NEMA 4X - Type 4X enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against corrosion, windblown dust and rain, splashing water, and hose-directed water; and to be undamaged by the formation of ice on the enclosure. they are not intended to provide protection against conditions such as internal condensation or internal icing.

NEMA 12 - Type 12 enclosures are intended for indoor use primarily to provide a degree of protection against circulating dust, falling dirt, and dripping noncorrosive liquids. They are not intended to provide protection against such conditions as internal condensation.

NEMA 13 -Type 13 enclosures are intended for indoor use primarily to provide a degree of protection against lint, dust, spraying of water, oil and noncorrosive coolant. They are not intended to provide protection against conditions such as internal condensation.

Stealth Computer Corporation has embraced these NEMA industry standards to ensure higher quality products offering benchmark comparisons for our customers.

COMPARISON BETWEEN NEMA ENCLOSURE TYPE NUMBERS AND IEC ENCLOSURE CLASSIFICATION DESIGNATIONS

NEMA Enclosure Type Number	IEC Enclosure Type Number
NEMA 4 & 4X	IP56
NEMA 12	IP52
NEMA 13	IP54

NOTE: This comparison is based on tests specified in IEC Publication 529

TABLE A-1 CONVERSION OF NEMA TYPE NUMBERS TO IEC CLASSIFICATION DESIGNATIONS (CANNOT BE USED TO CONVERT IEC CLASSIFICATION DESIGNATIONS TO NEMA TYPE NUMBERS)

What is Intrinsically Safe?

Intrinsic safety is a protection concept deployed in sensitive and potentially explosive atmospheres. Intrinsic safety relies on the equipment being designed so that it is unable to release sufficient energy, by either thermal or electrical means, to cause an ignition of a flammable gas.

Intrinsically safe is achieved by limiting the amount of power available to the electrical equipment in the hazardous area to a level below that which will ignite the gases.

In order to have a fire or explosion, fuel, oxygen and a source of ignition must be present. An intrinsically safe system assumes the fuel and oxygen is present in the atmosphere, but the system is designed so the electrical energy or thermal energy of a particular instrument loop can never be great enough to cause ignition.

Traditionally, protection from explosion in hazardous environments has been accomplished by either using explosion proof equipment which can contain an explosion inside an enclosure, or pressurization and/or purging which isolates the explosive gas from the electrical equipment.

Intrinsically safe equipment cannot replace these methods in all applications, but where possible can provide significant cost savings in installation and maintenance of the equipment in a Hazardous area. The basic design of an intrinsic safety barrier uses Zener Diodes to limit voltage, resistors to limit current and a fuse.



Most applications require a signal to be sent out of or into the hazardous area. The equipment mounted in the hazardous area must first be approved for use in an intrinsically safe system. The barriers designed to protect the system must be mounted outside of the hazardous area in an area designated as Non-hazardous or Safe in which the hazard is not and will not be present.

APPROVALS
Intrinsic safety equipment must have been tested and approved by an independent agency to assure its safety. The customer should specify the type of approval required for their particular application. The most common Agencies involved are as follows:

The ever-present Universal Serial Bus (USB) is now a standard feature on virtually every new PC. The "jack-of-all-trades" nature of USB has made it ideal for connecting additional peripherals without opening the computer. The drawback of the original USB standard (v1.1) was its relatively slow speed however most new PCs have adopted version 2.0 offering theoretical speeds up to 480Mbs. Both USB and Firewire feature "hot-swapping", which means you won't need to shut down and reboot your PC to attach or remove a peripheral.

FireWire, (technically known as IEEE 1394) is a serial input/output technology invented by Apple Computer with data transfer rates up to 400 megabits per second. A FireWire upgrade has been released and IEEE 1394b will offer transfer rates of up to 800 Mbps, reportedly fast enough to copy an entire CD in seconds. Firewire 800 is starting to show up in the market now with mass-market adoption expected in 2004.

While the two serial buses seem similar, they are intended to fulfill different bandwidth and cost needs. 1394 can move more data in a given amount of time, but is considerably more expensive than USB due to its more complex protocol and signaling rate. Applications that are best suited for 1394 are disk drives, high quality video streams and other high bandwidth applications. USB is appropriate for middle and low bandwidth applications such as audio, scanners, printers, keyboards, and mice.
USB and 1394 are complementary technologies. 1394 is for devices where high performance is a priority and price is not, while USB is for devices where price is a priority and high performance is not.

• www.usb.org
• standards.ieee.org

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