By no means is this article intended as the total training for installing electrical components in explosive environments. But there are some common cautionary items that even the most experienced technician will agree are baseline guidelines for anyone. You can't be too careful, nor can you take for granted the obvious. So I give to you the obvious.
1. Know your class/division standard
The NFPA Publication 70, NEC, and CEC are the most commonly used classifications in North America also known as the Class/Division system. The other system is known as the zone standard. Both systems are suitable and have been proven to be a safe standard to use. This document discusses the Class/Division standard.
2. Are there explosive gases or dust may in the installation area?
Enough said. Be careful.
3. Know what class of components you’re Installing.
There are three classes the components are categorized in:
Danger, Danger Will Robinson...Proceed with caution.
Class 1- Flammable vapors or gases may be present.
Class 2- Combustible dust may be present.
Class 3- Ignitable fibers or floating particles may be present.
4. Know what division your components are in.
When Installing Electrical Components in Explosive Environments, there are two divisions the components are categorized in:
Division 1- Ignitable concentrations of explosive hazards exists under normal operation and where explosive hazards can be caused by maintenance or equipment failure
Division 2- Ignitable concentrations of explosive hazards are handled, processed, or used but are in closed containers where they can only accidentally be released into the area.
5. Know what kind of gas you’re working w
There are four groups that gases have been separated into based on the maximum explosion pressure and the clearance needed between parts of a clamped joint in an enclosure. This can be found in the NEC section 500-5(a)(4) FPN no. 2
6. Know your Equipment’s Maximum Operating Temperature
The temperature classification is the maximum operating temperature that you should not exceed on the equipment’s surface which could create an ignition source. These classifications can be found in NEC section 500-5(d).
7. UL Publication 698 is the Industrial Control Equipment standard for use in hazardous locations.
Familiarize yourself with this publication before installing electrical components in explosive environments.
8. Know the Right Enclosure Type.
Type 7 Enclosures are designed to meet explosion proof requirements and Type 9 Enclosures are designed to meet dust ignition proof requirements. These are rated for indoor use. They can come with a Type 3R or 4 rating for outdoor use.
9. Know How to Seal Your Enclosures.
Conduit or cable seals must be used to prevent gas or dust from entering the enclosure through the cable entry point. You must seal the entry point within 18 inches of the entry point to the panel. Potted conduit or cable connectors are most commonly used for this.
10. Know Your Alternatives.
You can avoid using explosion proof enclosures by using intrinsically safe components. These components are designed so that they cannot produce enough energy to create an ignition source. These components, like positive pressure panels, use hermetically sealed components that are sealed by soldering, welding, or glass fusion to metal to stop any gases or dust from coming in contact with electrical arcs.
Josh McIver is a Field Applications Engineer in the Dallas office of Innovative-IDM. He can be reached at firstname.lastname@example.org