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Wiring an oven terminal block - why so difficult?

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Meatyfool
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Wiring an oven terminal block - why so difficult?

#160208

Postby Meatyfool » August 16th, 2018, 8:15 pm

New oven without cable so used pre-existing. Straight swap 13a single oven to 13a single oven. Just wire the ENL Wires to the correct terminals suitably marked. Hard not to be competent from a regs point of view!

But boy, do they make it difficult.

The old oven had straight connectors - just offer up the straight ends of wire and tighten the screw. Simples.

The new oven has a far more restrictive cable access - what’s more the three terminals were just screws. Should I just offer straight bare copper to one side of the screw and tighten up or should create a loop of copper to maximise the connective area as the screw is tightened?

I went with the latter. Just a couple of questions that arise. The oven will not be used until i’m Satisfied all is well.

1. The multi strand N and L both lost a strand whilst being manipulated into a loop. The end of that strand isn’t held in place by the screw. Can’t imagine it is an issue as the individual strands are all touching one another.

2. Multi strand wire doesn’t bend well without splaying out despite trying to twist it. Perhaps I should have soldered the ends? As a result the ends of some strands are sticking out a bit ie not hidden behind the screw. Still within the confines of the plastic surround of the terminal, and in no way at risk of connecting with any adjacent terminal. I am thinking that all the copper strands are supposed to be within the confines of the metal screw and the metal plate behind. Too close to plastic surrounding the terminal suggests the possibility of heating the plastic possibly to the point of melting. Am I right to be concerned?

Lastly, I am aware that the most likely cause for scorching a terminal block is loose connections. I am happy that I have tightened the terminals sufficiently.

Advice welcome!
Meatyfool..

Itsallaguess
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Re: Wiring an oven terminal block - why so difficult?

#160221

Postby Itsallaguess » August 16th, 2018, 8:56 pm

Meatyfool wrote:
New oven without cable so used pre-existing. Straight swap 13a single oven to 13a single oven. Just wire the ENL Wires to the correct terminals suitably marked. Hard not to be competent from a regs point of view!

But boy, do they make it difficult.....


What's the cross-sectional-area of the cores that you're wiring in?

I'm not sure you'll be able to get a drfinitive answer to your questions until we know that.

With that said, I wouldn't normally be too bothered about a single stray strand on a terminal, so long as it's still relatively captive in the area of the correct terminal, and there's no chance of it straying any further.

For info, 2.5mm three-core flex is usually rated to around 25 amps, so if you're using a 13 amp fuse in the plug for this oven, then there's a lot of strand-margin in there - but this comes back to you knowing if you're using 2.5mm csa flex or not....

Lastly though, can I just check that when you say in your second point -

'within the confines of the metal screw and the metal plate behind'

That there's not a free-moving metal plate underneath the screw-heads, which you could remove, wrap the twisted/stranded wires around the screw poking through it, and then offer the screw/plate/wire combination back into the terminal, to then screw onto another metal section of the terminal?

Sometimes there are what in essence are 'rectangular washers' under the terminal screws to completely capture the wires, and I just wanted to double check that this isn't the case here, perhaps?

Cheers,

Itsallaguess

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Re: Wiring an oven terminal block - why so difficult?

#160233

Postby Lanark » August 16th, 2018, 10:41 pm

When you cut the insulation off the end of the wire, you should do it in the same direction as the wires, not at a 90 degree angle. That way you won't lose any strands and wont have any damage to the strands which remain.

Its also a good idea to strip back quite a bit more than you think you will need, so theres plenty of copper to grab with a pair of pliers and wrap around the terminal, then cut off the excess.

I don't recommend soldering the ends in this situation.

Meatyfool
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Re: Wiring an oven terminal block - why so difficult?

#160273

Postby Meatyfool » August 17th, 2018, 11:43 am

Itsallaguess wrote:What's the cross-sectional-area of the cores that you're wiring in?

I'm not sure you'll be able to get a drfinitive answer to your questions until we know that.
Itsallaguess


If 2.5mm is "normal", then I must have 6mm - significantly more chunky.

The responses do give me comfort.

In regard to the point about the metal part behind the screw, if memory serves (am at work), it might be the loose washer arrangement you refer to, but I think it more likely loops around the plastic rear* and therein on to the wiring attached to the back of the terminal where the internal wiring starts off.

Meatyfool.

* Imagine a piece of paper folded in half and then offered up to wrap around a credit card (if you see what I mean!)

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Re: Wiring an oven terminal block - why so difficult?

#160285

Postby jfgw » August 17th, 2018, 12:23 pm

Single ovens normally run off of a 13A fused supply. Some come with a flex, some don't. I think the flex is usually 1.5mm^2 heat resistant (possibly 1.25mm^2), the instructions will specify a minimum size. Double ovens and hobs are normally connected to a 32A supply, usually using normal 6mm^2 twin and earth (although it should really be something heat resistant).

Solder cold-flows so, if you solder the ends, the connections will become loose. They will be tight just after you have tightened them but they will not stay that way.

Crimps are a better idea if you want to keep the strands together. Uninsulated bootlace ferrules are good where the wire is inserted straight rather than being wrapped around a screw,

https://www.rapidonline.com/truconnect- ... 00-33-1133

Eyelets and spades may be ok if the terminal box allows them (unlikely with most of the ones I have seen),

Eyelet: https://www.rapidonline.com/truconnect- ... 00-33-0205
Spade: https://www.rapidonline.com/truconnect- ... 00-33-0245

Sometimes what works is to strip and twist the ends, then double them over so the screw clamps all of the strands at least once.

Julian F. G. W.

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Re: Wiring an oven terminal block - why so difficult?

#160291

Postby Meatyfool » August 17th, 2018, 12:32 pm

Thanks Julian.

Spades or eyelets look like a more suitable connection. Our local ironmongers might even sell them in quantities less than 100!

The damn terminal block has a left entrance for the cable and room for three terminals top and bottom with the cable running between. I *might* be able to include a spade or eyelet in there somewhere. It al depends on how much plastic they have surrounding the terminals.

Meatyfool..

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Re: Wiring an oven terminal block - why so difficult?

#160311

Postby jfgw » August 17th, 2018, 1:48 pm

Meatyfool wrote:Thanks Julian.

Spades or eyelets look like a more suitable connection. Our local ironmongers might even sell them in quantities less than 100!

The damn terminal block has a left entrance for the cable and room for three terminals top and bottom with the cable running between. I *might* be able to include a spade or eyelet in there somewhere. It al depends on how much plastic they have surrounding the terminals.

Meatyfool..


Bear in mind that you need the proper crimping tool. You can get away without one with uninsulated bootlace ferrules as they compress quite easily under the screw (although you should really crimp them first). There are different crimpers for insulated crimps, uninsulated crimps, bootlaces, etc., etc.

Julian F. G. W.

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Re: Wiring an oven terminal block - why so difficult?

#160319

Postby csearle » August 17th, 2018, 2:29 pm

Meatyfool wrote:2. Multi strand wire doesn’t bend well without splaying out despite trying to twist it. Perhaps I should have soldered the ends? As a result the ends of some strands are sticking out a bit ie not hidden behind the screw. Still within the confines of the plastic surround of the terminal, and in no way at risk of connecting with any adjacent terminal. I am thinking that all the copper strands are supposed to be within the confines of the metal screw and the metal plate behind. Too close to plastic surrounding the terminal suggests the possibility of heating the plastic possibly to the point of melting. Am I right to be concerned?
As others have said, don't solder the strands together. The twisted strands should be underneath the screwhead (or rectangular washer if present). Once wrapped around the screw the end of the bunch of strands just need to be short enough not to be in danger of coming into contact with any other conductors. If the electrical contact is good then no heat should develop. Anyway, the plastic is usually of a type that doesn't readily melt.

I like the idea of using crimp lugs, if there's room for them.

Regards,
Chris

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Re: Wiring an oven terminal block - why so difficult?

#160387

Postby quelquod » August 17th, 2018, 9:01 pm

I agree that solder tends to flow under pressure at room temperature so it's not a good idea to use it in a compression fitting. (Mind you, so does copper, and any electrician will have come across umpteen roasted fittings where the connections loosened. Personally I don't like crimps - seen too many failures - and I prefer solder fittings and joints (seen failures there too of course) but it's a personal thing and crimps are certainly quicker.

I think in the OP's situation I'd have replaced with thinner flexible heat-resistant. Easier all round.

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Re: Wiring an oven terminal block - why so difficult?

#160392

Postby jfgw » August 17th, 2018, 10:41 pm

quelquod wrote:I agree that solder tends to flow under pressure at room temperature so it's not a good idea to use it in a compression fitting. (Mind you, so does copper, and any electrician will have come across umpteen roasted fittings where the connections loosened. Personally I don't like crimps - seen too many failures - and I prefer solder fittings and joints (seen failures there too of course) but it's a personal thing and crimps are certainly quicker.

I think in the OP's situation I'd have replaced with thinner flexible heat-resistant. Easier all round.


When I use a copper wire in a screw terminal, I tighten it, do something-else for a couple of minutes, then tighten it again. It always tightens further.

Crimps are used extensively within equipment with very few problems. As with most things, quality is key. I used to use them for connections to the terminal blocks of electric motors (potentially lots of vibration) and I did not come across a single failure. If you buy the cheapest (or do not use them correctly), expect them to fail.

Julian F. G. W.

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Re: Wiring an oven terminal block - why so difficult?

#160438

Postby csearle » August 18th, 2018, 11:15 am

jfgw wrote:Crimps are used extensively within equipment with very few problems. As with most things, quality is key.
Used to use a crimper with which I became less and less happy. Eventually replaced it with a very similar looking one but which had quite different protrusions within its jaw (and was more expensive). The force required to get it to the point where the ratchet released was considerably greater and I've felt confident about the crimping ever since. Use it almost daily. C.

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Re: Wiring an oven terminal block - why so difficult?

#160461

Postby Itsallaguess » August 18th, 2018, 1:28 pm

csearle wrote:
Used to use a crimper with which I became less and less happy. Eventually replaced it with a very similar looking one but which had quite different protrusions within its jaw (and was more expensive).

The force required to get it to the point where the ratchet released was considerably greater and I've felt confident about the crimping ever since. Use it almost daily. C.


I've had the same experience Chris.

I find the meatier 'ratchet' type of crimping tool much, much better than any non-ratchet tool I've used over the years.

The ones I find most reliable are these type -

https://www.toolstation.com/shop/p11261 ... het%20crim

I steer well clear of the non-ratchet type shown below, which I've found to be almost useless and downright dangerous -

https://www.picclickimg.com/d/l400/pict ... g-Tool.jpg

Cheers,

Itsallaguess

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Re: Wiring an oven terminal block - why so difficult?

#160484

Postby jfgw » August 18th, 2018, 5:21 pm

Itsallaguess wrote:I steer well clear of the non-ratchet type shown below, which I've found to be almost useless and downright dangerous -

https://www.picclickimg.com/d/l400/pict ... g-Tool.jpg


I used to use the non-ratchet type for non-insulated crimps without any failures that I know of. They are Stanley branded ones similar to these but metric, Imagehttps://www.horme.com.sg/product.aspx?id=1791 .

The metal is about twice as thick as on a typical cheaper crimper of the same style, and they are a lot more sturdy. I would no longer use them for crimping but still find them useful for their bolt cropper feature.

For bigger stuff, I used to use something similar to this,
Image
https://rhinotools.com.au/product/indent-crimper/

Julian F. G. W.


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