Bob & Bob,
Good suggestions. I plan on adding a "whole house" TVSS or MOV unit in the
near future. There's a lot of product out there.
One personal reply I received from someone in the surge suppression industry is
that the most useful suppression is generally graduated in steps. IOW, one
typically sees whole house clamping V at ~ 350/700VAC (Line to
Gnd/Line-to-Line). Then, step down the clamp inside the equipment to say...
2/3 the entrance protection clamping V. Still reasonable clamping V in the
event the whole house unit is bypassed.
Paul, W9AC
----- Original Message -----
From: rgroh@swbell.net
To: Robert B. Bonner ; Paul Christensen ; Amps Amps
Sent: Saturday, March 03, 2007 3:12 PM
Subject: Re: [Amps] MOV Sizing
Just had a thought on this subject - there are 'whole' house ac line surge
protectors - industrial type - that are intended to be connected directly on
the side of the the house breaker box. One source and example is:
<http://www.surgeassure.com/product.asp?prod=TE/1SSA&gclid=CLf3roe02YoCFShtSQodJy3NvQ
>
There are other brands and such available at electrical supply houses, etc.
Another source is Grainger - they have Square D versions
<http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?ItemId=1613542417
>
Anyways you could use one of these (they usually are a small black box which
are easy to bolt on to a box and to wire up) on your equipment.
Just a thought.
73
Bob, WA2CKY
----- Original Message ----
From: Robert B. Bonner <rbonner@qro.com>
To: Paul Christensen <w9ac@arrl.net>; Amps Amps <amps@contesting.com>
Sent: Saturday, March 3, 2007 11:35:13 AM
Subject: Re: [Amps] MOV Sizing
Paul, The two to ground would be the correct installation.
140V should be very adequate I would think. Keep them up off the chassis
because sometimes they blow BLACK and SOOTY. If you notice in many products
they shrink sleeve over the MOV's leaving the end open to let the fire and
smoke out but keep from trashing up your gear.
As a past electrician, my thinking on line to ground is.. FAULTS should
dissipate to GROUND not to the other line. Your powerline transformer is
not going to FAULT winding to winding away from 240V. However what will
blow up the amplifier is a lightning strike causing the whole system to
fault UP AND AWAY from ground.
If you want to spend money on additional MOV's for safety put two in
parallel. I think you'd almost never see the between lines MOV blow, but if
it did, it could make things worse.
BOB DD
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Paul Christensen
Sent: Saturday, March 03, 2007 6:41 AM
To: Amps Amps
Subject: [Amps] MOV Sizing
I am planning on adding a set of MOVs to the AC line of a recently acquired
Alpha 86 amplifier. I have reviewed Littlefuse's MOV Applications Guide but
I am still a bit unclear as to the optimum clamping voltage I should choose.
I would like to use three MOVs with one placed across the 240VAC line and
the remaining two placed between each side of line and GND. I am thinking
of MOVs rated at a nominal operating V of 140VAC, and 260V for the
line-to-line MOV with respective clamping voltages of 180V/360V. The MOVs
would be placed directly after the fuses.
Speaking of MOV placement, I have seen circuits were MOVs are placed ahead
of the fuses or circuit breaker, but this seems like a counter-intuitive and
dangerous practice. OTOH, there are numerous designs that employ AC line RF
bypass caps in front of the fuses as well but then... caps are not meant to
self-destruct during a fault condition.
Thoughts?
Paul, W9AC
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