My objective is to reduce incident energy on the distribution sections of existing low voltage 4000KVA switchboards. I woud like to utilize the main circuit breaker settings to lower the incident energy levels, let's use a SqD QED switchboard with Masterpact main breaker as an example.

The unknowns is releated to the barriers between the line side of the breaker and the load side buss so I pose the following questions.

1. Are the existing lineside/loadside barriers sufficent to permit main breaker settings to reduce incident energy levels in the distribution section of the board.
2. Can extra barriers be added and qualified in some way to permit the proposed energy redcution.
3. Has adding the extra barriers proven some level of "due diligence" in trying to improve the situation.

I look forward to reading the discussion

Thanks

At what point would the short circuit occur?

Are you concerned about reducing the load side AF thermal energy hazard?

Or, you want to reduce the hazard if a short circuit occured at the switchboard mains load side and the AF went over to the line side of the molded case circuit breaker?

I believe you would be best to contact a Sq. D rep. for the barrier question.
I do not know the design myself. I'm sure Sq.D would be glad to quote you a very expensive improved system. One thing with AF safety it comes with an expensive price tag.

Sorry I am not much help. Maybe someone else has seen a system as yours.

Clarification

Our main concern is a load side fault esclating to involve the line side buswork of the switchgear. The additional barriers would be safeguards to prevent this from hapening.

After much reading through other IEEE reports, it seems this topic is not definitiveley covered. Most Arc Flash study discussion papers freely use main circuit breaker settings to mitigate hazards in the feeder sections. Other papers put limits on the type of switchgear this would be permited. Some state ANSI C37.20.1 as minimum build standard.

So my question is...How is to be determined if the switchgear in question is adaquate to allow the use of main breaker settings in reducing feeder section incident energy? What criteria must the gear meet?

The standard that I go by is:
Is the Main in a separate compartment / section?

In some switchgear, the main has a separate section that is walled off from the distribution section. In others, the main is not.
MCC's and Switchgear can be the same way.

For these, I look at them on a case by case basis. There are some where the main may appear to be in a separate compartment, but if you pull the covers off the back, you will find it totally open, and an arc flash event could easily migrate to the line side of the main.

Most Panelboards do not have a separate section for the main breaker. I label the entire panel as if the main breaker does not exist.

I'm sorry if I am thinking wrong. I have seen this breaker once on a SQ.D demo truck its should have some great features to reduce the hazards.

If a fault occurred inside the enclosure on the line side because someone is working in the back of the enclosure with the power on and the flash carried over to the bus bars and kept escalating. That could be a big-big bang. And I am assuming the only protection upstream would be the HV fuse.

I believe this is a common problem at least between the MCCB line side and the transformers secondary (internal to the switchgear). There is no simple solution that I am aware of. There are some very costly ways of detecting the arc but one would have to consider the expense. To many lawyers looking for something like that so I am sure no one would tell you something like extra barriers would work. Not sure Sq.D. would. They are going to say turn off or wear a lot of PPE no matter what.

Why would someone be in this cabinet working with the power on? This would be my first question. Are you concerned about the racking in and out of the breaker? I would see that type of work only using CAT 4 PPE and only after your analysis. Lot of different racking options available.

Now, to hopefully answer your question on setting the breaker for reduced AF fault levels on the feeder.

First one should conduct a device coordination study to determine what device do you need the main switchgear breaker to coordinate with. After that you can adjust your settings to get the proper trip curve. I'll not explain all that, but if you need more help I will try.

Or, during maintenance work on the feeder you can lower the IT to the lowest value so if a fault does occur the thermal energy would be reduced to a safer level on the feeder if you allow that. After the work go back and raise the IT to the normal setting.

Unless your in a hospital and your working in the back of the cabinet hot I see no reason that a fault would occur inside the switchgear. Well excluding something like racking in and out. But this breaker has guide pens that should reduce the hazard in racking. Still would require a Cat 4 suit, I would think.