This article was posted 04/30/2007 and is most likely outdated.

Safety in High Voltage Vaults
 

 
Topic - Safety
Subject
- Safety in High Voltage Vaults

April 30, 2007
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Safety in High Voltage Vaults

 

Author prefers to be unknown.

 

ImageCurrently the National Electric Code allows live parts to be exposed in vaults accessible to only qualified persons.

 

Who is a qualified person? A design engineer who is deeply engrossed in design specifics? A contractor working in a hot vault on a beautiful spring day? A trained employee of the facility who has been in that vault 1000 times or more and totally takes the situation for granted?

 

Do we fail to redesign dangerous intersections because only lawbreakers die? Do we design bridges such that ignoring the weight tolerances by a few pounds will cause them to collapse? Do we, as design professionals, require that every user adhere to every rule in order to survive using our equipment?

 

It should not be legal for high voltage live parts to be exposed in an area where any imperfect human can walk into them. Ever.

 

Contractors are going to prop open the door to the hot, stuffy, vault when they are working there. You can put locks and alarms on the doors – they will figure out a way to get around them and get that door open to the fresh air. You can tell them to keep the vault door closed – but unless the foreman enforces the law and is present at all times – that door is going to be opened – making that room accessible to non-qualified persons – including children. You can require that contractors suit up whenever they are in a high voltage room – it isn’t going to happen. Oh, there are law abiding people. There are law abiding people who don’t think the law applies to them when it seems stupid. “I’m working on the other side of the room. I’m not going to be touching the high voltage parts.”

 

Exposed stabs scare me. If I need to be in such a room, I try to scare my employees as badly as I am scared. “Stay far away from that,” I tell them, “because, if you are near it and you trip, you die.”

 

On January 13, 2007, a college student did just that. According to the local newspaper, the young man tripped in a university high voltage vault, and he died. See:

http://www.jconline.com/apps/pbcs.dll/article?AID=/20070415/NEWS0501/704150350

 

We tend to make the victim guilty. “He’d been to a frat party; he was probably intoxicated. He ignored the railing in front of the door.”

 

There was no indication that he was inebriated – by all accounts, he was a model student and human being. He had left his coat in the building and was searching for a way in. He found the wrong door.

 

“The NEC is not designed to protect people from repeated stupidity,” you may say. “The vault door should have been locked. There should have been a sign. He shouldn’t have crossed the railing.”

 

Have you never forgotten to lock a door? Have you never seen stolen signs in college dorm rooms? Have you never crossed a railing?

 

Locks break; students pick them; people get carelessly comfortable in dangerous situations.

 

In this case, it seems that no law was broken. The vault was old, and was not required to have signage on the door. And the lock was old and there was no reason for it to be known if it was malfunctioning, because it was on a door that was seldom used.

 

All live parts over 100 V, no matter who has access, should be required by law to be enclosed to a height of at least 84”. All electrical room doors should have an immediately accessible working light switch with operational lights. These rules would have saved at least one life this year – and probably the lives of many others who died in a work-related accident that was discounted because the victim did not follow the rules.

 

If you know of other injuries or deaths related to exposed parts in high voltage vaults please post a comment with the details and your contact information.

 

Mike Holt’s Comment: The following is from the 2005 NEC, Article 110

 

III. Over 600 Volts, Nominal

 

110.31 Enclosure for Electrical Installations. Electrical installations in a vault, room, or closet or in an area surrounded by a wall, screen, or fence, access to which is controlled by a lock(s) or other approved means, shall be considered to be accessible to qualified persons only. The type of enclosure used in a given case shall be designed and constructed according to the nature and degree of the hazard(s) associated with the installation.

 

(B) Indoor Installations.

(1) In Places Accessible to Unqualified Persons. Indoor electrical installations that are accessible to unqualified persons shall be made with metal-enclosed equipment. Metal-enclosed switchgear, unit substations, transformers, pull boxes, connection boxes, and other similar associated equipment shall be marked with appropriate caution signs. Openings in ventilated dry-type transformers or similar openings in other equipment shall be designed so that foreign objects inserted through these openings are deflected from energized parts.

(2) In Places Accessible to Qualified Persons Only. Indoor electrical installations considered accessible only to qualified persons in accordance with this section shall comply with 110.34, 110.36, and 490.24.

(D) Enclosed Equipment Accessible to Unqualified Persons. Ventilating or similar openings in equipment shall be designed such that foreign objects inserted through these openings are deflected from energized parts.

 

110.33 Entrance and Access to Work Space.

(A) Entrance. At least one entrance not less than 610 mm (24 in.) wide and 2.0 m (6½ ft) high shall be provided to give access to the working space about electric equipment. Where the entrance has a personnel door(s), the door(s) shall open in the direction of egress and be equipped with panic bars, pressure plates, or other devices that are normally latched but open under simple pressure.

(2) Guarding. Where bare energized parts at any voltage or insulated energized parts above 600 volts, nominal, to ground are located adjacent to such entrance, they shall be suitably guarded.

 

(C) Locked Rooms or Enclosures. The entrance to all buildings, vaults, rooms, or enclosures containing exposed live parts or exposed conductors operating at over 600 volts, nominal, shall be kept locked unless such entrances are under the observation of a qualified person at all times.

 

Where the voltage exceeds 600 volts, nominal, permanent and conspicuous warning signs shall be provided, reading as follows:

DANGER — HIGH VOLTAGE — KEEP OUT

 

(D) Illumination. Illumination shall be provided for all working spaces about electrical equipment. The lighting outlets shall be arranged so that persons changing lamps or making repairs on the lighting system are not endangered by live parts or other equipment.

 

The points of control shall be located so that persons are not likely to come in contact with any live part or moving part of the equipment while turning on the lights.

 

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