Friday is a great time to post some of the stories that I have been reading this week.

• Copper thefts threaten infrastructure – This is something that happens more and more frequently whenever the price of copper increases.  I did notice that there were a lot fewer stories inthe local news regarding this type of theft when the price of copper dropped, but I expect it will be picking up again soon.
• Power lost in the Tenderloin - Well this story is actually about power being restored, but it seems that there was a blast in one of the underground vaults in the Tenderloin Area of San Francisco.  It piqued my interest when I was scanning Google News since last time I was in San Francisco (my first trip there) we stayed 2 blocks from this area.  It is by far the sketchiest place that I have ever been.
• Relationship between CEC and CSA Z462 – I found this in my Google Alerts, anything related to the recent release of CSA Z462 is interesting to me.  I am particularly interested in how industry is deciding to implement it.
• Devices to enable better control of Renewable Energy Sources – This is one of the things that I feel most people are over looking with their rush to put more renewable sources on the grid.  The North American electrical grid was not designed with these type of intermitent energy sources in mind.  The simple fact that you can’t reliably predict when the wind is going to blow, or if it is going to be cloudy is a major factor regarding the stabilization of the grid during heavy load.

If you have a link that is interesting please post it in the comments.  I have a wide range of interests when it comes to the Electrical Energy field, and safety in general.  If you have a link to a particular Arc Flash or other safety incident I am particularly interested in reading about it.

When an Arc Flash Study, currently being referred to an Incident Energy Study, is completed owners and operators start to look for ways to minimize the workers exposure to high incident energies.  One of the ways that this can be done is to ensure that all work is completed in a zero energy state.

This is not always possible, and when operating disconnecting devices the worker may be in danger.  Following are some options that can be used to reduce the incident energy, and associated flash protection boundaries.

1. Tighter Protection Coordination

One of the first steps to lower the incident energy of an arc fault is to review the Protection Coordination Study surrounding the specific buses that a lower incident energy would be attractive at.  The traditional philosphy regards to protection coordination is to ensure that faults are isolated in a strictly predictable manner.  This means that there is space on the Time-Current Curves to ensure that the protective device that trips is the one that the operator expects.

These studies are coordinated at worse case, a bolted fault, and an arcing fault will always be at a lower value.  This results in the required protective device taking longer to operate than is desired.  If possible a facility may be able to use a slightly smaller fuse, or tweak the breaker settings to use less space between the protective devices and in turn allow the desired device to trip sooner.

The negative of doing this is that in higher current faults the devices may not be coordinated, this may cause an up-stream device to operate extending the range of the outage unecessairly.

2. Selective Protection Coordination

There are new technologies being developed and released to the market everyday.  One of the technologies that I have been more impressed with is the ability to have multiple sets of Time-Current Curves installed in a circuit breaker.  These curves are selectable with a switch either on the wall of the electrical room or mounted on the breaker enclosure.  This will allow the operator to change the characteristics of teh breaker and have it trip in the instantaneously for a larger range of currents.  When this happens the clearing time of a fault is significantly reduced and in turn so is the incident energy.

When the breaker is in this instantaneous range it is no longer coordinated with the devices downstream from it.  If the worker does not replace the device in its normal operating mode when work is complete there is a significant risk of it operating when there is a fault, which will then shutdown more of the facility than is required.

Another consideration to remember when this method is used is that the breaker that feeds the equipment that is to be worked on must be the one that is altered.  If that breaker is in the same enclosure, then in most cases, the next up stream breaker must be moved into the instantaneous range.  The reasoning behind this is that there is still a risk of the feeder breaker located in the enclosure faulting which would then require the upstream breaker from it to operate to extinguish the fault.

3. Install a Fuse / Breaker

 I have included both these options in the same line on purpose.  If you have had a representative from either of these manufacturers give a presentation on Arc Flash from 2002 til recently I am sure that you have seen the fantastic videos showing how their respective equipment is the “bee knees” with regards to Arc Flash and reducing incident energy.

I believe that the reality of the matter is somewhat more complicated than replaceing your electrical infrastructure with one product and assuming that everything is going to work out fine.

My typical rule of thumb is this, if the available fault current is high, then fuses have the faster clearing time (as little as a ¼ cycle).  However if the fault current is lower a breaker may be the better way to go.

Conclusion 

There is never the perfect answer with regards to ways to reduce the Incident Energy of an Arc Flash.  Consult with the party that completed your study and with your operations people to determine what if any changes can be made to the system and operation to minimize the required PPE.  However always remember that PPE is the last line of defense and all other methods to ensure safe work procedures are employed are first.

 

If you have any suggestions or questions please let me know in the comments.

An arcing fault, which is the cause of an arc flash is described below.

Arcing faults (an Arc Flash) are defined as high-impedance faults, since any fault current must travel through air, as opposed to the low-impedance path normally associated with a short circuit. A short circuit study of the electrical system is required to determine the maximum available short circuit energy, which in turn may then be used to calculate the potential incident energy available.

There are intense heat and pressure waves associated with these types of faults.  This heat and pressure wave will cause shrapnel and molten metal to explode from the point of the fault.

The core temperature of an arc fault can easily reach 5000ºC (source), for comparison the surface temperature of the Sun is only 6000 ºC and the boiling point (not melting point, but BOILING) of copper is 2500ºC.

Assuming that the electrical protective device in the circuit operates fast enough to extinguish the fault so that these extreme temperatures do not cause greater than second degree burns to the operator, the ignition temperature of the typical non-PPE clothing the operator is wearing would have been reached, this burning will cause serious harm to the operator if they are not extinguished quickly

When proper PPE is worn for the calculated incident energy at the fault, the worker should walk away from the incident with a maximum of second degree burns.

Potential causes of an Arc Flash or Arcing Fault may include:

• Workers mistakenly dropping tools on live parts
• Pests entering switchgear through openings
• Faulty operation of a load break switch
• Dust or moisture accumulating to weaken air insulated bus bars
• Improper use of test equipment

From personal experience onsite and reading incident reports, the last three are the ones that are mostly likely going to be the cause of an Arc Fault.

Faulty Switches

Within an utility, institutional and industrial setting, electrical equipment does not always get the proper maintenance that it requires to have optimal operation.  With age, the ability of these mechanical devices to extinguish faults diminishes causing potential catastrophic failures

Electricians have been trained for a very long time to operate these breakers, switches etc from an arms length distance to the side.  This minimizes their body exposure to a possible failure.

Dust and Moisture

Industrial facilities such as refineries, pulp and paper plants, etc are not very clean environments, and as such there is a risk that there will be faults with electrical equipment due to the build-up of dust or introduction of moisture within the enclosures.  Modern company standards for electrical rooms have reflected this with the introdction of solid-state drives that are not as forgiving to dusty environments, and as such the new electrical equipment rooms are typically under static pressure to better control the enviroment.  PotashCorp of Saskatchewan is an example of one of the companies that are following this methodology.

This said, there are many existing electrical rooms that remain without such methodology.  To ensure that employees that usually work in these rooms are at the very least moderately protected, one company that I have worked with has a standard practice that anyone working in these rooms must wear 8 Calorie/cm² coveralls and safety glasses.  This level of PPE meets the majority of Incident Energy Levels within the electrical rooms in that facility.

Improper Use of Test Equipment

In the modern maintainence and operation of facilities the governing philosphy is to do all work on electrical equipment only after it has been grounded and isolated from the system.  This ensures that it is at a zero energy state and the risk of electrocution is minimized as much as possible.

There are still a number of situations that this is simply not practical, the most often offender being during commissioning or trouble shooting.  These activities most often requires the worker to test the voltage of the equipment to ensure they match the expected values.  With older test equipment, and cheaper modern equipment, there is a risk that the worker will not have the test equipment set properly.  If they try to check the voltage of a busbar while the meter is set for current, it acts like a short circuit and this will cause a fault that may lead to an arcing fault, which may lead to an ingury to the worker or people standing by.

What can you do.

One of the things that you can do to help mitigate a serious injury is to wear the correct PPE when working on equipment that has not be verified to be at a zero energy state.  Recent standard releases within North America (NFPA 70E in the US, and CSA Z462 in Canada) the level of PPE required when the possible incident energy is known.  If the levels are not known, speak with your managers and ask them to inform you of what the levels are.

When planning to work on live equipment, ensure that there is a job plan and everyone knows what their roles will be and what the emergency plan is.  With a comprehensive emergencuy plan an incident has a better chance to be contained and not excalating to harm others.

The TCU Student Paper is reporting that Employees injured in on-campus electrical accident it is expected that the cause of the injuries was an Arc Flash event.  To review what an Arc Flash Hazard click here.

There has not been details released regarding this event, so we do not know what the cause was, or what could have been done to prevent this accident.  Arc Flash Hazards are one of the least understood hazards within the workplace.  More than 2000 incidents occur every year, however it has only been recently that industry has begun to investigate methods to mitigate these problems within a market pressure that is requiring more and more matiance work to be done “on the run” without completely and effectively electrically isolating the equipment in question.

The the case at TCU, the proper PPE could have lessened the injuries.  Also if the accident happened during matience when the employees were exposed to live equipment, the equipment could have been de-energized.  If it happened while operating a breaker, the breaker may not have been maintained as per the manufacturer requirments.

There are many factors that can result in an incident.  I hope that there is a full report released on this incident and that the safety practices are revised.  TCU is lucky that the employees were only injured.

When an electric current passes through air between ungrounded conductors or between ungrounded and grounded conductors, the temperatures can reach 35000F.

Exposure to these extreme temperatures both burns the skin and causes the ingnition of clothing. Each year more than 2000 people are admitted to burn centers with severe arc-flash burns.

An arc-flash can and do kill at distances 10ft or greater.

Source: NFPA 70E-2004, Annex K.3

According to the title of the NFPA 70E standard it is the “Standard for Electrical Safety in the Workplace”. And that is just what it is. Now the better question would have been, do I need to understand NFPA 70E in my workplace?

Or how does NFPA 70E apply to me?

The typical workplaces that are covered by NFPA 70E are buildings, utilities, yards, parking lots, etc. However it does not cover ships, watercraft, underground mine installations, communication equipment and installations that are under the exclusive control of the electric utility.

In the last few years, NFPA 70E has been known synonymously with Arc Flash and Arc Flash PP. However that is only a small part of the standard in the whole. Arc Flash and Arc Flash PPE are covered only in Article 130, Working On or Near Live Parts. It is in this section that NFPA 70E talks about Limited Approach Boundarys as based on System Votage (Table 130.2(C)), the Protective Clothing and PPE Matrix (Table 130.7(C)(10)) and has many other useful tables to help to educate how to work on live equipment in the safest manner.

In fact if you go to the index the only place that the term Arc Flash is used is in Annex K. It is here where you can find a definition of what Arc Flash is, and the difference between Arc Flash and Arc Blast.

Some of the topics that NFPA 70E do discuss in depth is how to do maintence in different situations including Hazardous Locations, rotating equipment, Battery Rooms, and the PPE required in these situations. One thing the NFPA 70E stresses is that PPE is a last line of defense. Whenever possible Electrically and Mecahnically isolated the system that you or your employee is going to work on.

Finally NFPA 70E has great information in its Annexes. Some of this includes establishing a “Electrical Safety Program”, “Job Briefing and Planning Checklist” and “Cross reference Tables”.

If you work on energized equipment, even if it is only once a month or less. NFPA 70E will be evaluable to you in educating yourself and others on the risks involved and how to mitigate them most reasonably.

Finally if you liked this article or have questions please leave a comment.

Welcome to the site.  Sparky Resource is my pet project to discuss Arc Flash and all related matters.  I will be posting articles about NFPA, IEEE and other related materials.  Solutions, problems and news.

I hope to discuss the topic with little if any “sales prejudice” since I am a consulting engineer for a medium sized General Engineering firm.  I will discuss different presentations that I have been to that were given by fuse manufacturers, breaker manufacturers and try to point out the prejudices that are evident in what they say, and why you have to take everything that people tell you as defintes regarding Arc Flash with a grain of salt.

There will be some articles that will be technical in nature, so if you are reading this and don’t understand something please be sure to make a comment asking for clarification.  I will do my best to help you fulling understand the topics.