NFPA-70e PPE requirements when working inside cabinet

probably because robot cabinets are not able to generate significant arc in cases of a failure. power is delivered by comparatively small wires, say AWG10 and fault current is limited to few kA (4-8kA). that is puny in comparison with heavy busbars used in MCCs where fault currents can go way up (many 100s of kA).

i have not seen busbars in robot cabinets.

every line of work has it's tools and rules. and with number of robots out of there, there is plenty of empirical data to support need for (or not) for certain safety measures. but if you think you need to gear up, go for it.

i'm not in USA or using NFPA but if i recall NFPA requires that incident energy is calculated and equipment is properly labeled.

here is an example of calculating incident energy

this example used 480V circuit with fault current of 30kA and resulted in less than 1cal/cm^2

based on this, lowest NFPA required protection grade should be suitable as it is good for up to 4cal/cm^2.

so non-flammable (and non-synthetic) clothes, with face shield and gloves is plenty. no need for bear suit

the only time one is supposed to open cabinet and look at LEDs is when there is a reason to do so.

and when that is the case (some fault is present), problem already occurred and drives are already damaged or at least de-energized (intermediate circuit, aka DC -bus is low). i have seem few units damaged and... usually one need to look hard to spot it - if visible at all. it is nothing like scary videos of lava blasting out of the cabinet.

also it is very unlikely that conditions leading to arc flash (dead short or arc short) since everything is insulated. that is not the case in switchgear and MCCs - busbars are bare and the only insulation is air. so dropped tool is more than capable of creating short. creating short in a robot controller is quite hard.

Robot controllers should be installed inline with their SCCR rating; those ratings are on the low end of the spectrum for ArcFlash harzard. (The ratings will be in the specification of the control manuals)

I don't think I've ever seen a robot installed with a feed greater than 16kA; everything I do is the standard 10kA and that is more than enough to run a robot.

Assuming you're overall electrical feed complies; the only time you should need full arcflash PPE is if you have a panel mount controller that is feed with a much higher SCCR rating. And in that case, I'd question if the panel mount controller should be installed in such a enclosure.... I haven't looked for a long time, the ratings would exceed 10kA; but certainty won't be in the range of +50kA....

Quote from dorje777

I've gone to just about every OEM electrical maintenance class (Motoman, Fanuc, Kuka). Non of these required NFPA70e PPE when working inside the control cabinet with power on to access LED alarm codes. Is this a violation of NFPA70e or is this ok.

I would of thought during your attendance, would have given you ample opportunity to pose that question directly, as they alone are best served to provide you the correct and relevant information applicable to their product.

I am from the UK and have never come across NFPA 70E as any legal requirement.

In addition to this, I think it is important for those visitors and members from UK and Europe to not worry when they read this thread as I have located some interesting comparable information for UK and Europe:

Update to NFPA 70E 2021 | Electrical Safety (elecsafety.co.uk)

Quote from dorje777

Just wondering how the OEMs (Fanuc, Motoman, Kuka) run electrical maintenance training with non of the above. Maybe they know something I don't. I've reached out to them and am waiting responses. Will share.

I can hazard a guess at what kind of information they may provide and it will more than likely relate to:

- Training and documentation supports the system they provide, not the environment it is installed in.

- The supporting electrical maintenance documentation, tools, PPE required and competent personnel.

- Any deviation could result in a variety of scenarios, for which they are not liable for.

- All of the above include regulations and guidelines in accordance with the supplied documentation.

- Local risk assessment and methods of control applied under their controlled training conditions.

- The trainer is likely to enforce and carry out the training exactly as documented, no deviation.

You only need to look at OEM designs now, to see how they are improving from 20 years ago and focused more and more on reducing if not eliminating exposure to internal components by way of:

- Modular designs.

- Power components secured inside an internal chassis and inaccessible without physical removal.

- Connection points are finger proofed and also prevent attaching of measurement devices (probes).

- Troubleshooting by improved messages, led's and supported documentation.

- Carrying out module replacement when the controller is de-energised.

- Power off, remove suspect module, replace module, power on, confirm operation.

Long gone in robot controllers (although still used) where you ask shaky Dave the electrician to:

- Wield DVM probes around to measure/monitor voltages to determine faults.

- Attacking the power contactors with a screwdriver forcing them on and frying components.

- Taking relays, contactors apart and cleaning the contacts with the wife's nail file.

- Spraying cooling air on components suspect of over heating.

- Adding shorting leads to bypass what he thinks needs to be bypassed in order to get it running again.

It is the external electrical distribution interfaces and field peripherals that are manufactured by integrators that carry a more inherent risk than the robot controllers IMHO, but that doesn't mean the OEM of a robot controller can overlook said regulations and I would be very surprised if they cannot at least provide some sort of statement regarding NFPA 70E.

Interesting topic......thanks for raising it and I would be interested to hear of any responses you receive from any of the OEM's