmail.com
>
>
> -------- Original Message Below --------
>
> [RE-wrenches] Third Radian
>
> William Miller william at millersolar.com
> Tue Apr 25 23:03:03 PDT 2017
>
> Matt:
>
> I have a question for you:  I have often considered mounting Class T fuses
> directly to a bus bar as you have done.  Are you ever worried about
> physical
> strain on the fuse itself without a fuse holder?
>
> Thanks again for all of your input.
>
> William Miller
>
> Lic 773985
> millersolar.com
> 805-438-5600
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