Arc Flash Study in Unusual Switch Room

[Callumrb30]

Good Morning/Afternoon,

I am new to the forum and not 100% sure on etiquette for these kinds of queries, so I will keep it brief.

I am in the process of performing an arc flash study (using ETAP), and I have got an unusual looking switching room that I need to model (see attached image).

In the picture, you should be able to see LV circuit breakers mounted on a backboard, with no enclosures. Further to this, several of the CBs have exposed terminals/conductors, which can be seen rising from the top of the breaker and bending backwards behind the panel.

The question I have is - what is the most suitable electrode configuration to use from IEEE 1584? Clearly the breakers are not in enclosures, however the electrodes are not in open air, at least not fully.

Thanks for your time.

Kind regards,
Callum

 

[mls1]

The construction is similar to an MCC without an enclosure so if you use an MCC model you'll get MCC bus gaps in the IEEE 1584 equation and VCB electrode configuration. That will yield a conservative enclosure factor since there is no enclosure to concentrate the energy but that seems appropriate for this installation.

 

[che12345]

Dear Mr. Callumrb30
1. With due respect, the picture shows it looks like it is a display board of various breakers some 100 years ago to the present; in the " museum ? " or a display board by the manufacturer with 200 years of manufacturing history ?.
2. You don't see assemblies in is way in the present days!.
2.1 Go to any industry or even your school's switch room to have an up-to-date knowledge on how the present day MCC assembly looks like.
3. "... performing an arc flash study (using ETAP)," based on the " museum" display board is meaningless.
4. You are welcome to come back. I am at your service at all times, Sir.
Che Kuan Yau (Singapore)

 

[dpc]

che12345,

Life in Singapore may be different, but installations like the one in the photo still exist in the US at least, although they are not common. I'm not sure why you feel the need to mock a legitimate question.

I basically agree mls2, but I'd probably go with VCBB electrode configuration, based on the cables terminating on top of the molded case breakers. Judgement call, though.

Dave

 

[stevenal]

Modelling an enclosure where there is none to focus the energy seems overly conservative to me. Suggest running HOA and VOA and taking the more conservative.

 

[wbd]

che12345,
This is an old switchboard made out of probably slate panels along with some newer board material. In it's original configuration, it probably had knife switches with fuses on the front of the board but they were replaced with breakers at various times, hence the breakers from different eras. It would be nice not to see installations like this but they do exist. As noted above, no need to mock anyone on this, it is what the person has to deal with.

I agree with stevenal and would use an open air equipment configuration.

 

[Callumrb30]

Hi All,

Thanks for your comments, much appreciated!

@che12345 - Thanks for your comments. I am quite familiar with standard switch board configurations and agree that this is prehistoric and belongs in a museum. However, and as others have mentioned, this is what I'm dealing with. The clear recommendation is that it should be replaced with a safer, modern design.

I've gone with @stevenal recommendation and modelled both HOA and VOA. I had wondered if modelling VCB with an enclosure depth of 1mm (minimum), would be appropriate.

Thanks again,
Callum

 

[dpc]

Too lazy to check, but I think a 1 mm depth might be outside the range of the 1584 empirical equations.