Questions:
- Does the electrical guarding requirement at 29 CFR 1910.303(g)(2)(i) apply to voltages below 60 volts DC?
2. Will OSHA treat a failure to guard live parts operating below 60 volts DC as a de minimis violation?
Answers:
- The requirement applies to live parts operating at 50 volts or more AC or DC. The requirement does not distinguish between AC and DC voltages.
2. For a violation to be considered de minimus, the employer must be found to have deviated from OSHA standard requirements in a way that did not directly cause employee injury or contribute to employee health issues.
“You point out in your letter that some consensus standards consider live parts operating between 50 and 60 volts, DC, to be non-hazardous under certain circumstances. However, OSHA considers all voltages of 50 volts or above to be hazardous. Electric current, not voltage, passing through the human body causes injury, and the amount of current passing through an object depends on the resistance of the object.” (Boldface added by e-Hazard.)
“As explained in Appendix C to 29 CFR 1910.269, the internal resistance of the human body is 500 ohms, which is the minimum resistance of a worker with broken skin at the point of contact. The current through 500 ohms from a live part energized at 60 volts would be 120 milliamperes. This level of current, either ac or dc, is sufficient to cause serious injury.”
OSHA pointed out that serious injuries occurred in situations where the worker was exposed to only 12-volt or 24-volt DC vehicle batteries. While their 1910 standard states guarding is necessary for electrical equipment for 50V and above, the letter states that equipment under 50 volts is not always completely safe, either.
Due to the limits of a de minimus definition and in the light of what actually causes electrical injury, a violation of 1910.303(g)(2)(i) would NOT be considered a de minimus violation.
In our Low Voltage and High Voltage classes, we at e-Hazard stress the importance of creating an electrically-safe work condition. Even at voltages less than 50V AC or DC, hazardous situations can be presented to the electrical worker due to high amperage sources, explosive potential, or excessive electrical arcing.
Electrical safety is assured only with a proper workplace hazard evaluation. Energized work less than 50 volts (AC or DC) needs to fall in line with the requirements of NFPA 70E 130.2(A)(3).
Is there minimum clearances in front of a junction box that contains 50 volt or less wiring as per NEC.
The requirements to maintain clearances in front of electrical equipment in Article 110 appear in 110.26. The working space requirements are for “equipment operating at 600 volts, nominal, or less to ground and likely to require examination, adjustment, servicing, or maintenance while energized.” The article continues by stating the following:
“Access and working space shall be provided and maintained about all electrical equipment to permit ready and safe operation and
maintenance of such equipment.”
Electrical equipment in the NEC is defined as “a general term, including fittings, devices, appliances, luminaires, apparatus, machinery, and the like used as a part of, or in connection with, an electrical installation.” So technically, one could consider a network junction box “electrical equipment” and enforce the requirements of article 110.26. Table 110.26(A)(1) provided in this section states that from 0-150 volts, the minimum requirement for equipment 0-150 volts is a 36″ working space. Nothing can be stored or mounted in this space. The area must be kept clear for accessibility reasons.
Of course, as in other places throughout the NEC, exceptions exist. 110.26(A)(1)(b) specifically mentions low voltage equipment, allowing equipment not greater than 30 volts rms, 42 volts peak, or 60 volts dc to have smaller required clearances, but only by special permission. This special permission must be given by the Authority Having Jurisdiction.
So, back to your question on the low voltage junction box. The key to the answer revolves around the statement “access while energized.” Most low voltage junction boxes will not require “access while energized,” unless this particular junction box is used for voltage testing with exposed low voltage terminations. In my years of networking, I never had a junction box meet this requirement, as almost all network connectors completely cover the wiring being terminated. This eliminates “exposure” in the technical definition of the word.
Think back to a common 120 volt junction box in a home. These are often found in an attic, mounted in a tight space. This j-box would not be a code violation because one would not expect this situation to be one “likely to require examination, adjustment, servicing, or maintenance while energized.”
In my opinion, unless a very unique situation occurs, a typical network junction box would not require the working clearance access as defined by the NEC. As always, though, it is a very good idea to discuss this with your local electrical inspector, as this person is the AHJ and does have final authority in these gray areas of the NEC.
Arc welding involves open circuit (when not welding) voltages which are typically from as low as 20 volts to as high as 100 volts. How does 70E consider this as it is intentionally a power source for an open electrical arc?
Arc flash is not arc welding and that activity is covered by welding standards and work practices. Plugging and unplugging the welder is covered as is operating disconnects feeding it.
We desire to install a circuit breaker and power supply inside our arc flash enclosure. Enclosure is attached to side of main box and is interlocked to its door. We hope to keep communications, PLC power and lighting ON while arc flash box is locked out. I thought there was a rule about placing components inside disconnect boxs. Been looking and cant find a reason why this cant be done. Can you help me sort this out?