NFPA ArcFlash 3

[ukgraduate]

Hi Can someone please tell me the following:

1) When doing an engineering design of a plant is an Arcflash assessment required by NFPA? If so can someone please tell me the article to look for?

2) When doing an engineering design of a plant and purchasing equipment is an Arcflash labeling required by NFPA? If so can someone please tell me the article to look for?

We do have voltages all the way up to 34.kV and breaker above 800A on all voltages.

If it is required are there some exceptions so we dont have to do this?

Regards

UkGrad

 

[krisys]

Please note that the NFPA 70E which is the relevant standard which specifies the requirement of evaluating the Arc Flash Hazard in an electrical installation. NFPA is not the authority for Arc Flash. But it is a consensus standard. The outcome is to find out what kind of arc flash suit is required while working on the live installations as specified in OSHA.

The Arc Flash calculation will be done according to IEEE 1584 guidance. In NFPA 70E you have some shortcuts which may be used for the simple installations, instead of going for a detailed arc flash hazard study.

 

[maze02]

In addition to krisys earlier comments, please refer to the following articles/standard:

NEC 110.16 and OSHA 29.CFR 1910 Subpart S. I think those should answer your question.

 

[resqcapt19]

The rule in 110.16 in the NEC does not require any type of calculations. The rule only requires a "generic" arc-flash hazard label.

 

[RodneyDixon]

NFPA 70E - Standard for Electrical Safety in the Workplace
[ul]
Gives details of the requirements for:

[li]Selection of PPE[/li]
[li]Signage[/li]
[li]Shock Hazard Analysis[/li]
[li]Flash Hazard Analysis[/li]
[/ul]

Article 130.3 and associated sub sections give details of the requirements of arc flash hazard analysis.

As has been said by other members, NFPA is not an authority for arc flash but is generally accepted/adopted as such, even in the UK.

Your UK Operational Health & Safety Act will have general duty clause about protecting employees from recognised hazards which drives arc flash safety.

Also mentioned above is IEEE 1584 which you should make yourself familiar with.

 

[jraef]

Here's how it really works.

The OSHA spec REQUIRES that an employer provide a electrically safe workplace, including safety of personnel from the dangers of Arc Flash hazards. It then goes on to REQUIRE a program of electrical safety including hazard assessment, labeling and training. It then SUGGESTS one such as NFPA 70E as a prime example. So if your facility has employees, you must have a plan, you must execute the plan and follow up on it periodically. You can come up with your own plan, but if there is an accident and your plan was NOT up to the standard set forth in NFPA 70E, then you had better have some good lawyers to keep from getting shut down indefinitely.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[Marmite]

If you are designing a new plant you should be looking into it a lot deeper that what PPE you need to wear. PPE is the last line of defence. There are many steps you can take at the design stage to eliminate, reduce and control the hazard before thinking about PPE.
Things like switchgear which is arc containing, high speed reliable protection systems, remote operation, remote indication, location of protection relays away from the switchgear, remote motorised racking, non isolatable switchear, HV operational procedures, Permit to work systems, checking of switching schedules, restriction of access to switch rooms, segregation of switchgear etc etc.
All of these things go towards protecting workers from arc flash hazards as part of a broader safe system of work. Sticking a label on the gear and telling staff to wear a bomb suit because the incident energy is greater than X is not design.

Regards
Marmite

 

[wbd]

I agree with Marmite. PPE is the last line of defense and you should be looking at reducing the incident energy levels during the design phase. This could encompass:
1. Breakers with a Maintenance test switch which would allow switching in a faster trip for worker protection.
2. Arc flash relay in switchgear
3. Smaller transformers For example: if there is a 480V to 120/208V transformer that is 150KVA consider 2 transformers at 75kVA and separate panels off of that.

One very important item to note is that while an infinite bus is appropriate for sizing the interrupting ratings of equipment, it is not appropriate to use for arc flash. You need the available fault current from the utility to determine the incident energy levels. I can't stress that enough.

 

[br2015]

Wbd I like your explaination and totally agree on it.
As my understanding is correct it is only possible to reduce the incident energy by reducing the arcing time!
Therefore I have only one remark / question about your second topic "arc flash relay".
This arc flash relays are very fast for the arc detection (fibre optics) but using the standard breaker for the shut down of the arc. For sure it is faster than the use of an standard relay but in summation we are talking in minimum of 80, 100, 120ms operation time of the CB while you have the dangerous arc... so the bottleneck is the "slowly" active part in this case the breaker.
Now i see on an exhibition that there exist an active arc protection system called UFES. It is an fast detection also with fibre optics but using an very fast earthing switch to shut down the arc in les than 4 ms... Less than 4ms will reduce the arc incident energy to a minimum. I guess that is the sollution for the future...
Somebody here who has experience with this kind of systems or any doubts because it is very new on the market? I´m in contact with the manufacturer of this product but want also to listen a second mind about it.

 

[ScottyUK]

The downside of that type of solution is that the earthing switch turns an arcing fault into a bolted fault by deliberately closing a fault-rated switch or breaker across the bus in the hope that something upstream will clear the fault. It's not a new idea, it's basically a fault-thrower applied to arc protection. You want to be very sure that the upstream device is going to clear the fault. I'd seriously consider breaker fail protection if relying on this technology.

 

[br2015]

Scotty thanks for your feedback.
That was also my first doubt, but the manufacturer informed me that this system can trip in parallel to this fast earthing switch (for the arc protection) also the infeedeing breaker in order to interrupt the short circuit current... But also my standard protection erlays will locate an earthfault and trip the responsible breaker (hopefully).
I guess if the product works as described, it will solve all the arc problems which we have now.