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 Post subject: Protection Maintenance - arc flash considerations
PostPosted: Thu May 19, 2016 6:57 am 

Joined: Tue Jun 23, 2015 8:58 am
Posts: 1
Hello,

I'm looking for some clarification on the PPE requirements while working on metering and relaying equipment.

Protection Maintenance staff are performing maintenance on metering and relaying equipment. I have two scenarios:

1. staff require access to the back of this equipment which is inside of a panel. The equipment they are working on might be de-energized, however there might be other energized circuits adjacent to the work area (i.e 120VAC, 129VDC, 240VAC fed from <125kVA xfmr, nothing else). What PPE would be required for this scenario?

2. Staff require access to their equipment from the front of the panel. There are no energized circuits adjacent to their work area. The staff utilize insulated leads (up to 1000V), working on ABB Test Blocks with an ABB test handle, AREVA P991 test block with an ASEA test handle, PK blocks with PK test handles, GE test blocks with a GE test handle, Flexi test block with a Flexi test handle, a Westinghouse relays with fingers open, and CGE relays with a skid in order to perform this maintenance. What PPE would be required for this scenario.

Arc Flash Hazard calculations have been completed for all scenarios above but are likely over conservative when using the test handles or applying barriers to the exposed sources.


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 Post subject: Re: Protection Maintenance - arc flash considerations
PostPosted: Fri May 20, 2016 10:10 am 
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Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
what is missing here is a risk assessment. It would make a lot more sense if you did one. Since you made some references to European standards for meter probes for instance it is not clear what the regulatory domain is so I'm going to detail the general procedure from a North American perspective.

1. You did not specify the regulatory domain. Assuming U.S. then it is either generation, transmission, or distribution equipment, or else it is utilization equipment (FAA, maritime, construction, and mining also use different rules). Under Canadian rules it generally follows CSA Z462 which is substantially the same as utilization in the U.S. There are some differences between these two:
A. Under generation, transmission, and distribution as of 2015, it falls under 30 CFR 1910.269. A bare minimum of FR clothing is required unless it can be shown that the incident energy is under 2.0 cal/cm^2 and that there is no hazard of being splashed/hit from sparks or molten materials from nearby equipment.
B. Under utilization electrical hazards are not clearly spelled out. They become the domain of the general duty clause. OSHA has previously utilized NFPA 70E as guidance for recognized best practices and cited under general duty.

In either case what we have is a four step process. Both North American and European standards are very similar since for the most part North American standards have been adopted from European equivalents.
1. Look at whether or not a hazard is likely to occur. The criteria for "likely" is kind of vague but it is generally once in 100,000 years for a fatality or somewhat less for a severe injury. Another way of comparing risks is by comparison. Recordable shock incidents occur at a rate of about 2 workers per hundred thousand in the U.S. per year while arc flash is about half that rate. If the risk is less then this, then no PPE is necessary due to the hazard. As an example although meteor strikes do injure and kill people they are comparatively rare so we do not require meteor protection.

For shock hazards the rule is whether or not the worker can maintain the MAD (minimum approach distance) under generation/transmission/distribution rules or the restricted approach boundary under 70E. Note that the terms are different but the distances are derived from IEEE 516 for all applicable standards. This is for all equipment that is exposed. Exposed means not guarded, insulated, or isolated from accidental contact. It does not mean that it is protected against contact in an absolute sense. A lot of equipment meets this standard. Generally anything "touch safe" does but the "touch safe" criteria is more strict than the exposed criteria.

For arc flash hazards the employee has to interact with the equipment in such a way that it can cause an arc flash. This is a much more vague standard but the key is whether or not activity can cause an arc accidentally. Generally working on energized equipment with conductive tools or body parts that can bridge phase-to-phase or phase-to-ground is automatically included considering that human error is much higher than the above accident rates. When it comes to equipment itself it is generally more of a condition criteria. See OSHA 30 CFR 1910.269 Appendix E for a really good example list to start with. The table in 70E-2015 is not nearly as clear. It is available for free here:
https://www.osha.gov/pls/oshaweb/owadis ... &p_id=9873

2. Take steps if at all possible to reduce or eliminate the hazard such as by keeping panel doors closed, working from a distance, using insulated tools such as insulated meter probes that both completely prevent accidentally causing an arcing fault and protect the worker against shock, etc. If we can achieve #1 without going further then we have completed the process. U.S. standard is ANSI Z10 (also used by NFPA 70E) while European equivalent goes by several names but is generally known as ALARA or ALARP (As Low as Reasonably Achievable/Practicable).
3. Evaluate the magnitude of the hazard. For shock hazards if it is under 50 VAC in most regulatory domains then no PPE is required. There are some screwy domains (that's you New Brunswick) that don't adhere to the 50 V standard. For DC it is generally accepted as 100 V and 70E is being revised for the 2018 edition to meet this standard. The 50 VAC rule is a fibrillation-based standard while for DC it is more of a pain threshold since fibrillation does not occur.

For arc flash hazards if it is under 1.2 cal/cm2 for utilization equipment or under 2.0 cal/cm2 for generation, transmission, and distribution equipment, then PPE is not required for arc flash purposes except as mentioned above for generation/transmission/distribution where it is prohibitively difficult to ever claim that anything less than FR clothing is required. For some equipment there are table-based methods (70E, NESC, and OSHA 1910.269) when an engineering study has not been undertaken.

Note that the "arc flash hazard study" is usually based on a worst case scenario so for most of the equipment described it looks at the power conductors, NOT the control wiring as a separate system.

4. If PPE is still required after considering potential risks, removing risks whenever possible, and evaluating the hazard, then select PPE. For shock hazards it's voltage rated gloves and leather protectors. The table of requirements is again in IEEE 516 but is generally available everywhere and is very standard. Based on your description class 0 gloves would be sufficient. For arc flash there are some general rules which are covered under Annex H in NFPA 70E and a similar table exists in OSHA 1910.269. The two major differences are:
A. OSHA generally starts at 2 cal/cm2 where PPE is required while NFPA 70E starts at no PPE required (at 1.2 cal/cm2). Note again that the way that this is defined is so difficult to meet under 1910.269 that even if it is totally unnecessary according to the incident energy study, FR PPE may be required anyways and most utilities haven't tried to challenge it.
B. An arc flash rated face shield and balaclava becomes required under NFPA 70E starting at 4 cal/cm2 while it varies between 4 and 9 cal/cm2 depending on whether the hazard is 3 phase or single phase under OSHA 1910.269 (and a lot of vague hand waving).

So...getting back to your questions:
Quote:
1. staff require access to the back of this equipment which is inside of a panel. The equipment they are working on might be de-energized, however there might be other energized circuits adjacent to the work area (i.e 120VAC, 129VDC, 240VAC fed from <125kVA xfmr, nothing else). What PPE would be required for this scenario?


Keep in mind one glaring problem with your statements. The open circuit voltage of a CT is MUCH higher than 250 VAC. This is precisely the reason for a shorting block. When doing a safety analysis instead of looking at the expected conditions which is what we usually do from an engineering point of view, we need to look at the exceptions or extreme conditions as well such as breaking off a corroded CT lead. I'm just saying this because 10 kV+ voltages can exist in a switchgear control panel due to CT leads although the current is very small.

In terms of shock protection if you read the tables I mentioned if the employee can maintain the RAB/MAD and is using insulated tools then shock protection PPE is not required. The MAD/RAB for the voltages described is 0" (avoid contact). From personal (painful) experience the biggest problem here is that at least in the past we just ran #14 XHHW-2 or THHN to the metering and if you brush up against it accidentally, it can be a pretty painful shock. These days newer installations are usually much better insulated (meeting finger safe requirements), but it's still out there. Hanging a rubber blanket with some clothes pins over it avoids this issue (eliminate the hazard) as well as securing the door, and there's no "rubber shoulder protector". Probing around with uninsulated screwdrivers or fingers is obviously quite a different matter.

Beyond this as described as I mentioned above the 1910.269 regulatory domain may require FR PPE but not in any others even if an arc flash were possible.

Quote:
2. Staff require access to their equipment from the front of the panel. There are no energized circuits adjacent to their work area. The staff utilize insulated leads (up to 1000V), working on ABB Test Blocks with an ABB test handle, AREVA P991 test block with an ASEA test handle, PK blocks with PK test handles, GE test blocks with a GE test handle, Flexi test block with a Flexi test handle, a Westinghouse relays with fingers open, and CGE relays with a skid in order to perform this maintenance. What PPE would be required for this scenario.


Same answers as above. This doesn't change anything.


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 Post subject: Re: Protection Maintenance - arc flash considerations
PostPosted: Mon May 23, 2016 7:55 am 
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Joined: Fri Apr 15, 2011 7:43 am
Posts: 177
Location: Colorado
You mentioned your staff might have to "access to the back of this equipment which is inside of a panel". Without any other information it sounds like they are in an equipment cubicle of switchgear where there will be AC and DC present and as high as 240V. Without knowing more I can only make assumptions. Shock will always be possible and must be taken into consideration but depending on the maintenance being performed the equipment may have to stay energized for testing.

I can also assume the maintenance will be performed by qualified people. In the testing I do I always have 8cal clothing, safety glasses, ect. There is limited power and usually current limiting fuses. This is the minimum most of my clients require.


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