Our product is an energy meter with an internal flyback power supply that
mounts in Level III enclosures i.e. switchboards.

The voltage connections are Neutral, P1, P2, P3.

Neutral is required to be connected to the building Neutral.

P1 drives the power supply and the P1 Sense voltage divider.
The P1 protection circuit is a series 10 ohm fusible resistor and MOV to
There is a 250VAC rated X2 capacitor across the MOV.

P2 and P3 connections are not relevant to this issue.

UL 61010 Appendix I refers to some common MAINS supply systems.

Not having an earth connection, the closest standard configuration is
"Three-Phase Four Wire with earthed Neutral"

The standard Neutral to Phase voltage ratings for this configuration are
66, 120, 127, 220, 230, 240

The limiting factor in the product is the X2 rated capacitor at 250VAC.

I assume the "standard" voltage ratings allow for variation on the upper
side: a 240VAC system is expected to go as high as 264VAC.

Is the same thing true for the ratings of an X2 rated capacitor; is the
250VAC rating a nominal rating, where the part expected to support
250VAC+10% say?

The voltage rating we quote relates to both the power supply and the
measurement range.

The question is
* what voltage should we put on the nameplate
* what voltage can we claim that we can measure to while conforming to the

My guess is we should 240VAC on the nameplate, and note in the manual  that
the meter registers voltages as high as 264VAC

Any help, much appreciated!


Jon Keeble

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