Arc Flash Maintenance Switch

timm333

Senior Member
Location
Minneapolis, MN
I have a question about arc flash maintenance switch (AMS) as per NEC 240.87 (B)(3). NEC 240.87 (B)(5) allows the use of instantaneous trip; does it mean that if the instantaneous trip of older existing breaker is set below the available arcing fault current, then the maintenance switch would not be required?

Also for older existing breakers, is it better to install a separate maintenance switch, or should we use a newer trip sensor which has maintenance switch included in it? Thanks.
 

xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
Occupation
Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
I have a question about arc flash maintenance switch (AMS) as per NEC 240.87 (B)(3). NEC 240.87 (B)(5) allows the use of instantaneous trip; does it mean that if the instantaneous trip of older existing breaker is set below the available arcing fault current, then the maintenance switch would not be required?
Correct. (B) Method to Reduce Clearing Time. One of the following means shall be provided... (this of course assumes, the instantaneous element is adjustable below the arcing current - need to do a study to establish what the arcing current is).

Also for older existing breakers, is it better to install a separate maintenance switch, or should we use a newer trip sensor which has maintenance switch included in it? Thanks.
Depends on the cost and benefit.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I have a question about arc flash maintenance switch (AMS) as per NEC 240.87 (B)(3). NEC 240.87 (B)(5) allows the use of instantaneous trip; does it mean that if the instantaneous trip of older existing breaker is set below the available arcing fault current, then the maintenance switch would not be required?

Also for older existing breakers, is it better to install a separate maintenance switch, or should we use a newer trip sensor which has maintenance switch included in it? Thanks.
A 2020 change made it clear that the setting you are talking about must be the normal setting. In some cases, people were using the instantaneous setting as the arc energy reduction method so additional language was added to the 2020 code.
(5) An instantaneous trip setting. Temporary adjustment of the instantaneous trip setting to achieve arc energy reduction shall not be permitted.
 

timm333

Senior Member
Location
Minneapolis, MN
Thanks. It should be Ok to set the instantaneous to below the arcing current. Because there is no motor inrush current here as large breakers (1200 A and up) are used as main breakers of MCC (not as branch breakers for motors). Also coordination should not be an issue because coordination is done on fault current (not arcing current).

240.87 (B)(3) of NEC-2020 states that it is not permitted to lower the instantaneous setting in the field. Does it mean that if an existing breaker is used (instead of maintenance switch), then the existing breaker would have to be modified so that its instantaneous trip setting cannot be changed in the field?
 

timm333

Senior Member
Location
Minneapolis, MN
I asked the question because at the below link, the second bullet point on the left side says that “”2020 update to NEC Section 240.87 stipulates that it is not permitted to dial down an instantaneous setting in the field.”” Does it mean that when instantaneous trip is used (instead of maintenance switch), then instantaneous trip has to be fixed and canned be adjustable at the site?

https://www.eaton.com/us/en-us/comp...ion/arc-energy-instantaneous-adjustments.html
 

mayanees

Senior Member
Location
Westminster, MD
Occupation
Electrical Engineer and Master Electrician
I asked the question because at the below link, the second bullet point on the left side says that “”2020 update to NEC Section 240.87 stipulates that it is not permitted to dial down an instantaneous setting in the field.”” Does it mean that when instantaneous trip is used (instead of maintenance switch), then instantaneous trip has to be fixed and canned be adjustable at the site?

https://www.eaton.com/us/en-us/comp...ion/arc-energy-instantaneous-adjustments.html
I don't think so. I think you can adjust the Inst to trip for arcing fault currents, then leave it there. I think the 2020 added text intends to prevent adjustment of instantaneous manually for incident energy (IE) reduction when working on the equipment. I don't know why that line's in there because it would be nice to have a procedure that dictates for example that the Inst be adjusted to 5X for an IE of 4 calories. But for some reason they don't want that to happen.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
I don't think so. I think you can adjust the Inst to trip for arcing fault currents, then leave it there. I think the 2020 added text intends to prevent adjustment of instantaneous manually for incident energy (IE) reduction when working on the equipment. I don't know why that line's in there because it would be nice to have a procedure that dictates for example that the Inst be adjusted to 5X for an IE of 4 calories. But for some reason they don't want that to happen.
Usually the arc flash maintenance switch requires testing to confirm it is working, this would not be possible with a temporary field adjustment.
 

timm333

Senior Member
Location
Minneapolis, MN
Some breakers have an internal maintenance switch, and sometimes a separate maintenance switch is to be used. The incident energy goes down if the maintenance switch is turned on. If we use maintenance switch, should the maintenance switch be modeled in the software while performing the arc flash study, or should the arc flash study be done by the traditional method (without modeling maintenance switch in software)?
 

timm333

Senior Member
Location
Minneapolis, MN
I meant to say that on arc flash label, should we show the incident energy with maintenance switch On, or the incident energy with maintenance switch Off?
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
I meant to say that on arc flash label, should we show the incident energy with maintenance switch On, or the incident energy with maintenance switch Off?
IMO, you should only the the worst case. The maintenance switch values can be found in the Energized Work Permit instructions.
 

paulengr

Senior Member
IMO, you should only the the worst case. The maintenance switch values can be found in the Energized Work Permit instructions.

Cannot disagree more. This is a typical and very incorrect response from the “most conservative” crowd who believe they do the world a favor by providing essentially worthless information,

Most practitioners of arc flash studies produce multiple scenarios. One may be all motors off. Another all motors on at full load. Yet another may be a more typical diversity. It may also reflect both mains and a tie closed with an MTM system and under emergency backup generator power. Many of these cases, particularly emergency backup generators due to much lower available fault current result in much higher incident energy values. However many of them are useful for short circuit concerns but are unrealistic for incident energy purposes under normal operation and often all operational conditions. So if you put unrealistic values on the label because it is “conservative” you are not conveying realistic, valuable information at all. Garbage in, garbage out.

Second, the vast majority of use cases would NOT ever invoke an EEWP. If it does you are doing it wrong. You should not issue an EEWP fir every LOTO or you just pencil whip what is designed to be a rare event. The whole reason for the EEWP is the justification line…forcing people to really think if doing energized work is necessary or a good idea. The rest is just conveying work order details. Every electrical lockout for instance requires testing for absence of voltage, an energized task because we assume it is energized until proven dead. Most general electrical maintenance activities such as troubleshooting is often energized work (testing for voltage). The EEWP procedure recognizes and exempts these activities specifically because they always require energized work and requiring an EEWP would be wasteful and dilute the value of the procedure. I know of one plant actually doing this and the result is that they just fill one out for every single electrical task whether needed or not. So it just becomes a bureaucratic firm that just gets pencil whipped. Thus your methodology completely fails in most use cases, or abuses what should be a rare and onerous process.

Still we need to document it somewhere.

One option is to document the incident energy in separate procedure such as if the plant posts detailed LOTO procedures per machine as some do. Another option is to post the alternative values as part of the label. This is also where often you would document WHICH breaker gives the reduction. Many electricians mistakenly believe that using the maintenance switch of the breaker in front of them reduces incident energy where the correct breaker is the one upstream of the one they are about to work on. This may also be a way of conveying the alternative incident energy values when under emergency power conditions.

As to the 2020 NEC prohibition against changing settings what I have seen is plants turning on instantaneous and setting it on distribution breakers to the lowest setting. It often gets forgotten and left that way or the lowest setting causes nuisance tripping where the lowest setting needed to get below the arcing current is the best option. Granted this is exactly the same thing as changing settings but just flipping a switch prevents mistakes and this is likely what the NEC is after. I doubt they mean to lockout setting changes though electricians often just jack up settings without any consideration for the result of “fixing” what they assume is simply a nuisance trip.
 

xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
Occupation
Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
Cannot disagree more. This is a typical and very incorrect response from the “most conservative” crowd who believe they do the world a favor by providing essentially worthless information,
What Jim said is not an incorrect response. It’s impossible to know or control every factor in a power system. Conservative methods are needed because there is a lack of information and it is best to err on the side of caution. The study report can contain various scenarios, but the label generally reports the worst case value.
 

romex jockey

Senior Member
Location
Vermont
Occupation
electrician
Cannot disagree more. This is a typical and very incorrect response from the “most conservative” crowd who believe they do the world a favor by providing essentially worthless information,

Most practitioners of arc flash studies produce multiple scenarios. One may be all motors off. Another all motors on at full load. Yet another may be a more typical diversity. It may also reflect both mains and a tie closed with an MTM system and under emergency backup generator power. Many of these cases, particularly emergency backup generators due to much lower available fault current result in much higher incident energy values. However many of them are useful for short circuit concerns but are unrealistic for incident energy purposes under normal operation and often all operational conditions. So if you put unrealistic values on the label because it is “conservative” you are not conveying realistic, valuable information at all. Garbage in, garbage out.

Second, the vast majority of use cases would NOT ever invoke an EEWP. If it does you are doing it wrong. You should not issue an EEWP fir every LOTO or you just pencil whip what is designed to be a rare event. The whole reason for the EEWP is the justification line…forcing people to really think if doing energized work is necessary or a good idea. The rest is just conveying work order details. Every electrical lockout for instance requires testing for absence of voltage, an energized task because we assume it is energized until proven dead. Most general electrical maintenance activities such as troubleshooting is often energized work (testing for voltage). The EEWP procedure recognizes and exempts these activities specifically because they always require energized work and requiring an EEWP would be wasteful and dilute the value of the procedure. I know of one plant actually doing this and the result is that they just fill one out for every single electrical task whether needed or not. So it just becomes a bureaucratic firm that just gets pencil whipped. Thus your methodology completely fails in most use cases, or abuses what should be a rare and onerous process.

Still we need to document it somewhere.

One option is to document the incident energy in separate procedure such as if the plant posts detailed LOTO procedures per machine as some do. Another option is to post the alternative values as part of the label. This is also where often you would document WHICH breaker gives the reduction. Many electricians mistakenly believe that using the maintenance switch of the breaker in front of them reduces incident energy where the correct breaker is the one upstream of the one they are about to work on. This may also be a way of conveying the alternative incident energy values when under emergency power conditions.

As to the 2020 NEC prohibition against changing settings what I have seen is plants turning on instantaneous and setting it on distribution breakers to the lowest setting. It often gets forgotten and left that way or the lowest setting causes nuisance tripping where the lowest setting needed to get below the arcing current is the best option. Granted this is exactly the same thing as changing settings but just flipping a switch prevents mistakes and this is likely what the NEC is after. I doubt they mean to lockout setting changes though electricians often just jack up settings without any consideration for the result of “fixing” what they assume is simply a nuisance trip.
this fits here>
DES-012_TAB (abb.com)

DES-011_TAB (abb.com)
~RJ~
 

mayanees

Senior Member
Location
Westminster, MD
Occupation
Electrical Engineer and Master Electrician
I meant to say that on arc flash label, should we show the incident energy with maintenance switch On, or the incident energy with maintenance switch Off?
I use two labels for the equipment: one for the worst-case Incident Energy level; and one for the MX Switch scenario with clear indication of which is which.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
Cannot disagree more. This is a typical and very incorrect response from the “most conservative” crowd who believe they do the world a favor by providing essentially worthless information,
Why do you equate worst case as being conservative and thus worthless? This discussion was about labeling for maintenance switches not general labeling.

I have run more than 8 scenarios more than one time, in fact I think I ran 22 for one campus that had multiple sources for each building. The circuits typically fed by small generators do often have high incident energy values but they rarely represent a significant number of locations in a facility.

While EEWP are not need for most general troubleshooting, neither are maintenance switches usually used while facilities are in full operation or production. My experience has been EEWP are usually most appropriate for the same activities as using the maintenance switches.
 

timm333

Senior Member
Location
Minneapolis, MN
For low voltage systems, the arc flash PPE categories are mentioned in NFPA-70E table 130.7(C)(16) and also in NESC Table 410-1. After calculating the incident energy as per IEEE-1584-2018, if we determine the PPE categories as per NFPA-70E Table 130.7(C)(16) then we don’t have to worry about NESC table 410.1, is it correct?
 

xptpcrewx

Power System Engineer
Location
Las Vegas, Nevada, USA
Occupation
Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician
For low voltage systems, the arc flash PPE categories are mentioned in NFPA-70E table 130.7(C)(16) and also in NESC Table 410-1. After calculating the incident energy as per IEEE-1584-2018, if we determine the PPE categories as per NFPA-70E Table 130.7(C)(16) then we don’t have to worry about NESC table 410.1, is it correct?
NFPA 70E and NESC are two different standards with their own applicable scopes (NFPA 70E lists one of the items "not covered" as equipment under the exclusive control of an electric utility...).

The PPE category tables are only applicable when using the arc-flash PPE category method. They don't apply to evaluations conducted using the incident energy analysis method (as with IEEE 1584-2018).
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
The PPE category tables are only applicable when using the arc-flash PPE category method. They don't apply to evaluations conducted using the incident energy analysis method (as with IEEE 1584-2018).
But, NFPA 70E does allow a company to create their own 'PPE Lists' even if they do happen to lineup exactly with the NFPA Categories as long as they are properly documented. Many companies choose this option so they can continue to use their old labels and training procedures.
 
Last edited:

wbdvt

Senior Member
Location
Rutland, VT, USA
Occupation
Electrical Engineer, PE
From what I have seen installed in the field, the arc flash reduction switches are worthless. I say this because the ones I have seen installed are on the main breaker that is part of the switchgear line up and is in the same structure as the feeder breakers. This being the case and the equipment not being arc rated, the main breaker is ignored for the study so any perceived benefit of an arc reduction switch is lost.
 
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