Hi,

 For internal layers I am under the impression that higher voltage can be handled at the same distances as on external layers.

 The assumption here is internal glass and epoxy is a much better insulator than the air and solder mask on the external. 

 Yes / No? Any thoughts?
Bob K.

-----Original Message-----
From: TechNet <[log in to unmask]> On Behalf Of Decker, Scott Collins
Sent: Monday, January 28, 2019 12:34 PM
To: [log in to unmask]
Subject: Re: [TN] [External] [TN] IPC2221 Electrical Conductor Spacing Requirements

Steven,
  I would go with the maximum 31-50V option. For starts, the spacing for the 16-30 is pretty small, so unless you are working with some really high density trace spacing, use the 31-50V value. Understanding that this is for the B4 bare board external traces with a Soldermask. Even if you are on internal layers, I would use the higher value just to be safe. In my opinion, you are just looking to make it more robust and reliable in the long run. If you want cutting edge, maybe you push it, but over time, you might find yourself wishing you didn't? :-) Since you didn't mention what layers these lines were on or if you had Soldermask on the outside, but if not I would for sure go with the larger voltage spacing value. Hope that helps.
Later... 

Scott Decker | Senior Engineer, PCB Design Services CID+ | Electronic Systems Center COLLINS AEROSPACE
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steven Schell
Sent: Monday, January 28, 2019 9:55 AM
To: [log in to unmask]
Subject: [External] [TN] IPC2221 Electrical Conductor Spacing Requirements

Hello  Technetters,

I am trying to interpret the electrical clearance requirements in the IPC2221A standard, under section 6.3.
Table 6-1 lists minimum spacing requirements for various voltage ranges between conductors.
The table indicates that this is for AC or DC peaks.
I am trying to interpret that last part.
Our application has a tracking power supply that provides a variable DC output voltage.  The average DC voltage is between 16 and 30V, but the peak instantaneous DC voltage exceeds 31V.  
In this case, should I be complying with the minimum spacing requirements for 16-30V, or should I be complying with the minimum spacing requirements for 31-50V.

I guess I am not clear what the intent of the voltage thresholds is.

Thank you for any help or insight.