PCB voltage insulation

[tekman11]

Is it expectable to run a low voltage trace on the inner layer. the top/bottom carries AC max 275v.
The low voltage trace is routed on ground plane.  the power plane is un-routed. 
I'm concern about arcing between top and ground layer.

The PCB stack up: top, gnd, power,  bottom.  The distance between top and ground is ~28mils.
The two layers are separated by prepreg. The construction is FR4.

 
 thanks

[Rerouter]

I went digging, and accounting for aging effects, FR4 still has a dielectric breakdown voltage of 300V per mil, so would seem you are fine to do so,

http://www.magazines007.com/pdf/High-Voltage-PCDesign.pdf

[Zero999]

Don't forget that in order to comply with the regulations for reinforced insulation, it must be able to withstand much higher voltages, up to 6kV if I remember rightly, so 28 thou is probably the minimum thickness.

I hope you're also aware of the creapage and clearence requirements.