ondablade":1ovdwocp said:
Over here in Ireland we seem to get more like 220V on single phase mains Jake, with the possibility of pretty drastic drops below that if you are at the end of a line fed by a transformer, and there's been extra houses put on the line.
Universal problem! I once worked for a short while in the HImalayas. Between us and the xfmr was a blacksmith who made steel window grilles. Every time he struck an arc... we ended-up having to start video editing sessions at 2AM.
Our (effective monopoly) service provider contracts to supply between 207 and 254V - to EN50160 they say. But i've often heard of it going lower. It sounds like wiring should probably be sized to handle the currents generated at the lower end of the supply voltage range(?)
It doesn't work quite like that.
Your machines consume a certain power at a specified voltage, but they are just loads. No magic happens! The energy/sec (power) they consume is proportional to the voltage. If that drops, so does the power of the machine. Thicker wiring won't really help, except insofar as its own resistance will be lower, so you waste a bit less warming the wires up.
The wire thicknesses specified for lighting, ring mains, etc. take the resistance of the load into account: light bulbs have high resistance, so the 'contribution' of the wiring to the overall load is small - you can use thinner (higher resistance) wire as a consequence.
For machines, the load resistance is small, and the currents are large, and the wiring's resistance could otherwise become a significant proportion of the total. That's why you need thick wire.
My voltage in recent years is i think pretty good (but i've not checked), there was a new transformer installed quite recently. But maybe 220V is quite low compared to the 230/240V (?) you guys reportedly seem to get.
Actually ours is as iffy. The rules for supply were changed by those idiots in the EU some years ago, to 'harmonize' electricity supply. They compromised on a
nominal 230V. The official range, IIRC is -5% +10% (of 230V). (after Googling to check) Wrong! it's [insert whole basket of fruit!] changed AGAIN:
Voltage tolerance of 230 V +10%/−6% (216.2 V to 253 V), widened to 230 V ±10% (207 V to 253 V) in 2008. The system supply voltage remains centered on 240 V.
http://en.wikipedia.org/wiki/Mains_power_around_the_world
This has two serious negative implications (nb: this is bordering on politics, rather than engineering!): Firstly 207V is low enough to damage some designs of motors (some refrigeration pumps, for example), and secondly, the upper limit was raised. Over-voltage shortens the life of filament bulbs significantly, and can affect other components (for electrical/electronic devices where the internal voltages are proportional to the supply current). In the old days you could force the supply authority/company to alter the voltage tap on the local substation, to correct matters. Now they just laugh at you (from personal experience!).
The third implication is perverse: inattentive Far Eastern manufacturers, for whom we are 'just another Western market', look at the spec., and design to 230V,
not 240V. The result is lightbulbs that blow early, as they can be operating at 253V rather than the 230V they were designed for. The lifetime of a filament anything falls off very rapidly with overvoltage.
How long do filament and 'low energy' bulbs last around here? Far less time than they should! I have argued unsuccessfully with the energy supplier. At one point we were 0.5V RMS below the maximum permitted, "but your supply is within spec., sir."! Bring back SWEB and the CEGB!
Worse still, I believe Chinese motor winding companies are keeping cost down by designing to 230V too, hoping they'll get away with it. I have had three, brand-new squirrel cage machinery motors burn out within hours of first use
in the last six months. The supplier of two of them had a service department full of the wretched things!
I didn't realise that fuses could let the current get so high above their nominal rating without blowing, it means i guess that my 13A socket could indeed have been fairly heavily loaded.
Fuses are filaments. They won't last forever above their rated capacity, but yes, if slightly overloaded they can get very hot and still not blow quickly. The arcing you mentioned earlier may well have been screws working loose in either the plug or the socket, caused by repeated heating and cooling (from the adjacent fuse).
Interesting too on the ring main bit Eric, i've been reading up wiring recently so i could wire my shop and rather wondered at how it came about. :wink: I guessed that maybe it was something to do with the English tendency to be 'economical'.
Not economical: back then, totally skint! We only paid off the final tranche of war debt about two years ago, IIRC.
The Hammer machines i'm wiring for next week are all 3kW single phase - which comes out at about 14.5A at 207V.
Which at a nominal 14.5A @ 207V rather begs the question of whether or not 16A sockets would be OK. I've for safety more or less decided to go for 32A sockets and wiring - also to cover against the possibility of in future running larger stuff. e.g. it's looking like i'll be running a 4kW bandsaw on a rotary inverter which definitely will go well above 16A.
Whilst it won't hurt to put in heavier wiring, it doesn't work like that (see above). You must protect the circuit to the manufacturer's recommendation (i.e. the load printed on the machine's plate, or what they specify in the manual, if there's a significant startup surge). Upping the breaker/fuse capacity beyond that doesn't buy you anything, but reduces the safety margin.
Sorry about the rant. Hope some of it helps.
E.
