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How should incident energy from arc energy reduction methods be addressed on arc flash labels?
List normal incident energy only
List reduced incident energy only
List BOTH normal and reduced incident energy
Doesn’t apply
It depends
Something else
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 Post subject: Labels and Arc Energy Reduction
PostPosted: Sun Jul 11, 2021 9:41 am 
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NEC Article 240.67 and 240.87 provide requirements regarding arc energy reduction
Arc energy reduction methods are used to reduce the arc duration (device clearing time) and as a result, reduce the incident energy.

A common question is how to incorporate the reduced incident energy on arc flash labels (equipment labels)

So, this week’s question is:

How should reduced incident energy from arc energy reduction methods be addressed on arc flash labels?
• List normal incident energy only
• List reduced incident energy only
• List BOTH normal and reduced incident energy
• Doesn’t apply
• It depends
• Something else


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Mon Jul 12, 2021 7:20 am 
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The use of the maintenance mode arc flash reduction switch is not optional. Listing anything but the reduced energy level incorrectly implies the use of the switch is decided by the worker. Signage should clearly indicate the IE exposure listed is the maintenance mode value, and that maintenance mode is required.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Tue Jul 13, 2021 5:11 pm 
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stevenal wrote:
The use of the maintenance mode arc flash reduction switch is not optional. Listing anything but the reduced energy level incorrectly implies the use of the switch is decided by the worker. Signage should clearly indicate the IE exposure listed is the maintenance mode value, and that maintenance mode is required.

Absolutely the maintenance switch is optional.
For example a feeder to a Motor Control Center would normally be in the operating mode with the resultant high AFIE at the equipment while in production. During periods of maintenance, when production is not needed, the lower AFIE could be experienced.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Tue Jul 13, 2021 5:15 pm 
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My concern with listing both numbers is people choosing the improper value because they do not understand the label.
I have seen this occur in at least two different facilities.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Wed Jul 14, 2021 7:23 am 
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JBD wrote:

Absolutely the maintenance switch is optional.
For example a feeder to a Motor Control Center would normally be in the operating mode with the resultant high AFIE at the equipment while in production. During periods of maintenance, when production is not needed, the lower AFIE could be experienced.


Okay, I should have said it's use is not optional during maintenance.

The high IE during normal operation is not a concern, since no one should be doing maintenance with the switch in the normal position.

Also note that production should not be affected by using maintenance mode. Only protective coordination is affected.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Wed Jul 14, 2021 6:46 pm 

Joined: Fri Jul 10, 2009 10:14 am
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Location: West Central, OH
But when you maintenance mode changes incident energy from 7 to 3, does it really matter if it is used? We are really pushing upstream protection to lower base incident energy all the time so seeing this low energy at 480v substation secondary connections.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Sun Jul 18, 2021 5:29 pm 
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stevenal wrote:
JBD wrote:

Absolutely the maintenance switch is optional.
For example a feeder to a Motor Control Center would normally be in the operating mode with the resultant high AFIE at the equipment while in production. During periods of maintenance, when production is not needed, the lower AFIE could be experienced.


Okay, I should have said it's use is not optional during maintenance.

The high IE during normal operation is not a concern, since no one should be doing maintenance with the switch in the normal position.


So normal production troubleshooting should not be performed?
How about when the motor control center has a normal AFIE of 6.7 and a maintenance mode level of ,80?


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Mon Jul 19, 2021 7:16 am 
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JBD wrote:
So normal production troubleshooting should not be performed?
How about when the motor control center has a normal AFIE of 6.7 and a maintenance mode level of ,80?


If there is a possibility this troubleshooting would cause an arc flash, it should be performed with the switch in maintenance mode. No need to stop or alter production.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Mon Jul 19, 2021 12:53 pm 
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stevenal wrote:
If there is a possibility this troubleshooting would cause an arc flash, it should be performed with the switch in maintenance mode. No need to stop or alter production.


Voltage testing can always be a cause of an arc flash.
Many maintenance switch settings can not be selectively coordinated, thus they might affect production.
The values in my example came from settings so low equipment could not be stared without causing an instantaneous trip.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Wed Jul 21, 2021 6:20 am 

Joined: Fri Sep 28, 2018 7:32 am
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Location: Sioux Falls, SD
I much prefer labeling the hazards as they result from the system in normal operating conditions. Any adjustments that can be made (use of a transfer switch, maintenance mode switch, etc.) are task based. A separate risk assessment should be done for these tasks and a safe work procedure put in place to direct personnel and properly identify any changes this work has on the hazards they are exposed to.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Wed Jul 21, 2021 7:17 am 
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JBD wrote:

Voltage testing can always be a cause of an arc flash.
Many maintenance switch settings can not be selectively coordinated, thus they might affect production.


Voltage testing during normal production? I would suggest adding some permanent voltage metering/recording to eliminate this hazard.

Selective coordination only comes into play if a fault occurs. If faults happen so frequently that production is a concern, I would suggest a re-evaluation of the system. Safety versus production? Is this really a difficult choice?

Higher IE PPE is not the conservative approach. Lowering the IE is.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Sat Jul 24, 2021 11:30 am 
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stevenal wrote:
JBD wrote:

Voltage testing can always be a cause of an arc flash.
Many maintenance switch settings can not be selectively coordinated, thus they might affect production.


Voltage testing during normal production? I would suggest adding some permanent voltage metering/recording to eliminate this hazard.

Selective coordination only comes into play if a fault occurs. If faults happen so frequently that production is a concern, I would suggest a re-evaluation of the system. Safety versus production? Is this really a difficult choice?

Higher IE PPE is not the conservative approach. Lowering the IE is.


I guess I should have said NFPA 70E permitted maintenance during production 'like' voltage testing.

Selectivity during normal production is fine. Faults are not a common occurrence. It is just the maintenance switch lowers the protective device instantaneous setting to a level where some motor starting to look like a short circuit.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Mon Jul 26, 2021 7:16 am 
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JBD wrote:

Selectivity during normal production is fine. Faults are not a common occurrence. It is just the maintenance switch lowers the protective device instantaneous setting to a level where some motor starting to look like a short circuit.


Can't you increase the pickup to allow the starts? Pickup won't affect IE unless faults are not cleared.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Mon Jul 26, 2021 8:00 am 
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stevenal wrote:

Can't you increase the pickup to allow the starts? Pickup won't affect IE unless faults are not cleared.


No.
Any higher setting results in the normal, non-maintenance mode, IE level.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Mon Jul 26, 2021 9:50 am 
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JBD wrote:
stevenal wrote:

Can't you increase the pickup to allow the starts? Pickup won't affect IE unless faults are not cleared.


No.
Any higher setting results in the normal, non-maintenance mode, IE level.


I'm missing something here. IE depends on clearing time, distance from arc, electrode configuration and spacing, open air versus in a box, and arcing fault current. Changing the pickup changes none of those factors as long as the arcing fault current remains above pickup.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Tue Jul 27, 2021 6:31 am 
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stevenal wrote:

I'm missing something here. IE depends on clearing time, distance from arc, electrode configuration and spacing, open air versus in a box, and arcing fault current. Changing the pickup changes none of those factors as long as the arcing fault current remains above pickup.


You are missing the fact the maintenance switch moves the pickup point from being to the left of the arcing fault current to the right of it.

Maintenance switches affect the clearing time used in the incident energy equation. They serve no other purpose.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Tue Jul 27, 2021 7:24 am 
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JBD wrote:
You are missing the fact the maintenance switch moves the pickup point from being to the left of the arcing fault current to the right of it.

Maintenance switches affect the clearing time used in the incident energy equation. They serve no other purpose.


I agree with the second statement and not the first. Moving the pickup to the right of the arcing fault current would ensure no tripping occurs for the event you wish to lower IE for. I think you are confusing pickup (amps) with time (seconds or cycles).

In any case, maintenance switches should be part of an engineered approach to lowering IE. If maintenance mode results in inadvertent tripping during motor starts, suggest looking at ways of avoiding this result rather than not using the switch.


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 Post subject: Re: Labels and Arc Energy Reduction
PostPosted: Tue Jul 27, 2021 11:48 am 
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Here's a graph I recently made for our operators to illustrate how it works.
Attachment:
Protection curves .pdf [251.36 KiB]
Downloaded 18 times
Red is the normal TOC curve, black is maintenance mode. Both curves are adjusted to show relay plus breaker time. Both have the same pickup of 564 A. If the lower curve failed to work with normal load cycling, I would look at increasing its pickup.

For the low voltage folks, I offer this wisdom from WEG: "Choose a pickup setting for the Maintenance Mode
System that is:
1. Below 75% of calculated arcing current.
2. Above the total transient load current."
See https://static.weg.net/medias/downloadcenter/h3a/h68/WEG-arcflash-maintenance-mode-article-en.pdf


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