ARC Flash Boundary Requirements 2

[tulum]

This has been discussed in the past - but the threads are now closed.

We have many load centres (unit transformers) that have a HV switch with a dry type transformer and secondary distribution. As we are all aware the secondary transformer bus to the main breaker has a high arc flash (typically).

The end result is that the arc flash boundaries are bigger than the switchroom spacing on a lot of the installations.

My question is: "If you are just passing through the room do you need to suit up in the required PPE, or just when "disturbing" the system?"

The reason I am asking is that the transformer ventilation makes the transformer "open" to the environment, and the passer by....

Thanks TULUM.

 

[AggiesNM]

Wear suggested PPE when interacting/ disturbing the system. The Arc Flash boundaries for some switchgears can be 20 to 30 feet, you might even come across an adjacent panel board with just 5 to 10 feet of boundary. It's unlikely you will change to different PPE for every few feets of distance you walk in the room.

Wear atleast a cat.2 PPE when not intending to interact.

 

[rasevskii]

Well, this Arc-Flash situation is interesting. I think, at present, it only applies to plants in the USA. I can remember many installations (not in the USA) where everything electrical was in the same room: 34.5KV (SF6), 13.8KV, 6.9Kv and hundreds of 380V MCCs as well as relay panels, drives panels, etc. in one very large space. It was a chemical plant in the Middle East new in around 1997. (US designed).

If the Arc Flash rules have to be applied retroactively to existing older installations, that would be nearly impossible.
How would the operating staff have to Suit Up just to reset a relay or take a meter reading? That would be a walk-through situation I imagine.

Comments?

rasevskii

 

[rbulsara]

Depends up on what codes apply to you. In the USA, based on the current codes and practices, the answer is no. This does not prohibit people misinterpreting the intent of the standards and recommendations to the extreme.

Rafiq Bulsara

http://www.srengineersct.com

 

[dpc]

I would agree with Rafiq. As long as you are just "passing by" and no switching or maintenance is being done, I don't interpret NFPA 70E as requiring arc-rated PPE. Some companies have internal safety procedures that require PPE whenever entering an electrical room.



David Castor

http://www.cvoes.com

 

[Zogzog]

The definition if "Arc flash hazard" is very clear in the 2009 70E, it only exist when "Interacting" with equipment. Now what "interaction" means is bebateable but it is not "just passing by" for sure.

 

[tulum]

Thanks folks.

The reason I asked is that it seems that

(a) because the definition for the flash protection boundary itself does not directly mention that you must interact with the system for the PPE to be required (in the standards but not in the definition), most people are under the assumption that as soon as you step into the boundary you require PPE regardless of interaction....

(b) With the louvers on the dry type enclosure, the bus would be considered "energized and not enclosed"?

 

[jghrist]

NFPA 70E 130.3(B) says

Where it has been determined that work will be performed within the Arc Flash Protection Boundary ...

The boundary applies when work is being performed. PPE is required when within the boundary and when there is an arc flash hazard. FPN No. 1 of the definition of arc flash hazard in Article 100 states

An arc flash hazard may exist when energized electrical conductors or circuit parts are exposed or when they are within equipment in a guarded or enclosed condition, provided a person is interacting with the equipment in such a manner thay could cause an electric arc.

Walking through the area is not working or interacting with the equipment.

 

[tulum]

Great thanks.

 

[kevd]

Electrical equipment can fail spontaneously and therefore you need to assess the risk when transiting electrical rooms. Please have a look at the following incident that occurred on the Queen Mary 2 cruise ship recently

http://www.maib.gov.uk/publications...ety_bulletins_2010/safety_bulletin_4_2010.cfm

In this case if anyone had been in this compartment then I don't think PPE would have helped!

Thanks

 

[alehman]

I can see both sides of this question. Most electrical failures result from human interaction or as a result of automatic operation of the equipment. As exemplified in the QM2 case, things do fail spontaneously, but that is relatively rare.

It comes down to practicality, company policies and insurance requirements. No code or standard can cover every situation. A little reasonable judgement needs to be applied. It may not make sense to require PPE just walking past a passive panel or switchboard. I would be less comfortable if there were active controls regularly operating circuit breakers, and less comfortable still if breakers or switches were being operated manually.

The national codes in the U.S. do not require PPE. Work practices are not within the scope of the NEC. NFPA 70E is not a code suitable for adoption by building authorities, but rather a standard practice. OSHA recognizes NFPA 70E as a standard for safe work practice, but does not directly enforce it.

Alan
“The engineer's first problem in any design situation is to discover what the problem really is.” Unk.

 

[cjhut]

The magic words are exposed energized parts, which doesn't apply if all of you covers and barriers are in place.

 

[jghrist]

The magic words are exposed energized parts, which doesn't apply if all of you covers and barriers are in place.

FPN No. 1 of NFPA 70E 130.7(C)(9) says in part

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).

 

[LionelHutz]

No code or standard can cover every situation. A little reasonable judgement needs to be applied.

I agree. NFPA helps you understand the hazards but it can't cover every possibility. In the end, it's up to the employers and employees to assess the risks and decide how to handle safety at their facility. I doubt OSHA will accept "we followed the standard" as an excuse if someone gets hurt.