PIT Technology

[Goldberg]

I can't suppress the negative feelings I have about this whole thing:

http://www.voltimum.co.uk/news/1248...locks-with-Push-In-Connection-Technology.html

Has anyone given these a fair trial and have any evidence to support or negate the manufacturers' claims?

 

[ban-all-sheds]

You have to hope that the manufacturers have...

I know what you mean about unease, and I'm not at all convinced that push-in connectors are a 526.3 qualifying system to allow inaccessibility, no matter how much the manufacturers try to claim that "maintenance free" is a qualifier, but that's not a concern for these rail terminals.

Just pushing wires in doesn't seem right to me either, but try mulling on this (as I am) - every plug & socket is a push-in connection, and we accept those without a generic concern....

 

[Goldberg]

Indeed so, and I've been mulling left, right and centre for some time now.

From my POV, the key difference between a socket outlet and a CU rail terminal is the obviousness of degradation. Heavily loaded plugs get very warm when connections are poor, and socket faceplates discolour, but things can get very barbecued inside a CU before anyone notices.

I'm all for new technology where it helps, but I don't see how you can improve on a soldered or crimped joint, so I can't even go down the road of imagining inaccessible PITs. I'd rather cut a hole in the door of my microwave oven and treat Little Goldberg to the full 900W.

If a joint isn't suitable for soldering or crimping, i.e. if it's truly a junction, then I'd use a screwdown terminal JB with full and documented accessibility.

Surely anything else is just snake oil?

 

[Chri5]

Surely the push connect systems (there are a few types) represent the same transitional change that happened at BT (and the comms sector as a whole) in 1982/3 when IDC / krone connections replaced screw terminals, solder terminals and gun wrapping.

Yes, there were guys at BT that in fear, rushed out to stores and collected all the old box connections (with screw and solder/tag terminals) because they thought the new products with ICD were wrong, but............

When was the last time you saw a comms termination product for pro use that wasn't IDC / krone ?

The new electrical push, snap terminals will replace old screw terminal kit as time moves on. I've seen various light fittings that come with push fit and believe such a product will filter out to loop in / out roses, sockets and switches in due course.

A strong plus for the push type is that the termination is firm and due to the sprung nature of the terminal 'grip' has obvious advantages over screw terminals which could / can / might work loose via vibration, poor initial fitting etc

 

[Goldberg]

Surely the push connect systems (there are a few types) represent the same transitional change that happened at BT (and the comms sector as a whole) in 1982/3 when IDC / krone connections replaced screw terminals, solder terminals and gun wrapping.

Surely they didn't.

The IDC terminal is a solution to a problem, that being the difficulty of quickly and reliably stripping the insulation from the small gauge cores used in data and low power (e.g. POTS) networks. As long as you use the correct tool, an IDC terminal is reliable for a long time, but in any case the terminations are always in terminal boxes, or telepone socket boxes, or on panels distribution boards and enclosures. Also, poor connections, when they happen, are often of little consequence thanks to digital data streams and error correction technology.

PITs for power distribution is a whole different kettle of much smellier fish, because of the need for greater surface area at the point of contact. Given the tendency for heat to be generated when there's a high resistence, and the fact that such heat frequently goes unnoticed until a lot of damage has occurred, not having full control over the contact patch gives me the willies. Don't forget that a resistive appliance can seemingly gaily go about its duty of drawing a large current without a whisper of complaint, even when its supply is roman-candling away under the stairs.

For these reasons the comparison is flawed.

When was the last time you saw a comms termination product for pro use that wasn't IDC / krone ?

That would be yesterday.

I added a domestic telephone extension that had screw terminals at the faceplate.

The new electrical push, snap terminals will replace old screw terminal kit as time moves on.

I doubt it, in the same way that I doubt Adolf Hitler was a kind and well-meaning soul.

I've seen various light fittings that come with push fit and believe such a product will filter out to loop in / out roses, sockets and switches in due course.

I also believe it, in the same way that I believe Cherie Blair to be an honourable and upright citizen.

A strong plus for the push type is that the termination is firm and due to the sprung nature of the terminal 'grip' has obvious advantages over screw terminals which could / can / might work loose via vibration, poor initial fitting etc

I do see the potential advantage, but do you believe that springs last for as long as fixed cabling, and that they therefore pass the qualifying criteria for inaccessible junctions?

 

[electronicsuk]

We have been using a similar style of push-in terminal for a while now at my place of work, although admittedly not for domestic use. In the main we use them for ELV signalling and control circuits, but sometimes with currents up to a few amps. We've not experienced any more problems with these than we do with any other type of semi-permenant connection.

As to their performance for domestic or high power use, I'm also a little dubious, especially with solid conductors.

 

[Goldberg]

Thank you, electronicsuk.

I'm curious - is there some physical attribute of the PIT connection that makes you more confident with a stranded conductor than solid core?

 

[electronicsuk]

Thank you, electronicsuk.

I'm curious - is there some physical attribute of the PIT connection that makes you more confident with a stranded conductor than solid core?

It's merely a case of personal experience, it just seems as if small gauge stranded wires give a slightly more secure connection, probably on account of the fact that the conductors will compress more readily in the terminal.

 

[Chri5]

Funny thing is that I'd imagine the connection would be weaker on a stranded cable than a solid core.

Same as why IDC doesn't work well with standard wire. If a device (IDC or PIT or another) is designed for 0.5mm conductors then it becomes less effective when the device has to accept a stranded cable of 0.5mm which by virtue of it's design will deform to a lesser size at the bite point (normally 2 sides) of the connection.

So on the assumption that PIT or push fit cable terminations will be designed for 1.0mm, 1.5mm. 2.5mm and 4.0mm solid core, then using a stranded cable would give a lesser grip.
Maybe the sprung nature of the terminal can cope with the deformation of stranded cable, but am I wrong to think otherwise ?

As for service free junctions I agree that other than solder or crimp I wouldn't accept a push fit as service free.
I also have concerns of resistance measurement since most current termination methods for electrics tend to use the majority of the core circumference, a push fit bites far lesser amounts of the circumference.

 

[ban-all-sheds]

For that particular product they recommend ferrules (I guess pin terminals would also do) for small stranded sizes.

And they only go to 2.5mm², so not designed for really high current.

 

[electronicsuk]

Funny thing is that I'd imagine the connection would be weaker on a stranded cable than a solid core.

Same as why IDC doesn't work well with standard wire. If a device (IDC or PIT or another) is designed for 0.5mm conductors then it becomes less effective when the device has to accept a stranded cable of 0.5mm which by virtue of it's design will deform to a lesser size at the bite point (normally 2 sides) of the connection.

So on the assumption that PIT or push fit cable terminations will be designed for 1.0mm, 1.5mm. 2.5mm and 4.0mm solid core, then using a stranded cable would give a lesser grip.
Maybe the sprung nature of the terminal can cope with the deformation of stranded cable, but am I wrong to think otherwise ?

As you say, I think it is simply because of the spring mechanism, which on the smaller terminals that I have used seems to be capable of clamping almost all the way down when there's no cable in there. Obviously, very small cables will have to be ferruled, otherwise you wouldn't be able to push them in without the strands simply splicing apart under the stress.

 

[Chri5]

Ferules would sort the deformation, but then a (say) 1.0mm standard with ferule would be 1.2mm giving a problem with being 'oversize'.

As you mentioned the answer is more likely that the jaw length of the connection is longer, giving similar contact be virtue of the contact points being much longer than the diameter of the cable in question.

Well I know what I mean

I've used krone, ADC, AT&T, Nortel IBDN, idc 50 w splice machines, gun wrap, solder extensively and tend to think in the comms generic for electrical push and snap fit.

Looking at the Helacon plus samples I have, suggests the jaws grab no more surface area of the core to me ? but there is 2 x sets of jaws !

This one shows it better

And here's IDC / krone- couldn't find a better 'jaw' picture

 

[ColJack]

we've had PIT connections with us for a long time.. most of the fluorescents have been using it for years..

 

[Chri5]

Just looked at the OP original link

I'm sure some boards have had these units for a few years now. I'm almost certain that the last door entry control unit I installed had them.

I assume that the wire or wire with ferule (if required) is pushed home and the top cap closed, pushing a rod with some sprung force down on the wire.
I'm sure it works well, but I'd also imagine that they aren't designed for 1000's of times of use, I'd also worry about the potential for the sprung element to suffer memory loss (or fatigue) and the plastic to become brittle.

 

[ColJack]

your pic is of a screw terminal.. or at least the one with a wire in is..
the middle one is of a pish terminal.. just shove the wire in.. use a screwdriver in the hole to release it..

no idea what "cap" you're on about though...


we used similar for years on control panels for BT air conditioners..
the little orange "button" is just a plastic plug that does the same job as the screwdriver does... opens the contacts...