EP2251941A1

EP2251941A1 - A DC wall outlet/inlet with controlled connect and disconnect sequence to limit arcing

Info

Publication number: EP2251941A1
Application number: EP09160389A
Authority: EP
Inventors: Robert Schaacke
Original assignee: Femtogrid Energy Solutions BV
Current assignee: Femtogrid Energy Solutions BV
Priority date: 2009-05-15
Filing date: 2009-05-15
Publication date: 2010-11-17

Abstract

The invention relates to an electrical system including a DC voltage bus, an electrical device having a plug, and a DC wall outlet for electrically connecting and disconnecting the plug and the DC voltage bus. The DC wall outlet comprises holes for inserting the plug in. Upon insertion, no electrical connection is made. The connection is made only when, following the insertion, the plug is rotated. The system further includes a contact mechanism for electrically connecting and disconnecting each contact of the plug contacts to a corresponding contact of the DC voltage bus contacts in predefined sequences upon rotation of the plug, thus limiting or eliminating arcing.

Description

FIELD OF THE INVENTION

The invention relates to the field of electrical power distribution using an electrical system or electricity grid. In particular, the invention relates to a DC wall outlet/inlet for electrically connecting and disconnecting a plug of an electrical device and a DC voltage bus.

BACKGROUND OF THE INVENTION

Most of electrical energy is currently generated as a direct current (DC) energy due to a number of advantages that the DC-generated energy has over an alternating current (AC)-generated energy. One advantage is high efficiency associated with DC energy generation, especially with sustainable energy sources such as e.g. solar cells. Other advantages include high efficiency associated with conversion of the DC energy to higher or lower voltages and storage of the DC energy (e.g. in capacitors and batteries). In addition, electrical devices typically work better and consume less energy when operating on DC energy. In light of this, it would be beneficial to employ DC wall outlets/inlets for bidirectional distribution of DC-generated energy in consumer and industrial applications.
Unfortunately, when a plug of an electrical device is connected to or disconnected from a DC voltage bus via a typical DC wall outlet/inlet, an arc is often created. Arcing may cause fire, create EMC problems, and wear out contacts. Therefore, in domestic applications, AC wall outlets/inlets are currently used. However, distributing DC-generated energy via AC wall outlets/inlets results in inevitable energy conversion losses and safety issues.
DC switches that diminish arcing are known. For example, GB 780,222 discloses a rotary switch where contacts are made in a sequence upon angular displacement of contacts. However, this solution is not appropriate for electrical systems that include wall outlets and plugs because of the completely different applications, configuration and operation of such systems.
As the foregoing illustrates, what is needed in the art is a DC wall outlet/inlet for electrically connecting and disconnecting the plug and the DC grid without significant arcing.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an electrical system including a DC wall outlet/inlet that eliminates or significantly diminishes arcing and a method for operating such a system.
In the following, the term "wall outlet" is used to describe an outlet/inlet configured for either unidirectional distribution of energy (i.e. either drawing or supplying of energy) or bidirectional distribution of energy (i.e. both drawing and supplying of energy). Such an outlet/inlet may not necessarily be included in the wall. Instead, the wall outlet may be a part of in any member adapted to contain such an outlet/inlet.
An electrical system that includes a DC voltage bus, an electrical device comprising a plug, and a DC wall outlet is disclosed. The DC voltage bus includes a first set of contacts. The plug includes a second set of contacts for drawing/supplying a DC voltage from/to the DC voltage bus when an electrical connection is made between the first set of contacts and the second set of contacts. The DC wall outlet is configured for electrically connecting and disconnecting the plug and the DC voltage bus. The DC wall outlet comprises holes for inserting the plug in (more specifically, for inserting the pins of the plugs in). The insertion is made in a first translational direction. Upon insertion, no electrical connection is made between the first set of contacts and the second set of contacts. The system further includes a contact mechanism configured for electrically connecting each contact of the second set of contacts to a corresponding contact of the first set of contacts in a predefined connect sequence upon rotation of the plug in a first rotational direction. The contact mechanism is further configured for electrically disconnecting each contact of the second set of contacts from a corresponding contact of the first set of contacts in a predefined disconnect sequence upon rotation of the plug in a second rotational direction opposite to the first rotational direction.
An alternative electrical system that includes a DC voltage bus, an electrical device comprising a plug, and a DC wall outlet is also disclosed. The alternative system differs from the system described above in that the plug comprises holes for inserting the DC wall outlet in (more specifically, for inserting the pins of the DC wall outlet in).
The gist of the present invention lies in the fact that when a plug is inserted into a DC wall outlet (or when a DC wall outlet is inserted into a plug in an alternative system), no direct electrical connection is made between the contacts of the plug and the contacts of the DC voltage bus. The electrical connections are made only when, following the insertion, the plug is rotated. Furthermore, the electrical connections between various contacts are not made all at once, but, rather, in a predefined chronological sequence. Similarly, the electrical connections are not broken all at once, but also in a predefined chronological sequence, when the inserted plug is rotated in the direction opposite to the rotation to make the connections. Connecting and disconnecting the contacts of the plug and the contacts of the DC voltage bus in controlled sequences limits arcing.
Embodiment of claims 3 and 4 advantageously allow for the different locations of the contact mechanism.
Embodiment of claim 5 establishes advantageous connect sequence, while embodiments of claims 6-9 establish various advantageous disconnect sequences.
Embodiment of claim 10 allows accelerating making of an electrical connection between each of the contacts of the plug and a corresponding contact of the DC voltage bus.
Embodiment of claim 11 specifies that rotation of the plug is performed only after the plug (or the DC wall outlet, for the alternative system) is inserted. Thus, the electrical system must be such as to advantageously allow for both translational (i.e., insertion) and rotational movements.
A DC wall outlet and a plug configured for use in such electrical systems are disclosed, according to embodiments of claims 12 and 13.
Finally, two alternative methods for electrically connecting and disconnecting a DC voltage bus and a plug via a DC wall outlet are provided in claims 14 and 15.
Hereinafter, embodiments of the invention will be described in further detail. It should be appreciated, however, that these embodiments may not be construed as limiting the scope of protection for the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic illustration of a system of an electrical device connected to a DC voltage bus via a DC wall outlet according to one embodiment of the present invention;
FIG. 2A is a schematic illustration of a contact mechanism prior to the rotation of the plug in a first rotational direction according to one embodiment of the present invention;
FIG. 2B is a schematic illustration of a contact mechanism after the rotation of the plug in the first rotational direction according to one embodiment of the present invention;
FIG. 2C is a schematic illustration of predefined connect and disconnect sequences according to one embodiment of the present invention;
FIG. 3A is a schematic illustration of the plug contacts electrically connected to the DC voltage bus contacts prior to the rotation of the plug in a second rotational direction according to one embodiment of the present invention;
FIG. 3B is a schematic illustration of the plug contacts electrically disconnected from the DC voltage bus contacts after the rotation of the plug in the second rotational direction according to one embodiment of the present invention;
FIG. 3C is a schematic illustration of the plug contacts electrically disconnected from the DC voltage bus contacts after the rotation of the plug in the second rotational direction according to another embodiment of the present invention;
FIG. 4 is a schematic illustration of a system of an electrical device connected to a DC voltage bus via a DC wall outlet according to yet another embodiment of the present invention; and
FIG. 5 illustrates the functionality of the spring lock 424 according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a system 100 of an electrical device 120 connected to a DC voltage bus 110 via a DC wall outlet 130 according to one embodiment of the present invention. As shown, the DC voltage bus 110 includes bus contacts 115. The bus contacts 115 are a set of two or more contacts such as e.g. a hot wire, a cold wire, and a neutral wire. The electrical device 120 includes a plug 122 having plug contacts 125. The plug contacts 125 are another set of two or more contacts such as e.g. a high-voltage contact, a low-voltage contact, and a zero-voltage contact. When an electrical connection is made between the plug contacts 125 and the bus contacts 115, the electrical device 120 may draw or supply a DC voltage from or to the DC voltage bus 110.
As used herein, the terms "high-voltage contact" and "hot contact," the terms "low-voltage contact" and "cold contact," and the terms "zero-voltage contact" and "neutral contact" refer to contacts having the highest voltage, the lowest voltage, and the contact having a relation to protective earth, respectively. For example, "high-voltage contact" and "hot contact" may refer to +400 Volts (V) contact, "low-voltage contact" and "cold contact" may refer to -48 V contact, and "zero-voltage contact" and "neutral contact" may refer to 0 V contact. However, in other embodiments, the "zero-voltage contact" and "neutral contact" do not necessarily have zero voltages.
The electrical device 120 may draw a DC voltage from the DC voltage bus 110 if the electrical device 120 is one of the devices that operate on a DC voltage input, such as e.g. computers, light sources, televisions, etc. Other devices that operate on the DC voltage of the DC voltage bus include an energy management system, a large inverter system, an island inverter system (for stand alone AC power supply, typically used for providing AC power locally) and a double active DC/AC bridge. Generally, devices comprising a switched mode power supply are capable of operating with a DC voltage. Operation of devices at DC voltages saves power, while particular components (e.g. capacitors, diodes, and a power factor controller) can be saved or have an increased life time.
The electrical device 120 may supply a DC voltage to the DC voltage bus 110 if the electrical device 120 is one of the energy supply arrangements, such as e.g. photovoltaic arrangements, wind energy arrangements, and/or fuel cell arrangements.
The details regarding the operation of the DC voltage bus 110 may be found in European patent application number 09150715.2 , titled "Femto Grid," filed January 16^th, 2009.
As also shown in FIG. 1, the system 100 further includes the DC wall outlet 130 for electrically connecting and disconnecting the plug 122 and the DC voltage bus 110 by making and breaking an electrical connection between the plug contacts 125 and the bus contacts 115. As described in greater detail below, the system 100 includes a contact mechanism 140 configured for electrically connecting each contact of the plug contacts 125 to a corresponding contact of the bus contacts 115.
In the particular embodiment of FIG. 1, the plug 122 includes pins 127 and the DC wall outlet 130 includes holes 135. As used herein, the term "pins" refers to protruding elements and the term "holes" refers to hollow elements configured in such a way so that the "pins" may be be inserted into "holes."
An electrical connection is made as follows. First, the plug 122 is inserted (more specifically, the pins 127 of the plug 122 are inserted) into the holes 135 of the DC wall outlet 130. The insertion is made in a first translational direction 151, which is the direction connecting the plug contacts 125 and the holes 135. Upon the insertion, no electrical connection is made between the plug contacts 125 and the bus contacts 115. Following the insertion, the contact mechanism 140 is configured to electrically connect each contact of the plug contacts 125 to a corresponding contact of the bus contacts 115 in a predefined connect sequence upon rotation of the plug 122 in a first rotational direction. Rotating the plug 122 in a first rotational direction may be e.g. rotating the plug 122 in a clockwise direction, as shown in FIG. 1 with an arrow 152.
In other words, an electrical connection between the plug contacts 125 and the bus contacts 115 is only made after two movements. The first movement is a translational movement and the second movement is a rotational movement. As a result of these two movements, electrical connection between each contact of the plug contacts 125 may be made with one corresponding contact of the bus contacts 115.
The contact mechanism 140 is further configured to electrically disconnect each contact of the plug contacts 125 from a corresponding contact of the bus contacts 115 in a predefined disconnect sequence upon rotation of the plug 122 in a second rotational direction opposite to the first rotational direction. Rotating the plug 122 in a second rotational direction may be e.g. rotating the plug 122 in a counter-clockwise direction, as shown in FIG. 1 with an arrow 153. In other embodiments, directions shown with arrows 152 and 153 may, of course, be reversed.
In various embodiments, the contact mechanism 140 may be included either in the DC wall outlet 130 or the plug 122, e.g. as a printed circuit board (PCB) configured for having predefined connect and disconnect sequences.
In an alternative implementation (not shown in FIG. 1), an electrical system may differ from the system 100 in that a DC wall outlet includes pins and a plug includes holes. In such an alternative system, an electrical connection is made as follows. First, the DC wall outlet is inserted (more specifically, the pins of the DC wall outlet are inserted) into the holes of the plug. The insertion is made in a first translational direction, which is the direction connecting the pins and the holes. Upon the insertion, no electrical connection is made between plug contacts and bus contacts. Following the insertion, similarly to the system 100, a contact mechanism is configured to electrically connect each contact of the plug contacts to a corresponding contact of the bus contacts in a predefined connect sequence upon rotation of the plug in a first rotational direction. The contact mechanism is further configured to electrically disconnect each contact of the plug contacts from a corresponding contact of the bus contacts in a predefined disconnect sequence upon rotation of the plug in a second rotational direction opposite to the first rotational direction.
FIG. 2A is a schematic illustration of the contact mechanism 140 prior to the rotation of the plug 122 in a first rotational direction and FIG. 2B is a schematic illustration of the contact mechanism 140 after the rotation of the plug 122 in the first rotational direction according to one embodiment of the present invention. In FIGS. 2A and 2B, the plug contacts 125 are shown as contacts A, B, and C.
As shown in FIG. 2A, when the plug 122 is rotated clockwise, the contacts A, B, and C make electrical connections with the three bus contacts 115 at contact moments 1, 2, and 3, respectively. The distance between the contact A and the contact moment 1 is smaller than each of the distances between the contact B and the contact moment 2 and between the contact C and the contact moment 3. Therefore, the contact A makes an electrical connection with a corresponding bus contact before the contacts B and C make their respective connections. As shown in FIG. 2B, the contact A makes an electrical connection with the corresponding bus contact at the contact moment 1 via a contact material 201. The contact material 201 is configured to maintain an electrical connection between the contact A and the corresponding bus contact as the plug 122 is turned further in the first rotational direction (in this case, further clockwise).
The distance between the contact B and the contact moment 2 is smaller than the distance between the contact C and the contact moment 3. Therefore, the contact B makes an electrical connection with a corresponding bus contact before the contact C makes a connection. As shown in FIG. 2B, the contact B makes an electrical connection with the corresponding bus contact at the contact moment 2 via a contact material 202. Similar to the contact material 201, the contact material 202 is configured to maintain an electrical connection between the contact B and the corresponding bus contact as the plug 122 is turned even further in the first rotational direction (in this case, even further clockwise).
Finally, the contact C makes an electrical connection with a corresponding bus contact at the contact moment 3 via a contact material 203. Since, after that moment, all three contacts A, B, and C made electrical connections with the corresponding bus contacts 115, the plug 122 and the DC voltage bus 110 are electrically connected. After that, as previously described herein, the electrical device 120 may draw or supply a DC voltage from or to the DC voltage bus 110.
FIG. 2C is a schematic illustration of a predefined connect sequence for the contact mechanism 140 illustrated in FIG. 2A and FIG. 2B according to one embodiment of the present invention. In this embodiment, the contacts A, B, and C of the plug contacts 125 are low-voltage, zero-voltage, and high-voltage, respectively, and the corresponding contacts of the bus contacts 115 are cold contact, neutral contact, and hot contact. As shown in FIG. 2C, as the plug 122 is rotated clockwise, the low-voltage contact (i.e., the contact A) makes an electrical connection to the cold contact first (at the contact moment 1). Next, the high-voltage contact (i.e., contact C) makes an electrical connection to the hot contact (at the contact moment 2). Last, the zero-voltage contact (i.e., contact B) makes an electrical connection to the neutral contact (at the contact moment 3, the neutral contact is indicated in FIG. 2C as "0"). Thus, in this embodiment, the contact mechanism 140 is configured for having the predefined connect sequence operable to, first, connect the low-voltage contact of the plug 122 to the cold contact of the DC voltage bus 110, second, connect the high-voltage contact of the plug 122 to the hot contact of the DC voltage bus 110, and last, connect the zero-voltage contact of the plug 122 to the neutral contact of the DC voltage bus 110.
FIG. 2C further illustrates a predefined disconnect sequence as the plug 122 is rotated in the opposite direction (in this embodiment, counter clockwise). As shown, the contact mechanism 140 is configured for having the predefined disconnect sequence operable to, first, disconnect the zero-voltage contact (i.e., contact B) from the neutral contact at the contact moment 3, second, disconnect the high-voltage contact (i.e., contact C) from the hot contact at the contact moment 2, and last, disconnect the low-voltage contact (i.e., contact A) from the cold contact at the contact moment 1. Such a disconnect sequence some times is referred as a "last make first break" sequence.
As now described in FIGS 3A-3C, in other embodiments, the plug 122 and the DC voltage bus 110 may be disconnected in other manners.
FIG. 3A is a schematic illustration of the plug contacts 125 electrically connected to the bus contacts 115 prior to the rotation of the plug 122 in a second rotational direction and FIGS. 3B and 3C are schematic illustrations of the plug contacts 125 electrically disconnected from the bus contacts 115 after the rotation of the plug 122 in the second rotational direction according to different embodiments of the present invention. As shown in FIG. 3A, switches 301, 302, and 303 are closed, maintaining electrical connections between each of the plug contacts 125 and a corresponding contact of the bus contacts 115. As shown in FIG. 3B, one of the switches 301, 302, or 303 may be opened first (in the case illustrated in FIG. 3B it is the switch 301), before the other switches are opened. Thus, the contact mechanism 140 is configured for having the predefined disconnect sequence operable to, first, disconnect one contact of the plug contacts 125 from the corresponding contact of the bus contacts 115, and, second, disconnect the other contacts of the plug contacts 125 from their corresponding contacts of the bus contacts 115. If the plug contacts 125 include a low-voltage contact (shown in FIG. 3B as contact A), a zero-voltage contact (shown in FIG. 3B as contact B), and a high-voltage contact (shown in FIG 3B as contact C), the preferred disconnect sequence would be to disconnect the low-voltage contact prior to disconnecting the high-voltage contact and the zero-voltage contact (as shown in FIG. 3B with the switch 301 being open). An alternative disconnect sequence would be to disconnect the high-voltage contact prior to disconnecting the low-voltage contact and the zero-voltage contact (not shown in FIG. 3B). Yet another alternative disconnect sequence would be to disconnect the zero-voltage contact prior to disconnecting the low-voltage contact and the high-voltage contact (not shown in FIG. 3B).
Alternatively, one or more of the switches 301-303 may be configured to provide a short circuit between two or more of the plug contacts 125. If the plug contacts 125 include a low-voltage contact (shown in FIG. 3C as contact A), a zero-voltage contact (shown in FIG. 3C as contact B), and a high-voltage contact (shown in FIG 3C as contact C), the preferred disconnect sequence would be to, first, provide a short-circuit between the low-voltage contact and the zero-voltage contact (as shown in FIG. 3C with the switch 302 providing a short circuit between the contacts A and B), and, second, disconnect the high-voltage contact.
While FIGS. 2A-2C and 3A-3C refer the elements of the system 100, the same description would apply to the alternative system described above. Furthermore, while the above embodiments discussed electrically connecting each of the plug contacts 125 from corresponding bus contacts 115 sequentially one after another, in other embodiments, the predefined connect and disconnect sequences may include connecting or disconnecting several contacts at the same time, as long as one or more of other contacts are connected or disconnected at a different time.
FIG. 4 is a schematic illustration of a system 400 of an electrical device having a plug 422 connected to a DC voltage bus 410 via a DC wall outlet 430 according to yet another embodiment of the present invention. The plug 422, the DC voltage bus 410, and the DC wall outlet 430 are analogous to the plug 122, the DC voltage bus 110, and the DC wall outlet 130 described above. Furthermore, a PCB 440 is analogous to the contact mechanism 140 described above.
As shown, the system 400 further includes a front plate 423, a ring 421, a spring lock 424, a spark plate 426, a fuse 441, and a back plate 442. The front plate 423 may have a visual indicator indicating whether an electrical connection is made between contacts of the plug 422 and contacts of a DC voltage bus (plug contacts, bus contacts, and the DC voltage bus are not shown in FIG. 4, but are analogous to the plug contacts 125, the bus contacts 115, and the DC voltage bus 110 described above).
The side of the ring 421 facing the spring lock 424 includes a four-leaf flower extension, shown in FIG. 5 as extension 500. The spring lock 424 includes two springs (shown in FIG. 5 as springs 501 and 502) and two locks (shown in FIG. 5 as locks 521 and 522). The springs 501 and 502 press on leaves 511-514 of the extension 500, accelerating electrical connection between each contact of the plug contacts and one contact of the bus contacts by clicking each of the plug contacts in place upon the rotation of the plug 422. A user of the plug 424 receives a tactile feedback when electrical connections are made correctly, which provides an acceleration by sudden reduction of the necessary rotational force.
The spark plate 426, which may be connected to the contact mechanism in the form of the PCB 540, is configured to suppress sparking upon electrically connecting the first of the plug contacts and the corresponding contact of the bus contacts. The fuse 441 is configured to limit the amount of current drawn/supplied from/to the DC voltage bus 410. The back plate 442 is configured to connect the DC voltage bus 410 to the PCB 440.
The system 400 may be described as an "insert, turn, and snap lock" system. In one embodiment, all pins of the plug 422 are the same and the plug 422 may be inserted into the DC wall outlet 430 in one way only (the pins are not shown in FIG. 4, but are analogous to the pins 127 described above). Electrical connection between the plug contacts and the bus contacts will only be established once the plug 422 is inserted, turned and the pins snap lock. The pins may be a mushroom-type pins, and, once connected, will not release due to their flat tops. On extreme cable pull force, the front plate 423, along with the PCB 440 and the plug 422, will be released from the base part (i.e., from the back plate 442). The base part may contain safe AMP cable connections such that there are no bare contacts when the load is connected. Electrical reconnection may be made easily by the means of snap fits.
One advantage of the present invention is that arcing may be limited or eliminated by electrically connecting and disconnecting the pins of the plug and the wires of the DC voltage bus in controlled sequences. In addition, the systems 100 and 400 provide child lock protection because electrical connections cannot be made without turning the plug and, once connected, the mushroom-type pins may not be released without turning the plug in the opposite direction.
While the forgoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. Therefore, the scope of the present invention is determined by the claims that follow.

Claims

An electrical system comprising:
a DC voltage bus comprising a first set of contacts;

an electrical device comprising a plug having a second set of contacts for drawing/supplying a DC voltage from/to the DC voltage bus when an electrical connection is made between the first set of contacts and the second set of contacts;

a DC wall outlet for electrically connecting and disconnecting the plug and the DC voltage bus, wherein:
the DC wall outlet comprises holes for inserting the plug in,

the insertion is made in a first translational direction, and,

upon insertion, no electrical connection is made between the first set of contacts and the second set of contacts; and

a contact mechanism configured for:
electrically connecting each contact of the second set of contacts to a corresponding contact of the first set of contacts in a predefined connect sequence upon rotation of the plug in a first rotational direction, and

electrically disconnecting each contact of the second set of contacts from a corresponding contact of the first set of contacts in a predefined disconnect sequence upon rotation of the plug in a second rotational direction opposite to the first rotational direction.
An electrical system comprising:
a DC voltage bus comprising a first set of contacts;

an electrical device comprising a plug having a second set of contacts for drawing/supplying a DC voltage from/to the DC voltage bus when an electrical connection is made between the first set of contacts and the second set of contacts;

a DC wall outlet for electrically connecting and disconnecting the plug and the DC voltage bus, wherein:
the plug comprises holes for inserting the DC wall outlet in,

the insertion is made in a first translational direction, and,

upon insertion, no electrical connection is made between the first set of contacts and the second set of contacts; and

a contact mechanism configured for:
electrically connecting each contact of the second set of contacts to a corresponding contact of the first set of contacts in a predefined connect sequence upon rotation of the plug in a first rotational direction, and

electrically disconnecting each contact of the second set of contacts from a corresponding contact of the first set of contacts in a predefined disconnect sequence upon rotation of the plug in a second rotational direction opposite to the first rotational direction.
The system according to claims 1 or 2, wherein the contact mechanism is provided in the DC wall outlet.
The system according to claims 1 or 2, wherein the contact mechanism is provided in the plug.
The system according to any one of claims 1-4, wherein:
the first set of contacts comprise a hot contact, a cold contact, and a neutral contact;

the second set of contacts comprise a high-voltage contact, a low-voltage contact, and a zero-voltage contact; and

the contact mechanism is configured for having the predefined connect sequence operable to:
first, connect the low-voltage contact to the cold contact,

second, connect the high-voltage contact to the hot contact, and

last, connect the zero-voltage contact to the neutral contact.
The system according to any one of claims 1-5, wherein:
the first set of contacts comprise a hot contact, a cold contact, and a neutral contact;

the second set of contacts comprise a high-voltage contact, a low-voltage contact, and a zero-voltage contact; and

the contact mechanism is configured for having the predefined disconnect sequence operable to:
first, disconnect the zero-voltage contact from the neutral contact,

second, disconnect the high-voltage contact from the hot contact, and

last, disconnect the low-voltage contact from the cold contact.
The system according to any one of claims 1-5, wherein the contact mechanism is configured for having the predefined disconnect sequence operable to:
first, disconnect one contact of the second set of contacts; and

second, disconnect the other contacts of the second set of contacts.
The system according to claim 7, wherein:
the second set of contacts comprise a high-voltage contact, a low-voltage contact, and a zero-voltage contact; and

the predefined disconnect sequence is operable to disconnect the low-voltage contact prior to disconnecting the high-voltage contact and the zero-voltage contact.
The system according to any one of claims 1-5, wherein:
the first set of contacts comprise a hot contact, a cold contact, and a neutral contact;

the second set of contacts comprise a high-voltage contact, a low-voltage contact, and a zero-voltage contact; and

the contact mechanism is configured for having the predefined disconnect sequence operable to:
first, provide a short-circuit between the low-voltage contact and the zero-voltage contact, and

second, disconnect the high-voltage contact.
The system according to any one of claims 1-9, further comprising a spring lock configured to accelerate electrical connection between each contact of the second set of contacts and one contact of the first set of contacts by clicking each of the second set of contacts in place upon the rotation of the plug in the first rotational direction.
The system according to any of of claims 1-10, wherein the rotation is performed after the insertion.
A DC wall outlet configured for use in the system according to any one of claims 1-11.
A plug configured for use in the system according to any one of claims 1-12.
A method for electrically connecting and disconnecting a DC voltage bus having a first set of contacts and a plug having a second set of contacts via a DC wall outlet, the method comprising the steps of:
inserting the plug into holes of the DC wall outlet connected to the DC voltage bus, wherein the insertion is made in a first translational direction, and, upon insertion, no electrical connection is made between the first set of contacts and the second set of contacts;

rotating the plug in a first rotational direction to electrically connect each contact of the second set of contacts to a corresponding contact of the first set of contacts in a predefined connect sequence; and

rotating the plug in a second rotational direction opposite to the first rotational direction to electrically disconnect each contact of the second set of contacts from a corresponding contact of the first set of contacts in a predefined disconnect sequence.
A method for electrically connecting and disconnecting a DC voltage bus having a first set of contacts and a plug having a second set of contacts via a DC wall outlet, the method comprising the steps of:
inserting the DC wall outlet into holes of the plug connected to the DC voltage bus, wherein the insertion is made in a first translational direction, and, upon insertion, no electrical connection is made between the first set of contacts and the second set of contacts;

rotating the plug in a first rotational direction to electrically connect each contact of the second set of contacts to a corresponding contact of the first set of contacts in a predefined connect sequence; and

rotating the plug in a second rotational direction opposite to the first rotational direction to electrically disconnect each contact of the second set of contacts from a corresponding contact of the first set of contacts in a predefined disconnect sequence.