Lets try to clear this up OK, I've heard of a few reports of fried cable and confusion.

Cable needs to be rated based on the power source feeding it, thats all. It doesn't matter how many sources e.g. generators there are its just the output type.

It doesn't really matter if you lose a bit along the way, don't get hung up about making everything lossless.

Storage devices have an important role if you have multiple generators. As far as I can tell a machine accepts one "packet" of power per tick, e.g. the output of one generator only. A storage device (batbox, MFE, MFSU) accepts multiple packets, allowing generator outputs to be combined. This is why some configurations tend to need a batbox to work well.

Level 0 power (tin cable, up to 5eu/packet)

This level is output by:
Solar panels (not arrays)
Water mills
Wind turbines (its possible to exceed 5eu and fry the cable with a high enough tower and a storm)

Tin cable loses 1eu/packet every 40 blocks. Most of the sources will be 1eu so the maximum cable is 39 blocks long

THE OUTPUT FROM A BATBOX WILL FRY TIN CABLE

Level 1 power (copper cable, 32eu/packet)

This level is output by:
Batbox (no matter how weak the supply to the box is)
Generator
Geothermal generator
LV solar array (can anyone confirm?)
LV transformer
Nuclear reactor with no more than 3 fuel rods, not touching.

Insulated copper loses 1eu every 5 blocks. Since the loss is rounded down a 4 cable run is lossless. Don't obsess about this though, a LV source (32eu packets) will lose half its power after 80 blocks but that's still 50% efficient after 5 chunks!!

A 1eu source like a solar panel will lose all power after 5 copper cable unless regenerated with a batbox or transformer, this is why you use tin cable for solar panels

Level 2 power (gold cable, 128eu/packet)

This level is output by:
MFE
MV transformer
Redstoned LV transformer
Most modest nuclear reactors

Level 3 power (diamond/glass fibre cable, 512eu/packet)

The detector and EU splitter cables are also reported to be level 3 despite using iron cable in the recipe

This level is output by:
MFSU
HV transformer
Redstoned MV transformer
Some nuclear reactors
Railcraft Energy unloader without transformer upgrade (note that without the upgrade it won't recognise MFSU carts, however with the upgrade it will blow up glass cables, MFSUs etc.

Note that glass fibre cable is practically lossless at 1eu per 40 blocks. Fed with HV you'll be out of chunk load radius before you see loss.

Iron cable can be used as a cheap alternative. Supplied with HV its 50% efficient at 320 blocks so the loss is managable.

Level 4 power (iron cable, misleadingly called HV cable)

This level is output by:
Redstoned HV transformer
Crazy nuclear reactors
Railcraft Energy unloader equipped with a transformer upgrade
Some Gregtech machines with sufficient upgrades

Cable should be 50% efficient at 1280 blocks, so if you don't mind the extra transformers then iron cable is an alternative to glass fiber cable

Beyond level 4 (no cable available)

The only sources currently able to fry iron wire are a nuclear reactor that's 6 chamber and almost all fuel rods and some of the more extreme Gregtech devices. In Tekkit the reactor will explode after about 5 seconds if uncontrolled, though in FTB you have quad-fuel-rods and more cooling options.

The lightning rod is apparently 8192eu/p as is the "supercondensator" on its low side.

Although untested its probable that an energy unloader with two transformer upgrades may output 8192eu/p.

Some machines can be directly connected to a beyond 2048EU reactor and with sufficient transformer upgrades they will not blow up.

It has been reported that two HV transformers directly connected could withstand a reactor output beyond 2048. My observation is the output appears to clamp to 2048eu anyway. What is meant to happen is each transformer behaves like a machine and only draws 2048eu/t regardless of packet size. The power is meant to be split across multiple transformers. This is used in Feed The Beast to allow 8192eu/p power.

An energy link can be direct connected, I've tried this. Engine generators appeared to return only a fraction of the power though.

Railcraft energy loaders might accept >2048EU (untested in Tekkit classic, worked at 8192eu/p in FTB single player)

Redpower "Blutricity" (Tekkit and Ultimate only)

Blutricity has only one cable type (not counting jacketed cable). Note that machines pass on power like cable does so its not necessary to wire around them, daisy chaining works and even just stacking things together.

Cable losses are hard to estimate as redpower uses a more complex approach that takes into account paralleling and allows current flow to reverse

Blue solar systems tend to need one or more bt-batboxes, mainly to allow operation at night.

Retrievers need very little power and can be attached to long cables

Blue power furnaces seem to benefit from a nearby battery and about 8 solar panels, note that in auto-fed systems the battery can run out fast.

I believe it takes 2 BT batboxes and about 10-12 solar panels to run a redpower pump continuously. Why would you want to: well the RP pump is the only one that can output liquid blocks as well as suck them up.

Good guide mate - I've always wondered what cable I should use for what devices / distances. This helps a LOT

Thanks for the appreciation. It seems a bit wrong when people use diamond cable for everything, also tin cable is confusing as you can get ludicrous eu/tick through it if you hook enough solar panels or water mills together.

I think the next topic might be energy storage, I hear stories of huge arrays of MFSUs, but if you want to store more energy than one MFSU holds I'd have thought diamond chests filled with lapotrons would be a better bet, with a retriever setup to transfer empties to a charging bench, and a second one to transfer full ones to a discharging bench.

I turn all my excess power to uu-matter though

I suppose one good reason for a MFSU farm is if you want to OUTPUT at faster than 512 eu/tick. Since each unit can output a packet per tick the more in parallel the more power is output, but since the mass fab appears to be the only thing that can use that much power you might as well feed it directly and skip the storage.

For what its worth in Feed The Beast the Gregtech mod adds a sort of 8192eu/p power tier but doesn't add a new cable to handle it unless you count the superconductor.

The lightning rod is the most obvious example of 8192eu/p, and the recommended solution is multiple HV transformers connected directly. I think a railcraft energy loader with two transformer upgrades will handle it but I haven't had a lightning strike in SSP and I haven't dared test it in SMP yet due to item cost.

As far as I know the old style Gregtech fusion reactor would output to HV transformers OK and the new one doesn't output EU power anyway so there doesn't really seem to be much use for supercondensators?

Can't find any use for it either. You still -can- use it, of course but there really is nothing where you -need- to use it.
By using AESU or HV-transformers you can always convert to 512eu packets.

The new fusion reactor does indeed output something different, Plasma! . Another fun tankable liquid that can be transported anywhere using endertanks. So when combined with plasma generators at locations where ever you want you'll have an output of 2048Eu/t split into 4x 512 packets.
This adds the nice fact that you dont need to step down from EV.

I'm not sure about this but does it allow you to transport plasma in buckets?

Buckets don't work but you can fill it into cells. Just place an empty cell into the plasma generator or use the liquid transposer from thermal expansion.

Liquid transposer works pretty well and you can hook it up to an ME system and automate the process. I think it was "supposed" to allow buckets but it doesn't seem to work.

IC2 Experimental is a bit strange now. If I recall correctly the "official" ratings are now:
Tin 32EU/t
Copper 128EU/t
Gold 512EU/t
Iron 2048EU/t
Glass 8192EU/t

but its worth noting that recent mod releases have EU checking turned off meaning that anything can run at any EU level. Some other mods do still check EU levels though, particularly Dartcraft's version of a macerator (force grinder) which will blow up at >128eu.

Currently power sources add, meaning that enough LV sources combined will add up to MV.