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The main standard that applies to screw type wire pressure terminals is UL486A-B.
UL486A-B covers the testing of most standard wire terminal clamping units whether for Factory or for Field wiring applications.
UL486A-B is one of UL’s core standards that is referred to in almost every other electrical standard the uses wire terminals.
While it can be helpful for many traditional applications if a connector or terminal has already been formally tested to UL486 before being used in an end use assembly, the use of a pre-tested UL marked connector is not mandatory. The presence of a UL mark can restrict the innovation that might be otherwise possible with no restrictions inferred by the UL file.
PCB applications are rarely traditional. Indeed, the Recognized label from UL (UL486A-B classification code ZMVV2) requires that the connector, even if already approved under UL486, be tested again in the final assembly for similar and additional capabilities. The way in which the connector behaves in the final assembly is rightly considered to be crucial to its ultimate operating performance. For more information on ZMVV2 components see the article on UL Recognized Component Marks.
Consequently the UR mark is not nearly as useful as one might think since the heavy lifting still remains in terms of satisfying the UL requirements as mounted and used in the final assembly.
The option to use an “unmarked component of a UL investigated assembly”, sometimes referred to as an "Unlisted Component", is always open and provides the flexibility to add to or modify the use to which the terminals is put such as use of non-standard wire types, wire combinations, screw types, modified ampere ratings, intermittent peak currents evaluations, forced cooling methods and many variations in use that are not covered in a standard UL486A-B testing program.
Specific uses for an end use assembly terminal can then form part of the UL file for that end use device and is UL factory inspected to the specifications along with other components in the assembly. These Unlisted Components may be referred to in the UL Listed assembly file as UL486A-B classification code ZMVV3. For more information on how UL handles Unlisted Components see the UL Unlisted Component Program article.
This minimizes potential conflict of field interpretation of the requirements of the previously marked connector, such as the “conditions of acceptability” and the end application.
Since UL recognized connectors are always retested in the assembly whether already approved or not in the connector form, it is often faster and simpler to use an unmarked component.
IHI pretested unmarked connectors are built to the same standards as parts which have been tested as wire connectors. IHI provides technical support to help guide customers meet the requirements in the end product assembly, backed by customer testing programs to prove out designs for UL approval and, as important, provide long and reliable product life.
The principal testing for wire terminals comprises of heat rise and mechanical pull out testing.
UL HEAT RISE TESTS
IHI PCB terminals have resistances in tens of micro-ohms, well inside of IEC testing requirements for low volts drop under test currents, which is vital for the PCB designer to keep I^2*R watts of heat generation low in the assembly.
Heat rise of the assembly is more to do with the designer’s choice of foil weight, trace widths and number of layers, as well as wire gauge matched to design current.
It is common in PCB power applications for the power wire gauge to be specified either for Factory Wiring carried out by the OEM, or strictly specified field wiring that must be adhered to by the customers to maintain the warranty.
Since it is common for a narrow choice of wire to be specified by the OEM to insure correct operation of the whole device (heat rise in the device being critically related to gauge) and there is often only a single worst case version of the wiring to test which simplifies UL testing when the connector is a an unmarked component of a UL tested assembly.
UL WIRE PULL OUT TESTS
UL provides OEM’s with two choices of pull out force for a wire terminal connector.
All of IHI PCB terminal lugs are designed to meet UL486A-B high pull out forces when suitably mounted on the PCB. These forces are quite high as they were designed for electrical terminations where no strain relief was designed in.
UL therefore provided a de-rated pull out test for those applications where strain relief is designed in to the device. This is very common on appliances and printed circuit board applications where it is not desirable to put the PCB or soldered components in tension from wire connections.
UL486E allows this pull out force de-rating and it may be used to test an unmarked component of a UL tested assembly.
OF A UL TESTED ASSEMBLY
An advantage of using an unmarked connector in the UL assembly is that the OEM controls the entire UL file – the assembly and the unmarked component which will be specified in detail the OEM assembly file.
Adding to and making changes to the OEM UL file with regard to the terminal connector does not require updates to the terminal supplier’s UL file for that component.
UL486A-B STANDARD WIRE PULL OUT TEST FORCES AND UL486E STRAIN RELIEF CONCESSION LOWER FORCES COMPARED
|UL486A-B & UL486E WIRE PULL OUT FORCE COMPARED (COPPER WIRE ONLY)
|UL486A-B STANDARD FORCE
|UL486E STRAIN RELIEF CONCESSION FORCE
|AWG / kcmil
The UL486E pull out forces are 1/7th to 1/3rd the level in the standard UL486A-B so there is a considerable concession given by UL for devices having an approved strain relief.
IHI PCB lug terminal connectors are designed to meet the full pull out force of UL486-A-B whether they are UL listed, or are unmarked, unlisted components. IHI terminals also withstand the full torque on the wire binding screw that is needed to maintain the full UL486A-B pull out forces on the wires of each size.
It is important to remember that the electrical capabilities of the terminal are equally as important as the mechanical ones, so having adequate wire binding pressure for a gas tight connection over time is still essential even if the OEM chooses to use the low pull out force testing option allowed by UL486E.
All PCB terminals should be provided with strain relief to limit temporary or permanent pull on the wires and terminals mounted to the PCB (see solder creep characteristics).
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