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

William Miller william at millersolar.com
Thu Apr 27 19:41:21 PDT 2017


Jerry:

I thought splices or connections were forbade in condulettes. This sounds inherently code non-compliant. Do you have information to the contrary?

William

> On Apr 27, 2017, at 4:41 PM, Jerry Shafer <jerrysgarage01 at gmail.com> wrote:
> 
> 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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