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Design Options for Low-Cost UL Approved Cable Assemblies - Q&A

Epec Engineered Technologies
Written by Epec Engineered Technologies
Posted on September 28, 2022 at 8:48 AM

At the conclusion of our webinar, Design Options for Low-Cost UL Approved Cable Assemblies, we had several questions submitted to our presenter, Steven J. Goodman, User Interface & Cable Assembly Product Manager at Epec. We have compiled these questions into a readable format on our blog.

Q&A From Our Live Cable Assembly Webinar

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Question: What is your process for attaching the wire to PWB?

Answer: I believe that's a printed wiring board. The response we'd want to give would be to attach a wire to a PWB or a PCB. You either need to crimp onto something that's then attached to the board, or you're going to solder it directly to the board. Some projects actually will do both. The crimped wires are usually attached to some kind of connector that's then made into a PCB, a header connector, or some type of a similar interconnect.

It's also important to note that attaching a wire to a PCB, that process itself is not covered by UL, but there are two IPC specs that I can offer guidance on. The first is IPC 610, which is wildly common for us here at Epec. That covers soldering. An example of that would be connecting jumper wires to a circuit board or something of that nature. The other IPC spec worth mentioning is IPC 620. That defines the crimp process of how to attach a wire to a crimp tunnel, and, you know, stuffing that into a connector housing or body is similar.

Question: We need plenum-rated multi-conductor cable. Can you customize this?

Answer: No, unfortunately, we can't. This is a good question because plenum applications are unique, and they're usually for commercial buildings where wires run within vents and within the ducting of the building. Usually, these are high airflow areas that are at severe risk for fire or fire spread. The plenum-rated materials actually are a specialty because they're fire resistant, and also, they don't emit toxic smoke or fumes. And obviously, both of those things are extremely important, but it comes with an added cost and a much smaller supply chain. And to be honest, the plenum-rated cables aren't common for us. But instead, the UL wire we do support typically goes into enclosures, mechanical assemblies, electro-mechanical box builds. And with those, the flammability rating we have is VW-1 or a horizontal flame rating. And both of which are typically satisfied for those, you know, low airflow type of applications.

Question: Do you have UL material for wire bond?

Answer: I think this refers to the actual individual wire in the wire bond operation. So, with that said, the wire bond operations usually offer an ultra-small diameter single conductor strands of wire. It's really just a single strand of copper. And sometimes, they'll have a tinning applied to them to help with the soldering operation. But most individual wires used in the wire bonding operations, they're tiny. They're a few thousands of an inch diameter to maybe 20 thousandths of an inch. But they're unjacketed. There's no thermoplastic. It's really just copper. So, the UL spec doesn't apply to that.

Question: What about solid conductor wire? Does this impact UL?

Answer: That's a good question. So, there's usually no impact to UL because most wire types are actually dual-certified for both a single solid strand of wire, as well as the multi-conductor strands of wire, something that's highly flexible, and almost looks like a wire brush type of cross-section. The UL will define the temperature rating and max voltage, but there's no mention of current within the UL spec. That's actually a function of the wire cross-section. And whether it's a stranded conductor or a single solid conductor. And the latter will actually take a higher current rating. I think the biggest difference between the designs, you know, outside of just the physical appearance of the cross-section is just the overall flexibility of the two. But that has no impact on UL.

Question: Our team needs an inexpensive cable product. Of the cable types presented in the webinar, what's your recommendation?

Answer: That's a good question. We recommend finding the best readily available wire that meets your project's needs. So, finding the best is a relative term. I definitely start with the temperature and voltage ratings of your project. Next, you're going to want to study the material of the jacket and make sure that the environment you're using the cable will be okay with that type of material.

If you're looking for specific UL specs that are inexpensive and readily available that we can recommend, I'd say UL 2464 is an excellent choice. That's a multi-conductor cable. It's wildly inexpensive, and it's used everywhere. For a single-conductor wire, the UL 1007 actually has a dual certification for UL 1569. Just really expanding its temperature limits. But that wire type is literally the most common single conductor wire type that we have here at Epec. So, I think if your team needs an inexpensive cable product, UL 2464 or UL 1007 are probably your best choices.

Question: Looking for AWG 28/30 for an aircraft fuel tank, would you have a part number available?

Answer: There are UL wire specs that may approach the performance requirements necessary for an aircraft fuel tank, but most mil-aero wire and cables that would be suitable for this environment are compliant to M27500. Within the family of wires for M27500, there are numerous that have nylon coated, PTFE, or FEP jackets that may be appropriate for your application. Epec does not extrude M27500 wire, but we do extrude TXL/GXL wire which is rated for automotive applications with exposure to fuel. If you need support manufacturing this cable, Epec can terminate and assemble complex harnesses using M27500 wire that is rated for use within an aircraft’s fuel tank.

Question: Is there flat cable multi-conductor rated to 125C with UL approval?

Answer: To better answer this question, we need to know the wire AWG size and number of conductors you need for the flat cable. We also need to know the pitch or center-to-center spacing of each wire. Depending on what you are trying to accomplish, there are numerous UL-approved wire types that may be appropriate. TXL and GXL are automotive grade XLPE jacketed wires and are rated for 125C. But these are typically in single conductor forms and would need to be formed into a flat cable. This is no problem since single conductor wires can be fused or laid together within a carrier film creating the traditional flat cable construction.

Question: Can you help determine a low-cost connector to use?

Answer: Yes, there are many options to consider. First, we need to know if you are looking for a wire-to-wire solution or a wire-to-board solution. Additional information about wire termination options is available on our blog. With so many options available, you should start with the mating connector requirements. If no mating connector is specified, we recommend identifying one of the common single or dual-row connector types offered by Molex, TE, or JST. Spending a few minutes on one of the major online electronics distributor websites should help you identify an appropriate connector housing and the corresponding crimp terminal. Once designed, Epec can help evaluate if there are any form, fit, function equivalent connectors available that offer a cost or lead-time savings.

Question: Can Litz wire be used in custom cables?

Answer: Since the purpose of a wire harness is to electrically connect two or more devices, yes, Litz wire can be used. But since Litz wire is not common, and its cross section is unique, the details of your eventual custom cable must be reviewed more carefully. Terminating Litz wire within a harness is straightforward as long as the properties of the Litz wire are unaffected. Litz wire can be bundled with other conductors to form a larger multi-conductor cable. Loss and the overall performance should be assessed ASAP especially if the Litz wire will be used in high frequency and high-power applications.

Topics: Cable Assemblies

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