Re: Soon to arrive my HDTV

Cinder Lane wrote:
> On Sun, Apr 6, 2008, 10:34am (EDT-1)
> remove.budnews@[EMAIL PROTECTED]
 (bud--) wrote:
> 
>> Plug-in suppressors are required by UL to have
>> MOVs (protective elements) from H-N, H-G, N-G.
> 
> First of all, plug-in suppressors are not required to have MOVs at all.
> MOV suppressors are just *one* type of suppressor.  Series suppressors
> do not have MOVs, and thus are not subject to MOV explosion or joule
> limitation.

The IEEE guide says "The vast majority (>90%) of both hard-wired and 
plug-in protectors use MOVs to perform the voltage-limiting function. In 
most AC protectors, they are the only significant voltage limiters." 
MOVs are so widespread because they have high energy dissipation 
capacity in a small package at relatively low cost.

You are right that there are other protection technologies. You probably 
have to look closely to find them. A UPS that does full time conversion 
from a battery is one (not the type commonly used in houses). A 
ferroresonant transformer another. I have not seen independent 
evaluation of "series suppressors".

With high ratings plug-in suppressors are unlikely to ever fail (one 
reason some units have protected equipment warrantees).

Service panel suppressors are exposed to larger surges, but are 
available with even higher ratings (and there probably aren’t practical 
alternatives to clamp-type suppressors for a service).

> 
> Second of all, suppressors with H-N, H-G, and N-G are *common-mode*
> type.  UL does *not* require suppressors to be common mode. 

Everything I have ever read says UL listed MOV based plug–in suppressors 
are required to have MOVs from H-G, N-G, H-N.

> In fact, in
> the USA normal-mode (H-N only) is better.  Surges routed directly into
> the ground wire (H-G) can damage modems. 

As I said in my first post:
"Note that all interconnected equipment needs to be connected to the 
same plug-in suppressor, or interconnecting wires need to go through the 
suppressor. External connections, like cable, also need to go through 
the suppressor. Connecting all wiring through the suppressor prevents 
damaging voltages between power and signal wires."  That protects modems.

Proper use of multi****t suppressors when equipment is connected to both 
power and signal is a major point of both guides.

And repeating:
"According to NIST guide, US insurance information indicates equipment 
most frequently damaged by lightning is
     computers with a modem connection
     TVs, VCRs and similar equipment  (presumably with cable TV 
connections).
  All can be damaged by high voltages between power and signal wires."

> Surges routed into the neutral
> will arrive at the earth ground just as efficiently as those routed into
> the ground wire.

Plug–in suppressors do not protect primarily by earthing a surge
Plug–in suppressors do not protect primarily by earthing a surge
Plug–in suppressors do not protect primarily by earthing a surge

Only clamping H-N doesn’t do anything for common mode surges (although 
common mode power surges are converted to normal  mode by the N-G bond 
required in US services).

Only clamping H-N will leave H and N at about half the surge voltage at 
the panel. That might well be 3,000V to ‘ground’ at the suppressor. It 
might well also be 3,000V to cable or phone wiring. That doesn’t protect 
modems, or anything connected to 'ground'. The point of plug-in 
suppressors is the voltage on *all* wires is clamped to the common 
ground at the suppressor. Then the voltage between all wires - power, 
‘ground’, cable, phone – is safe for the connected equipment.

-- 
bud--