6.1 Power architecture
EIS power comes in two power interfaces. A power interface is a set of rails with its own connectors, its own way of reaching a module, and its own limits:
- PWR-BUS, the bus: +12 V and −12 V, and optionally +5 V, that a power supply feeds through bus boards and power ribbons to each module's power header;
- PWR-DC12: nominal 12 V DC from an external adapter or a supply, which enters a product at a DC entry.
PWR-BUS is Core; PWR-DC12 is an optional interface (8.1). A product takes a power interface at an entry and gives it at outlets, and its claim file lists each (4.2). An interface's rules apply to a product that has an entry or an outlet of it; a passive module, with neither, owes none of them but BUS-011, which binds every module (6.4).
The designators follow one rule: the word after PWR names the interface's topology, and a number its rail voltage. BUS, the Eurorack bus, is defined by its header pinout rather than by one voltage, so it has no number; DCnn is a single nn V DC rail fed from an adapter, the trade's DC jack.
This clause, 6.2 (sources), and 6.3 (0 V) hold what both interfaces share. The bus has 6.4 to 6.6, and PWR-DC12 has 8.1. A maker's own power entry at other rails is outside EIS: the product names it in its claim file as an entry EIS does not cover, and it adds no requirement. Mains voltage, safety certification, and the internal construction of a supply are outside EIS.
Power interfaces
| Interface | Rails | Made by | Distributed by | Enters a product at | Clauses |
|---|---|---|---|---|---|
| The bus (PWR-BUS) | +12 V, −12 V; +5 V optional | power supply | bus board and power ribbon | power header, 2 × 5 or 2 × 8 | 6.4, 6.5, 6.6 |
| 12 V DC (PWR-DC12) | 12 V: one +V and −V pair | external adapter, outside EIS, or a power supply with PWR-DC12 outlets (6.2) | PWR-DC12 outlets of a bus board, a module, or a supply, and DC cables | DC entry, any variant of 8.1 | 8.1 |
Sources, distribution, and entries
On each interface, a source makes the power: a power supply, for a row or for the one product it is mounted on. Distribution passes it on without converting it. A product takes it at a power entry: a module's power header or its DC entry. A source or a distribution product delivers at outlets: a supply's output terminals, a bus board's headers, and the PWR-DC12 outlets (DC-BAR21 jacks or DC-VH2 headers) of a bus board, a module, or a supply.
One product can sit on both interfaces:
- a power supply that takes PWR-DC12 at a DC entry and delivers the bus is a PWR-DC12 entry and a bus source;
- a dual-source module has a power header and a DC entry;
- a supply mounted on one product is an entry of the interface it takes and a source of the one it makes.
Rules for every power interface
A product shall publish, for each power entry, the maximum current it takes on each rail at the entry's nominal voltage, stating 0 for a rail it does not draw (PWR-001). A power supply, a bus board, and any product with power outlets shall publish the maximum current it delivers on each rail, in total and at each outlet (PWR-002). The person assembling a system budgets a row with these figures (ASM-001).
A product whose power entries are alternatives, each able to power it alone, shall not require more than one of them to be connected at the same time (PWR-003); the installer connects one (ASM-003). Entries that feed different circuits, such as a DC entry for one board and the bus for another, are not alternatives, and the claim file says which the product needs.
A module shall not source current into a rail of any of its power entries (PWR-004). A module with its own +5 V regulator leaves pins 11 and 12 of its power header undriven, and a module with a DC entry does not feed its DC rail onto the bus.
Every power entry's 0 V, and the −V of a DC entry, is the product's one 0 V (GND-001, 6.3).
A row of modules is a large capacitive load on its source; a supply states the capacitance it starts into (6.2), and EIS recommends that a product limit the inrush its own decoupling draws.
Row wiring
Row wiring is the discrete conductors, not a power-interface connector, that join a power supply to its bus boards, linked bus boards to each other, and a case DC entry to the supply, bus board, or PWR-DC12 outlets it feeds. A bond of 0 V to the chassis or earth is not row wiring; it follows PWR-008.
Terminals. Where a product takes or gives a rail or 0 V on row wiring, each terminal shall be an M4 screw, stud, or threaded standoff that clamps a ring terminal under a lock washer, rated for at least the current it carries, and the product shall publish the conductor sizes its terminals accept (PWR-005). That covers a supply's outputs, a bus board's input and its links, a DC entry panel's outputs to the supply, and the input of a product with PWR-DC12 outlets. A supply's terminal is marked with its rail or 0 V (SUP-003); EIS recommends the same marking on every other row wiring terminal.
Conductors. A row wiring conductor shall be insulated stranded copper rated 105 °C or more, with a crimped ring terminal at each end, of at least 18 AWG (16 AWG above 3 A, 14 AWG above 5 A, 12 AWG above 8 A, 10 AWG above 15 A), and shall carry no more than 25 A, a 0 V conductor carrying the larger of the +12 V and +5 V currents together and the −12 V current (PWR-006). A joint shall not rely on solder alone (PWR-006). A 0 V link may instead be a tinned copper braid with crimped or pressed ring ends, or a copper bar, of no more resistance (PWR-006). Metric wire meets the temperature rating as silicone (H05SJ-K) or 105 °C PVC; H05V-K and H07V-K are 70 °C wire and do not. Row wiring from a case DC entry carries what the adapter can deliver into a fault, not only the load: EIS recommends sizing it for the entry's published current, or fusing it at its conductor's rating. A wire nut, an insulation-displacement splice, a soldered strand under a screw, and a bare wire wrapped around a stud are not row wiring.
Resistance. Each row wiring conductor shall measure no more than 5 mΩ from ring terminal to ring terminal, and the 0 V conductor between a power supply and a bus board, or between linked bus boards, no more than any rail conductor beside it (PWR-007). The figure is Hinton Instruments' limit for supply cables, the place where one module's current couples into every other module's 0 V (Normative references). The table gives the longest conductor of each gauge that meets it, stranded copper at 1.05 times the ASTM B258 solid figure, allowing 0.25 mΩ for each crimp and its bolted joint; a conductor measured at 5 mΩ or less conforms whatever its length.
Bonds. Where a product bonds its 0 V to its chassis or to a protective-earth terminal, the bond shall be a conductor of at least 14 AWG, or copper of its own board of that section, landed by a ring terminal, a bracket, or a standoff on an M4 or larger stud or screw that presses metal GND-004 accepts under a toothed lock washer, or a bus bar of equivalent section (PWR-008). A DC entry panel whose board copper reaches its panel through brass brackets and ends at an M4 CHASSIS stud makes the bond that way (6.3).
An installer who joins a supply and bus boards from different makers wires them the same way (ASM-008, 9.1).
| Terminal (PWR-005) | For example | Rated |
|---|---|---|
| threaded standoff, vertical, through-hole | Keystone 7795 (snap-in, M4 internal thread) | 15 A |
| threaded standoff, right angle, through-hole | Keystone 7794 (press-fit) or 7769 (solder) | 15 A |
| press-fit or THR power terminal | Würth Elektronik REDCUBE with M4 internal thread, such as WP-BUFU | the maker's rating, far above a row |
| screw and nut, or a stud, through a bus bar or a chassis | M4 screw, ISO 7045 or ISO 4762, with an ISO 4032 nut | the bar's section |
| Conductor (PWR-006) | Or metric | Carries at most | Longest at 5 mΩ (PWR-007) | Longest 0 V link at 2 mΩ (ASM-009) | Ring terminal |
|---|---|---|---|---|---|
| 18 AWG (0.82 mm2) | 1 mm2 | 3 A | 200 mm | — | red, 22 to 16 AWG |
| 16 AWG (1.31 mm2) | 1.5 mm2 | 5 A | 320 mm | — | red, 22 to 16 AWG, or blue, 16 to 14 AWG |
| 14 AWG (2.08 mm2) | 2.5 mm2 | 8 A | 510 mm | — | blue, 16 to 14 AWG |
| 12 AWG (3.31 mm2) | 4 mm2 | 15 A | 820 mm | 270 mm | yellow, 12 to 10 AWG |
| 10 AWG (5.26 mm2) | 6 mm2 | 25 A | 1300 mm | 430 mm | yellow, 12 to 10 AWG |
EIS recommends:
- an insulated or heat-shrink ring terminal sized to the conductor, with a 4.3 mm hole (M4 or #8), crimped with the ratchet tool its maker names;
- a split or toothed lock washer under the screw head or nut, or a screw with a captive one; at most two ring terminals on one terminal, back to back;
- terminals at least 14 mm apart, center to center, so that the widest ring a terminal accepts turns without touching its neighbor;
- a supply that ships its M4 screws and lock washers, and publishes their length and the torque for its terminals;
- stranded tinned copper, 105 °C PVC (UL 1015 at 600 V or UL 1569 at 300 V), or silicone (UL 3135) where the wire flexes;
- the supply placed close to the bus board's input, so that its conductors stay short, and the bus board's input near the middle of its headers;
- each rail conductor run together with its 0 V, bundled or twisted, to keep the loop small;
- a 0 V link (6.3) of 12 AWG or heavier, or a tinned copper braid or a bar of the same resistance (PWR-006), inside the 2 mΩ ASM-009 sets; the table gives the longest link of each gauge;
- red for +12 V, blue for −12 V, black for 0 V, and green-and-yellow only for an earth bond; EIS names no color for +5 V.