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Re: [Amps] MOVs on HV PS

Subject: Re: [Amps] MOVs on HV PS
From: Larry Benko <>
Date: Mon, 05 Mar 2007 15:43:56 -0700
List-post: <>
I have several surge/RF filter devices made by Tripp-Lite and they have 
3 MOVS in them.  They also have UL/CSA rated caps across all 3 wires but 
the caps to the neutral line have smaller capacitance so as to no trip 
GFI devices.  Everything in the unit is on the downstream side of a 
circuit breaker which is in the hot lead.  No fault can cause continuous 
neutral currents that way.  I see no problem with this design and should 
the surge/RF filter be placed a long way from the service entrance, your 
local equipment does have a measure of protection for large voltage 
spikes from either hot/neutral to the chassis alievating the local 
equipment to have to sustain this brief voltage.

Larry, W0QE

Tom W8JI wrote:

>>On Mon, 05 Mar 2007 19:40:20 +0000, Rick Stealey wrote:
>>>If I understood W8JI recently, Tom said MOVs should not be 
>>>installed in a
>>>piece of equipment, forcing the surge to green wire 
>>>ground, but rather
>>>should only be at the service entrance (or single point 
>I actually said the MOV can't connect to the safety ground 
>or chassis, it can only connect from hot to neutral or 
>across the line on a 240 system.
>We aren't allowed to connect anything to the chassis or the 
>safety ground (including control or filament transformers) 
>that can provide any current because an open safety ground 
>would present a hazard.
>I sometimes use a UL/CSA rated bypass cap from neutral to 
>the safety ground (or chassis) when it is the only way to 
>get rid of RFI, but I'd certainly never use anything that 
>might provide a fault path from the hot mains terminal to 
>the safety ground! There are accepted bypass caps but MOV's 
>hard-fault with lots of current, so you wouldn't want one in 
>a position where it could dump the power line hot lead to an 
>exposed conductor like the chassis.
>73 Tom
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