I see on AndyMark’s new product page that they’ve recently added ferrule crimps and a tool to crimp them. I understand these are used to get a more robust connection of stranded wire in Wago, Weidmuller and clamps designed for solid wire. However, I noticed something disturbing about the crimps on AM: their electrical ratings. AM has four sizes. Comparing the maximum breaker usable with that wire gauge (2017 rules) and the connector’s rating yields:
Wire Gauge Max Breaker Crimp Rating
12 AWG 40A 35A
16 or 18 AWG 20A 18A
20 AWG N/A 17A
If I understand the rules correctly, using this connector on a 12AWG wire would mean that you would not be able to use a 40A breaker on that circuit, and likewise 16 or 18 AWG wire with the ferrule would require a breaker of 18A or less. I’ve looked at a few ferrules online, but do not see current ratings for them. Is this a general problem with ferrules, or just these?
This is not an issue with ferrules in general, its just these connections are not designed for that kind of current. CTR electronics has a good video on these in conjunction with robotics competition news: https://www.youtube.com/watch?v=AJzCYzr5gXU . These are really designed to work with the weidmuller connectors specifically with VRM, PCM, and the like where you should really never have that high an amperage running through them anyway, and really the only reason why they have twelve gauge connectors is for connecting pumps to the PCM and the main power supply wires to the VRM and PCM. These also do work well with wago lever-nuts and such, but not really designed PDP main motor supplies where you would pull 40 amps or especially solid wire clamps. this was, as states in the video, developed for teams who struggle with their wiring and getting a proper connection in the weidmuller connectors where the wires can pullout easily if they are not inserted properly.
this is not my understanding of how ferrules work at all. We get a square crimp out of our tool.It seems to me that we get plenty of contact with the terminals. When you use bare wire in a wago connection, it doesn’t come out looking like flat paintbrush does it?
Ferrules are great tools that create secure, foolproof connections. But don’t take my word for it.
Even at this rate, I wouldn’t use them with the PDP. See the linked 40A snap action breaker spec sheet on AndyMark, 150% (60A) load is rated for up to 47 seconds before tripping and still within spec. A lot of FRC teams use old and abused breakers which might make that time even higher. If you have a system that truly limits current effectively then that’s one thing, but I would not rely on snap action breakers to stay within electrical ratings.
Depends on the exact ferrule and crimper. Some will maintain the round shape and just add divots, others will make a square or hexagonal shape out of the ferrule. Whatever it is when using a ferrule it’s difficult to be certain an electrical connection has been made beyond a couple small points. In my experience the Wagos have enough tension to “paintbrush” the wire, they are intentionally designed to apply enough pressure to lightly embed the the contacts into the copper wire.
I would say they smush (technical term) the wires more than embed into them… but regardless, whatever method works you, use a pull test to make sure the wire is seated firmly in the wago terminal.
That being said, most electrical connectors, including those mentioned in this thread so far, have some effect on performance… whether that effect is acceptable is up to the application and the implementer(s). I highly recommend the critically acclaimed Trilogy of Connectors if this is a topic of interest to you. Volume 2 really links the other two books in the series together (It’s not actually a trilogy in that sense - I just wanted to make a pun).
If that were the case, you wouldn’t want to use a ferrule in any clamping contact application. However, ferrules are made specifically for screw-down and clamping contacts.
There exists a wide variety of crimping tools for ferrules, that crimp into a wide variety of shapes. Almost all of these offer at least one flat surface.
Furthermore, just because the stranded wire is now encapsulated in a ferrule doesn’t mean there’s no deformation of the ferrule under contact pressure. The ferrule will still conform somewhat to the terminal, but that deformation will no longer result in strands fraying as they do with stranded wire in the same terminal.
OK, I am digging back to the original choice of WAGO connectors for the PDP. They are intended for stranded wire only and the data suggests that the current rating be derated for at least two AWG sizes when using solid wire due to the contact area. Ferrules may be used on stranded wire but only if the indicated WAGO ferrule is used with a the WAGO crimper. The ferrule reduces install time for production line assembly.
Please note from the picture above, that stranded wire conforms to the shape of the contact to provide the maximum surface area contact. This occurs on all four sides of the wire when installed in the contact. I have not seen a failure on the PDP contacts when using stranded wire. I have seen a variety of failures using poor termination techniques and solid wire.
When using the ferrules for the Weidmuller connectors, again follow the manufacturer recommendations for ferrule and crimp tool.
Using ferules have a few advantages. They cut down on wire whiskers that can cause shorts. especially in densely packed panels. They compress all the strands together insuring good electrical contact and decreasing opportunities for corrosion. The make sure all the stands end up in the terminal which can be hard to do for small gauge wire.
Everybody says to use “their” crimper and ferules. I think that is partially marketing and partially because they cannot control the quality of other companies products. What is really important is that you use a decent crimper and ferules that fit your wire regardless of the gauge rating.
There’s an implication here that doesn’t strictly follow from the rules: you assume that the vendor’s rating controls the legality.
But that’s not really a defensible way to read the rules.1 After all, for many reasons, most published specifications inherently assume something about the conditions that may not be true in a given application. One common issue is that current ratings often assume something about the ambient temperature and ventilation. Hypothetically, the ferrule’s rating may assume warm ambient conditions as might be found in an unventilated appliance, and describe the continuous-duty current needed to raise the ferrule to the temperature at which its insulating boot softens unacceptably. (This is likely well below the temperature at which the metallic connection degrades.) What if your duty cycle is the last 15 s of a match and your breaker protects against prolonged overcurrent, your cooling employs forced convection, and you have high-temperature heatshrink over the boot and the insulating jacket of the wire anyway? (Or you removed the boot so you could add that heatshrink.) Or what if there is no rating, or there are multiple ratings with unclear application?
You might well be in a situation where the published rating is simply inappropriate for the conditions, and if so, relying on that rating in those circumstances is at best a crude approximation. What if you can do better, and establish an application-specific rating, through testing or calculation? The rules do not preclude this, as the test is simply whether the gauge or rating is appropriate. Yes, that’s a discretionary standard, but inspectors are empowered to use discretion to evaluate the sufficiency of a robot’s construction relative to the rules. (And I think that’s a good way for FIRST to construct this rule: requiring a strictly standards-compliant installation would be difficult for teams to work with, and difficult to enforce fairly.)
So I think the real question should be: how can inspectors apply that discretion predictably and consistently in a way that provides adequate safety? And what should a team prepare in order to take advantage of that latitude?
That said, obviously the guidance posted previously relating to implementation is valuable. It doesn’t really do any good to have a robot which you can prove is safe, but which performs unacceptably because you’re wasting power or dropping voltage due to an undersized conductor.
1 Such as 2017’s R58, which says: “Branch circuits may include intermediate elements such as COTS connectors, splices, COTS flexible/rolling/sliding contacts, and COTS slip rings, as long as the entire electrical pathway is via appropriately gauged/rated elements.”
Have you ever looked up the rated current for 12awg wire? It varies widely depending upon the assumed operating conditions. In ‘chassis wiring’ it’s rated to 41A, but is rated for much less in ‘power transmission’ applications. These differences have to do with the assumptions surrounding the intended usage.
Are these ferrules rated in the same way as ‘chassis’ or ‘power transmission’ wiring? What is the ambient temperature assumed to be? What about the duty cycle? Etc. I don’t see any of those ratings on AM’s website, so it’s hard to say how that 35A rating stacks up with the 9.3-41A rating of the 12awg wire it gets attached to.
Keep in mind the only legal battery connector is rated for 50 amps. (Oops in 2017 you could use any SB connector. Most use the SB50) :] These kind of ratings of for worst case continuous service often with a generous safety factor. The wide current ratings for wire used under different conditions is a good demonstration of different conditions need different ratings. Most of the specifications in the NEC is from something catching on fire. The way you get UL certification on a product is to send it to a laboratory where they try to catch it on fire.
Terminals carrying the UL rating are tested for continuous current over time. A 35 amp APP contact, for instance, will be connected to constant current source of exactly 35 amps and then monitored for temperature rise over at least a 24 hour period. UL has very specific test procedures as to ambient temperature and enclosures based on the application. If a terminal carries various ratings dependent on AC/DC, enclosed, open air, bundled cable, etc. each variation will be tested. Often, series resistance will also be measured. In addition, depending on customer and UL rating, testing to failure may also be performed. In addition, manufacturers will also run their own tests and also perform life testing for repeated terminations. (I have seen life testing in the millions of operations for components I use.)
The ferrules in this discussion are not rated for current but for wire size. That is, the rating is based on using the #12 ferrule on #12 wire not on #18 wire. In the correct use of the ferrule, the current rating of the wire will not be degraded by the use of the ferrule. However, the rating is also only valid when using the correct crimp tool. Don’t try using these ferrules and crimp them with pliers.
It is for this reason that I do not recommend using those yellow hobby store connectors for wiring motors on FRC robots. They are not UL rated at all and I have seen ratings from 30-60 amps depending on supplier. Those are not illegal in current robot rules but they are not the best to use.
APP connectors in the 15-45 amp range all have the same contact area but are different parts to accommodate the wire size needed for the rating.