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 Post subject: Arc Flash Assessment on breakers with adjustable settings
PostPosted: Wed Jan 22, 2020 3:15 pm 

Joined: Tue Dec 02, 2014 7:46 am
Posts: 14
What is the best method to do arc flash assessment for circuits protected by circuit breaker with adjustable LT & ST pickups? For instance on a 800 amps circuit breaker ST pickup settings varies the arc fault from category 1 to category 3

Settings on the beaker are not lockable.

Is it recommended to set the setting on highest and then label the equipment accordingly for higher category PPE.

Thank you
Sheel Pandey


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 Post subject: Re: Arc Flash Assessment on breakers with adjustable setting
PostPosted: Fri Jan 24, 2020 6:06 am 
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Joined: Wed May 07, 2008 5:00 pm
Posts: 823
Location: Rutland, VT
I think you need to be careful on that setting philosophy as there is more to determining breaker settings than just arc flash.

What about coordination with other breakers?
What about conductor protection?

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Barry Donovan, P.E.
www.workplacesafetysolutions.com


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 Post subject: Re: Arc Flash Assessment on breakers with adjustable setting
PostPosted: Fri Jan 24, 2020 9:11 am 
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Joined: Mon Jan 18, 2010 11:35 am
Posts: 523
Location: Wisconsin
SheelPandey wrote:
Is it recommended to set the setting on highest and then label the equipment accordingly for higher category PPE.


It depends on the company Electrical Safe Work Practices.
Most of my customers will provide labels based on the actual setting of the breaker or relay. The vast majority of adjustable devices can be 'sealed'.

However, I have had a few customers that wanted the labels to be the worst case.


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 Post subject: Re: Arc Flash Assessment on breakers with adjustable setting
PostPosted: Mon Jan 27, 2020 9:07 am 
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Joined: Tue Oct 26, 2010 5:00 pm
Posts: 188
Location: Maple Valley, WA.
When we perform a Protective Device Coordination and Arc Flash Study, we first focus on Selective Coordination of the devices. Then we perform the Arc Flash study and identify locations where the arc flash energy is higher than desired. Then we focus on trying to reduce settings without sacrificing selective coordination. Sometimes it is impossible (with the existing equipment) to obtain low arc flash energy and selective coordination. At these locations, it may be necessary to change the trip unit or relay types that will do both.

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Robert Fuhr, P.E.; P.Eng.
PowerStudies


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 Post subject: Re: Arc Flash Assessment on breakers with adjustable setting
PostPosted: Mon Feb 03, 2020 7:20 am 

Joined: Tue Oct 29, 2019 6:23 am
Posts: 19
As is reflected in the answers posted by others the normal expectation is that the CB is set based on some logical basis, usually a coordination study performed while considering expected loads, transient loads, cable and equipment ratings, etc. And the AF study is performed using those settings. Possible iterating the process if Ei results are undesirable and can be improved by slightly different OCPD settings or selections.

In modern adjustable CBs the settings should be lockable and require a password or a deliberate action to bypass the protection. If,in the subject facility, there is a real risk that personnel are changing settings for whatever reason, not recording those changes and the people performing tasks or exposed to the hazard are not aware, then it may be prudent to take worst case into consideration.

It comes down to risk analysis and risk management. The common experience is that the desired settings are the settings and it flows from there, but if there is a risk or probability that that is not the case then "you" need to decide if the residual risk is acceptable and if not implement an action or control that reduces the residual risk to an acceptable, at a minimum. Using worst case EI numbers may be one way, another may be to implement administrative procedures that verify settings before a worker executes task or approaches the hazard, etc. What ever you do needs to fit within the electrical safety policies and procedures of the facility, be reasonable within the context of the skill sets of the workers potentially exposed, fit within the context of how equipment is maintained and operated, etc.

Hope this helps... I think the answer that I provided, in short is... it depends! :shock: :)


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 Post subject: Re: Arc Flash Assessment on breakers with adjustable setting
PostPosted: Mon Feb 03, 2020 7:25 am 
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Joined: Tue Jan 19, 2010 2:35 pm
Posts: 138
The real answer, as someone else probably has said "it depends". It depends on several questions. First, are you performing a coordination study? If so, then you might adjust several pick up settings for other breakers as well as this one. Is there a high arc flash hazard that could be addressed by adjusting the instantaneous pick up setting of this breaker? What affect would adjusting the pick up setting have on the facility operations? Meaning, if the breaker tripped, what are the affects on the rest of the building? What about safety? Is safety the number one priority for these people? And of course, what affect does adjusting the pick up have on any down stream OCDs?
So, if you have a very high arc flash hazard with the breaker properly coordinated, yet adjusting the setting a bit lower would greatly affect the arc flash hazard (usually it does help) however, lowering the instantaneous would adverse affect the overall coordination, you'd want to discuss this with your client so they understand about the good, the bad and the ugly for the options.


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