Resistor rating for surge test

[LectroNoob]

I'm designing a new circuit and I have to use SMD resistors directly on 240Vac. The thing is, this device may undergo surges of 6kV (for a couple of uS) and I don't know which package to use to prevent arcs through or over it. It's a 300K so I don't really worry about power and current. Is there a table somewhere for surge vs package of a resistor?

[T3sl4co1l]

Yes, the datasheet gives numbers on that.

You may find you'll need an inconvenient number of resistors in series, following the ratings exactly.  Pulse ratings (with respect to pulse width) are less often provided, and the parts that provide them are more expensive because they've been tested for that purpose.  YMMV.

I normally see 3-4 in series, 1206 size, in an application like that.  Mind that commercial mains is only tested to 1.5/2.5kV surge, not 6.

Resistor ratings aside, note that the layout needs adequate clearance.  For example, IEC 60950-1 requires total creepage and clearance such that, in event of a single component failure (i.e., one resistor shorting), the remainder is adequate.  This is where 3-4 x 1206s comes from.

You may find that it's easier to solve this problem with a few THT resistors, rated for HV or pulse duty.  Depends also on what degree of confidence, of standards compliance, and budget, you require.

Tim

[LectroNoob]

Thank you for your reply.

The problem is space for such a high number of resistors.
They would have to be placed next to each so the surge would jump to one another without going through the resistor.
Maybe THT is the way to go on that one.

Clearance has been taken care off.

[spec]

Hi LectroNoob

A transient voltage suppressor (TVS) may solve your problem and protect the electronics in general: look at the bi directional TVS:

https://www.littelfuse.com/~/media/electronics/datasheets/tvs_diodes/littelfuse_tvs_diode_smcj_datasheet.pdf.pdf

[Benjawran]

It's the information I'm looking for as well.

[PartialDischarge]

Try one unit of the chv2512, I bet they can repeatedly handle 6kv for a few us, but you will have to test. The board will need a cut and probably a bit of coating though.

https://www.mouser.es/datasheet/2/54/HV-777595.pdf

Otherwise use a Vishay VR25, it is rated for that pulse, cheap and small

https://www.mouser.es/datasheet/2/427/vr25vr37vr68-837991.pdf