MCC Arc Flash Labels

[klett@abingdon-va.gov]

We just had arc flash labels installed on our MCC's. Half of the MCC's now have a "Danger" label located at the top of each section. If the work to be performed is done within a bucket that is installed, shouldn't it have it's own label? As of right now, I would have to shut down the entire MCC just to replace a control voltage fuse.

A second question is how do you verify that the power is off if there is not a level off PPE that would allow you to open the door to measure voltage?

 

[zog]

We just had arc flash labels installed on our MCC's. Half of the MCC's now have a "Danger" label located at the top of each section. If the work to be performed is done within a bucket that is installed, shouldn't it have it's own label? As of right now, I would have to shut down the entire MCC just to replace a control voltage fuse.

A second question is how do you verify that the power is off if there is not a level off PPE that would allow you to open the door to measure voltage?

I assume the MCC does not have a main breaker?

Your 2nd question is a bit of a catch 22 that has been discussed at length here, you should be able to find those discussions using the search feature

 

[klett@abingdon-va.gov]

I assume the MCC does not have a main breaker?

They do have a main. And thanks, I'll look for those.

 

[ron]

We just had arc flash labels installed on our MCC's. Half of the MCC's now have a "Danger" label located at the top of each section. If the work to be performed is done within a bucket that is installed, shouldn't it have it's own label? As of right now, I would have to shut down the entire MCC just to replace a control voltage fuse.

A second question is how do you verify that the power is off if there is not a level off PPE that would allow you to open the door to measure voltage?

If there is a main breaker, is there a label for the line side of the Main with different information than the individual sections? Since each bucket is theoretically exposed to line side energy, all of the buckets and sections likely have the same rating because they are protected by the same main breaker.

For the second item, maybe you can check voltage downstream in some way to validate the power being out on the upstream.

 

[klett@abingdon-va.gov]

If there is a main breaker, is there a label for the line side of the Main with different information than the individual sections? Since each bucket is theoretically exposed to line side energy, all of the buckets and sections likely have the same rating because they are protected by the same main breaker.

All of the labels are the same. I would assume the calculation is for the load side of the main, otherwise wouldn't a calculation from the service entrance is all that would be needed?

I'm just thinking that if you are working on the load side of a breaker in a bucket, then a calculation from that breaker is what you would go by. And if you were removing/installing a bucket, you would go by the calculation from the main.

 

[jim dungar]

I'm just thinking that if you are working on the load side of a breaker in a bucket, then a calculation from that breaker is what you would go by. And if you were removing/installing a bucket, you would go by the calculation from the main.

What would prevent a plasma ball from traveling under/through the starter bucket and onto the MCC bussing ahead of the bucket?

Has your company performed a risk analysis for working in MCC buckets, as part of your Electrical Safe Work Practices program? Or, was the label placement done simply by following the practices of the entity performing the arc flash study?

 

[ron]

All of the labels are the same. I would assume the calculation is for the load side of the main, otherwise wouldn't a calculation from the service entrance is all that would be needed?

I'm just thinking that if you are working on the load side of a breaker in a bucket, then a calculation from that breaker is what you would go by. And if you were removing/installing a bucket, you would go by the calculation from the main.

If the main is in its own section, then for that section the calculation would be the worst case, likely the line side of the main providing protection. Then the buckets can "count on" the main to provide protection for the load side buckets.

 

[zog]

If the main is in its own section, then for that section the calculation would be the worst case, likely the line side of the main providing protection. Then the buckets can "count on" the main to provide protection for the load side buckets.

I agree, since the OP's MCC does have a main there are options for arc flash reduction such as maintenace switches that can be used to reduce the arc flash hazard when doing tasks such as bucket removal.

There are also remote bucket extractors available so they can be pulled with the worker outside of the arc flash boundary.

 

[wbdvt]

We just had arc flash labels installed on our MCC's. Half of the MCC's now have a "Danger" label located at the top of each section. If the work to be performed is done within a bucket that is installed, shouldn't it have it's own label? As of right now, I would have to shut down the entire MCC just to replace a control voltage fuse.

A second question is how do you verify that the power is off if there is not a level off PPE that would allow you to open the door to measure voltage?

Are these generic labels bought from a supply house? The word "Danger" does not necessarily restrict work but depends on the context of the entire label. In order to determine the PPE needed, either an engineering study needs to be performed or determined from the tables in NFPA 70E. However, in order to use the tables, one needs to adhere to the parameters of the tables such as fault current and clearing time.

I have seen labels that have "Danger" on the top but the incident energy is very low. The "Danger" on the label is there because the label contains, in addition to information on the arc flash hazard, information on the shock hazard. Since under the right conditions, current in the order of milliamps can be fatal, therefore the Danger heading.

Concerning your second question: This relates somewhat to whether you have had an actual study performed or are using tables. The table method, if you are adhering to the parameters, has either a PPE Category of 2 or 4 for 600V Class MCC's which would enable you to perform a voltage test. If a study was done, it could have the incident energy values at different working distances which could allow a voltage test with less PPE. For example, using voltage test probes taped to the end of a hotstick to increase distance.

Note that all my references to tables are based on NFPA 70E-2015.

 

[big john]

It appears that the OP is asking whether it's acceptable to reduce the level of PPE needed when the protection located within a bucket reduces the incident energy for most of the equipment within that same bucket. My answer is no; you would have to base your PPE on the highest incident energy within the equipment that you were working on.

130.2 Electrically Safe Working Conditions.
Energized electrical conductors and circuit parts to which an employee might be exposed shall be put into an electrically safe work condition before an employee performs work if either of the following conditions exist:
(1) The employee is within the limited approach boundary.
(2) The employee interacts with equipment where conductors or circuit parts are not exposed, but an increased likelihood of injury from an exposure to an arc flash hazard exists.

If you there are no exposed energized parts within the bucket once the bucket breaker has been used to de-energize the circuit, then you are no longer within the limited approach boundary. However, it is undeniable that there would still be a significantly increased likelihood of injury if a fault were to occur on energized line-side of the bucket, so it appears to me that PPE would have to be used and selected based on the present line-side incident energy, per 130.5(C)(1).

I've seen the results of a spontaneous line-side failure in a bucket and if I had been the guy in there checking control fuses at the time, I would've suffered very serious if not fatal burns unless I'd been wearing PPE rated for the line-side incident energy.

 

[klett@abingdon-va.gov]

An engineering firm was contracted to perform the analysis. The labels were made specifically for the equipment.

To rephrase the question, shouldn't each bucket have its own label? For example, a section in one MCC has a flash hazard of 306 cal/cm^2 (the section with the main is 37017). So as of right now, I would have to disconnect the entire MCC just to replace a fuse in a bucket that is still in place?

 

[jim dungar]

An engineering firm was contracted to perform the analysis. The labels were made specifically for the equipment.

To rephrase the question, shouldn't each bucket have its own label? For example, a section in one MCC has a flash hazard of 306 cal/cm^2 (the section with the main is 37017). So as of right now, I would have to disconnect the entire MCC just to replace a fuse in a bucket that is still in place?

There are no 'real standards' for labeling. Per, NFPA70E, each company must develop their own Electrical Safe Work Practices program (ESWP). This program should address the issue of labels including their content and their application.

In my experience, the labeling of individual MCC buckets is absolutely not a common practice.

Have you discussed this with the study firm? What did they offer as their reasoning?

 

[kentirwin]

Below is what 2015 70E states for equipment labels.


130.5(D) Equipment Labeling. Electrical equipment such as
switchboards, panelboards, industrial control panels, meter
socket enclosures, and motor control centers that are in
other than dwelling units and that are likely to require examination,
adjustment, servicing, or maintenance while energized
shall be field-marked with a label containing all the
following information:
(1) Nominal system voltage
(2) Arc flash boundary
(3) At least one of the following:
a. Available incident energy and the corresponding
working distance, or the arc flash PPE category in
Table 130.7(C)(15)(A)(b) or Table 130.7(C)(15)(B)
for the equipment, but not both
b. Minimum arc rating of clothing
c. Site-specific level of PPE

 

[big john]

...For example, a section in one MCC has a flash hazard of 306 cal/cm^2 (the section with the main is 37017). So as of right now, I would have to disconnect the entire MCC just to replace a fuse in a bucket that is still in place?

My position is that if there is the possibility for a fault within the bucket that would involve the line-side conductors and thus expose you to 306 cals. of incident energy that is available at the MCC bus, then that is the rating for the bucket, so no, you would not have a separate sticker for each bucket.

 

[GoldDigger]

True unless there are current limiting fuses in the main section. Just a breaker will reduce the total energy from what it could be directly from the service by limiting the time if not the current.

 

[klett@abingdon-va.gov]

My position is that if there is the possibility for a fault within the bucket that would involve the line-side conductors and thus expose you to 306 cals. of incident energy that is available at the MCC bus, then that is the rating for the bucket, so no, you would not have a separate sticker for each bucket.

So unless the incident energy can be lowered, there is no way to perform any maintenance within a bucket without shutting down the MCC? And troubleshooting definitely cannot happen?

 

[ron]

So unless the incident energy can be lowered, there is no way to perform any maintenance within a bucket without shutting down the MCC? And troubleshooting definitely cannot happen?

Agreed

 

[wbdvt]

An engineering firm was contracted to perform the analysis. The labels were made specifically for the equipment.

To rephrase the question, shouldn't each bucket have its own label? For example, a section in one MCC has a flash hazard of 306 cal/cm^2 (the section with the main is 37017). So as of right now, I would have to disconnect the entire MCC just to replace a fuse in a bucket that is still in place?

So if I read this correctly, the section with the main is 37,017 cal/cm²?????? Please confirm that is what you meant as I find that improbable for a number of reasons but won't go into them if that is not what you meant.

 

[petersonra]

My position is that if there is the possibility for a fault within the bucket that would involve the line-side conductors and thus expose you to 306 cals. of incident energy that is available at the MCC bus, then that is the rating for the bucket, so no, you would not have a separate sticker for each bucket.

my guess would be that the IE calculation is for the line side of the main.

it is probably somewhat lower by the time it gets to the bucket.

but, unless there is some kind of calculation to show what that lowered IE is, I think you are stuck with the label that is there.

 

[mayanees]

confusing discussion

confusing discussion

The MCC should have one label that represents the incident energy at the line side of the main breaker. This is because the sections aren't isolated from each other, so an arc flash on the line side of the main could propagate through the entire MCC. It's typical to have one label per MCC, and not separate labels for each bucket. A smarter design is to have the mcb remote from the MCC, so the MCC can take advantage of an IE reduction associated with the mcb.
But an IE level of 306 calories is unrealistic for a typical 480 Volt MCC.
This sounds like the firm that did the Study did not use the industry-standard 2-second timeout.
As suggested in an earlier post, go back to the firm that did the Study and have them explain why there's 306 calories indicated on the label. That's higher than the expected level at the secondary of a 480 Volt, 3000 kVA transformer by abut 300%.
And if it's really 37,017 calories, there's a huge error.
You've paid for the Study. They owe you an explanation.
And as also mentioned in earlier posts, the risk factor hasn't been evaluated, which is now allowed by the 2015 70E.
But you've got inaccurate IE levels, so you should start there.
That's the problem with folks doing these studies. Anyone can buy the software and press the buttons, but there's a lot more to it than that.