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| Assemble a cable with NEMA L5 connectors. Reliable? |
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| Gregg:
I’ve had a lot of experience with L5-20 plugs and receptacles in data centers where we used thousands of them. In 15 years I only experienced one failure like you have shown and it was because the screw to a conductor wasn’t tight. That seems to be the case with what you have pictured. On the other hand you are drawing more power than you should for the application if there are 4 of the fixtures on a single 20 amp circuit considering the elevated temperatures near the ceiling of a stage and you should de-rate the load by 20% for continuous use. Either reducing the load to three fixtures per circuit or going to a 30 amp circuit with 10 ga wire would pay off in the long run. What I found about tightening stranded wire in those type connectors is to tighten them and then wiggle / tug on the wire and tighten again to cause the strands to seat against each other properly. Hubbell used to make the premium connectors followed closely by Leviton; Pass and Seymour used to be just OK. |
| dmills:
Loose screw was clearly the proximate cause, but datacentre is a very benign environment in a lot of ways. You see this occasionally in the entertainment industry, thread lock helps, but the cables tend to have a really hard life, PM is the answer. I am slightly surprised to see it happening in a cable that is just left in situ, it is far more common in stuff that gets thrown in and out of flight cases all the time. The thing about this failure is that a slightly loose screw tends to cascade into this fairly quickly due to the increased I^2R losses adding more heat. Thermal imaging could work, but it is a small target from the floor and probably right next to some very hot lights, you would need a better then average camera. |
| richard.cs:
The melting on the neutral but not the line is a clear indication of a high resistance connection. The currents on the two sides are equal yet only one has gotten hot. It's hard to tell much more from the photos but as other posters have said loose screws would be the most common cause. If it happens "all the time" to cables they assemble definitely get somewhere else to do it. Being from the UK I am not familiar with that connector but judging by your photos and a quick googling it does look pretty flimsy. We have Ceeform / IEC 60309 for this kind of use* which is rather robust though could still be damaged by a poorly terminated cable. People routinely use the 16 A size for welders and similar at 20-30 A (when they should use the 32 A size) but it's very rare for anything bad to happen. They normally have tunnel terminals like these: https://i.ytimg.com/vi/RMEfYaICLj4/maxresdefault.jpg with the better quality ones having two screws per pin. Do your connectors have something like that or are they a "wrap wire around screw" design? The latter tends to give much poorer connections and reliability. Accepted best-practice here is to crimp a ferrule onto the stripped end of the flexible cores and then fit a good-quality connector. If I were to tell a supplier here I wanted crimped ferrules, a connector with double-screw tunnel terminals and everything done up to a controlled torque they wouldn't question it or think it unusual (but the very cheapest places might not have the tooling for either or just be too lazy). *Though a lot of (most?) stage lighting here uses 15 A roundpin BS546 for historical reasons. |
| Monkeh:
--- Quote from: richard.cs on May 05, 2018, 01:48:01 pm ---Do your connectors have something like that or are they a "wrap wire around screw" design? The latter tends to give much poorer connections and reliability. --- End quote --- As I recall this style is generally a clamp plate arrangement, like barrier strip. Not generally a problem and often fine with bare stranded wire, too. But idiots can still make a mess of it. Rest of the arrangement's as shoddy as ever, though. Long overdue a modern replacement. |
| dmills:
Most UK theatres (Touring and gig lighting are a bit different) use the old 15A standard for dimmed power, and (often) 16A 60309 for non dim, this is nice as plugging a discharge mover into a dimmer can make bad things happen to both mover and dimmer. A properly crimped ferrule is best practise but you don't actually see it that often. I have seen plenty of 60309 in the larger sizes suffer exactly this failure, more common at 32A and up however, nothing quite like getting THAT smell from the 125A Three phase connector on the generator just as the first dance of the wedding starts..... Regards, Dan. |
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