Chassis Power Inlet Issues:

Physical drawing of an AC inlet emi filter showing 3 sides

AC Inlet modules come in a number of different styles, mounting methods and options;
The list below details each of the possible options available. In all most all cases the Inlet module is a female case with male pins. There are also combination units that contain both an inlet and outlet section.

AC Module Styles
The three main types:
... IEC320 (now IEC 60320),
... NEMA 5-15,
... MIL-DTL-2726 (Circular, blade or round contacts)
... MIL-C-5015 (Circular, round contacts)

MIL Socket and commercial plug AC power cable

The MIL-C-5015 is a three or four terminal connector not a module and does not have any of the options mentioned below. The IEC320 style has three straight blades, while the NEMA 5 style uses a rounded blade for the ground blade. The MIL-DTL-2726 series [detail below] are one to three terminal connectors, using either flat blade contacts or round contacts, at voltages between 125, 250 and 450 volts AC.

AC Module Mounting
One of three options are available to mount the Inlet Module to the chassis back panel or bulk-head;
... Flange Mount [Screw On Panel Mount],
... Snap-In,
... Screw Mount.
However the MIL-C-5015 style is only available has a metal flange mount. The Flange Mount style is the most common for industrial use, while the Snap-In is used most often for normal commercial usage. The IEC320 is available as either Flange Mount, Snap-In, or Screw Mount. When using Snap-In modules be sure to select one that matches the width of the panel. Common sizes work with panel widths of 0.80mm, 1.5mm, 3mm, and 4mm thickness.

Terminal Connections
There is also one of three options available to connect to the AC module or connector;
... Wire Stub,
... Solder Terminals,
... Quick Connect Terminals [shown above]
... PCB Mount,
The exact location of the attachment points varies. The terminals may be located at the rear of the unit or the top, and may be straight or right angle. The size of the terminals may also be selected. Two common sizes include .187 or .250 for Quick Connect [QC], or .157 or .098 for Solder Terminals. The wire stub style may either be just a few inches of insulated wire or a wire assembly with the ends terminated by some form of solderless connector. When installing a power cable or discrete wires to the rear of the terminal be sure to use the correct Cable color code.

EMI Protection
AC Power Modules may be Filtered or Non-Filtered. Non-Filtered modules are simple connectors, while Filtered modules have EMI filters like the one shown below. Note that AC modules with EMI filters are much larger than modules with out the filter. A separate EMI filter may be procured when space behind the AC module is at a premium.

Also refer to the next page showing both the schematic and module diagram of a RF Power Line Filter, using either a bolt-lug connection, or blade style connection: RF Power Line Filter Diagrams.

Fused Modules
AC Modules may be obtained with an integrated fuse holder and in some cases a holder for a spare fuse. However the exact value of the fuse is determined by the power supply. Refer to the Fuse Manufacturers page for manufacturers of fuses and a brief tutorial on how to select the fuse value.

Switched Modules
AC Modules may be supplied with a power switch as an option. Normally the switch is placed on the AC side of the EMI module [if present]. The switch will disconnect both the Line and Neutral sides of the incoming AC line.

Low Drop-Out Modules
AC Power Modules may also contain a Bleeder Resistor to drain of current under no load conditions. The Bleeder resistor would be placed in parallel with the inlet capacitor, not shown above. [Definition of Bleeder Resistor].

Surge Protected Modules
AC Power Modules may also contain a surge protection device. In this case a Transient Voltage Suppression (TVS) diode [transorb] will be placed in parallel with the AC inlet capacitor [shown above]. The TVS will be in addition to a fuse [if present].

Module Grade
AC Inlet Modules are either Commercial Grade or Medical Grade devices. Medical Grade Filters provide low leakage current meeting medical and dental equipment requirements.
Commercial Grade Power Supplies, Medical Grade Power Supplies.

Vibration Issues
Any vibration issues can either be solved by using a screw mounting MIL-2767 or MIL-5015 connector or by using a Retainer Clip to attach the incoming power cord to the AC module. The retaining clip will screw into the same location as the flange and fold down to hold the back of the incoming power cord.
Anti-Vibration Products.

Voltage Selection
A switch may also be present on the inlet to select the incoming operational voltage, values include 100/120/230/240V. However in some cases the voltage selection switch may be part of a power supply, and then not located on the inlet.

Vendors; Manufacturers of AC power sockets.

Design Guidelines
In a chassis with ac service connected to it, the grounding terminal of its receptacle shall be internally bonded to the chassis frame. If solder is used, the connection of the equipment grounding conductor shall not depend on solder alone. Related page; Chassis Grounding Issues.

Input/output ac power connections to the chassis shall comply with NEC requirements.

Plugs and sockets for connecting any AC power source shall be NRTL [Nationally Recognized Testing Laboratory] approved for the application.

AC power sockets and plugs shall not be used for purposes other than the connection of AC power.

Any connector used to provide power at 50 V or greater shall not allow personnel to make inadvertent contact with the power source.
All terminals and live parts with a potential of 50 volts or greater shall be guarded to protect from accidental contact or bringing conductive objects in contact with them.
Connectors operating at 50 V or greater shall be rated or recommended for their intended use.
The exposed, non-current carrying, metal parts of panel mount connectors operating at 50 volts or greater shall be bonded to the chassis.

If plug pins of cord-connected equipment receive a charge from an internal capacitor, the pins shall not be capable of rendering an electric shock or electric burn in the normal or the single fault condition 5 seconds after disconnection of the supply.

Plug-in type connectors intended to be connected and disconnected by hand shall be designed so that the grounding conductor connection makes first and breaks last with respect to the other connections.

All Equipment Enclosures containing exposed energized circuits over 600 volts nominal should be marked Danger High Voltage Keep Out with a label that is permanent.

Signal and control cables should be separated from power cables as much as practicable.

Equipment Racks; next page in equipment chassis design

Index page; How To Specify a Equipment Chassis

MIL-DTL-2726 connector types:
MIL-DTL-2726/6 Receptacle, Plug, Electrical, 3-Pin Grounded, Alternating Current, 125-Volt, 40-Ampere
MIL-DTL-2726/12 Receptacle, 3-Pin Grounded, 125-Volt, 40A AC
MIL-DTL-2726/13 Receptacle, Cap Assembly
MIL-DTL-2726/17 3Pin Grounded Enclosed Receptacle 125v AC 40A
MIL-DTL-2726/26 Receptacle, Plug, 4-Pin, 60-Ampere, 208/117-Volt, 3-Phase
MIL-DTL-2726/27 Receptacle with Switch, 60-Ampere, 208/117-Volt, 3-Phase, Interlocking, Grounded
MIL-DTL-2726/37 Receptacle, 15A, 125V, 60Hz, Bladed, Grounded
MIL-R-2726/38 Receptacle, Plug, 15A, 125V, Bladed, Grounded
MIL-R-2726/39 Receptacle & Switch, 15A, 125V, Bladed, Grounded
MIL-R-2726/40 Receptacle Channel, 15A, 125V, Bladed, Grounded
MIL-DTL-2726/43 Receptacle, (Bladed) 15-Ampere with 3-Ampere Switch, Type DPST, 125-Volt, Grounded, Totally Enclosed
MIL-DTL-2726/73 Receptacle, 15-Ampere, 125-Volt, Bladed Type, Grounded (Portable)

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