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: [email protected] -------- 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 _______________________________________________ List sponsored by Redwood Alliance List Address: [email protected] Change listserver email address & settings: http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org List-Archive: http://www.mail-archive.com/[email protected]/maillist.html List rules & etiquette: www.re-wrenches.org/etiquette.htm Check out or update participant bios: www.members.re-wrenches.org
