Introduction

This control panel is like thousands of control panels out in facilities today, and maybe even many in your facility. It controls a machine on the factory floor. It has four motor starters, individual circuit breakers for those motor circuits, ice cube relays, small fuses, and a control transformer. And on the door there are pushbuttons, indicating lights, rotary switches. In the lower right

corner of the panel is the main circuit breaker. With the door closed, we can still operate the breaker through the hole in the door. Pretty typical of many control panels. The question is how do we de-energize this panel to establish an electrically safe work condition.

Circuit Breakers

Circuit breakers have a line and load side. The line side is where the incoming power is connected. The load side is where the downstream loads are connected. In this case, the downstream loads are everything else in this panel and all of the motors and other components in the control circuit outside the panel. Everything downstream from this main breaker is being protected from over-currents by this breaker.

The question is, does this circuit breaker de-energize this panel? The answer is no. Opening this breaker de-energizes everything in this panel as well as the downstream loads, everything except for the line side of the breaker itself. When this circuit breaker is opened, turned off, the line side of the breaker is still hot. With the line side still energized by the incoming power, the panel has to be considered energized because the main breaker still has a shock and arc flash hazard. You could not use this breaker to establish an electrically safe work condition for this panel.

Electrically Safe Work Condition

To properly de-energize this panel to establish an electrically safe work condition, you would need to locate the circuit breaker or disconnect that feeds power to your control panel. Your lockout tagout procedures should indicate the location of this breaker or disconnect. Once that is found you would open that disconnect or circuit breaker and apply your locks and tag. Return to the control panel and follow through with all of the required lockout tagout procedures. The most important of which is the live-dead-live test to verify zero voltage. Always Test-Before-Touch. And of course, always wear the required PPE while verifying zero volts. Every circuit has to be considered energized until you’ve proven it’s not.

Troubleshooting Example 1

As a troubleshooting example, let us use a situation in which the operator of this machine reports that one of its four conveyors stopped running. You show up and ask the operator what led up to this problem, and they state that that conveyor has been making a lot more noise than usual. A squealing sound. You suspect a mechanical problem, and on an inspection of the conveyor pulleys, it is evident that a bearing has failed thus causing too much load on the motor. Next, we go to the control panel and see that it has an arc flash label that states an arc flash rating of 11 cal/cm2 and a voltage of 480. We must don the appropriate PPE to protect you from such an arc flash and voltage. Because we are only going to do a visual inspection and we are wearing the proper PPE we can proceed. We do an orderly shutdown of everything the panel controls then open the main breaker. We then open the control panel door and see that the motor starter has tripped for that motor. Everything else in the panel appears fine, we reset the motor starter, and close the door. We place our lock and tag on the main breaker, and we perform all other procedures required by our lockout tagout procedures and proceed to repair the bearing.

Troubleshooting Example 2

In the next example, the operator reported the conveyor wouldn’t turn on. There was no mention of a squealing noise. During our initial troubleshooting, we attempt to turn on that conveyor manually and we hear the motor starter turn on, or pull-in as we say,  inside the cabinet. But, the conveyor is still not moving. We don the appropriate PPE, open the control panel door and begin our visual inspection of the panel. We immediately notice the motor starter for conveyor four is showing signs of heat damage. A  dark smoke-like film is on the area covering the motor starter contacts. This, we know from experience, is an indication of poor contact being made by the starter contacts. The other starters don’t show this damage. Now we know we are going to have to remove and replace the starter or at least disassemble it for inspection and repair. In either case, we’ll need to completely de-energize the panel. At this time we’ll need to close the control panel door and open the main breaker. We then must go to the upstream circuit breaker for this panel, turn it off and apply our lock and tag. Upon returning to the control panel, wearing the appropriate PPE we open the control panel door. Using an appropriate volt-meter, we test that meter on a known live circuit, then measure incoming line leads phase-to-phase and phase-to-ground and do verify that we indeed have zero volts. We then retest the meter on a known live circuit to confirm the meter is still working. That is the Live-Dead-Live test. Now we can remove the PPE and begin our repair work. We find the contacts badly damaged from not making proper contact and the carbon buildup inside the starter is preventing the contact assembly from moving freely. We replace the motor starter, and now all conveyors are working fine.

A Shield May Not Work

Some people have suggested that if you add a plastic or metal shield to the main breaker that covers the energized line leads that should solve the problem. It actually can create a whole new problem. OSHA requires electrical equipment to be “accepted, or certified, or listed, or labeled, or otherwise determined to be safe by a nationally recognized testing laboratory.” Underwriters Laboratory is such a lab. If you add a plastic or metal shield to your breaker, it is no-longer UL Listed because it didn’t have your shield when tested. The shield could cause the breaker to operate differently than when it was manufactured and tested, resulting in an unsafe situation.

Control Panel Design

This next piece of advice doesn’t help you with existing control panels but could make your future panels safer and easier to work with where 70E is concerned. That advice is to ask the OEM of your new panels to put this main breaker in a separate box on the side of the panel. Putting the main circuit breaker in a separate enclosure is becoming quite common now, and manufacturers of these boxes are offering this option. Hoffman’s SEQUESTR line of enclosures is one such offering.

Circuit Breaker Panel Boards

I used a control panel as an example here, but all of this applies to circuit breaker panel boards as well, not just control panels. Opening the main breaker of a circuit breaker panel does not establish an electrically safe work condition. If you’re going to add a circuit breaker, for example, turning off the main breaker for the panel board is not sufficient. You will need to open the circuit breaker that feeds this panel to establish an electrically safe work condition.

Conclusion

In conclusion, it is essential that we know what does and what does not make an electrical panel electrically safe. It must be spelled out in your lockout/tagout procedures which disconnect, or circuit breaker removes power from the equipment that will enable us to create the electrically safe work condition. We will wear the appropriate PPE any time the equipment has an energized circuit component above 50V.

Relevant courses

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Avoiding tight fitting clothing is essential if that clothing is being worn to protect you against the thermal effects of an arc flash. NFPA 70E states that the worker must avoid tight-fitting arc flash gear and that loose fitting clothes provide more thermal protection because of the “air spaces.” I often see and hear about companies adopting the policy of one single arc flash suit should take care of all of our needs. The maintenance department can share the same suit. The policy of one arc flash suit for the entire maintenance department is a big mistake.

An arc flash suit is the heavier arc flash protection needed in incident energy exposures generally above 25 cal/cm2. Arc flash suit hoods are required for any energy above 12 cal/cm2. The issue is this. If one of the maintenance people in your group is 6 foot 4 inches tall and weighs north of 300 pounds and another worker is 5 foot 7 inches and weighs 160, they can’t wear the same suit. But, I have seen situations where this is precisely the case. It is an impossibility that two people with substantially different body types can wear the same suit, and for safety reasons, they shouldn’t be wearing the same suit.

The reason an ill-fitting suit is a problem is that loose fitting arc rated clothing gives you more thermal protection than tight clothes, and, in addition to that, the wrong size suit can obstruct movement preventing you from completing the task safely. What if a major league baseball team all had to wear the same size uniform? I don’t think the fielding, throwing or hitting would be as good because their movements would be restricted. Go Cubs. I am here to argue that an arc flash suit is more important than a baseball uniform. To ensure that everyone is fitted correctly and the equipment properly stored and cared for, professional teams employ an equipment manager. Maybe your facility needs an equipment manager. I know you aren’t working with the same equipment budget as the Yankees. But how nice would that be?

Besides restricting movement, sleeves that are too short can be an issue if you extend your arm and your sleeve no-longer reaches your hand; subsequently, your wrist and forearm become exposed. 70E requires that the arc flash clothing provides full coverage.

One of my favorite comedy scenes in a movie has to be the “Fat Guy In A Little Coat” scene in Tommy Boy. Not surprisingly, small of stature, David Spade’s sports coat did not fit Chris Farley, with hilarious results. Funny in a movie, not amusing with PPE.

Manufacturers and distributors, on their websites, have detailed sizing charts for assisting you in getting the arc flash suit that fits your body. Head to toe measurements are included, and there are different sizing charts for men and women. Most want your chest, waste, height, other manufacturers need your arm length, inseam, among other measurements. One manufacturer states in the sizing instructions that workers under 5’8” and taller than 6’4” need to have a custom suit. Other manufacturers offer sm, med, LG, XL, XXL, XXXL. You would have to figure where you are on this type of a scale.

Here are links to a couple sizing charts:  Oberon    National Safety Apparel

Arc flash suits are expensive, and I certainly understand why companies want to limit the costs of implementing NFPA 70E.  Your company needs to develop a plan for ensuring all qualified workers have the appropriate suit to wear.

Arc flash suits come in a variety of types. You can purchase bib overall type pants and an accompanying jacket and hood. There are regular type pants, with a jacket and hood. It is important that you shop around, look at many websites of manufacturers and distributors. Look at all of the sizing options and determine what is right for you.

A comment I have heard on more than one occasion is, “I don’t want to wear an arc flash suit that someone else has been sweating in.” Good point, I wouldn’t either. Let me state right now, that in my opinion, the only live work we should be doing in an arc flash suit is verifying zero volts during our live-dead-live test required for lockout tagout. Our first step in providing protective measures after we have completed a risk assessment is the elimination of the hazard. Working de-energized. This, of course, will require us to establish an Electrically Safe Work Condition (ESWC). So hopefully no one is wearing an arc flash suit for an extended period of time. I do realize on really hot and humid days you don’t have to wear them very long before you are sweaty.

Arc flash suits have to be stored in such a way that they won’t become damaged. A dedicated cabinet, storage closet or bags will help limit the damage. Some people turn them inside out to help them dry and avoid mold and the suit getting stinky. One helpful accessory that is available is a cooling unit which is a blower that mounts to the suit and provides air flow throughout the suit as you wear it. Another accessory is cooling vests designed to be worn under an arc flash suit.

Your facility needs to have suits in various sizes so all qualified workers are protected through the range of arc flash exposures. This is an expensive garment performing the critical function of protecting the wearer from a high energy arc flash event. A lot of thought needs to go into the proper sizing of arc flash suits and how many we need to buy.

Our Training That Addresses This Issue

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NFPA 70E permits either of two methods be used when selecting arc flash PPE. The PPE category method, which relies on tables, or the incident energy analysis method, which calls for an electrical power system analysis to be performed by electrical engineers. What many don’t realize is that because of the parameters in the PPE tables both methods require a power system analysis.

When using the PPE category method for selection of arc flash PPE, you must ensure that your equipment is within the clearing time and fault current parameters listed in the tables. If your circuit is not within these parameters, the standard states you can not use these tables and instead you must use the incident energy analysis method.

An electrical power system analysis involves electrical engineers using engineering software, and data collected in the field, to create a model of the electrical distribution system of your facility. This data includes transformer information, wires sizes, fuses, breaker model numbers and settings, all overcurrent-protection devices, etc. Collecting, modeling and analyzing this data can be time-consuming and costly; which is why many facilities struggle with getting it done. This study would provide you with your available fault current and clearing times that you must have to use the PPE category tables. Just a bit more work by the engineer and you would have a complete incident energy analysis.

From NFPA 70E Table 130.7(C)(15)(a) a 480-volt panelboard calls for category 2 arc rated PPE. The table further states the parameters of 25,000 amps of available fault current and a two-cycle fault clearing time. If your fault current or clearing time is outside of these parameters, it is possible the Cat 2 PPE recommended will fall short of the protection you need. There is no way of knowing these parameters without doing a power system analysis?

Another example would be an upstream current-limiting fuse protecting the panel you are about to open for troubleshooting. The informational note to Table 130.7(C)(15)(a) states that a current-limiting fuse has a typical clearing time of .5 cycles if it is within the current limiting range. This is an informational note and not part of the standard language however someone might be tempted to use this clearing time as their clearing time without knowing if the fault current is within the current limiting range of the fuse. Current-limiting fuses are very fast acting fuses and can reduce arc flash energy but only if there is enough current to drive the fuse into its current limiting range.

When selecting arc flash PPE the standard doesn’t allow us to assume we are at a .5 cycle clearing time. We have to verify we are and we can’t do that without getting electrical engineers involved.

The most important thing to keep in mind is that this is the same information you would have to collect and almost all of the calculations you need to perform an incident energy analysis. Just a little more work by the engineer and you will have a complete incident energy analysis. At this point, you would have no use for the tables. Most often the incident energy analysis recommends less PPE be worn, gives you a chance to mitigate the arc flash energy and is a better method.

Selecting arc flash PPE by either method is never an exact science. There are too many variables and unforeseen circumstances. The more of these variables you can control the more accurate your selection will be. One thing is for sure, wearing arc rated PPE helps reduce injury from arc flash. We need to do all we can to make sure we are wearing the proper PPE.

Relevant ETP Training
nfpa.org

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