Sparkies: Electrical wiring conundrum

[braailus]

. The 3000 w element will draw in excess of 13 Amps (depending on your mains supply voltage

in the uk the declared voltage is 230v so 13.05A,realistically the uk voltage sits at 240v or more, so current consumption will be closer to 12.5A,whatever current it is 1.5mm will handle that sort of current day in day out without getting excessively hot,its rated current at 60c is 16A

and use silicone insulated or some other heat resistant type of wire.

why? the temperature inside the enclosure isnt going to get much above ambient

I am not sure what the current ratings are on the crimp connectors but I would lose them if I were you.

more than enough for the job,there used all over the place,and crimps are the most common method of terminating large cables,you wont find many screw terminals that can take a 500mm

I am not sure about the regulations where you are but 2,5mm (or more ) wire is used for heating elements and plug circuits where I am.

All depends on the type of element,no need for 2.5mm if its a 15w element and 2.5mm is a bit small for an 10kw water heater, normal 13A socket are wired in 2.5mm unless it pyro then you can drop down to 1.5.if its a 16A socket 1.5mm is allowed depending on the cable length,and if its a 5A socket then 1mm is good enough

In that case, there is obviously no problem is there.

I would stick to my advice. We usually protect 1,5mm wire with a 10 amp circuit breaker and 2,5 with a 20amp. Although you say that your supply is 220/230v, it is possible that it may be much less at the point of connection (due to a million and one reasons). This could cause the current to increase. Connecting to the element will impart some heat to the cable. These all add up. We could debate this all day and use Ohms Law and any regulations we could throw at it. Fact remains, there is a problem with the installation and this is dangerous, especially for someone not experienced in the use of mains supply.

Why live on the edge for a few bob. I would do it right and know that I will not have a problem in the future.

That is what I would do anyway

[braailus]

Just btw, I am not sure if it is the same in the UK but our market is getting flooded with inferior Chinese components. This includes plugs, connectors etc. We use 15 Amp plugs with round pins in SA. Our plugs always used to have solid copper pins to connect. The Chinese plugs now have hollow pins that are formed by bending sheet metal in a cylindrical shape. They generally are not exactly the same diameter as the socket and therefore do not make proper contact. This and the fact that they do not conduct as well as they should, causes heat problems due to voltage drop and therefore increased current consumption. In this case with the element, the wire "should" handle the current so either the supply is low enough to cause excess current or there is a bad connection, hence my suggestion to loose the crimp connectors.

Again, if it were me, I would fix the whole shebang as per my suggestion. In doing this, it will be fixed for good.

[cqout]

I thought I would put my 2 pence in here lol!
Firstly - crimps are considered perfect for connecting/joining/terminating cables and is actually prefered over screw terminals as the can not come lose if crimped correctly using a ratchet type crimp tool
Secondly I would personally use a 2.5mm flex for wiring a 3kw element as they are being used over a prelonged period - although 1.5mm flex is rated at 16amps this is in free air and we as homebrewers put them inside enclosures and next to hot items therefore reducing there current carrying capacity

I hope this helps

Chris

[Andy]

Brilliant chaps, all great advice!

2.5mm wire, soldered sounds like the best option *but* it's going to be fiddly. If I wanted to persevere with (decent) crimps then would the ratchet tool linked to by Pinto be a sound investment ?

[Jim]

............ Although you say that your supply is 220/230v, it is possible that it may be much less at the point of connection (due to a million and one reasons). This could cause the current to increase. ..........

Sorry, I have to take issue with that statement. The element has a fixed impedance, depending on the voltage at which it was designed to dissipate 3kW. If the supply voltage is reduced, the current will reduce (not increase as you state) and the total power dissipated by the element will also reduce. If the supply voltage is higher than design (e.g. if the element was designed for 230V and the actual supply is 240V) then more current will be drawn and the element will dissipate more than 3kW.

Ohms law.

[UpTheToon]

I built a PID controller powering a 3Kw element after lots of reading and re-doing and I thought it was safe... then part of the mains cable that was inside the enclosure went up after about 15 brews taking half the (very untidy) wiring with it.

I've since re-did it with 2.5mm wire and correct crimp sizes with a half decent tool (and in a metal box with din rails). No fire yet!

Good luck.

[Aleman]

Funnily enough I have always been told that you do not solder anything with mains voltage or higher, always use crimps or screw fittings especially for high current usage. In theory a good solder joint has minimal resistance, but it's making a good solder joint in the first place that is the trick.

Certainly +1 for 2.5mm cable

[Pinto]

Funnily enough I have always been told that you do not solder anything with mains voltage or higher

Yep, although I've come across many commercial appliances and connection with tinned ends. I'm guessing it's something to do with the low melting point vs the potential for high current joints to heat up. It was also drummed into us never to tin cable ends entering a screw down termination as solder is "slippery" and it greatly increases the chances of connection pulling out

[themadhippy]

Funnily enough I have always been told that you do not solder anything with mains voltage or higher,

best not look at some of network distribution cable joints then,and there are some who insist solid core cable is soldered not crimped.
If your 1.5mm is melting with 13 or even 16A you have a problem somewhere else,it takes a lot more than 16A to cause damage,if you look around youll find plenty of 0.75mm cable thats designed for use on 16A circuits

[Andy]

TMH, would your take be then that 1.5mm cable should be fine with decent crimps and a good connection ?

Does the cable bend radius come into this at all ? One of the cables was short and on a tight arc.

[AnthonyUK]

Bend radius on purely conductive cables is not usually an issue.
Cable termination is taken very seriously in the aviation industry and everyone involved was regularly tested on PTT (precision termination tools).
Crimped connections are used on the biggest cables on aircraft which is for battery and generator use so when done correctly there is no issue.
Looking at your pics I would agree that the issue is with the crimp not the cable.

[themadhippy]

would your take be then that 1.5mm cable should be fine with decent crimps and a good connection

yes

Does the cable bend radius come into this at all ? One of the cables was short and on a tight arc

anything putting a strain on the cable or connector isnt good,if the connection is iffy in any way keeping it under strain is only going to make it worse

Bend radius on purely conductive cables is not usually an issue.

but it is, bend too sharply and you risk damaging the conductors and insulation,one bits in compression ,the other in tension,thats why theres a minimum bending radius for cables,think its 2.5 for pvc,so 1.5mm should only bend around a radius of 3.75mm or more

[Waffty]

Soldering is perfectly safe way of joining electrical cable BUT and there is a BUT, it has to be done correctly and using the correct solder/soldering techniques.

The easiest way of soldering two cables together, is to tin them first, then place then side by side and apply heat and possibly some more solder. This is fine for low voltage/current but as soon as the voltage/current rise then you could have a problem, as in essence the thin layer of solder joining the two cables becomes the weakest link, it can generate a resistive 'hot spot' and depending on the solder, it can melt, resulting in a flexible joint.

So if you do plan to use solder, it's best to use multi strand cable, 'splay' the strands open on both cables and push them together, basically meshing the two cables together. This will keep the 'mass' of the cable surface area and provide a simple mechanical joint. Then simply apply the solder to this mechanical joint, this way, you will remove any potential 'hot spots'.

I also agree that a crimped connection, with a 'puka' ratchet type crimper, that crimps the whole circumference is perfect for this type of joint. I have a ratchet crimper and can safely say if I ever need to change a crimped connection, then it can only be removed by cutting it off and not pulling it off, as I used to be able to do with my old crimper.

As for my 2p on cables, most domestic appliances are only designed to be on for a short periods of time i.e kettles, toasters, showers (questionable), vacuum cleaners etc. If you have an electric wall paper steamer, you'll see the difference between the cable, the plug and element connection, as they're designed for longer use. So if you base your designs on wall paper steamers and or electric irons, you won't go too far wrong.

[themadhippy]

The easiest way of soldering two cables together, is to tin them first, then place then side by side and apply heat and possibly some more solder.

easiest yes,but like all soldering its best to make a decent mechanical joint first,on singles wrap 1 around the other like

then solder.For stranded, like you say mesh them into each other , then twist each strand around as above, 1 strand wraps around its own cable just above the insulation to stop things splaying out whilst your twisting everything together ,done correct youve got a small but very strong joint,even before youve got the solder out

[braailus]

............ Although you say that your supply is 220/230v, it is possible that it may be much less at the point of connection (due to a million and one reasons). This could cause the current to increase. ..........

Sorry, I have to take issue with that statement. The element has a fixed impedance, depending on the voltage at which it was designed to dissipate 3kW. If the supply voltage is reduced, the current will reduce (not increase as you state) and the total power dissipated by the element will also reduce. If the supply voltage is higher than design (e.g. if the element was designed for 230V and the actual supply is 240V) then more current will be drawn and the element will dissipate more than 3kW.

Ohms law.

Hi Jim

This is how I see it.

P = VI

I = P/V

P= 3000

If V = 250 , I= 3000/250 = 12 Amps
If V = 200, I= 3000/200 = 15 Amps

(Just using round figures for ease of calculating). I may be wrong to approach it from total load point of view but this is what happens with lighting. The wattage remains constant and is made up by a factor of the voltage and ampere. If the voltage drops the current increases and visa versa. This is why you always leave headroom in the design of a system to cater for fluctuations is supply voltage.

Either way, I am a firm believer in leaving some headroom. Makes for more reliable systems.