User Electronic and Electrical Equipment Inspection Criteria
Any electrical or electronic equipment users bring to the APS will have to be inspected. In some cases, this inspection will be quite simple, e.g., if the equipment has already been inspected by a Nationally Recognized Testing Laboratory (NRTL) and is used for its designed purpose. Other equipment will require a more thorough inspection (this may include NRTL inspected equipment if it is assembled into an apparatus with other components). The inspection is based on an eight-part list of criteria. Paraphrased, those criteria are:
- The equipment must be suitable for its intended use (and if appropriate, installation). For example, a heater controller intended to control a 1000W heater cannot be used to control a 2000W heater. The equipment, if powered from line power, must have a properly rated short-circuit safety device (fuse or circuit breaker).
- The mechanical construction of the equipment must be sufficiently robust. Remember that a beamline is not an electronics test laboratory; equipment may get rough handling and must be able to withstand that without presenting hazards, either to users or to other equipment. Enclosures must be able to contain any electrical faults and must prevent users from coming into contact with live parts.
- The internal wiring must be neatly done and carefully routed. Wires must be of sufficient size (gauge) to carry the currents present or potentially present, and must be properly insulated for the voltages on them. Proper grounding must be present.
- Any exposed electrical conductors must be insulated. For example, a barrier terminal strip mounted on the outside of equipment must be covered. In joining wires, wire-nuts and electrical tape are not allowed. External connectors must be appropriate to the purpose; for example, AC-cord-type connectors cannot be used to connect heaters to controllers.
- The equipment must be able to withstand the heat it generates in use, even in the case of failures (e.g., short circuits), without presenting further hazard. No external part, unless protected by guards, can become hot enough to cause burns.
- Any device which will allow arcing (switches, for example, or mechanical relays used to control power to other devices, like heaters) must be able to contain those arcs.
- Equipment should have labels stating the proper input power (e.g., if AC line powered, the label should state the required voltage, frequency and current), the intended use of the equipment and any cautions regarding its use.
- The equipment must, in general, not present any hazards to users. This includes factors besides electrical concerns. For example, enclosures should not have sharp edges where users can contact them.
These rules are simply those of general good practice in instrument construction. If you are unfamiliar with proper construction techniques, you should consult with experts before you begin building your equipment. For unique equipment or equipment of your own design, you should be prepared to present documentation of the design, especially an electrical schematic.