Top Electrical & Product Safety Mistakes for 2011

It’s a little early to close the books on 2011, but hopefully many of you are reviewing your 2011 goals and thinking about your plan for implementing your 2012 goals.  You should also be considering Electrical and Product Safety goals for 2012.

To assist you in making your Electrical and Product Safety goals for the upcoming year, I thought I would share the top safety mistakes that I have seen this year.

• Not using updated safety standards because they are (or seem to be) too expensive to procure
• Relying on equipment installers to correct any design errors
• Not performing a risk assessment
• Following standards and not understanding the merits of using risk assessments
• Not designing equipment so that maintenance can be accomplished safely
• Designers failing to recognize when they need to have safety experts involved
• Relying on Safety, Health & Environmental professionals to be experts in specific areas of safety, e.g. electrical safety, functional safety, etc.
• Relying on training and personal protective equipment (PPE) instead of designing out safety hazards
• Not using basic statistical techniques

Over the coming months, I will explore some of the safety mistakes from this list and provide you with suggestions, metrics, or concepts to help you reduce, minimize, or eliminate them within your organization.

In the mean time, if you have a list of safety mistakes or questions related to electrical and product safety, please send me an e-mail or give me a call.

Equipment Grounding Connections - Part 2

In the last posting, I noted that the grounding connection within an electrical cabinet needs to be accomplished in such a manner that there is a reliable contact between the ground conductor and the enclosure.  To ensure that a reliable contact is achieved, non-conductive materials (e.g. paint or lacquers) must be removed around the connection.

The next component of the grounding connection of the electrical equipment is to ensure that the connection is sufficient to a reliable connection over the length of use of the equipment.  One part of this is to ensure that screws or bolts that connect the ground conductor to the terminal and the ground terminal to the enclosure are properly tightened.  Component and hardware manufacturers publish proper tightness (torque) specifications in data sheets or other documents.  Terminals that are UL Recognized or UL Listed can be found on the UL website associated with the requirements for the specific component.

If tightness specifications are not available, other references can be used.  Common torque specifications for SAE Grade 6 and Grade 7 Carbon Steel are as follows [1,2]:

Bolt Size (inches)	Number of Threads	SAE Grade 6 Carbon Steel		SAE Grade 7 Carbon Steel
		Tightness (lb ft)	Tightness (Nm)	Tightness (lb ft)	Tightness (Nm)
1/4	20	12.5	16.9	13	17.6
3/8	16	43	58.3	44	59.7
7/16	14	69	93.6	71	96.3
1/2	13	106	143.7	110	149.1
9/16	12	150	203.4	154	208.8
5/8	11	209	283.4	215	291.5
3/4	10	350	474.5	360	488.1
7/8	9	550	745.7	570	772.8
1	8	825	1,118	840	1,139

Carbon steel hardware is typically used to connect the ground terminal to the enclosure.  Copper, brass, and aluminum are common materials used in hardware to secure ground conductors to the ground terminal.  The tightness specifications for hardware made of other grades of steel, copper, brass, aluminum varies depending on its size, the number of threads, and the inherent properties of the material itself. 

To properly tighten the hardware that secures the ground conductor to the ground terminal, and the ground terminal to the enclosure must be done to specifications and using appropriate tools (e.g. torque wrenches).  Relying on the strength or lack of strength of the technician or electrician is not appropriate for creating and maintaining a reliable connection.

References:

1.                  Glover, T.J. (ed) (1993), Pocket Ref.  Sequoia Publishing, Inc: Littleton, CO USA, p. 251

2.                  Unit Conversion, Torque Converter, Retrieved 2011 September 04, Available [on-line] http://www.unitconversion.org/unit_converter/torque.html

Equipment Grounding Connections

Most engineers, electricians, and equipment manufacturers know that conductive (metal) electrical cabinets are required to be properly bonded to earth through a grounding conductor.  Article 250.4 of the National Electric Code (NEC) details the requirements for the grounding and bonding of electrical enclosures in grounded (Article 250.4(A)) and ungrounded (Article 250.4(B)) systems.  While grounded and ungrounded electrical systems are different, the requirement for conductive materials that are likely to become energized (i.e. enclosures) are the same; they shall be installed in a manner that creates a low-impedance path for ground-fault currents.

In practice, how does one properly bond a conductive (metal) enclosure to ground, especially since these components are treated to resist corrosion? 

Article 250.12 of the NEC requires that all non-conductive coatings around threads and other contact surfaces shall be removed as to create good electrical continuity.  For enclosures constructed from aluminum or stainless steel, the process is straightforward as no corrosion resistance treatment is typically applied to the enclosures due to inherent corrosion resistant properties of the material.  To bond the enclosure to ground, simply install an equipment grounding terminal on the inside of the enclosure and connect the grounding conductor.

For enclosures constructed from steel, the process of properly bonding the enclosure to the grounding conductor is not as simple as placing a grounding terminal inside of the enclosure and securing it with a bolt and a nut.  Because paint or lacquers are used to prevent corrosion, they interfer with low-impedance connections and must be removed.  Proper removal of paint or lacquers or other corrosive protective coatings is not achieved by using “star washers” to “dig” into the paint.  While “star washers” can pierce the paint and lacquers, these devices are inconsistent in ensuring a low-impedance connection for ground-fault currents.  The only method for ensuring a low-impedance connection for ground-faults is to physically remove the paint or lacquer around the equipment ground lug terminal.  This can be achieved through sanding, masking or other methods.

To ensure proper bonding and grounding of the electrical equipment, make sure that the main grounding terminal and all other equipment bonding locations are properly cleaned prior to securing the ground lug to the enclosure. 

As a rule of thumb, the minimum amount of paint or lacquer to be removed should be twice the radius of the bolt or PEM stud used to connect the ground lug to the enclosure.  Equipment manufacturers, in some cases, have removed paint or lacquer around the equipment ground connection up to the size of the equipment grounding terminal (see above).  While removing a large portion of paint or lacquer to ensure a proper bond between the enclosure and the grounding conductor is acceptable, one needs to ensure that corrosion resistance of the steel enclosure is maintained. 


The actual area of paint or lacquer that is removed around the enclosure grounding connection depends on the type of grounding connection, specification requirements, testing requirements, and specific manufacturing processes.  In all cases, enclosures using paint or lacquers for corrosion resistance must be cleaned prior to connecting the grounding terminal to the enclosure.

What is your Design Safety Margin?

When designing components, equipment or machines, engineers use information from a variety of sources.  This could be information from specifications from a component manufacturer, customer requirements, or requirements from a safety standard.  To ensure sufficient tolerance in the design of the component, equipment or machine the design engineer needs to account for component, manufacturing, installation, and environmental variability.  Accounting for this variability is accomplished by incorporating a safety margin or de-rating factor into the design process. 

Example 1

Let’s consider the operating voltage of a general use AC capacitor.  The manufacturer‘s specifications state that the component has a maximum operating voltage of 600 V.  The equipment where this AC capacitor is intended to be installed in is to operate at 480 V with a tolerance of 10 percent.  The engineer establishes a 15 percent safety margin to the operating voltage of the capacitor.  Working through the math, the following is obtained:

1.                  Voltage tolerance of 480 V source is 408 V to 552 V.

2.                  New maximum operating voltage of the AC capacitor is 540 V

In this example, the maximum AC capacitor rated by the manufacturer was reduced from 600 V to 540 V.  Since the equipment is intended to operate on a power source that has voltage range up to 552 V, this capacitor should not be used or steps should be taken to ensure that the capacitor is appropriate for the limitations established.  This could include using an alternate component with a higher rated operating voltage, using capacitors in series, or controlling the voltage tolerance of the source.  It is never a good idea to reduce the safety margin unless a sound engineering analysis has been performed.

Example 2

Let’s consider the spacings between phases of opposite polarity for input terminal lugs of a power distribution unit (PDU).  The UL safety standard states that the terminal lugs shall have a spacing of least 1 inch at 480 V.  The PDU is intended to operate at 480 V with a tolerance of 10 percent.  The engineer establishes a 15 percent safety margin.  Working through the math the voltage ranges from 408 V to 552 V.  At 552 V the spacing between the terminal lugs is 1.15 inches.  Accounting for the defined safety margin, the spacing between the terminal lugs is increased to 1.33 inches.

In this example, the spacings of the field connected terminal lugs need to be increased from the dimension of 1.0 inch to at least 1.33 inches between phases of opposite polarity.  The increase in separation of the terminal lugs in the PDU may not affect the terminal lugs specified, but it may affect the particular location that they are installed.

Conclusion 

Every component, equipment or machine has specifications that can be subjected to the addition of a safety margin by the design engineer.  The addition of the safety margin may or may not change how a component, equipment or machine is designed, installed or used.  When incorporating a safety margin reduces the specifications to a point where the component, equipment, or machine is outside of the tolerances, alternative designs need to be considered.  Regardless of the actions taken, safety margins need to be considered in the design process of all equipment or machines. 

Product Safety & Risk Assessments

There is more to a safe product than exceeding safety requirements.  Assessing whether a product is safe, the product needs to:

·         Exceed all industry safety standards
·         Exceed all “best engineer practices”
·         Be designed for the intended environment and application
·         Be designed to protect users against foreseeable misapplications
·         Be provided with effective labeling and instructions

Assessing compliance to a specific industry standard is relatively straight-forward.  For an industrial control panel that is intended to be applied in the US, the following standards are minimum requirements:

·         OSHA 29 CFR 1910 – General Industry
·         UL 508A – Standard for Safety, Industrial Control Panels
·         NFPA 70 – National Electric Code
·         NFPA 79 – Industrial Machines

Depending on the technology deployed in the industrial control cabinet and its intended application, additional standards may be relevant.  This includes those related to electromagnetic compatibility, life safety, emergency power systems, hazardous conditions, etc.

When attempting to evaluate the equipment to intended environments and applications and to protect users from foreseeable misapplications, one needs to look beyond industry standards.  One method to analyze these scenarios is to perform a risk assessment.

A risk assessment is a tool used to identify hazard conditions associated with the design, manufacture, installation, operation or de-commissioning of the product.  The major components of risk assessment are:

·         Identify the hazards
·         Assess the hazards
·         Develop controls & make decisions
·         Implement controls
·         Supervise and evaluate

When a thorough risk assessment is used in conjunction with meeting industry standards, “best engineering practices”, and proper labeling and instructions, the product will be better designed than those that do not undergo a risk assessment, and be less likely to cause injury from normal or abnormal operation.

In addition to the increased safety attributes from conducting a risk assessment, there are also financial incentives for an organization.  This includes those associated with increased profitability as fewer resources are required to be accrued to account for the potential of product damages, recalls, or related injuries.

Product Safety

Product safety is an essential aspect of the design and deployment of any product into the marketplace.  Many manufacturers are aware of the requirements to have their product evaluated to national or international safety or performance standards (e.g. ASTM, ANSI, IEC, IEEE, NFPA, UL, SAE).  However, these standards are only the minimum requirements.

Companies need to go beyond meeting minimum product safety standards for two reasons: legal and financial.

Legal Aspects of Product Safety:

The US courts have ruled that a company that merely complies with the minimum product safety standards has done an insufficient job of evaluating the safety of their product.  The US and international courts have also ruled that companies that have been subjected to product safety recalls of their products must report these cases to other markets where the products are sold.

Financial Aspects of Product Safety:

If a company’s product is subjected to a recall, either forced by a government or voluntary because of a poor design, the company can struggle with market acceptance of current or future products.  This reduces the sales and profit potential of the company. 

Large companies can overcome the negative consequences associated with products that have poor safety records or that face product safety recalls.  But, at what costs too marketshare, earnings potential, or overall corporate image? 

Small and medium size companies typically do not have the financial resources to overcome poor product performance or product safety recalls.  These companies are usually required to liquidate, sell out, or are reduced to much smaller organizations.

To avoid product recalls or reduce product failures in general, the best method is comply with all relevant national and international standards regardless of where the product is being sold, to thoroughly review the design and performance attributes of the product, and to perform risk assessments on how the product is intended to be used and not used by the customer.