As there were ridicolously many questions regarding wiring, i think a "small" guide would be appropriate.
First and foremost: Tiering
Energy in IC² is generally divided into 3 tiers:
Tier 1: T1 is the lowest energy level. It's current reaches from 1-32 EUt. All machines can take T1 voltage without any issues. Batterys are the commong T1 storage items (being (de)chargeable in all machines). BatBoxes are outputting T1 and thus the optimal T1 Storage. LV-Transformers can switch voltage between T1 and T2.
Tier 2: T2 is the mid energy level. 33-128 EUt. Most machines explode if coming into contact with this, the advanced ones can handle this, though. Crystals are the storage devices for T2 machines. They cannot be used by T1 machines anymore, though. MFE's are the T2 storages, emitting 128 Eut. MV-Transformers can swithc voltage between T2 and T3.
Tier 3: T3 is the highest machine energy level. 129-512 EUt. Only a very few high-tek machines can directly aborb and use T3. Lapotron Crystals are T3 storages, only chargeable in T3-Storages (MFSU) and only dechargeable in their likes or said high-tek machines. HV-Transformers can switch voltage between T3 and HV.
HV: HighVoltage is an theoretical "T4". HV can not be used by any machine, but only converted back into T3 by other HV-Transformers.
Energy Store/Transformers:
To regulate the energy flow and store unused energy, you can choose of a few devices.
Electric Storage Blocks:
Known from IC1, these blocks are meant to store energy locally, provide a GUI to interact with the network and emit energy again.
They come in 3 tiers:
T1: BatBox: Cheap, 40k Storage, emits 32EUt.
T2: MultiFunctionalElectricunit: Not cheap, 600k Storage, emits 128 EUt
T3: MultiFunctionalStorageUnit: Expensive, 10kk Storage, emits 512 EUt
There are few mechanisms all electric storage blocks have in common: All of them have 5 inputs and 1 ouput. Energy can only flow into them if you wire the output sides (blank) and the blocks will only emit energy from their output sides (cable-dot). Electric storage blocks can not take any current tiered higher then their own output. F.e. a MFE will explode if you feed him more then 128 EUt.
Applying redstone current to any Storage block will prevent it from emitting energy, unless it's full (in this case it will ignore redstone and always emit energy).
You can rightclick any side of the block with a wrench to change it's output direction to the side you clicked on. If you click the already-set output side, it will dismount the block (warning, energy stored inside the block while dismounting it will be lost!)
Transformer Blocks:
With IC², you now have three Transformers, tiered, at your disposal.
T1: LowVoltage-Transformer: Transforms 32EUt to 128EUt
T2: MidVoltage-Transformer: Transforms 128EUt to 512EUt
T3: HighVoltage-Transformer: Transforms 512EUt to 2048EUt
Generally, Transformers have two seperate applications:
1. transforming upwards, emitting their "high current" from the triple-side
2. transforming downwards, emitting their "low current" from any of their single-sides
Applying redstone to a transformer will cause it to transform upwards, otherwise it will transform downwards, by default.
Transformers always send full packets. If you power a upwards-MV-Transformer with 256 EUt, it will take 2 ticks to charge up his 512EUt packet before sending it.
Vice versa,transformers emit up to four times their low-current to prevent bottlenecking. If you power a downwards-LV-Transformer with 128 EUt, it will emit 4 pulses of 32 EUt each tick.
You can change the triple-side (texture with 3 dots), like the output-side of storage blocks, with a wrench.
Choice of Cables:
Currently, there are 4 different main types of cables, you can choose from. Cables have different attributes, namely conductivity and capacity:
Conductivity: Cables are not supra-conductors, if you run current along them, the energy transported with the current will diminish, the further it travels. Some cables can transmit energy further, others not. Conductivity is generally measured in "Loss per distance". F.e. 1EU/b means a current of 30EUt running along 5 blocks of this cabletype will loose 5EU while travelling, effectively only delivering 25 EUt to the end of the cable. 0.5EU/b is better, in this case you would only loose 2 EU per pulse (5 distance * 0.5EU/b = 2.5 EU ~= 2 EU (always rounded down)).
Capacity: Capacity is plainly the amount of EUt a cable can transport before it will overheat and melt, similar to machines exploding when supplied too much energy. Feeding a cable with capacity 64 anything past 64 EUt (examples: 65 EUt, 128 EUt, 9001EUt) will all cause the cable to melt in an instant.
Insulation: As well, the different cable types have an additional "value" called "Insulation". You can craft all cables without insulation. Some cables have special recipes, which allow you to craft them with Insulation, too. Otherwise, you can add insulation to cables by either using the InsulationCutter on placed cables, or crafting cables with rubber in your crafting window.
Insulated cables have a slightly better conductivity. Additionally, insulated cables are less likely to shock you (because, yes, HV on uninsulated cables can deliver lethal shocks to players nearby). Some cables cannot insulated, some cables can be insulated multiple times. Thus "Insulation" refers to the "amount of layers of insulation" you need to make a cable 100% safe, as well representing the maximum number of layers applyable.
Copper Cables: Capacity 32EUt, Conductivity -0.2EU/b, Insulation 1 -> 6250 ppm loss/block
Gold Cables: Capacity 128EUt, Conductivity -0.4EU/b, Insulation 2 -> 3125 ppm loss/block
HV (Iron) Cables: Capacity 2048EUt, Conductivity -0.8EU/b, Insulation 3 -> 391 ppm loss/block
Glass Fibre: Capacity 512EUt, Conductivity -0.025EU/b, Insulation 0 -> 49 ppm loss/block
Notes:
- The relative loss numbers assume using the full capacity through transformers
- Glass fibre cannot be and doesn't need to be insulated. It has a much different crafting recipe, too.