3 Creepage, clearance and isolation The spacing distance between components that is required to withstand a given voltage is specified in terms of clearance and creepage. A visual representation of the distinction between these terms and their applicability to board-mounted components is shown in. Clearances from Buildings of high and extra-high voltage lines IE Rule 80 Vertical Distance High voltage lines up to 33KV = 3.7 Meter Extra High Voltage = 3.7 Meter + Add 0.3 meter for every additional 33KV Horizontal clearance between the conductor and Building High Voltage Up to 11 KV =1.2 Meter 11KV To 33KV = 2.0 Meter. Maybach empire kontakt free download. Assuming you are really after clearance the shortest point to point distance, through air: The british standard: BS EN 60064-1:2007 is a very good reference point to capture the point of inception with regards to corona discharge. For an Inhomogeneous field, two conductors 15.2mm apart will have a corona inception voltage at 10kVdc. Extra high voltage (EHV; transmission) – over 230 kV, up to about 800 kV, used for long distance, very high power transmission. Voltage (kV) Minimum Clearance. Cocut free download.
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Are you protecting yourself from electric shock and burns? You're not if you fail to comply with the following three clearance requirements in Sec. 110-26 of the National Electrical Code (NEC): 1) at least a 3-ft clearance in front of all electrical equipment; 2) a 30 in.-wide working space in front of equipment operating at 600V or less; and 3) minimum headroom clearance of 6 ft or the height of the equipment, whichever is greater. Let's look at these three clearances in detail.
Depth of working space Sec. 110.26(a)(1)
The depth of the working space in front of exposed live parts must be at least as great as the distances outlined in Table 110-26(a). You must measure distances from live parts or from the front of the enclosure or opening in which the live parts are enclosed. The working clearance in front of the equipment on which you're working is also dependent on the composition of the facing wall and whether it houses live electrical parts. As you'll note in the Table, there are three conditions noted for two voltage levels 150V or less and 151V to 600V-to-ground. For example, the clearances of a 120V/208V, 3-phase, 4-wire system fall under the 150V-to-ground or less category while a 277V/480V, 3-phase, 4-wire system falls in the 151V- to 600V-to-ground classification. The text below Table 110-26(a) explains the application and use of all three conditions.
Condition 1, Table 110-26(a)
Condition 1 describes a situation in which the electrical equipment is installed in or on a wall that faces an insulated wall, constructed of wood or metal studs, and sheetrock or wood panels. If you make contact with the insulated wall while touching live parts of the equipment, you're isolated from the grounded slab or earth. Therefore, Condition 1 allows for a reduced working space. Before the 1965 NEC, Condition 1 only required a 2-ft workspace in front of electrical equipment.
Condition 2, Table 110-26(a)
Condition 2 pertains to a situation in which the electrical equipment is installed on a wall that faces a conductive (grounded) wall. A conductive (grounded) wall (made of concrete, brick, or tile) can connect the body to ground if touched. If you make contact with this type of wall while touching a live part or conductor, you will create a circuit path to ground, which could lead to electrocution. Because this danger is present, the Code requires a larger workspace when voltages range from 151V to 600V.
Condition 3, Table 110-26(a)
Condition 3 exists when the electrical equipment is installed in or on a wall that faces another wall of electrical equipment. With electrical equipment installed in this manner, there are live parts on both sides of the room. In this case, you may be subjected to phase-to-phase voltage or phase-to-ground voltage when servicing the equipment. Because you could be exposed to a fatal shock from live parts on either side of the workspace, the NEC requires a greater clearance for your safety.
Width of working space Sec. 110-26(a)(2)
This space requirement creates sufficient room for you to work on the equipment without contacting live parts and metal parts. You must also provide for a 90 opening of equipment doors and hinged panels in the workspace. This allows you to have adequate room to repair, adjust, or reset overcurrent protection devices without placing your body between the panel door and the panelboard. This requirement first appeared in the 1987 NEC.
Height of working space Sec. 110.26(a)(3)(e)
As a general rule, you must maintain a minimum headroom clearance of 6 ft from the floor or platform up to any overhead obstruction. This workspace is mandatory and applies to service equipment, switchboards, panelboards, and motor control centers. The overhead workspace protects employees from accidentally touching grounded objects and exposed live parts at the same time. As mentioned earlier, this act would complete a circuit to ground connection, which could cause a fatal electric shock. In addition, electricians or maintenance workers should never have to stoop or bend down to gain access to service, repair, or modify components inside electrical equipment.
Summary
While trying to adhere to these requirements, it's easy to lose sight of what you're going to all this trouble for: You install electrical equipment with adequate workspace for the safety of those servicing it. This workspace is required and must be maintained around all electrical equipment where parts of an energized system may be serviced. Before designing workspaces with clearances less than those described in this article, consult with the authority having jurisdiction (AHJ) and ask for a variance in writing.
Workspace Origins
Installations built before the 1978 NEC only require a minimum clearance of 2 ft in front of electrical equipment. The 30-in.-wide rule has been used since the 1971 NEC. Headroom clearance has been required since the 1965 NEC.
IEEE Std 510-1983 IEEE Recommended Practices for Safety in High Voltage and High Power Testing
1. SCOPE
Excerpts from IEEE Standard 510-1983 have been listed in this section in order to caution all personnel dealing with high voltage applications and measurements and to provide recommended safety practices with regard to electrical hazards.
Considerations of safety in electrical testing apply not only to personnel but to the test equipment and apparatus or system under test. These recommended practices deal generally with safety in connection with testing in laboratories, in the field, and of systems incorporating high voltage power supplies, etc. For the purposes of these recommended practices, a voltage of approximately 1,000 volts has been assumed as a practical minimum for these types of tests. Individual judgement is necessary to decide if the requirements of these recommended practices are applicable in cases where lower voltages or special risks are involved.
- All ungrounded terminals of the test equipment or apparatus under test should be considered as
energized. - Common ground connections should be solidly connected to both the test set and the test specimen.
As a minimum, the current capacity of the ground leads should exceed that necessary to carry the
maximum possible ground current. The effect of ground potential rise due to the resistance and
reactance of the earth connection should be considered. - Precautions should be taken to prevent accidental contact of live terminals by personnel, either by
shielding the live terminals or by providing barriers around the area. - The circuit should include instrumentation for indicating the test voltages.
- Appropriate switching and, where appropriate, an observer should be provided for the immediate deenergization
of test circuits for safety purposes. In the case of dc tests, provisions for discharging
and grounding charged terminals and supporting insulation should also be included. - High Voltage and high-power tests should be performed and supervised by qualified personnel.
2. TEST AREA SAFETY PRACTICES
- Appropriate warning signs, for example, DANGER – HIGH VOLTAGE, should be posted on or near the
entrance gates. - Insofar as practical, automatic grounding devices should be provided to apply a visible ground on the
high-voltage circuits after they are de-energized. In some high-voltage circuits, particularly those in
which elements are hanged from one setup to the next, this may not be feasible. In these cases, the
operator should attach a ground to the high-voltage terminal using a suitably insulated handle. In
the case of several capacitors connected in series, it is not always sufficient to ground only the highvoltage
terminal. The exposed intermediate terminals should also be grounded. This applies in
particular to impulse generators where the capacitors should be short-circuited and grounded before
and while working on the generator. - Safe grounding of instrumentation should take precedence over proper signal grounding unless other
special precautions have been taken to ensure personnel safety.
3. CONTROL & MEASUREMENT CIRCUITS
Leads should not be run from a test area unless they are contained in a grounded metallic sheath
and terminated in a grounded metallic enclosure, or unless other precautions have been taken to
ensure personnel safety. Control wiring, meter connections, and cables running to oscilloscopes fall into this category. Meters and other instruments with accessible terminals should normally be placed
in a metal compartment with a viewing window.
Temporary Circuits
Pcb High Voltage Clearance
- Temporary measuring circuits should be located completely within the test area and
viewed through the fence. Alternatively, the meters may be located outside the fence,
provided the meters and leads, external to the area, are enclosed in grounded metallic
enclosures. - Temporary control circuits should be treated the same as measuring circuits and housed
in a grounded box with all controls accessible to the operator at ground potential.
4. SAFETY RULES
A set of safety rules should be established and enforced for the laboratory or testing facilities. A copy of these should be given to, and discussed with, each person assigned to work in a test area. A procedure for periodic review of these rules with the operators should be established and carried out.
5. SAFETY INSPECTION
A procedure for periodic inspection of the test areas should be established and carried out. The recommendations from
these inspections should be followed by corrective actions for unsafe equipment or for practices that are not in keeping with the required regulations.
NOTE: A safety committee composed of several operators appointed on a rotating basis has proven to be effective, not only from the inspection standpoint but also in making all personnel aware of safety.
6. GROUNDING & SHORTING]
- The routing and connections of temporary wiring should be such that they are secure against
accidental interruptions that may create hazard to personnel or equipments. - Devices which rely on a solid or solid/liquid dielectric for insulation should preferably be grounded
and short-circuited when not in use. - Good safety practice requires that capacitive objects be short-circuited in the following situations:
- Any capacitive object which is not in use but may be in the influence of a dc electric field
should have its exposed high-voltage terminal grounded. Failure to observe this
precaution may result in a voltage included in the capacitive object by the field. - Capacitive objects having a solid dielectric should be short-circuited after dc proof
testing. Failure to observe this precaution may result in a buildup of voltage on the
object due to dielectric absorption has dissipated or until the object has been
reconnected to a circuit.
NOTE: It is good practice for all capacitive devices to remain short-circuited when not in use.
- Any open circuited capacitive device should be short-circuited and grounded before being
contacted by personnel.
7. SPACING
- All objects at ground potential must be placed away from all exposed high voltage points at a
minimum distance of 1 inch (25.4 mm) for every 7,500 Volts, e.g. 50 kV requires a spacing of at least
6.7 inches (171 mm) - Allow a creepage distance of 1 inch (25.4 mm) for every 7,500 Volts for insulators placed in contact
with high voltage points.
8. HIGH-POWER TESTING
- High-power testing involves a special type of high-voltage measurement in that the level of current is
very high. Careful consideration should be given to safety precautions for high-power testing due to
this fact. The explosive nature of the test specimen also brings about special concern relating to
safety in the laboratory. - Protective eye and face equipment should be worn by all personnel conducting or observing a highpower
test where there is a reasonable probability that eye or face injury can be prevented by such
equipment.
NOTE: Typical eye and face hazards present in high-power test areas included intense light
(including ultraviolet), sparks, and molten metal.
- Safety glasses containing absorptive lenses should be worn by all personnel observing a high-power
test even when electric arcing is not expected. Lenses should be impact-resistant and have shade
numbers consistent with the ambient illumination level of the work area but yet capable of providing
protection against hazardous radiation due to any inadvertent electric arcing.
9. GENERAL
- All high-voltage generating equipment should have a single obvious control to switch the equipment
off under emergency conditions. - All high-voltage generating equipment should have an indicator which signals that the high-voltage
output is enabled. - All high-voltage generating equipment should have provisions for external connections (interlock)
which, when open, cause the high-voltage source to be switched off. These connections may be
used for external safety interlocks in barriers or for a foot or hand operated safety switch. - The design of any piece of high-voltage test equipment should include a failure analysis to determine
if the failure of any part of the circuit or the specimen to which it is connected will create a hazardous
situation for the operator. The major failure shall be construed to include the probability of failure of
items that would be overstressed as the result of the major failure. The analysis may be limited to
the effect of one major failure at a time, provided that the major failure is obvious to the operator.
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