Molten contacts and a lesson in observation - Page 1
Forum section: electronics / projects

author: calzap
author_rank: Frequent Contributor
timestamp: July 20, 2021, 08:00:29 pm
content: So, it’s hot days and the house AC runs a lot during daytime at our ranch. But even though the inside fan unit runs, nothing is stirring in the outside compressor unit. I check the breaker, and it’s tripped. I reset it and the fan on the compressor unit works but can’t determine from sound if the compressor is going. It’s not; no cool air from the inside ducts.I wondered why the breaker tripped and soon found out. I turned the breaker off and opened the electrical compartment on the compressor unit. Wow … soot, molten metal, melted insulation and more! See the first pic. Looked like catastrophic failure of the contactor. But wait … the fan and compressor both get power from the contactor, and the fan works. Closer inspection reveals it was the connection between one of the compressor wires and a lug on the contactor that failed.I decide to replace the contactor. A call to the local electrical supplier revealed they could get a replacement shipped from Utah. I could get one immediately from a different supplier in the big city (Sacramento), but that would be a 2-3 hour round trip in heavy traffic. I noticed the contactor was 3-pole even though we have single phase power. Guess the AC manufacturer has a 3-phase compressor option for units going to apartment and commercial buildings. The contactor still worked, so I could do a “temporary” fix by trimming the burnt wire ends, applying new terminals where needed, and moving wires from the damaged pole to the unused pole.Before getting started, I made a careful drawing of connections and consulted a picture I made 4 years ago when the capacitor had to be replaced. The pic is below. You should be able to see what I missed 4 years ago. I had an HVAC tech out to the ranch 3 years ago to repair different equipment. For a decent price, he offered to do a thorough inspection and evaluation of the AC system of the house. Yeah, he missed it too.A picture of the “temporary” fix is below. I ordered a replacement contactor. Chances are it’ll sit in reserve.As a final note, all the inside wire of the compressor unit is AWM (appliance wiring material). This wire is not legal for building wiring in the US, but is common in, yup, appliances. This stuff can be strange, and the AWM in the compressor unit was no exception. The wire to the fan was 18 AWG, but the outside diameter was the same as 10 AWG building wire … massively thick insulation. The wire to the compressor was 10 AWG and same OD as the wire to the fan. The conductor was stranded and composed of numerous fine wires … much finer than in building wire.Mike in California

author: bill_c
author_rank: Regular Contributor
timestamp: July 21, 2021, 01:38:49 am
content: Put a #6 stranded wire in a lug similar to that, tighten it as much as you want, then move the wire around a bit. Sometimes you can just pull the wire out of the lug. Vibration can do the same thing.I had that happen on a 480V 200kW generator breaker (on the generator side), Melted the top half of breaker, the wires, and the front panel.

author: coppercone2
author_rank: Super Contributor
timestamp: July 21, 2021, 06:25:23 am
content: I wonder if a ferrule would prevent that failure

author: calzap
author_rank: Frequent Contributor
timestamp: July 21, 2021, 07:18:46 am
content: Quote from: coppercone2 on July 21, 2021, 06:25:23 amIt probably would have if it was the right kind of ferrule properly applied. I think the stranded wire with many fine strands was a culprit, and a ferrule would have rectified its mushy, fragile nature. Building wire of that size is used frequently in set-screw lugs with little problem. But building wire has fewer, thicker strands.Mike

author: coppercone2
author_rank: Super Contributor
timestamp: July 21, 2021, 08:09:23 pm
content: it seems that only a certain conductor class range has good performance with screw terminals

author: mansaxel
author_rank: Super Contributor
timestamp: July 21, 2021, 08:53:18 pm
content: It is a very bad design to have the set screw push straight down on the strands.A much, much better solution is to have a cage pulled up by a screw like in this DIN rail "Reihenklemme" (terminal block):There are contactors available that get this right, and when torqued to spec will not run hot, and will not let the cable be yanked out.A ferrule would help because it precompresses and protects the bundle of strands. Also, it makes for safer reattachment when replacing the contactor. But it of course needs crimping with the proper pliers; I've got a Knipex 975304 and I highly recommend this tool.Why, to this European, does all HVAC wiring in the US look like shit? And all the devices, like contactors, switches, conduit, et c. look like they're from the 1950s? I watch a few videos of AC tech "HVACR Videos" on the Tube, and I'm like Whiskey Tango Foxtrot at the sheer crap they put up with.Some starting points for discussion:European wiring:US wiring:

author: pqass
author_rank: Super Contributor
timestamp: July 21, 2021, 09:47:34 pm
content: Quote from: mansaxel on July 21, 2021, 08:53:18 pmYeah, it can get gnarly after a few years/decades. The fresh stuff should try to look like this:If you meant appliance internal wiring, it doesn't look that bad. Don't A/C compressor units look the same everywhere?

author: WattsThat
author_rank: Frequent Contributor
timestamp: July 21, 2021, 10:42:23 pm
content: QuoteBecause the panels are built by the lowest bidder to what are most times no specifications for the minimum quality or components. In the US, most industrial panels are of a better build quality, HVAC is the bottom of the barrel cheap. Ultimately, the engineering firms specifying HVAC equipment don’t get paid to write new specs so it never happens.Unless specifically called out by a customer, most HVAC specifications do not require wire numbers or single point to point wiring as seen in euro-centric equipment. This allows for the nightmare of the daisy chaining of control voltage which results in the mess you see in the photos.In the US, you’ll see distinctly different levels of quality in wiring and panels:Residential at the bottom, Commercial (were most HVAC is found) and then Industrial. It is at the residential level and most commercial installs that you find only solid wire up to 20 amps and the twist on wire nuts.

author: wizard69
author_rank: Super Contributor
timestamp: July 22, 2021, 12:20:23 am
content: Ferrule have their uses but they are also highly overrated in my opinion. The primary issue with this sort of wiring is the lack of proper torquing of the various set screws and is in fact why the NEC in the latest revision is trying to address the problem. One study indicated that over 80% of the screws are not torqued properly, often way too loose. The goal is to move to the use of torque wrenches for these sorts of assemblies. Also electrical connections will loosen over time so a good PM program is a must.Now Ferrules can help with stranded wire, especially the finer stuff when installed in set screw type lugs. In the end what the ferrule is really helping with is getting all the wires into the lug properly. I'm not convinced that they help with the type of lug or terminal that uses a clamping washer.Quote from: calzap on July 21, 2021, 07:18:46 amThere are lots of good reasons to use ferrules even with machine tool wire and similar. For example it is far easier to service equipment with nicely ferruled wires. A noted they can help a lot with finer wires especially those used in high flex cables or when the wire is too small for the set screw. Personally I have a love hate relationship with wire ferrules, they do solve problems but in some way I see them as over rated.

author: Renate
author_rank: Super Contributor
timestamp: July 22, 2021, 12:24:00 am
content: European cabinets on DIN tend to be neater, but they don't default to a standard distribution panel.You have to add the bus bars yourself.European (at least German) wall boxes are a joke compared to US ones, they have much less room inside.Me? I'll admit to preferring double boxes with single plaster rings.In any country:Rotating screws against bare wires just sucks.Either cage sockets or screws to screw terminals.

author: coppercone2
author_rank: Super Contributor
timestamp: July 22, 2021, 12:59:33 am
content: i don't know how you can over rate a part that goes between 5-25 centsit also gets rid of a massive short circuit problem with frayed wires

author: daqq
author_rank: Super Contributor
timestamp: July 22, 2021, 07:33:08 am
content: Now to be fair, I've seen similar unholy abominations here as well. TheCurse of the Lowest Bidderis not affected by borders.

author: calzap
author_rank: Frequent Contributor
timestamp: July 22, 2021, 03:40:17 pm
content: Quote from: Renate on July 22, 2021, 12:24:00 amI've traveled a lot in Europe, mostly west and south, and noticed the small size of panel boxes in apartments and houses. Never took the cover off but have wondered if the working space inside might be cramped. Figured there might be some latitude because having 220 VAC outlets and lighting allows for smaller gauge wires per circuit. Then too, there are usually fewer outlets per room in Europe than the US and fewer total circuits capacity in the panels. Wiring and panels in older buildings, especially in the south and east, can be just as disorganized as in older buildings in the US. Both in the US and Europe, not hard to find unprotected cables attached to inside and outside ceilings and walls of older buildings.Mike

author: Renate
author_rank: Super Contributor
timestamp: July 22, 2021, 05:40:40 pm
content: I had an example that this thread pushed me to finally do something.A 12 V system with a 4 AWG wire (~21 mm²).But the silly wire was pretty finely stranded.There was no need for it to be other than coarse stranded.It was through a place that I didn't know if I could just pull in something different.It went to a terminal with a direct action pinch screw.I was getting up to a volt drop over the connection.One strand said, "Hey, I'm kinda getting crushed here, if you guys just rearrange yourself a bit I'm sure that I could get some elbow room."I didn't have any ferrules that size.I gooped it up with flux and used a propane torch to tin it with solder.Then I filed off the excess solder and left it bright and shiny.

author: mikerj
author_rank: Super Contributor
timestamp: July 22, 2021, 05:57:44 pm
content: Quote from: Renate on July 22, 2021, 05:40:40 pmSolder seems like it helps initially, but it creeps under stress even worse than the bare copper.

author: Renate
author_rank: Super Contributor
timestamp: July 22, 2021, 06:05:34 pm
content: Quote from: mikerj on July 22, 2021, 05:57:44 pmI believe you, but it was getting bad.I'm not sure that there is room for a ferrule though.

author: mansaxel
author_rank: Super Contributor
timestamp: July 22, 2021, 11:26:24 pm
content: Quote from: Renate on July 22, 2021, 06:05:34 pmTinning stranded cable is illegal in mains applications in Sweden, just because of the creepiness. With a pinch screw, a pin lug or a ferrule nearly is mandatory. For such areas, a dual-hole lug and 2 off 1/4" (or M6) screws is the best, but you gotta do what you gotta do.

author: wizard69
author_rank: Super Contributor
timestamp: July 23, 2021, 05:48:48 am
content: Quote from: Renate on July 22, 2021, 06:05:34 pmIf there isn't room for a ferrule you have trouble. Do realize that there are alternatives that sometimes are workable. If the device you are connecting to supports it ring terminals can be a viable alternative. In some cases a forked terminal can do the job.

author: jmelson
author_rank: Super Contributor
timestamp: July 23, 2021, 05:19:53 pm
content: Just had another connection burn off my 46 year-old air conditioner compressor. It had kovar studs coming out of the compressor with 1/4" QC lugs welded to them. One particular place the female crimp terminal has burned up several times. I decided to get rid of the 1/4" QC and found a big screw/clamp terminal, and attached that to the kovar stud and the wire. Well, we will see how long this lasts.Jon

author: phil from seattle
author_rank: Super Contributor
timestamp: July 23, 2021, 09:26:12 pm
content: QuoteClearly you haven't looked in enough places in the US. Almost all industrial cabinets are tidy, using DIN Rail gear and ferrules these days. Residential breaker panel wiring is not quite as tidy but fairly clean and doesn't use stranded wire. Even my 70 year old house that has had about 10 remodels over the years has a decently laid out and clean electrical panel, despite still have one run of knob and tube.Personally, I am a huge fan of using ferrules and DIN rails.

author: mansaxel
author_rank: Super Contributor
timestamp: July 23, 2021, 10:23:12 pm
content: Quote from: phil from seattle on July 23, 2021, 09:26:12 pmYeah, there's good things in the US too, indeed. It's the sub-species of electric machinery that's called "commercial HVAC and refrigeration" that's pathetic. Wire nuts, bundles of wires not adjusted for length and simply cable-tied into a ball of yarn, no cable guides, no sheathed cable for 3-phase to consumers, and so on and so forth.

author: calzap
author_rank: Frequent Contributor
timestamp: July 24, 2021, 12:19:05 am
content: Quote from: phil from seattle on July 23, 2021, 09:26:12 pmJust to be clear, stranded wire is not common in residential construction in the US because it must have flexible armor or travel in conduits. It’s much cheaper to have an electrician to apply NM cable to framing than to place conduits and pull wire. The NEC does allow stranded wire in residential construction. If you look at the panel pic in the post above by pqass, in the lower right, you’ll see a pair of blue and white stranded wires. And the feed wires to the panel are stranded. Of course, it has to be the right size, type, etc. And, yeah, it can be used in listed set-screw lugs.I have experience with commercial wiring, where conduit is common. So, when we had an apartment constructed in a building on our ranch, I did the wiring with ENT (flexible plastic conduit) and THHN stranded wire. Went pretty quickly. Nice thing is the ease of doing modifications and additions. Later, a circuit was added to the apartment using existing conduit. Was easy and didn’t require fishing cable or tearing into walls and ceilings.Mike

author: james_s
author_rank: Super Contributor
timestamp: July 24, 2021, 12:53:29 am
content: Quote from: mansaxel on July 21, 2021, 08:53:18 pmYou're comparing a nice brand new industrial panel to an obviously very old, crusty and heavily molested rat's nest that looks like it might be in some forgotten corner of a commercial business basement. It has obviously been added to, modified and monkied with over a long period, decades most likely with different tenants having different needs and people of different skill levels working on it. Your pictures are like showing a brand new expensive European car and comparing it to a worn out and used up 30 year old American beater with a bunch of questionable modifications and repairs.We have industrial cabinets here with DIN rails too, they look exactly like that, but there is also old junk and I bet if you dig hard enough and look in the right places you'll find some scary hacked up installations like that in your own country too. As for the HVAC stuff, I don't think residential air conditioning is nearly as common in Europe as it has been in the USA. Here it was pretty much ubiquitous in the hotter regions as far back as the 1960s and until very recently when things have been changing due to efficiency mandates the systems were built pretty much the same way they were in the 60s. If it ain't broke, why fix it? They may look a bit primitive inside but they're generally reliable despite being built to a cost. Most people never open up the service panel on their AC unit and never see what the control gear looks like, they don't have any reason to care that it doesn't look like a top notch industrial cabinet. It's a low cost residential appliance.

author: coppercone2
author_rank: Super Contributor
timestamp: July 24, 2021, 01:29:33 am
content: can't say im arguing too much, a nice industrial panel is $$$some people really like their wire nuts tooit goes from a wire nut and maybe a zip tie to a rail, plastic molds, screws, etc. its like 3x more stuff.

author: mansaxel
author_rank: Super Contributor
timestamp: July 24, 2021, 07:49:37 am
content: Quote from: james_s on July 24, 2021, 12:53:29 amI admit I did some searching to find a suitably horrible HVAC wiring pic, but if you look atHVACR Videosall you see is a long series of dangling wire stringed haphazardly around machinery, spliced with wire nuts when too short and bundled with cable ties when too long. All of it is commercial facility installs. In California (which is where I believe he is) refrigeration of people and produce is close to a core activity in restaurants, right?I've got two heat pumps at home, one Panasonic air/air and one IVT geothermal. An IVT installation instruction video in Swedish is available, skip to 6:35 for the electrical part:Mine is slightly older, but that is the standard level here. For residential, mind you.

author: Kjelt
author_rank: Super Contributor
timestamp: July 24, 2021, 08:07:21 am
content: Didn't read the entire topic but for TS now you're AC is open, also discharge and measure the capacitance of the motor capacitor. If it is less than 70% of the original value, replace it.That is one of the first parts to go nextHad that experience three years ago after 15 yrs of operation, noticed that the motor would not start easy everytime and there was only 5uF left from the initial 47uF.

author: tooki
author_rank: Super Contributor
timestamp: July 24, 2021, 04:43:17 pm
content: Quote from: Renate on July 22, 2021, 06:05:34 pmGiven that the ferrule crimping process compresses away much of the air space between strands, its final crimped size is similar to the bare stranded wire.And since it can’t be emphasized enough: get rid of the tinned section ASAP, it’s a fire hazard in waiting.

author: Vovk_Z
author_rank: Super Contributor
timestamp: July 26, 2021, 09:03:58 pm
content: Quote from: coppercone2 on July 21, 2021, 06:25:23 am+1. It (stranded wire) definitely will burn without some kind of ferule.

author: james_s
author_rank: Super Contributor
timestamp: July 26, 2021, 09:27:59 pm
content: I've never seen ferrules used in any sort of domestic equipment, even where stranded wire is used such as wiring run in flexible conduit.

author: tooki
author_rank: Super Contributor
timestamp: July 27, 2021, 02:31:19 pm
content: Quote from: james_s on July 26, 2021, 09:27:59 pmLiving in the US, I never saw them, either. Here, they're required by code now, so they've become commonplace.Whether required or not, I highly recommend using them, they make all sorts of wire termination jobs easier, not to mention safer. (For example, I use Pomona screw-mount banana plugs for temporary custom test leads. With a ferrule, even comparatively thin wires hold securely under the set screw, and are MUCH easier to feed in, since the strands can't spread into a mess.)

author: ajb
author_rank: Super Contributor
timestamp: July 27, 2021, 07:11:51 pm
content: Quote from: tooki on July 24, 2021, 04:43:17 pmAnd for tight situations, you might want to use a ferrule crimping tool that produces a shape that matches the terminal opening. So square or trapezoidal crimps for terminals with rectangular openings, hexagonal crimps for round openings. It won't make a ton of difference, but it may make things easier even if the ferrule otherwise fits.Alternatively, there are crimp-on terminals that provide a pin or flat blade to fit in screw terminals. At 4AWG you might even be able to find a reduction lug with a larger screw terminal opening in the back that will fit a ferrule and provide a pin or blade that will fit into the existing terminal.

author: james_s
author_rank: Super Contributor
timestamp: July 27, 2021, 09:04:27 pm
content: Quote from: tooki on July 27, 2021, 02:31:19 pmThey do seem like a good idea, until this thread I never knew they existed, I'll have to look around and see if I can get some as well as the tool for them.

author: tooki
author_rank: Super Contributor
timestamp: July 27, 2021, 11:42:52 pm
content: Quote from: james_s on July 27, 2021, 09:04:27 pmThe Chinese clone ferrule crimpers (the kind that squeeze from all sides, either 4 or 6 depending on type) work very well, just as usable IMHO as a Knipex that costs 10x as much. Well worth the $15. See the attached pic for the style I mean.Quote from: ajb on July 27, 2021, 07:11:51 pm100% confirm. I own a hex crimper, but can use square and trapezoidal ones at work, and you’re absolutely right that sometimes, one shape or the other is better. I’ve been meaning to order a cheap Chinese square crimper for home use.Quote from: ajb on July 27, 2021, 07:11:51 pmYeah, there are, but the quality of the tool and terminal is much more critical than with ferrules, so I’d sooner use ferrules when possible.(For those new to the topic: a ferrule crimp isn’t intended to be a gas tight crimp like terminal crimps are. Ferrules are just to keep strands together. It’s still the screw terminal’s own compressive force that fully compresses the strands.)

author: KaneTW
author_rank: Frequent Contributor
timestamp: July 28, 2021, 12:49:08 am
content: Quote from: james_s on July 26, 2021, 09:27:59 pmI've only ever seen solid wire or stranded+ferrule or stranded+cage clamp except for one case that was a ticking fire hazard.

author: james_s
author_rank: Super Contributor
timestamp: July 28, 2021, 12:52:44 am
content: Quote from: KaneTW on July 28, 2021, 12:49:08 amClearly it's a regional thing. They're just not something that was ever common here, maybe they are used in our industrial cabinets, I have not done a lot of work with those, but they are not used in American domestic applications. I don't know if code allows them or not, it's hard to say with that kind of thing.