The Electrical Code

Tunnel Installations over 1000 Volts, Nominal

110.51 General. When installing devices that need 1000 volts or more caution needs to be taken to avoid harm to human life when the devices need servicing so that the person does not get electrocuted. This should not be even said right. We need to take caution for ourself and for our electrical brothers. I again need to say that if your using this to install equipment that needs 1000 + volts your not qualified. In the US we have electrical engineers that sign off before wires get energized, this insures that someone is taking responsibility for the installation. This is a short one compare to the last one.

“(A) Covered. The provisions of this part shall apply to the installation and use of high-voltage power distribution and utilization equipment that is portable, mobile, or both, such as substations, trailers, cars, mobile shovels, draglines, hoists, drills, dredges, compressors, pumps, conveyors, underground excavators, and the like.

(B) Other Articles. The requirements of this part shall be additional to, or amendatory of, those prescribed in Articles 100 through 490 of this Code.

(C) Protection Against Physical Damage. Conductors and cables in tunnels shall be located above the tunnel floor and so placed or guarded to protect them from physical damage.”

110.52 Overcurrent Protection.To elaborate overcurrent protection even at these levels of voltage we need to caution that the breaker is rated correctly.

“Motor-operated equipment shall be protected from overcurrent in accordance with Parts III, IV, and V of Article 430. Transformers shall be protected from overcurrent in accordance with 450.3.”

110.53 Conductors.The code wants more protection to the wires that are ran in tunnels. Basically.

“High-voltage conductors in tunnels shall be installed in metal conduit or other metal raceway, Type MC cable, or other approved multiconductor cable. Multiconductor portable cable shall be permitted to supply mobile equipment.”

110.54 Bonding and Equipment Grounding Conductors. We install grounding for traditional means for lower voltage devices. When doing it in these conditions the code wants use to adhere to a 1000 foot minimum. Also they tell use were the wires shall go and if the wire has is bare or has some type of insulation. They don’t say it here but it is specified that grounding needs to be green in color to identify it as such.

“(A) Grounded and Bonded. All non–current-carrying metal parts of electrical equipment and all metal raceways and cable sheaths shall be solidly grounded and bonded to all metal pipes and rails at the portal and at intervals not exceeding 300 m (1000 ft) throughout the tunnel.

(B) Equipment Grounding Conductors. An equipment grounding conductor shall be run with circuit conductors inside the metal raceway or inside the multiconductor cable jacket. The equipment grounding conductor shall be permitted to be insulated or bare.“

110.55 Transformers, Switches, and Electrical Equipment.This is just saying to make sure that the equipment cannot be destroyed be some accident.

“All transformers, switches, motor controllers, motors, rectifiers, and other equipment installed below ground shall be protected from physical damage by location or guarding.“

110.56 Energized Parts.Make sure equipment is enclosed as manufacture suggests.

“Bare terminals of transformers, switches, motor controllers, and other equipment shall be enclosed to prevent accidental contact with energized parts.“

110.57 Ventilation System Controls.Tunnels are considered, in some conditions, confined spaces. And in theses spaces OSHA has rules that need to be followed to make the work and habitable conditions are met for safety.

“Electrical controls for the ventilation system shall be arranged so that the airflow can be reversed.“

110.58 Disconnecting Means. This tells us where to install the switch to the equipment that is being fed by. A lot of times there should be a means of labeling the devices so that there is no questions as to what it controls.

“A switch or circuit breaker that simultaneously opens all ungrounded conductors of the circuit shall be installed within sight of each transformer or motor location for disconnecting the transformer or motor. The switch or circuit breaker for a transformer shall have an ampere rating not less than the ampacity of the transformer supply conductors. The switch or circuit breaker for a motor shall comply with the applicable requirements of Article 430.“

110.59 Enclosures. In this case we want to make the equipment that we use to be able to live through what ever the environment will throw at the equipment. This only references the enclosure but it also early on in this article it makes reference that we need to use metal in the installation for the wires. So yes when doing this type of insulation we can make it completely water proof and resistant from other things(like dust, human contact and more.).

“Enclosures for use in tunnels shall be drip proof, weatherproof, or submersible as required by the environmental conditions. Switch or contactor enclosures shall not be used as junction boxes or as raceways for conductors feeding through or tapping off to other switches, unless the enclosures comply with 312.8.“