Yes we are talking about RMS voltage. In order to be used for
Protection Class II, the realy needs to be certified as 250V 
insulation according to IEC60664 (double insulation, Pollution 
degree 3, Overvoltage category III, Voltage rating 250 V ). In
order to achived this, the isolation volatge needs to be much 
higher (3750V AC RMS between the relay contacts and the coil 
contacts).

Regards,
Xiaofan


-----Original Message-----
From: Howard Winter
Sent: Wednesday, September 28, 2005 2:34 AM

> I had to developed some seperate product for Japanese market
> since it is said that the mains voltage is slightly lower than
> the North America (100V versus 110V nomainal and 10% ripple).
> 
> In China the norminal is 220V and in Singapore norminal is 230V.
> So we often have to consider 253V as the higher end of
> AC voltage. The 3V extra than 250V may cause problem with
> the certification body since some relay manufacturers specify
> the isolation voltage (re-inforced insulation) to be 250V.

Hang on!  We're talking about AC RMS voltages - surely isolation has 
to be tested against *peak* voltages, which will be over 300V in the 
ranges we're talking about.

Cheers,


Howard Winter
St.Albans, England


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