Adding a Knock Out to an Existing Panel - Does it Void UL Listing?

[djr3203]

Hey All,

Did a search and couldn't find a previous post... Does anyone know if it is acceptable to add a knock out to the side of an existing panel in which there is no more room on the top of the panel for a new conduit? Would doing this void the UL listing of the panel?

Thanks for any info you can provide.

DJR

 

[jraef]

Punching a hole an leaving it as a hole? Yes, you will have violated the UL listing of the box.

Punching a hole and using it to make an appropriate connection with a listed device that meets or exceeds the rating of the enclosure when properly installed, then properly installing it? Perfectly fine.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[djr3203]

Gotcha. So there really isn't any restrictions to how many knock outs you can add to a panel? I feel like at some point wouldn't it undermine the panelboards ability to withstand the forces imposed on it during an arc flash incident?

Although I just called some other contractors I know and they said they do add knock outs all the time.

Thanks for responding jraef!

DJR

 

[dpc]

If the concern is arc-flash - the panelboard has no arc-flash rating. It is not tested for arcing fault as part of the UL requirements. So nothing you do to the panel will impact the arc-flash evaluation.

 

[jraef]

I suppose that at some point as it comes to resemble Swiss cheese, you may find that a mfr will not support that many holes being punched because it compromises the structural integrity of the steel, but why would one do that?


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[djr3203]

DPC, you're right and I didn't mean to imply the panel was rated for arc flash (obviously that is really incorrect). Obviously arc flash incident energies are for determining PPE requirements for live work.

I meant to say the explosion resulting from the fault. I thought, that depending on the AIC rating of the panel, the panel was tested to handle that short circuit current for UL listing. I thought that to pass the test, the panel had to be able to take the listed short circuit current for a set amount of cycles without a certain amount of damage to the panel.

Jraef, ya I figured it would probably take a lot of holes to really compromise the enclosure, but you never know if you have someone foolish who does punch the enclosure to swiss cheese. I just didn't want to get caught with a technicality that made my solution incorrect and called out by an inspector.

Thanks for the input!

DJR

 

[racookpe1978]

Make a rational engineering decision.

 

[ogbuehi]

I've always wondered this as well. I have seen some panels with 60+ circuit breakers. It just seems that if a knockout was punched for every CB, the box might not be structurally sound anymore.

 

[waross]

Consider that some panels are supplied with NO knock-outs. All the KOs must be field punched or cut.

Bill
--------------------
"Why not the best?"
Jimmy Carter