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Topic Title: Push fit connectors
Topic Summary: Push fit vs screw connectors
Created On: 06 March 2011 11:33 am
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 06 March 2011 11:33 am
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Thripster

Posts: 811
Joined: 22 August 2006

Hoping there is somebody here with professional knowledge detailing how it came to be that screw terminals are liable to work loose and therefore more dangerous than push fit connectors. Presumably, the argument that screwed connections may work themselves loose applies to all screwed connections, including lamp fittings, socket outlets, cooker terminals in the back of the cooker, MET's, breaker terminations in CU's to name but a few............. what steps are therefore being taken to replace all of these within the industry with push fit terminals? Perhaps my perception is incorrect and that the working loose of the screws is not the main driver for changing to push fit connectors - if so, is there somebody who can explain more fully (I believe that amateur additions to the traditional JB is another reason for the change)? I am fully prepared to take on board the reason for the change and adopt the new practices but, being a cynic feel that there is a slight whiff of incomplete science/commercial lobbying going on here though happy to be proved incorrect. What REAL, scientific data is available to show that screwed connections have resulted in accidents/fires etc - who compiled this data and is it available for inspection?

What push fit connectors are recommended on 10mm² cable in inaccessible position for shower cable in a domestic environment?

Thanks for any comments
 06 March 2011 11:56 am
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mikejumper

Posts: 2810
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Originally posted by: Thripster

Hoping there is somebody here with professional knowledge detailing how it came to be that screw terminals are liable to work loose and therefore more dangerous than push fit connectors. Presumably, the argument that screwed connections may work themselves loose applies to all screwed connections, including lamp fittings, socket outlets, cooker terminals in the back of the cooker, MET's, breaker terminations in CU's to name but a few............. what steps are therefore being taken to replace all of these within the industry with push fit terminals?

Screwed terminals have been in general use in the electrical industry for over 100 years.
Would they have lasted that long if there was an inherent problem with them? I don't think so.
We'd all be a lot busier if that was the case.
 06 March 2011 12:22 pm
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Cremeegg

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Joined: 13 July 2007

The push fit connector reps will point you to compliance with all manner of chiefly American standards especially the Naval requirements that relate to vibration proof connectors.

I use them widely for lighting circuits, downlighters etc but my main concern is the surface area of the contact. A screw connector can squash down the wires to fill the available space giving a large surface area of contact through which the current can pass. A push fit connector has a more limited contact area - typically a flat sprung surface that pushes on the circular section wire.

At <1A on a typical lighting circuit it doesn't worry me but I've never used the 6mm2 push fits when you are talking about a 30+A cooker cable. Similarly I wouldnt use one for a 40+A shower supply.
 06 March 2011 12:59 pm
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AJJewsbury

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Push terminals have been used for years inside fluorescent light fittings and seem to have proven their reliability (usually it's the fuse or screw terminals or ballast itself that dies). I think it's a case of if something's quicker, probably cheaper, more convenient for the initial installer and just as safe, it's going to catch on. I remember using IDC connections for the first time on phone wiring and thinking how much of an improvement it was over the 'bare the wire and wrap around screw' procedure we had previously - just position, clunk and you're done.
- Andy.
 06 March 2011 01:09 pm
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sparkingchip

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Cremeegg is right about the cables squashing down under a screw, but you can over do it! the push fit don't sever a conductor due to over tightening.

Andy
 06 March 2011 01:10 pm
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Jaymack

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Originally posted by: Thripster
Hoping there is somebody here with professional knowledge detailing how it came to be that screw terminals are liable to work loose and therefore more dangerous than push fit connectors.

If you consider the screw, it is really a spiral wedge or ramp. The reason why screws become loose over a period of time, is due to loss of the friction which holds the "wedge" in place and also material creep, this is accelerated by temperature variations - heating and cooling at the screw interfaces.
Push fit, spring type connectors would expand and contract, in unison with temperature variations and maintain pressure at the interfaces.

Regards
 06 March 2011 01:54 pm
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Starfire

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Originally posted by: AJJewsbury

Push terminals have been used for years inside fluorescent light fittings and seem to have proven their reliability (usually it's the fuse or screw terminals or ballast itself that dies). I think it's a case of if something's quicker, probably cheaper, more convenient for the initial installer and just as safe, it's going to catch on. I remember using IDC connections for the first time on phone wiring and thinking how much of an improvement it was over the 'bare the wire and wrap around screw' procedure we had previously - just position, clunk and you're done.

- Andy.


But I have replaced enough overheated push terminals, caused by bad contact, inside light fittings to make me avoid them wherever possible.

That being said, those inside fittings are built to a price - cheap. others designed for the task may be better.
 06 March 2011 02:48 pm
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aligarjon

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i tried some out a while back, one of the things i didn't like is that you can only use them once,so if testing you have to destroy them. they are also too big if joining several neutrals in a switch for example. As for the choc block connectors, you need to watch what you are using, there is some real rubbish out there, even from the main wholesalers where they won't tighten or they can be overtightened and broken. Gary

-------------------------
Specialised Subject. The Bleedin Obvious. John Cleese
 06 March 2011 02:54 pm
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normcall

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"one of the things i didn't like is that you can only use them once"

Ahh, the ones I use, you turn the cable to release it. Fiddly, but I know what you mean.

-------------------------
Norman
 06 March 2011 05:27 pm
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Cremeegg

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Fiddly but an approved methos of reusing them - or use those with levers.
 06 March 2011 05:28 pm
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londonlec

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Originally posted by: aligarjon

i tried some out a while back, one of the things i didn't like is that you can only use them once,so if testing you have to destroy them. they are also too big if joining several neutrals in a switch for example. As for the choc block connectors, you need to watch what you are using, there is some real rubbish out there, even from the main wholesalers where they won't tighten or they can be overtightened and broken. Gary



The small Wago ones have a (very small) hole that you can just get a tester probe into... like the long bender Megger probe.
 06 March 2011 06:56 pm
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ant1uk

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The Wago ones are the best I've used so far, I tested some when I was sent a sample from the manufacturer before I brought some and was very impressed on the amount of pressure you can put on them.

As with any join screw or push fit make sure you give the cable a pull to make sure you have a tight grip.
 06 March 2011 08:27 pm
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Cremeegg

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Wago are bigger than the Hellerman Tyton ones which can be tricky but Wago do a good box to keep everything tidy.
 06 March 2011 08:54 pm
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daveparry1

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I've been using the Hellerman Hellacon's recently, they seem to work very well but are not re-usable and 1.00mm or 1.5mm flex won't go past the contact spring, although I suppose it would if you tinned the strands first,
Dave.
 06 March 2011 09:01 pm
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Cremeegg

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Beg to differ Dave - try a twisting motion left and right whilst pulling on wire. It will pull out and can be re-used. For any flex I always use the Wago ones with levers - for solid cores then either will do.
 06 March 2011 09:03 pm
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ant1uk

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Joined: 22 June 2010

I was using some bt push fit connectors this week on an external bt box and one thing you have to make sure is that you push both sides down to make sure they make contact as I found out the phone line was dead until I did this. hehe
 06 March 2011 09:37 pm
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daveparry1

Posts: 8020
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try a twisting motion left and right whilst pulling on wire.
-------------------------
Thanks for that Cremeegg, must admit I've never really tried to get one off,
Dave.
 06 March 2011 10:27 pm
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Thripster

Posts: 811
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Thanks for your comments. What I am looking for is a copy of the scientific research carried out which demonstrates that push fit connectors are inherently safer than screw terminals - I wish to know which organsiation carried out the research, how many test connections were tested, over what period and the testing criteria. As stated previously, if screw connections are inherently unsafe, then I would need to know what steps are being made to phase out all screw terminal connections. I understand that push connectors are easier to use but I want access to the real data supporting the change in the regulations stating that screwed connections are unsafe unless accessible. Just because everybody is doing it doesn't prove that the old technology is unsafe.

Regards
 06 March 2011 10:45 pm
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ant1uk

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I would assume the manufacturers may direct you to the specs
 06 March 2011 10:49 pm
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daveparry1

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Is this for some sort of research project you're doing Thripster, or is it just purely out of interest? If it's the latter I think you must have too much time on your hands! I don't think the regs have ever said that screwed terminations are un-safe, just that they shouldn't be used in places that are not accessible for maintenance,
Dave.
IET » Wiring and the regulations » Push fit connectors

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