Power tier

In IC², power tier refers to a range of EU per tick (EU/t) by which blocks and items are grouped, which defines certain ways they behave.

Incorrectly matching power tiers between equipment usually results in either a lack of functionality or a surplus of explosions. (Even if it's only one, any number of unwanted explosions is a surplus!)

Power tiers

Tier	Name	Range	Tier-appropriate cable
1	Low Voltage (LV)	32 EU/t or less	Tin Cable
2	Medium Voltage (MV)	128 EU/t or less (down to LV)	Copper Cable
3	High Voltage (HV)	512 EU/t or less (down to MV)	Gold Cable
4	Extreme Voltage (EV)	2048 EU/t or less (down to HV)	HV Cable
5*	Insane Voltage (IV)	Technically anything above EV range Typically identified as 8192 EU/t (Glass Fibre Cable max transfer rate)	Glass Fibre Cable

Machines (if they are EU acceptors or producers) typically have tooltips including Power Tier: followed by a number, to help you avoid explosions (or trigger them, if you're the HAYO-ish sort).

*As of 2.6.133-ex110, nothing in IC² is labeled as Power Tier: 5.

Block interaction

Any EU acceptor, meaning a machine or EU storage block, can accept up to the maximum EU/t for its power tier without problems. Anything above that usually* causes it to explode, destroying it completely and possibly taking a bit of the surroundings with it. It can accept lower tiers of EU/t, though if it only has a little EU storage (or none, as in the  Mass Fabricator) or has several  Overclocker Upgrades installed, providing less than the maximum EU/t can cause interruptions. Storage blocks just fill a bit more slowly.

If a machine is compatible with  Transformer Upgrades, each one installed will raise the machine's power tier by 1, allowing originally low-tier machines to be directly powered by higher-tier cables, generators, or storage blocks.

*The Creative Generator being a notable exception.

Item interaction

Electric items also have a power tier, though the tooltip does not indicate it (the tier can usually be inferred from the EU storage item used in its recipe).

An item can only be charged by something of the same or higher tier; an  Electric Wrench (tier 1) can be charged in anything, but a  Nano Saber (tier 3) can only be charged in an  MFE or  MFSU. (This is also true of EU charging items, and what they can charge.)

Likewise, lower-tier machinery cannot be powered by higher-tier energy items; an  Energy Crystal cannot be discharged to power a  Macerator, unless it has at least two  Transformer Upgrades installed.