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 Post subject: Non Qualified - 600V Class MCCs
PostPosted: Fri Mar 13, 2009 12:43 pm 
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I have been following some threads regarding wheter the Arc Flash Protection Boundary is in effect when the MCC door is closed - it appears to be an unsettled question!
At our facility the operations people (non qualified) operate the disconnects for 480v motor starters - to lock out a piece of equipment so that mechanical work can be done on the system. They wear Category 0 clothing. All of our MCC's have an arc flash warning sticker that shows the incident energy at 18 inches and the HRC. The operators are trained to stand off to the side when they operate the disconnect, and the starter bucket door is latched closed.
In your opinion, what is the maximum incident energy level (or HRC) that you would allow the operator to operate a disconnect for a 480v starter with only Category 0 clothing?


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PostPosted: Fri Mar 13, 2009 7:49 pm 
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psThomas wrote:
I have been following some threads regarding wheter the Arc Flash Protection Boundary is in effect when the MCC door is closed - it appears to be an unsettled question!


What makes you think it is unsettled? Pretty straight forward. Unless the equipment is arc rated you need to wear PPE even with the doors closed.

psThomas wrote:
At our facility the operations people (non qualified) operate the disconnects for 480v motor starters - to lock out a piece of equipment so that mechanical work can be done on the system. They wear Category 0 clothing. All of our MCC's have an arc flash warning sticker that shows the incident energy at 18 inches and the HRC. The operators are trained to stand off to the side when they operate the disconnect, and the starter bucket door is latched closed.


They need to wear the PPE on the label.

psThomas wrote:

In your opinion, what is the maximum incident energy level (or HRC) that you would allow the operator to operate a disconnect for a 480v starter with only Category 0 clothing?


1.2cal/cm2


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PostPosted: Mon Mar 16, 2009 6:16 am 
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I agree with Zog. FPN #1 in 130.7.9 is found above the PPE table in the 2009 70E. It states "The collective experience of the task group is that in most cases closed doors do not provide enough protection to eliminate the need for PPE for instances where the state of the equipment is known to readily change (e.g., doors open or closed, rack in or rack out)." Opening or closing the breaker is changing the state of the equipment. I know that FPN's are not officially part of the code, but after an accident it would be pretty hard to justify ignoring them.


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PostPosted: Mon Mar 16, 2009 7:44 am 
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Location: Spartanburg, South Carolina
Table 130.7(C)(9) shows an HRC 0 for CB or fused switch or starter operation with enclosure doors closed. If the Note 2 limits are not exceeded, and an incident energy hazard analysis has not been made, wouldn't this suffice?

At 600V, with a working distance of 455 mm, an arc gap of 25 mm, and using the 65 kA and 0.03 sec from Note 2, the IEEE 1584 equations give an incident energy level of 5 cal/cm². This would seem to indicate that the closed doors are considered to reduce the hazard/risk. FPN No. 1 is not unequivocal when it comes to operating a starter. This could be one of the cases where the risk was considered low and the category was reduced. The sentence referring to closed doors refers to "instances where the state of the equipment is known to readily change(e.g., doors open or closed, rack in or rack out)." It can be interpreted that operating a starter is one of these instances, but it could also be interpreted otherwise.


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PostPosted: Tue Mar 17, 2009 7:42 am 
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What we are saying is to open/close a 480v disconnect with the MCC door closed and latched with the operator standing off to the side - he can only do this if it is a Category 0!? (operations people don't have FR clothing and face shields)

Can some others give their opinion on this? Our 480V MCC's range from Cat 0 to Cat 2. A latched MCC door can't withstand a Cat 2 sized fault or a Cat 1 sized fault?


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PostPosted: Tue Mar 17, 2009 8:48 am 
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What do your people wear when verifying that the voltage has been removed from the switch as required by 70E? In order to do this, you must open the door and verify with a test instrument. In that case, the door is now open and you must be suited up to the appropriate level. It must be considered energized until proven otherwise. Have them wear the appropriate equipment since they're going to open the door and do the verification test anyway.

Our guys wear the appropriate level PPE for switching and lockout and anyone not wearing it is moved an appropriate distance away or out of the room entirely until the switching and verification is complete.


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PostPosted: Tue Mar 17, 2009 1:19 pm 
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TxEngr wrote:
What do your people wear when verifying that the voltage has been removed from the switch as required by 70E? In order to do this, you must open the door and verify with a test instrument. In that case, the door is now open and you must be suited up to the appropriate level. It must be considered energized until proven otherwise. Have them wear the appropriate equipment since they're going to open the door and do the verification test anyway.


Excellent point, I was over simplifying. We have 3 different ways that this is handled when a lock out is to be performed for a 480v system.
(1) The electrician performs a voltage test and then will open the disconnect and he places a signed tag that indicates a voltage test has been performed. This is the most common method.
(2) If there is a visible blade disconnect, and the operator has been trained how to look and determine that all three phases are open (this is the voltage test), the operator will open the disconnect and lock out.
(3) We also have a handfull of locations where we have a Voltage Warning Alert that an operator can use to lock-out. (Operator verifies that 2 lights per phase are on, he opens the switch and verifies that all lights are off. If there are any lights not functioning or the sequence of events is not as I described the operator has to stop the lock-out procedure and call an electrician.)

In all 3 methods a test start has to be performed. Mehtod (2) and (3) are only for mechanical lock outs - like clearing a jam or changing machine settings - this could occur 1 to 20 times a shift. If an electrician is performing work on the motor or the circuit(s) then method (1) has to be done - "test before touch" principle.

In all of these cases the operator could be the one to close the switch/disconnect when the equipment is to be run. Again, everything I described is for 480v motors. Only an electrician can open and close switch/disconnect for higher voltage motors (at our facility it is 4160V).


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PostPosted: Tue Mar 17, 2009 7:12 pm 
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There is room for interpretation. Art 130 is defined for work on live and exposed equipment. It never goes so far as to state it is for 'all' electrical work. By reference logic dictates that we must draw some line, ie, the light switch on the wall is making and breaking a 120V circuit which by an unrestricted intrepretation would require Level 0 clothing. Not likely for short sleeve office workers in polyester clothing. Contrary to what some might say I would venture that even the NFPA cousel did not mean to include the operation of a light switch by all office workers. The statement in the 2009 code about rapidly changing state, to me implies high energy changing of state, ie switchgear breakers. I do not believe it includes all switched devices and every change of state behind metal enclosed gear. If it does, then by default, the IE ratings and risk is the same regardless of open or closed doors, or covers. We know from the PPE Matrix that enclosed equipment has a lower PPE requirement than the same equipment exposed.

There is another logic that I employ. THE NFPA 70E is NOT part of OSHA and is only enforceable under the General Duty Clause. OSHA has stated that anyone following a program as outlined by 70E would not be cited upon an accident. So if you have a program in place that conforms to 70E and you exercise your judgement for areas not specifically defined by 70E, like PPE required to operate metal enclosed devices, I would speculate that you have conformed to the intent. You can NOT be cited against a specific statue in OSHA because none exists. I seriously doubt an OSHA officer would be able to cite you for a failure when you have a complete and documented program, conforming to all the major outlines, but employing your own judgement for areas that are not clearly defined.

I know I'll raise issue with some that it is clearly defined by the change of state notation, but then I ask why not the light switch? The cousel did not state an IE level or PPE, just a condition of change of energy state. Every switch regardless of IE undergoes a change of energy state. The most logical conclusion is that they meant to refer to the high risk energy change of state like switchgear breakers in/out or open/close. Can you carry this logic to MCC buckets and opening or closing a disconnect, sure, but you also can choose not to, or to limit it to something specif, like size 4 and larger starters.


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PostPosted: Wed Mar 18, 2009 7:37 am 
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Excellent clarification psT. In situations 2 and 3 where you are using some visual form of verification, is this for a starter or a disconnect at the equipment from after the starter? At facilities I have worked at, they were typically lockable disconnects for maintenance and had in interlock that would ensure that the motor was not running before the switch was pulled. This significantly reduced the risk since there would be little or no energy left on the system and we allowed mechanics to open and close the switches.

I would probably review the policy of allowing operators to close switches after lockout. Even though 70E treats closed door equipment as not requiring the full PPE, from a general knowledge of hazards it would probably be prudent to have an appropriately clad qualified person do the switching.

Now, that said, we all have welding disconnects and other switched devices available that are operated by mechanics wearing minimul or no arc flash PPE and that is sufficient.

This is an excellent discussion and I hope to hear from others as well.

TxEngr


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PostPosted: Fri Oct 02, 2009 11:35 am 
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I agree with Haze10. We have to draw the line somewhere. What about plugging something into a 120v outlet. Do you wear gloves when doing that? Some might say your not comparing the same hazard but it seems the same applies.

I believe the NFPA70E committe has tried to make the program as simple as possible otherwise the material would be >3 inchs thick to even try and cover the viarables involved with systems.

While a RK1 or RK5 fused device feeding a 600v class MCC switching on/off seems to me to be a low hazard when you are feeding the MCC via a RK1 type fuse. The same may not apply to other systems. Again you have to use some common sense and use your electrical knowledge to determine the upstream protection's clearing times and the hazards.

Sure the tables can help but is only a guide line. Only an accurate study (based on the values we have today) can provide the correct values of heat released as a result of a short circuit.


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PostPosted: Tue Mar 16, 2010 2:34 am 
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Osha says it's ok for a operator to loto a piece of equipment by shuting off cb and testing pb to confirm equipment is off. Is this method ok for electrical work or just mechanical repair?


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