Arc Flash when operating breakers

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jott

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Is operating breakers in switchgear considered working on live equipment and require the PPE indicated on the Arc Flash warning label?


This issue came up because there is a site that had 4000A switchgear with no labels, they were replaced in kind with new 4000A switchgear but an Arc Flash study was completed and labels were installed as required. Several of the main sections are dangerous. The operations personal received training that they must meet the level of PPE on the label to operate breakers, so they say they cannot operate any of the switchgear with a dangerous label. This switchgear does not have remote control, it is main tie main with PLC control but manually directed from controls above the main breaker. Is it correct that the operations personal cannot safely operate this equipment? Does opening and closing breakers in switchgear with the doors closed require the same PPE as having the doors open? I?m looking in 70E and OSHA but I can?t seem to find anything that says operating breakers requires a lower level of PPE, only that hazards must be evaluated, but I can?t find any guidance for when it would be appropriate to lower the PPE required. How do others interpret this?


Thanks much.
 
jott said:
Is operating breakers in switchgear considered working on live equipment and require the PPE indicated on the Arc Flash warning label?


This issue came up because there is a site that had 4000A switchgear with no labels, they were replaced in kind with new 4000A switchgear but an Arc FlasHow do others interpret this?


Thanks much.
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Just the way you do. It is not hot work in terms of voltage contact, but if the arc flash rating is dangerous, you have to d-energize upstream device score operating. Or fit a remote operating device.

The doors may not withstand the pressure wave from an arc, and so may be just as hazardous as or more hazardous than doors open

That is subject to separate evaluation. In the absencea of that, do not use those breakers as switches or take steps to reduce the rating.
Please excuse ought-to-correct.ought-to-correct
 
Can the study be run again to determine the boundary with the cover closed/ deadfront on? I think that will answer the question.
 
mgookin said:
Can the study be run again to determine the boundary with the cover closed/ deadfront on? I think that will answer the question.
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Probably not.

Neither NFPA 70E, not IEEE1584, contain any methodology for reducing incident energy based on wether there is an open or closed door. The risk of initiating an arc is treated separately from the incidenet energy calculation.
 
jott said:
Is operating breakers in switchgear considered working on live equipment and require the PPE indicated on the Arc Flash warning label?
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working on energized equiment and interacting with it in a manner that can cause an arc flash are two separate issues.

You must wear arc flash PPE if you are within the Arc Flash boundary and there is a risk of an arc flash.
You must act like you are working on energized equipment (e.g. use voltage rated PPE and tools) when you are within the restricted approach boundary.
 
jott said:
Thanks much for all the replys you have all be helpful.
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I know it is common with molded case circuit breakers for them to be vented of the line end of the breaker in the area of the line end termination. As such should there be and internal issue with the contacts and arc chutes those vents could be a means for the arc to extent outside of the breaker at the line end. If the air around the line side terminations is given the opportunity to ionize the arc that may extent from the inside of the breaker may involve another line/phase to ground and escalate from there.
The vents are often time hard to detect because of the way that is molded into the case but are clearly evident in some navy breakers where this often a fine screen over the opening as I recall.
Even though this would be an extremely rare occurrence that's what PPE is for.
 
We recently had faults in a 5kV line starter and more recently a 15kV air circuit breaker that were initiated when the device was closed. Had someone been operating the device locally (both were operated remotely) they could have been possibly severely injured.

I become more of a proponent everyday of wearing CAT rated gear while operating switching devices within the arc protection boundary, though in the case of gear doors flying open I'm not sure it would help much...
 
wiigelec said:
I become more of a proponent everyday of wearing CAT rated gear while operating switching devices within the arc protection boundary, though in the case of gear doors flying open I'm not sure it would help much...
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Best thing when worried about doors is to watch where you stand while operating. (Unless you are not sure what part of the wall will be coming at you.):)
An Arc Flash can turn corners.
 
wiigelec said:
We recently had faults in a 5kV line starter and more recently a 15kV air circuit breaker that were initiated when the device was closed. Had someone been operating the device locally (both were operated remotely) they could have been possibly severely injured.

I become more of a proponent everyday of wearing CAT rated gear while operating switching devices within the arc protection boundary, though in the case of gear doors flying open I'm not sure it would help much...
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Arc blast (blowing of panel doors) from arc flash is a consequence of high arc incident energy. So if the arc incident energy is reduced, the arc blast risk is reduced. Retrofitting the switchgear with quick trip device and kirk interlock key may help in that direction.
If financially sound, arc resistant switchgear, the best option.
 
Sahib said:
Arc blast (blowing of panel doors) from arc flash is a consequence of high arc incident energy.
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Not always.
A small amount of fault current that lasts for an extremely long time will have a resultant high arc fault incident energy level but a very low blast force (similar to arc welding).

Arc blast usually comes from the 'rate of rise' of the fault current, as well as the total amount of incident energy.
 
Arc blast (blowing of panel doors) from arc flash is a consequence of high arc incident energy.
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The 5kV fault was a phase-phase fault with a very slow trip time (2 sec) on a CAT 3 (15 cal) bus. 3/8" thick terminations were vaporized and propelled at the gear 4 feet across the way, and the room was filled with smoke. This would have resulted in severe burns to the unprotected in front of the contactor. This was a perfect example of why IEEE 1584 calculations are based on 3-P (worst case) faults.

The 15kV fault was a phase-phase fault on a CAT 3 (12 cal) bus that quickly escalated to a ground fault. I haven't yet had a chance to look at the TCC's so I can't tell you the fault duration, but I imagine it was on the order of several cycles. Not a lot of burning and vaporized copper in this instance, but forceful impact and significant smoke. Standing in front of the breaker during this fault would have resulted in little burn injury and a major whack from the breaker door which is about 4 feet tall.

Retrofitting the switchgear with quick trip device and kirk interlock key may help in that direction.
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That only works when the bus is equipped with a main breaker and not tied directly to the secondary of the transformer, which seems to be the way they liked to do things in these parts in the '70s.

If financially sound, arc resistant switchgear, the best option.
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Yup...
 
Safety First

Safety First

On our site we have 6 switchgears rated at 4k amps. There has not been any arc flash studies to determine the incident energy of an arc flash for each switchgear in regards to racking and opening/closing of breakers. We are contracted electrical services and do not own any of the equipment. The company who contracted us refuses to pay for an arc flash study yet we still are required to maintain the equipment. Our safety requires that since there are no available incident energy ratings on any of the switchgears, that we have to use Hazard Category 4 protective equipment as rated by NFPA 70E for protective equipment in which requires a 40/cal rated full suit. So for any racking or opening/closing of breakers this seems like a viable solution due to the infrequency of racking switchgear breakers. It takes 2mins to put on the 40cal suit and 15 seconds to rack the breaker and close the contacts. If you plan on working on this equipment for long or profession please take the time to make sure you are protected. At the end of the day the business owners do not care who works for them or what happens to you. IE the lack of arc flash studies being done so you the employee know the incident energy ratings of the equipment you work on and which ppe to wear to protect you. Remember that the NFPA hazard categories of PPE are only the required minimum to keep from killing you, not severly maiming you for life, and that a person outside of the arc flash blast area should be watching you while you are racking these breakers to pull you out if something happens and to contact EMS.
 
Uh-oh

Uh-oh

User2,

I assume your 4000-amp switchgear is low voltage, under 600V, in which case I can pretty much assure you that the 40 cal suit won't protect you on that system, as the incident energy (IE) level is probably closer to 120 calories/ sq inch, for which there is no safe way to access it locally.

The most important thing you can do is get the arc flash analysis performed so you know exactly what your dealing with. 70E dictates that it is your employer's responsibility to inform its employees and contractors of the danger, and it sounds to me like they've just given you the highest recommended PPE for energized work, 40 cal/sq-cm, without knowng the actual hazard.
 
Sahib said:
In short, on amount of incident arc energy per unit time.
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Short is good, but not when it is incorrect.

Let E(t) be the total incident energy as a function of time.

For some value of t arc has extinguished and E(t) becomes constant. That is theq total incident energy.

The amount if incident energy per unit time is the first derivative of that function, E'(t).

But the rate of rise of the current,as cited earlier is related to though not identical to the second derivative, E''(t).
 
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