We are working with a customer that claims that OSHA and NFPA70E do not allow any work to be done (even opening the panel doors) within a control panel with 120VAC present. The control panel is fed with a 120VAC single pole 20A breaker. It uses finger safe terminals and equipment so our claim is that there are no exposed energized electrical components. The only live work that would be performed is voltage verification of the 120VAC for troubleshooting purposes. There are other components within the control panel that are 24VDC. Our interpretation of the NFPA70E is that with no exposed electrical components there is no Arc Flash requirement. The same argument is made for the shock hazard for this panel. Any maintenance performed within the control panel on 120VAC equipment would have that equipment de-energized using a local distribution fuse or breaker within the control panel. Working on equipment fed with 24VDC would be perfectly acceptable while the panel is energized with 120VAC. The limited approach boundary for the 120VAC would be "No Contact". How are others handling this type of scenario?

Ask the customer if he suits up to plug in a table lamp, pencil sharpener or coffee maker. Each of those poses more of a shock hazard than the condition you describe.

What is meant by "do not allow any work to be done"? From an arc flash stand point it is highly unlikely there is a risk. From shock, I can see there is a risk of shock. Risk is part of the job, excessive risk is not. That being said, I agree that the "best??" method is to design a system to eliminate the risk - like 48V controls. I also agree that "work being done" at 120V present risk. Opening a controls cabinet with 120V only with a 20A breaker seems excessive but what needs to be done in there? Troubleshooting? moving wires? changing fuses?

There is a move to making control systems safer but it is slow. There is way to many old timers stuck in their ways and they are teaching the younger guys the exact same thing.

I used to work at 120V without thinking about it. Now I stop and think about it.

Just this weekend I was correcting receptacle wiring in a small shop. Found a shared neutral on three breakers, no breakers tied together and not in the same conduit. Always a little surprising to find 120V on a neutral. Yes I got a shock from a neutral on a dead circuit.

I recommend you review the requirements around testing, inspecting and measuring because that's probably what you're talking about, not maintenance.

Remember, you cannot perform maintenance, which is not the same as testing, with the power left on - unless you can prove it is more dangerous to shut the power off than it is to leave it on. However, my guess is when you said maintenance, you're not actually touching an energized component to maintain it, but just to test. If so, then you only need to observe the voltage and arc flash hazards at the panel and do not need to shut it off. And if it's only a 20 amp 120 volt circuit, do the calculations and label it. I'll bet it's less than 1.2 calories of arc flash hazard. If so, the PPE is minimal. More a case of using voltage PPE than arc flash.

"We are working with a customer that claims that OSHA and NFPA70E do not allow any work to be done (even opening the panel doors) within a control panel with 120VAC present."

I don't think there is anything you can say to change this person's mind. If it is really important, you may have to get a mutually agreed to expert to come in and give a little lecture and explain these things to both of you. This is a political problem, not a technical one.

In agreement with the others. Your client has misinterpreted "Working Energized" There are 2 catagories- Diagnostic and Repair. True enough we do not want workers performing repairs on electrical systems above 50VAC such as tightening, connecting, installing, etc. However diagnostic such as testing or troubleshooting in most cases has to be done with the power on. This is where PPE, safe procedures and proper test instruments come in. I would suggest that your client register for a 70E workshop or class ASAP

70E is wishy washy at best even with shock on the 50 V thing. It alludes to the idea that a hazard may exist even below 50 V. I think only Roberts actually makes that claim based on some very sketchy Chinese reports and ignoring the voltage dependence of the IEC shock curves. So its easy to get off track.

No standard takes a stand at any voltage on arc flash. The published data shows a transition to sustained arcing around 200-300 VAC and some data from Duke shows 130 VDC is right on the 1-2 cal/cm2 threshold at 20 kA so obviously 120 VAC is below that. OSHA documented what could only be called an arc flash injury requiring hospitalization from 120 VAC in 2009 but it was hands only, below the threshold used in 70E. This is a consequence of 70E jettisoning a lower limit of any kind and pushing PPE for everything in the 2015 edition (no HRC 0).

Finally with all the fear mongers out there with respect to electrical safety I'm not sure training is a good idea depending on who does it.

Here is an OSHA Letter of interpretation on voltage on the line side of a disconnects, which is relevant to this discussion.

https://www.osha.gov/pls/oshaweb/owadis ... p_id=25438

"The panel in your scenario may be considered de-energized depending on the design of the equipment and the work to be performed. In your scenario, the panel, while not technically de-energized as there is still power to the supply side of the disconnect, provides adequate employee protection if the design and installation of the panelboard is of dead-front construction"

HI all,
What am I missing here in the before mentioned OSHA letter addressing the issue of de-energizing? Is it in error where the letter says de-energizing is not needed?
Thanks

Question 4: If the upstream disconnect [Location A] is higher than eight (8) feet off the ground, is lockout required to control that energy source as well, or can one just shut off power using a switch stick, provided that this disconnecting switch is clearly visible to him or her and the work does not go beyond an employee's shift?

Answer: If it is necessary to open a disconnect upstream to de-energize electric equipment as required by §1910.333(b), then the employee would [b]not need [/b]to follow complete lockout/tagout procedures on the upstream disconnect [Location A]. Neither the location of the disconnecting switch, nor the duration of the project, obviates the need for proper lockout/tagout procedures.

Looks like a typo. All the other text is inconsistent with the "not."

It's an error. I can think of 6 cases right off where LOTO is definitely not required.

The first one is once equipment is out of service and not being maintained. In this case it is a violation to have it locked out.

The second is for minor servicing and maintenance which is an exception for the general LOTO requirements in Subchapter J.

The third exception is for energized work which falls under either the special exceptions or requires an energized work permit following the early 70E edition that OSHA adopted for utilization equipoment.

The fourth exception is that tags but not locks are required for construction under 1926. At this point I'd almost consider it a typo though too because all of the literature that OSHA puts out for the construction industry pushes LOTO. 1926 also is not aggressive towards energized work, partly because the utility industry falls partly under it.

The fifth exception is that utilities have no energized work permit requirement and generally work on everything energized, even to the point where locks are not required and tag-only systems are required under some sections of 1926.269. There are at least four different LOTO procedures under 1910.269 and each is slightly different from not only the other 3 but also from Subchapter J, O, and S.

The sixth case is for normal production and falls under Subchapter O. This is sort of hand-in-hand with the "minor servicing and maintenance" exception in Subchapter J but much more broad in the things that it can cover. By way of an example in a plant that I've been in several times they have "operator tags". You can stop the equipment, put an operator tag on it, pull the key out of a key switch, and then proceed to adjust the machine, stock, belt alignments, open doors...all without ever de-energizing the machine. Doing exactly the same tasks in order to service and repair the machine requires LOTO.

The letter of interpretation obviously doesn't fall under any of these.

Arc flash approach boundaries like Arc flash limited approach boundary, Restricted approach boundary and Arc flash hazard boundary will be labeled as per the Arc flash hazard risk category chart depending their Arc flash zones. Any queries, Please visit <deleted link to commercial website>

There is no such thing as an "arc flash limited approach boundary". There is simply an arc flash boundary. It's a single number. The arc flash boundary does NOT EXIST if the work being done is unlikely to cause an arcing fault (e.g. normal operations).

There are two shock protection boundaries. The first one is not identified with any kind of name and appears in multiple OSHA regulations as well as IEEE C2 that is intended specifically for unqualified workers or the general public. It is usually 3'6" for fixed parts or 10' for overhead wiring but there are cases where it can be closer (4' when tramming equipment under a power line) or further (goes up as voltage increases into medium voltage and higher). Under 70E and OSHA Subchapter S it is identified as the "limited approach boundary".

The second shock protection boundary applies to qualified workers. It is identified as the minimum approach distance (MAD) under all IEEE standards, OSHA 1910.269, and IEC standards. Under 70E and OSHA Subchapter S it gets strangely renamed to the "restricted approach boundary".

There is a third mythical boundary. It was called the "prohibited approach boundary". Under IEEE 516-2009 (all these shock boundaries come originally from that standard), this is the approach distance without an inadvertent movement adder. Since 70E gave it the same treatment as the MAD (aka restricted approach boundary) it was dropped in 70E-2015. It does have some practical value. There is no standard for the required spacing for exposed electrical equipment but most designs use a distance that is the same as the prohibited approach boundary.

As with arc flash, shock boundaries do NOT EXIST when equipment is not EXPOSED. Exposed is defined as not guarded, insulated, or isolated. So for instance when the door of most MCC's is open and all the contacts are recessed so that accidental contact will not happen it is not exposed so there is no shock hazard. Conversely when the covers are removed off a panelboard and all the bare open busbars are accessible, this is exposed and so shock hazards exist if the panel is not locked out.

There are two hazards...shock and arc flash. They are two separate hazards. The only thing that links them together is that doing energized work on exposed electrical equipment without proper protection (insulated tools, insulated workers) could cause an arc flash if someone accidentally bridges two conductors or a conductor and a ground such as slipping and touching the ground and an energized bus with an uninsulated scewdriver.