Electricity: conductors and insulators – With fluids or vacuum – Boxes and housings
Reexamination Certificate
1999-04-14
2002-04-16
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
With fluids or vacuum
Boxes and housings
C174S067000, C220S242000
Reexamination Certificate
active
06372983
ABSTRACT:
FIELD OF THE INVENTION
The present invention provides an enclosure for protecting electrical components installed in a location where a flammable gas or vapor is expected to be present.
BACKGROUND OF THE INVENTION
Enclosures may be used to provide protection for an electrical component such as, for example, an electrical switch, a motor starter, a motor, or an electrochemical fuel cell. These enclosures are typically accessible by opening so that the electrical component placed within the enclosure housing may be accessed and/or serviced. Thus enclosure housings typically comprise at least two pieces that fit together to provide a protective enclosure around the electrical component. In addition to protecting the electrical component against physical damage, in locations where a flammable gas or vapor may be present, it is also desirable for the enclosure to protect the electrical component from exposure to combustible concentrations of the flammable gas or vapor which the electrical components may ignite. So called “restricted breathing” enclosures typically employ gaskets or other sealing mechanisms between separate housing pieces to improve the sealing between the separate pieces. Restricted breathing enclosures are constructed so that the likelihood of a surrounding atmosphere entering the enclosure is reduced to as low a level as possible.
However, gasketed or “sealed” enclosures can not guarantee complete sealing against the penetration of flammable gases by diffusion. This is especially true for gases with a high diffusion rate, such as hydrogen. In addition, it is also believed that even gasketed enclosures “breath” (i.e. fluids pass between the surrounding atmosphere and the enclosure interior). Breathing may be induced by pressure differentials between the enclosure interior and the surrounding atmosphere. Such pressure differentials are affected by temperature changes caused when heat producing components are operated within the enclosure. There may also be other causes for flammable fluid penetration into the interior of an electrical component enclosure, such as, for example, defects in the seal or misalignment of the seals. Furthermore, in addition to flammable fluids which may originate from the atmosphere surrounding the enclosure, flammable fluids may also originate inside the enclosure from electrical components themselves, such as, for example, electrochemical fuel cells.
Therefore, unsealed or even “sealed” openable equipment enclosures, may allow flammable fluids to accumulate therein because of diffusion, breathing, or internal generation of flammable fluids. Thus, when an enclosure is installed in a location where a flammable fluid is expected to be present, it is recognized that there is a potential for a combustible concentration of the flammable fluid to accumulate within the enclosure. Accordingly, for electrical components capable of igniting flammable fluids, electrical codes require particular types of enclosures to be used when such components are installed in a location where a flammable fluid is expected to be present. The nature of the required enclosure depends upon the likelihood and expected frequency of a flammable fluid being present, and other factors such as the likely duration of exposure and the concentration of the flammable fluid. Because these factors may be different at different locations, some electrical codes define different zones which reflect the degree of exposure associated with locations where a flammable fluid is expected to be present.
For example, the Canadian Electrical Code defines such locations as being a Zone
0
, Zone
1
, or Zone
2
location. A Zone
0
location refers to locations where there is the greatest exposure to a flammable fluid. In a Zone
0
location, a flammable fluid atmosphere is expected to be present either continuously or for long periods. A Zone
1
location refers to the next level of exposure to a flammable fluid. For example, Zone
1
typically refers to locations where exposure to a flammable fluid is not continuous, but a flammable fluid atmosphere is likely to occur either during normal operation, or frequently because of repair or maintenance operations, or because of leakage. Also, a location may be classified as a Zone
1
location if it is adjacent to a Zone
0
location from which flammable fluid atmospheres could be communicated. A Zone
2
location typically refers to a location where there is a possibility of exposure to a flammable fluid, but the likelihood of such an exposure is less than in a Zone
0
or Zone
1
location. For example, exposure to a flammable fluid may occur during system upsets or by being adjacent to a Zone
1
location where a flammable fluid is expected to be present. In Zone
2
locations, exposure to flammable fluid is not likely to occur during normal operation, and if flammable fluid is present, for example, because of a system upset, the flammable fluid is only expected to be present for a short period of time. The aforementioned Canadian Electrical Code generally conforms with international electrical codes such as, for example, International Standard IEC
79-15: 1987.
The Canadian Electrical Code sets out the type of electrical component enclosure that must be used in Zone
0
, Zone
1
and Zone
2
locations. For example, the Canadian Electrical Code requires a special flame-proof enclosure for most electrical components installed in Zone
1
or Zone
2
locations. Flame-proof enclosures are also known as explosion-proof enclosures. In Zone
1
and Zone
2
locations, because some exposure to flammable fluids is expected, it is assumed that flammable fluids will eventually accumulate within the flame-proof enclosure. These flame-proof enclosures are made to withstand an internal explosion so that when flammable fluids do accumulate within the enclosure, and are ignited by internal components, the flame-proof enclosure safely contains the explosion. Flame-proof enclosures are designed to contain explosions rather than to prevent them; accordingly, flame-proof enclosures do not depend on keeping flammable fluids outside the enclosure, so these enclosures typically do not employ gasket seals.
However, a problem with flame-proof enclosures is that because they are made to withstand an internal explosion, they are heavy, physically large, and relatively expensive. For example, a model EJB 106 flame-proof enclosure made from cast aluminum by Crouse Hinds, A Division of Cooper Industries, Syracuse, N.Y., weighs about 28 pounds and costs about US $600 compared to a similar sized non-flame-proof enclosure made from plastic or sheet metal that weighs about 5 pounds and costs approximately US $60. Another problem is that, while flame-proof enclosures may contain the explosion, they do not prevent an explosion. Accordingly, the components to be installed in such enclosures are generally made more robust to survive such explosions, adding to the weight, size, and cost of such components.
Accordingly, there is a need for an electrical component enclosure for use in Zone
1
or Zone
2
type locations that is lighter, smaller, and less expensive than a flame-proof enclosure. There is also a need for an electrical component enclosure that may be used in Zone
1
or Zone
2
type locations that prevents flammable fluids from igniting within the enclosure, so that smaller, lighter, and less expensive components may be installed in enclosures located in environments where a flammable fluid is expected to be present.
In Zone
2
type locations, Canadian and international electrical codes require flame-proof enclosures for electrical components which during normal operation generate sparks or have hot surfaces capable of igniting the flammable atmosphere. However, for electrical components that can only ignite the flammable atmosphere during a component failure, gasketed restricted breathing enclosures instead of flame-proof enclosures are permitted. Restricted breathing enclosures are lighter, smaller, and less expensive, compared to flame-proof enclosures. Restric
Ballard Generation Systems Inc.
McAndrews Held & Malloy Ltd.
Nino Adolfo
Reichard Dean A.
LandOfFree
Enclosure for electrical components installed in locations... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Enclosure for electrical components installed in locations..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Enclosure for electrical components installed in locations... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2913297