john87

IGNORING FRICTION, if you pull on a rope, no matter how it is directed, the tension is the same anywhere in the rope, yes?? Now, you tie a rope to the bottom of a tree and throw it over a branch. You now dangle on the rope. Say you weigh 150 pounds.. The tension in the rope is the same everywhere, yes?? So, you now have a rope with a tension of 150 pounds in each "leg" over the branch. The downwards force on the branch can easily be seen to be 300 pounds. Follow me?? john..

Hi All, just saw this on facebook. Anyone missing a chipper??

Bloody hell!!! That was close!! john..

Have to be fair, I think that £275 for that is giving it away.. If i was a monied type and wanted one i would happily pay £1275 for that... john..

Great till you have an accident, kill someone and go to jail for manslaughter, very clever.. john..

I agree with your version, that is what i always understood. It would be like trying to drive a 16ton rigid on a car licence but saying that you will not carry anything with it [Even then i would think it would be over 7.5ton] john..

Well, i am certainly no tree expert, but, the house was built in the 1930's, yes? The tree was not there then.. The house has no damage. Heave or not, if you think about it, there is no way that the ground is going to expand to a larger volume than it occupied on the day the house was built, 90 years ago, before the tree, that is an impossibility and a matter of common sense. So no worries with the house.. I would think the extension would be ok too. As for the shitty tree with its TPO, Don't the whole place look better without the thing! Why ****************wits plant trees in their gardens is beyond me.. john..

Single phase or three phase?? I would imagine you are fine, the motor would have burnt out by now otherwise. i will calc the cable size for you later, but a lot depends on the source of the power as this could be 2 feet from the consumer unit which could be 30 feet from the local substation, or is could be a shitty overhead supply 500yards long.. john..

Hi There, You could have an extension lead 500 yards long, it makes no difference so long as you have calculated the size needed. The current rating of the cable rarely comes into it. The usual factors are "earth fault loop impedance" [so that fuses and circuit breakers will operate correctly] and "volt drop" so that motors will start correctly and contactors not drop out etc You have to calculate the size, as most of the cable calculators online are a mile out as they go about things backwards.. 1, First step is select the OCPD [over current protection device] [that is fuse etc] size and TYPE you need. 2, Calculate the max EFLI for the breaker selected. 3, Calculate the max allowable volt drop. 4, Select a cable to suit 2 and 3 above. Obviously the cable nominal current rating has to be higher than the load rating AFTER you have applied the derating factors, [grouping, how installed, [in the ground, clipped to wall, insulation etc] ambient temperature, max conductor temperature] but in the real world, you can EASILY, and usually do, end up with a cable with a nominal current rating FAR FAR higher than the load current, purely to meet the criteria for EFLI and volt drop.. john..

As you say you can get CY and SY, [the CY has a copper braid and the SY a steel one] but they are not intended as power cables, [they do not meet any standards for this] but for control circuits. The braid is to stop EMF interference affecting whatever they control They are also HORRIBLE to handle as you say, especially in the cold. You can also have problems caused by the braid if the cable is damaged as the braid is not sufficient to act as a CPC, but IS sufficient to "liven up" whatever it is connected to. The HO7 [HO7RN-F] is specifically made and INTENDED as "flex", that it why it has the "F" bit standing for "flexible conductors" which is why they ARE fine, that is the idea of it, they will flex without cracking in the same way as you could bend a sheet of paper to and fro as much as you liked, but if you did the same with thick card, it would fail before long. Have a read of this.. https://www.elandcables.com/media/13rlt2rk/ec-statement-on-the-use-of-sy-cy-yy-cables-rina-18th-ed-with-summary.pdf john..

Hi there, Done some number crunching for you.. Just to carry 16A with the required max volt drop over that distance, [35m] works out at 2.5mm2 cable. BUT, as i said the governing factor will be EFLI [so that the circuit breaker operates] and, do not forget that to START the motor will take about 6 to 10 times this current, so you are in practice, to start the motor reliably you are going to want a much larger cable or the motor simply will not start [and contactors will drop out due to undervoltage] and you will end up in a right mess.. So, taking an educated guess at the SUPPLY characteristics, you want the following, assuming the breaker protecting the circuit is a C32. I am also assuming that you require a neutral too IF, you want an armoured cable to bury in the ground, you want a 10mm2 four core, and you will use the armour as CPC [earth] Note, you CANNOT use an armoured cable as "flex", it is not designed to be repeatedly bent, and besides, it would be terrible to handle.. This cable would be about 21mm in diameter and weigh about 36kg. IF, you want flex, you want something called "HO7" This is the most beautifully supple, lovely, rubber covered stuff, Lovely to handle even in the freezing cold. With this, you want 10mm2 FIVE core..This cable would be about 24mm in diameter and weigh about 35kg. The armoured cable will cost you about £264, plus the glands and adaptable boxes to terminate it into, and someone that knows what they are doing to fit the glands and terminate it for you.. [this is very tricky to do properly unless you know what you are doing] If you want the HO7 flex, it will cost you about £390, plus a "trailing socket" for one end and a plug for the other.. Any questions, ask.. john..

Yes, it is 11.5A per phase, but then with the PF and Eff, it will be just over 16A per phase. Calculations are difficult as we do not know anything about the supply characteristics.. You are supposed to have a maximum volt drop of 5% in general and 3% for lighting, so lets say we will go for 3% in our extension cable as the rest will be used up in the installation cabling.. I could not find an online calculator that actually worked, so i will do the sums manually later and post back.. john..

That is a good idea!!

Hi Gareth, Ok, an 8kw motor, so that is 8000/1.732/400 = 11.5A but then guessing PF .8 and efficiency 90% just over 16A ?? Then you would need an allowance for starting currents.. Pretty big cable?? john..

As i think Gareth is about to mention, the extension lead is not going to be that simple and you really need to get an electrician with a brain involved. That is a very long run.. It is NOT NOT NOT, just a question of getting a "16A" extension lead.. You see, at that length of run, EFLI and volt drop are going to be the governing factors for the following reasons.. 1, If the volt drop is too high, the motors will struggle to start if they start at all. 2, If EFLI is too high, in the event of a fault, the breakers will either trip too slowly or not at all. Either way, it will result in damage or electrocution.. I once sold a compressor to a farmer They connected it to a very long run of 2.5 twin and earth, The thing barely started... A few days later, said farmer turns up all irate.. I go and have a look, and what had happened, is the motor had failed to start. As it was such a long run of cable, even though there was effectively a dead short, the "circuit" could not pull enough current to trip the breaker, so the power stayed on and the whole lot got hotter adn hotter until the motor had literally melted into a blob of aluminium and copper.. You see, a circuit breaker is selected to suit the load.. THEN a cable is selected on the basis of Volt drop and EFLI, which means that you could need a cable suited to, say, 70A for your 16A load.. Tell us exactly what it is you want to run and we can advise further.. john..