[Amps] MOVs

Mike Tubby mike at tubby.org
Wed Jan 9 14:25:24 EST 2013


In the UK the AC supply is single phase 230V AC (was 240V AC until we
re-aligned with the rest of Europe), there are three wires:

    Live (Phase) => 230 VAC
    Neutral (Return) => 0V ref Live
    Earth (Safety) => 0V ref Live

In some systems Neutral and Earth are bonded in other systems they are
separate and while similar potential may vary by 10-20 volts and are
different impedances.  Supply is always drawn from Live (Phase) and
returned via Neutral.

The most common voltage rating for an MOV for use on AC supplies is 275V
AC (430V DC) - see Premier Farnell:


and search for "MOV" and then look at the "Volts AC" column and select
the 275V parts - you will have many makes, sizes, capacities to choose from.

It is not uncommon to use three devices wired L-N, L-E and N-E to
protect against all forms of spikes and earth faults.

Mike G8TIC

On 07/01/2013 17:50, Vic K2VCO wrote:
> I have a power supply that needs to work here in the US and in Israel,
> where power is supplied as one phase of 240V plus a safety ground. I
> am not sure if one of the 240V lines is grounded as well. The power
> supply doesn't require 120V for anything, so there's no neutral.
> What is the correct way and ratings for MOVs to protect against line
> transients?
> Here in the US I would use a 130V MOV from each hot wire to ground.
> But clearly that wouldn't work in a place where one side of the 240V
> line is grounded.
> I suspect (but am not 100% sure) that the standards in Israel are
> similar if not the same as in the UK.

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