Appendix O: Guidelines


O1: Guidance on Instrumentation Crates and Bins

Classifying Certain Modular Instrument Equipment as LBL Class 1B:

Classifies in advance certain instrumentation module systems, and data collection systems, as Class IB equipment under Appendix P of LBNL/PUB-3000, Chapter 8, Electrical Safety.

The LBNL ESC considers, under the conditions listed below, VME crates, CAMAC crates, and similar modular instrumentation system crates or bins, as Class IB equipment, under the definitions in Appendix P of Chapter 8, Electrical Safety, of the LBNL Publication 3000. The conditions for Class 1B consideration are:

  1. All AC line power for the bin or crate comes from one source, and all wiring is confined to shielded, grounded enclosures;
  2. No AC power, higher than Class 1B, is exposed at the back plane of the crate or bin;
  3. No single power supply output exceeds 50 V with respect to ground, unless it is current-limited to 5 mA, maximum;
  4. No single power supply is capable of more than 1000 watts output;
  5. The crate or bin is not modified (excepting (a) insulating barriers added for protection, and/or (b) fuses or load breakers added for power limitation) in any way that exposes the user or others to Class 2B hazards, or higher;
  6. Module extenders that expose hazards of Class 2B or higher may not be considered as Class 1B components.

If all the numbered conditions listed here are met, the crate or bin may be treated as Class 1B equipment under Chapter 8 rules.

The burden falls to the researcher and supervisor to ensure these conditions are met if the equipment is to be treated as Class 1B. Otherwise, it is considered Class 2B, or higher. Publication 3000, Chapter 8, or members of the LBNL Electrical Safety Committee, the LBNL Electrical Safety Engineer, or the Division Safety Coordinator can provide advice and guidance to classification and requirements. The intent is to allow work on these modules by knowledgeable researchers who may not have become “qualified electrical workers” so long as there is no potentially fatal, direct electrical hazard.


Background and Intent — Classifying modular instrument equipment as LBL Class 1B:

The entire DOE research community uses popular, standardized modular electronics systems for certain data collection equipment and for experiment timing and control systems. This proposal will define VME, VXI, CAMAC, and certain other low-hazard modular systems as Class 1B equipment (within LBNL/PUB 3000, Chapter 8, requirements) to allow experimenters who are not classified as “qualified electrical workers” to use this equipment and make certain repairs and adjustments on this equipment, so long as they are not exposed to Class 2B, or higher level hazards (voltages above 50 V, if capable of more than 5 mA, or power levels above 1 kW). The user so working assumes the obligation to ensure the equipment is within Class 1B, and to stop work if exposed to voltage above 50 V

Most modular systems use multiple smaller power supplies to provide low voltage power to the modules used. The low voltage power supplies are under 50 volts output. Further, the power available from any one power supply section is normally below 1 kW and does not rise out of hazard Class 1B. Unless a user is directly exposed to AC line voltage, the entire system may be considered as Class 1B equipment, which does not require the user to be a qualified electrical worker.

The user may not consider the equipment as Class 1B if there is any possibility of contacting any two power supplies whose combined output voltage will provide more than 50 V, unless the combined current is limited to 5 mA, and the combined power is limited to 1 kW.

At times, it may be necessary to open one of these modules while the equipment is in the energized state for troubleshooting or making adjustments. This is usually impossible to do while the module is in the bin or crate, so an extender fixture (a card, or cable) must be used to move the module of interest out of the bin or crate so covers can be removed and circuitry accessed. NIMs (Nuclear Instrumentation Modules), when mounted on an extender, may expose the user to 120 V AC: for this reason, any module with 120 VAC power inside it (most often NIMs), must be considered Class 2B, and can only be worked on by a qualified electrical worker, as defined in Chapter 8 of LBNL/PUB- 3000. In addition, proper PPE (personal protection equipment) must be used, and the work requires a job briefing and, at a minimum, supervisor’s approval. It is possible an energized work permit is required.

The burden falls to the researcher and supervisor to ensure these conditions are met if the equipment is to be treated as Class 1B. Otherwise, it is considered Class 2B, or higher. Publication 3000, Chapter 8, or members of the LBNL Electrical Safety Committee, the LBNL Electrical Safety Engineer, or your Division Safety Coordinator can provide advice and guidance to classification and requirements. The intent is to allow work on these modules by knowledgeable researchers who may not have become “qualified electrical workers” so long as there is no potentially fatal, direct electrical hazard.

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