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 Post subject: LV SWG Arc Flash calculation (with panelboards)Posted: Thu May 16, 2019 4:38 am

Joined: Thu May 16, 2019 4:10 am
Posts: 5
Hello

I have a Siemens LV SWG, 5000A, 600V, 3ph, 100kA.

For Arc Flash calculation in ETAP I asigned it as SWG and calculate the incident energy for 24in working distance.

In fact, the SWG has 3 compartments: in the middle is bus bar compartment and in the front compartment, except first two cubicles, there are panelboards for fused disconnect switches.

It is true the load side and the line side of fused DSWs are very close to operator when open the door , there is the reason for a smaller working distance.

We are working in a team of two. My colleague with is my supervisor in this project, consider we have just to reduce the working distance to 18in.
We obtain 51cal/cm2.

I disagree with this approach and I need a confirmation on this forum if possible.

Arc flash incident energy is calculated to the bus bars compartment and the 51cal/cm2 is not applicable to the accessible live part in panelboard. We should consider a panelboard in a SWG. In this case the incident energy is maximum 24cal/cm2.

My analyse is based on the fact bus bar compartment and front panelboard compartment are insulated from an arc flash point of view. I need a confirmation for it.

The SWG is used at about only 60% of its nominal current capacity and about 50% of its short-circuit capacity and is relativelly new (2008).

With an arc flash label of 51cal/cm2 it is prohibited to work on any panelboard without tripping the main CB. It doesn`t make sense for me to shut down the plant for changing a 30A heater fuse.

In plus, in panelboard, there are termination shields on the line live side and warning lables about procedures, which, in my mind, is applicable when you open the door and work under voltage, for example to check or replace a fuse.

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 Post subject: Re: LV SWG Arc Flash calculation (with panelboards)Posted: Mon May 20, 2019 8:25 am
 Sparks Level

Joined: Tue Jan 19, 2010 2:35 pm
Posts: 152
There are many unknowns in your description.
Is this a switchgear or switchboard? You say SWG, which I assume means switchgear, but you also mention 30 amps fuses and a panelboard.

It would be useful for you to post pictures. Specifically a picture of the nameplate on the gear as well as pictures of the gear itself and the room it's in. Seeing those could help members to get a better idea of the context.

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 Post subject: Re: LV SWG Arc Flash calculation (with panelboards)Posted: Mon May 20, 2019 8:33 am
 Sparks Level

Joined: Tue Jul 01, 2014 8:40 am
Posts: 106
Hello,

You are asking us to provide confirmation on something unfortunately you have not provided us with allot of detailed parameters on. As mentioned below if you could pleae provide the members with some photos and further description. I anticpate that SWG is referring gto switchgear?

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 Post subject: Re: LV SWG Arc Flash calculation (with panelboards)Posted: Tue May 21, 2019 11:07 am

Joined: Thu May 16, 2019 4:10 am
Posts: 5

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 Post subject: Re: LV SWG Arc Flash calculation (with panelboards)Posted: Tue May 21, 2019 11:08 am

Joined: Thu May 16, 2019 4:10 am
Posts: 5
and the panelboad nameplate, SWG front compartment starting cubicle 3

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 Post subject: Re: LV SWG Arc Flash calculation (with panelboards)Posted: Tue May 21, 2019 11:13 am

Joined: Thu May 16, 2019 4:10 am
Posts: 5
SWG front and side view

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 Post subject: Re: LV SWG Arc Flash calculation (with panelboards)Posted: Wed May 22, 2019 6:32 am
 Arc Level

Joined: Mon Jan 18, 2010 11:35 am
Posts: 544
Location: Wisconsin
I treat that type of construction as having (1) Arc Flash value, based on the incoming lugs, for the entire switchboard line up. I don't believe there is an internal compartmentalization at all. An Arc Flash in one of the fusible switches could easily propagate to the horizontal cross bus and then across the main protective device.

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 Post subject: Re: LV SWG Arc Flash calculation (with panelboards)Posted: Wed May 22, 2019 9:40 am

Joined: Thu May 16, 2019 4:10 am
Posts: 5
Now I have the Siemens confirmation, the equipment is a Switchboard.
I found in ETAP a tool, is a manual setting calculator for arc flash energy, really nice tool.

It confirms, the 18in working distance is outside the restricted boundary area and the energy at this distance, as expected, is about 24cal/cm2.

Thanks a lot to all of you who expressed the interest in this topic.

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 Post subject: Re: LV SWG Arc Flash calculation (with panelboards)Posted: Mon Jun 03, 2019 7:21 am

Joined: Thu Jan 25, 2018 7:13 am
Posts: 2
Location: DFW Area TX
So, according to the nameplate data the restricted approach boundary would be 12" but that has zero relevance on the arc flash incident energy. Two separate hazards. Just my opinion...but we teach they are separate.

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 Post subject: Re: LV SWG Arc Flash calculation (with panelboards)Posted: Mon Jun 03, 2019 8:28 am
 Sparks Level

Joined: Tue Jan 19, 2010 2:35 pm
Posts: 152
I have a Siemens LV SWG, 5000A, 600V, 3ph, 100kA.

For Arc Flash calculation in ETAP I asigned it as SWG and calculate the incident energy for 24in working distance.

In fact, the SWG has 3 compartments: in the middle is bus bar compartment and in the front compartment, except first two cubicles, there are panelboards for fused disconnect switches.

It is true the load side and the line side of fused DSWs are very close to operator when open the door , there is the reason for a smaller working distance.

We are working in a team of two. My colleague with is my supervisor in this project, consider we have just to reduce the working distance to 18in.
We obtain 51cal/cm2.

I disagree with this approach and I need a confirmation on this forum if possible.

Arc flash incident energy is calculated to the bus bars compartment and the 51cal/cm2 is not applicable to the accessible live part in panelboard. We should consider a panelboard in a SWG. In this case the incident energy is maximum 24cal/cm2.

My analyse is based on the fact bus bar compartment and front panelboard compartment are insulated from an arc flash point of view. I need a confirmation for it.

The SWG is used at about only 60% of its nominal current capacity and about 50% of its short-circuit capacity and is relativelly new (2008).

With an arc flash label of 51cal/cm2 it is prohibited to work on any panelboard without tripping the main CB. It doesn`t make sense for me to shut down the plant for changing a 30A heater fuse.

In plus, in panelboard, there are termination shields on the line live side and warning lables about procedures, which, in my mind, is applicable when you open the door and work under voltage, for example to check or replace a fuse.

Looking at the ID tags and photos, This gear does not look like it is a switchgear. Based on the photos, I'd urge you to treat the entire gear as a switchboard and label the entire swtichboard with the highest arc flash calculation, that is UNLESS you can insure the main breaker is properly isolated from the rest of the switchboard.

My concern is propagation of an arc that starts inside the main disconnect cubical. If the main breaker is properly isolated by a barrier from the rest of the board, then you could consider labeling with two arc flash values. One at the main and one for the rest of the board. The arc flash at the main breaker is probably very high. But I'd imagine the arc flash values fall sharply after the main breaker.

There are some options to consider. First, I'd contact the manufacturer (have the ID tag available) and ask if the main breaker in this gear is isolated to prevent an arc from spreading to the rest of the gear. Second, you might consider the fusing on the primary of the transformer feeding the board. If this is a utility provided and owned transformer, you should be able to get information on the fuses. It's possible the fuse may help limit the arc flash, however, I don't think considering the fuse is necessarily a wise idea and I don't think relying on a primary fuse is always wise. Finally, if the manufacturer states that main breaker is isolated to prevent an arc from spreading to the rest of the board, does the main breaker have an "instantaneous" trip option? If it does, it's likely the instantaneous trip could be set to reduce the arc flash hazard downstream in the switchboard portion. It is also possible there's a maintenance setting or switch on the main breaker. If there is, I'd recommend using the maintenance switch or setting when working on the switchboard.

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