Arc Flash Labeling Multiple Voltage Srouces

[Captslowe]

Hello,

I am completing an arc flash study for a building with new electrical equipment. The contractor installed a 480VAC panel that feeds a stepdown transformer ~50' away. This transformer then feeds back into the aforementioned panel with 208VAC. Meaning the panel in question has two voltage sources.
I have looked through the 2021 NFPA 70E and cannot find anything that would be related to this in Article 130.5

Would I label this panel the worst of the 480VAC and 208VAC incident energy? Both?
What is the nominal system voltage I would put on the label?

 

[jim dungar]

Would I label this panel the worst of the 480VAC and 208VAC incident energy? Both?

I have done these with a single label showing the worst case incident energy and the highest voltage. Remember the arc flash warning label is for selecting proper PPE it does not replace equipment nameplate labeling requirements, such as a warning of multiple voltage sources.

This situation also comes up when customers want labels on transformer enclosures.

 

[Captslowe]

I have done these with a single label showing the worst case incident energy and the highest voltage. Remember the arc flash warning label is for selecting proper PPE it does not replace equipment nameplate labeling requirements, such as a warning of multiple voltage sources.

This situation also comes up when customers want labels on transformer enclosures.

Ok. Single label is what I was thinking.
Is there a reason to select the higher of the two voltages? Shock boundary?

As for the multiple voltages, the panel labels reflect this information.

For the transformer enclosures are you referencing the primary and secondary of the transformer?

Thank you!

 

[jim dungar]

Yes, you need to be wearing PPE appropriate for the maximum exposed voltage.

Most smaller, ≤300kVA, dry type transformers do not have separate compartments for the primary and secondary.

 

[petersonra]

Hello,

I am completing an arc flash study for a building with new electrical equipment. The contractor installed a 480VAC panel that feeds a stepdown transformer ~50' away. This transformer then feeds back into the aforementioned panel with 208VAC. Meaning the panel in question has two voltage sources.
I have looked through the 2021 NFPA 70E and cannot find anything that would be related to this in Article 130.5

Would I label this panel the worst of the 480VAC and 208VAC incident energy? Both?
What is the nominal system voltage I would put on the label?

I don't see why you could not label the IE for both voltages if it trips your trigger. I don't know what it would gain you though.

 

[Captslowe]

I don't see why you could not label the IE for both voltages if it trips your trigger. I don't know what it would gain you though.

I don't want to confuse any person that might be working in the panel by having two labels with two different ratings on the panel.

 

[petersonra]

I don't want to confuse any person that might be working in the panel by having two labels with two different ratings on the panel.

I don't see how having two ratings that were clearly labeled as to what they mean would be especially confusing. But it is a judgment and cost call. If you don't want to do it, then don't.

Personally, I would be more worried about making sure it is clear there are multiple voltages present and where they come from, and how to disconnect them.

 

[Captslowe]

I don't see how having two ratings that were clearly labeled as to what they mean would be especially confusing. But it is a judgment and cost call. If you don't want to do it, then don't.

Personally, I would be more worried about making sure it is clear there are multiple voltages present and where they come from, and how to disconnect them.

Yeah, I get it. You and I might find two labels not confusing, but one label is impossible (hopefully) to misinterpret.

As for the multiple voltages... That is already clearly labeled from the installer.

Thank you

 

[wbdvt]

But why put two labels? Suppose the person working in the cabinet is only there to work on the 208V system and wears appropriate arc rated PPE for the incident energy level at 208V but causes an arc that propagates to the 480V equipment and then the incident energy is the 480V IE (possibly higher) but the PPE is inadequate for that level?

I label situations like this with the worst case IE and shock hazard. Then the person is protected for worst case.