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Screw terminals vs crimped rings and studs?

jdz

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Trying to decide if I want to continue with ring terminals on everything, or move some stuff over to din rails and terminal blocks (ul listed, 600v, etc)... What says everyone?

Everything in your house wiring is screw terminals, and it saves an expensive ring crimper and/or doubts about whether you truly got a good crimp or not (short of cutting one open and checking) -- however, it seems like everything DC tends to be crimped and bolted? What am I missing?
 
Trying to decide if I want to continue with ring terminals on everything, or move some stuff over to din rails and terminal blocks (ul listed, 600v, etc)... What says everyone?

Everything in your house wiring is screw terminals, and it saves an expensive ring crimper and/or doubts about whether you truly got a good crimp or not (short of cutting one open and checking) -- however, it seems like everything DC tends to be crimped and bolted? What am I missing?
One of the primary differences is that the AC wiring in a house is solid wire .... Not stranded wire. Stranded wire doesn't do well on most screw terminal connections.

There is also more current in a DC circuit than an higher voltage AC circuit. A 12V circuit would have 10 times more current than a 120V circuit to supply the same amount of power. The higher current makes all the connections much more critical to prevent voltage loss and over heating.
 
One of the primary differences is that the AC wiring in a house is solid wire .... Not stranded wire. Stranded wire doesn't do well on most screw terminal connections.

There is also more current in a DC circuit than an higher voltage AC circuit. A 12V circuit would have 10 times more current than a 120V circuit to supply the same amount of power. The higher current makes all the connections much more critical to prevent voltage loss and over heating.
Hey Bob -- thanks for the reply.

Solid wire is more common, but stranded is allowed and used all over the place (THHN/THWN), and the highest amperage connections back to the pole / transformer are also stranded and secured by screw terminal. The DIN rails appear to be appropriately rated (600v/150a UL for https://www.dinkle.com/en/terminal/DK35N)... Any other ideas?
 
It really depends on the type of terminal and conductor. Most conductors are fine in a mechanical terminal connection. But fine strand conductors can be an issue. In a clamping type terminal there's no problem. But in a set screw type terminal a ferrule should be used to avoid damaging the strands. And to allow full compression and connection of the entire conductor.
 
Solid wire is more common, but stranded is allowed and used all over the place (THHN/THWN), and the highest amperage connections back to the pole / transformer are also stranded and secured by screw terminal.
The difference is that stranded THHN and the like are stranded with heavier gauges. Something like 6- 14 awg strands. Due to the heavier strands, it stands up to a screw terminal very well.

The fine strand wiring more commonly used in a battery circuit/inverter/solar is more like 1,000- 30 awg strands. Those tiny strands don't do well under the point load of a screw terminal.
That's why a ferule or ring terminal is normally used.

There are screw terminals built for fine stranded wire, but they're less common and include a piece of metal between the screw and wire.
You can see the sheet metal pieces in the screw terminals below.

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Trying to decide if I want to continue with ring terminals on everything, or move some stuff over to din rails and terminal blocks (ul listed, 600v, etc)... What says everyone?

Everything in your house wiring is screw terminals, and it saves an expensive ring crimper and/or doubts about whether you truly got a good crimp or not (short of cutting one open and checking) -- however, it seems like everything DC tends to be crimped and bolted? What am I missing?
It all depends on the current you are drawing. But crimp terminals are superior as you tend to make better contact and have heavier clamping down forces. There are plenty of pictures of AC house wires arcing, DC would be even worse. I say a crimper is well worth it.
 
The difference is that stranded THHN and the like are stranded with heavier gauges. Something like 6- 14 awg strands. Due to the heavier strands, it stands up to a screw terminal very well.

The fine strand wiring more commonly used in a battery circuit/inverter/solar is more like 1,000- 30 awg strands. Those tiny strands don't do well under the point load of a screw terminal.
That's why a ferule or ring terminal is normally used.

There are screw terminals built for fine stranded wire, but they're less common and include a piece of metal between the screw and wire.
You can see the sheet metal pieces in the screw terminals below.

Doing a little more digging, it looks like the UL listing on the DIN terminal blocks may not cover fine strand wire typically used in PV/DC

From (https://lugsdirect.com/GuideToFlexFlexibleFineStrandedWireCableMechanicalLugsFAQ.html)

Q. Do I have to buy lugs that are UL rated for the fine stranded classes that I want to use? Flex wire has been used for years with standard lugs so why all the fuss?

A. Yes, UL and NEMA and NEC have made it completely clear that use of any wire connector that is only rated with UL486A-B is NOT adequate since this BASE standard does not automatically cover wires outside of standing classes B and C, the so called "rigid stranded" classes. Only wire classes in the base standard are tested by UL and other NRTL's unless the scope of the testing is widened with an additional testing plan, for the other wire classes.

So ONLY wire lugs that have been specifically designed and tested to work with fine stranded wires AND specify the fine wire classes and sizes in the product labeling, are allowed to be installed in panels or other UL / NEMA / NEC controlled electrical installations.

So it sounds like unless you're using THHN or other "standard" course strand wire, the DIN rail terminals may not in fact be appropriately rated.

Also found an interesting thread here (https://diysolarforum.com/threads/thhn-or-welding-wire.10755/) that discusses why THHN is somewhat impractical to use on larger sizes (it doesn't bend easily)...

So! You could do it, but you probably don't want to. Thanks everyone!

Edit: Just to try and close the loop on this -- I went ahead and reached out to Dinkle by email to ask about whether their UL rating includes FLEX or fine strand wire... Will update when I hear back.
 
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