Hello,

I would like to upgrade my gravity hot water system to a fully pumped
one. I have been reading the faq and honeywell diagrams.

Should I use two 2-port valves (1 CH; 1 HW) or should I use one 3-port
valve? Using a 3-port valve halves the cost but the faq said 3-ports
were more unreliable. How unreliable are they?

Is there any advantage to splitting the house in two and having one
valve for upstairs CH and one for downstairs? It might be useful to
run CH upstairs only overnight on a low thermostat setting, just to
keep off the chill; it would be a waste to heat downstairs when
everyone's in bed. Are there any other times it would be useful and
worth the expense?

I am unsure how to wire a 3-port valve. The 2-port seems
straightforward and has a built in switch. I am not clear that the
3-port valve has a switch to signal it is open; does it?

The pages I read suggested connecting the orange wire (only B port
open) to the pump. I'm sure I have misunderstood because if that's the
case what switches the pump on when you use port A only or A and B?

There seems to be some controversy: should CH be port A or port B, and
why should it make any difference? Is it that the valves fight against
a spring and that as long as the B port is open the mechanics are
fighting against the spring?

Is the idea that CH is on port A which is unenergised and the HW is on
port B, the theory being that the HW will warm up quickly so that the
valve is not energised for long? If so, does this mean that using
2-port valves is more energy inefficient?

Thanks,
Sam.

In article ,
Sam writes:
Hello,

I would like to upgrade my gravity hot water system to a fully pumped
one. I have been reading the faq and honeywell diagrams.

Should I use two 2-port valves (1 CH; 1 HW) or should I use one 3-port
valve? Using a 3-port valve halves the cost but the faq said 3-ports
were more unreliable. How unreliable are they?

Also, with a 3-port valve you always have an open path for
anything like pump run-on timers. With 2-port valves, you
may need to make special provision for this.

Is there any advantage to splitting the house in two and having one
valve for upstairs CH and one for downstairs? It might be useful to
run CH upstairs only overnight on a low thermostat setting, just to
keep off the chill; it would be a waste to heat downstairs when
everyone's in bed. Are there any other times it would be useful and
worth the expense?

It can be. Depends on size of house and usage patterns,
and how long it takes to heat up and retain that heat.

I am unsure how to wire a 3-port valve. The 2-port seems
straightforward and has a built in switch. I am not clear that the
3-port valve has a switch to signal it is open; does it?

A 3-port is always open somewhere. It has a built-in switch
to signal the normall closed side being open. I believe there
are standard wiring diagrams for the different Plans on the
web.

The pages I read suggested connecting the orange wire (only B port
open) to the pump. I'm sure I have misunderstood because if that's the
case what switches the pump on when you use port A only or A and B?

There seems to be some controversy: should CH be port A or port B, and
why should it make any difference? Is it that the valves fight against
a spring and that as long as the B port is open the mechanics are
fighting against the spring?

Is the idea that CH is on port A which is unenergised and the HW is on
port B, the theory being that the HW will warm up quickly so that the
valve is not energised for long? If so, does this mean that using
2-port valves is more energy inefficient?

I think it's usually H/W on A and C/H on B. This is to fit in
with the standard wiring diagrams. Turning it round the other
way might require addition of non-standard parts such as relays,
and confuse the hell out of anyone coming to repair it.

I use a 3-port valve to switch separate upstairs and downstairs
heating zones. I put downstairs on A and upstairs on B, on the
basis that if it broke I can still heat downstairs, and that
indirectly heats upstairs to some extent. Also, downstairs is
heated more than upstairs, so the valve spends more time powered
off than powered up with the synchronous motor stalled.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

In an earlier contribution to this discussion,
Sam wrote:

Hello,

I would like to upgrade my gravity hot water system to a fully pumped
one. I have been reading the faq and honeywell diagrams.

Should I use two 2-port valves (1 CH; 1 HW) or should I use one 3-port
valve? Using a 3-port valve halves the cost but the faq said 3-ports
were more unreliable. How unreliable are they?

The actuator of a 3-port valve has more components (extra microswitch,
diode, etc) than the 2-port equivalent and is more prone to failure. Mine
last about 2 years on average. Because they play a strategic role in the
control of the system, their failure can have a more profound effect, and is
sometimes more difficult to diagnose. They also have the disadvantage that
they can only control 2 zones - usually one HW and one CH - whereas you can
have multiple zones with 2-port valves just by adding more valves. 3-port
valves have the *advantage* that they always provide a flow path (unless
*all* your radiators are fitted with TRVs) - so you're less likely to need a
by-pass circuit to deal with the pump over-run phase, if required by your
boiler.

Is there any advantage to splitting the house in two and having one
valve for upstairs CH and one for downstairs? It might be useful to
run CH upstairs only overnight on a low thermostat setting, just to
keep off the chill; it would be a waste to heat downstairs when
everyone's in bed. Are there any other times it would be useful and
worth the expense?

It is certainly worth it if there are longish periods when you only want to
heat part of the house, and provided the pipework lends itself to a split of
that sort. [I can't do it because I have solid floors downstairs and the
down rads are fed from a single shared circuit which runs between the
floors.] If you *do* go for multiple zones, then it answers your first
question, 'cos you'll need 3 x 2-port valves to provide 2 x CH + 1 x HW
zones.

I am unsure how to wire a 3-port valve. The 2-port seems
straightforward and has a built in switch. I am not clear that the
3-port valve has a switch to signal it is open; does it?

The pages I read suggested connecting the orange wire (only B port
open) to the pump. I'm sure I have misunderstood because if that's the
case what switches the pump on when you use port A only or A and B?

It needs to be wired according to the wiring diagram for Y-Plan systems -
see the Y-Plan section of http://content.honeywell.com/uk/homes/systems.htm.
In either the HW-only or HW+CH (position) the boiler and pump are fed from
the timer's HW output, via the cylinder stat. In the CH-only position, they
are fed by the actuator's orange wire output which is internally switched to
the grey wire input.

There seems to be some controversy: should CH be port A or port B, and
why should it make any difference? Is it that the valves fight against
a spring and that as long as the B port is open the mechanics are
fighting against the spring?

Is the idea that CH is on port A which is unenergised and the HW is on
port B, the theory being that the HW will warm up quickly so that the
valve is not energised for long? If so, does this mean that using
2-port valves is more energy inefficient?

Thanks,
Sam.

My Danfoss valve has CH on A and HW on B, and wouldn't work properly if
connected the other way round. I imagine that other makes are the same for
the sake of standardisation. The actuator's motor moves the valve in only
one direction, with a spring return to move it the other way. When unpowered
it sits in the B (HW) position. The valve is only drawing power in the mid
and CH-only positions - unlike 2-port valves which draw power whenever they
are open. This means, for example, that a 3-port valve may not move all
summer when only the HW is being heated. Whilst this might save energy, it
also increases the risk of the valve seizing up - so 'exercising' it every
now and then is a good idea.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On 10 Jan 2008 14:56:47 GMT, (Andrew
Gabriel) wrote:

Is there any advantage to splitting the house in two and having one
valve for upstairs CH and one for downstairs?

It can be. Depends on size of house and usage patterns,
and how long it takes to heat up and retain that heat.

Thanks for your reply. I see below that you have two zones. Can you
tell me more about your set-up and usage? What should I do to work out
whether I should do the same? I'm in a 1970's build so no modern-day
super insulation!

A 3-port is always open somewhere. It has a built-in switch
to signal the normall closed side being open. I believe there
are standard wiring diagrams for the different Plans on the
web.

The diagrams I found confused me! I hadn't appreciated the always open
aspect until you said. I assume the pump needs to switch on when
either thermostat calls for heat. Do you just run wires from both
'stats to the pump?

I think it's usually H/W on A and C/H on B. This is to fit in
with the standard wiring diagrams.

That's what the FAQ says IIRC but I whilst googling I found reference
that one manufacturer prefers you to use HW on B because this means
the valve is energised for a shorter period if I understand correctly.

downstairs is
heated more than upstairs, so the valve spends more time powered
off than powered up with the synchronous motor stalled.

Really? How does this work? You heat downstairs in the early evening
and then switch to heating the upstairs at night?

Thanks again.

"Sam" wrote


Is there any advantage to splitting the house in two and having one
valve for upstairs CH and one for downstairs?

I had my heating system upgraded last year.
1970s detached house - 4 bedrooms.
Decided to have the upstairs and downstairs zoned separately.

Advantages: previously the whole house was heated from 3:30pm when the kids
return from school - now downstairs from 3:30, upstairs from 7:30. Haven't
got round to looking at the resulting gas saving although this will be
enhanced by the new boiler that was fitted I guess.

Disadvantages: Hallway is noticably cold (obviously) due to cold air
"falling" from landing. The installation is a bit more complex when
considering future maintenance.

Also have a look at the location of the pump in a new system. My previous
set-up had a pumped return rather than pumped flow which leads to quite a
bit of additional pipe work being required.

HTH

Phil

In article ,
Sam wrote:
Hello,

I would like to upgrade my gravity hot water system to a fully pumped
one. I have been reading the faq and honeywell diagrams.

Should I use two 2-port valves (1 CH; 1 HW) or should I use one 3-port
valve? Using a 3-port valve halves the cost but the faq said 3-ports
were more unreliable. How unreliable are they?

My first one did some 20 years and was replaced in '99. Replacement still
fine. Both Honeywell.


Is there any advantage to splitting the house in two and having one
valve for upstairs CH and one for downstairs? It might be useful to
run CH upstairs only overnight on a low thermostat setting, just to
keep off the chill; it would be a waste to heat downstairs when
everyone's in bed. Are there any other times it would be useful and
worth the expense?

I am unsure how to wire a 3-port valve. The 2-port seems
straightforward and has a built in switch. I am not clear that the
3-port valve has a switch to signal it is open; does it?

Depends what you mean by open - because some types are always open. They
have a micro switch to prove the state.

Wiring diagrams here - or do a search for others offering similar.

http://content.honeywell.com/uk/homes/applicat.htm

--
*Remember, no-one is listening until you fart.*

Dave Plowman London SW
To e-mail, change noise into sound.

On Thu, 10 Jan 2008 16:05:49 -0000, "Roger Mills"
wrote:

The actuator of a 3-port valve has more components (extra microswitch,
diode, etc) than the 2-port equivalent and is more prone to failure. Mine
last about 2 years on average.

That's not very long. It's not very reassuring.

They also have the disadvantage that
they can only control 2 zones - usually one HW and one CH - whereas you can
have multiple zones with 2-port valves just by adding more valves.

Couldn't you have a 3-port for CH or HW, with the CH port connected to
another 3-way for upstairs (A), downstairs (B), or both (A+B)?

For more than two zones, I see your point.

3-port valves have the *advantage* that they always provide a flow path (unless
*all* your radiators are fitted with TRVs) - so you're less likely to need a
by-pass circuit to deal with the pump over-run phase, if required by your
boiler.

Someone else mentioned this "pump over run". What is it and how do I
find out if I have it?

It needs to be wired according to the wiring diagram for Y-Plan systems -
see the Y-Plan section of http://content.honeywell.com/uk/homes/systems.htm.
In either the HW-only or HW+CH (position) the boiler and pump are fed from
the timer's HW output, via the cylinder stat. In the CH-only position, they
are fed by the actuator's orange wire output which is internally switched to
the grey wire input.

I think taht's the point I was missing: I hadn't realised that in
addition to the orange wire they were also connected to the stat. I
knew there had to be two connections!

Something that escaped me until I thought more about it was this:

I thought what if the valve is set to CH+HW but the tank fills up,
won't the pump stop pumping? When I thought more I realised that when
the stat is satisfied it turns the valve to CH only.

Thanks again.

"Sam" wrote in message
...
On Thu, 10 Jan 2008 16:05:49 -0000, "Roger Mills"
wrote:

The actuator of a 3-port valve has more components (extra microswitch,
diode, etc) than the 2-port equivalent and is more prone to failure. Mine
last about 2 years on average.

That's not very long. It's not very reassuring.

On the other hand, we've been in our house for 18 years and the 3-port valve
is still working fine.

In an earlier contribution to this discussion,
Sam wrote:


Couldn't you have a 3-port for CH or HW, with the CH port connected to
another 3-way for upstairs (A), downstairs (B), or both (A+B)?

Not without a lot of complication in the wiring department, bearing in mind
the way in which - unlike 2-port valves - some of the wiring is shared by
motor driving and boiler/pump running functions. Far better to use 3 x
2-port valves which will probably cost very little more than 2 x 3-port
valves. The 3-port valve is designed for one very specific application, and
doesn't readily lend itself to departures from the standard Y-Plan setup.


Someone else mentioned this "pump over run". What is it and how do I
find out if I have it?

Most modern-ish boilers - which hold relatively small quantities of water -
require it. Old heavy cast iron boilers usually don't. When the boiler is in
full flight and the room stat decides to turn it off, the flame is cut
instantly but the water goes on getting hotter due to the residual heat in
the metal parts. There needs to be a flow of water through the boiler for
long enough to carry away this residual heat - otherwise the boiler
literally boils. This is achieved by allowing the boiler to control the pump
rather than controlling the pump directly by wiring it in parallel with the
boiler. If your boiler needs it, there should be something about it in the
installation manual. Also, if you look at the boiler's wiring connections,
there will be a permanently live input - in addition to the switched live -
and there will be pump connection terminals.

For pump over-run to work, there must always be a flow path open for the
water to follow. A 3-port valve always has at least one port open. A 2-port
valve doesn't - and all (2 or 3) could be closed when all demands are
satisfied. You would then need a by-pass circuit - preferably using an
automatic by-pass valve - to provide that flow path.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

On Thu, 10 Jan 2008 17:46:11 -0000, "Roger Mills"
wrote:

Most modern-ish boilers - which hold relatively small quantities of water -
require it. Old heavy cast iron boilers usually don't.
[snip]
If your boiler needs it, there should be something about it in the
installation manual. Also, if you look at the boiler's wiring connections,
there will be a permanently live input - in addition to the switched live -
and there will be pump connection terminals.

My boiler looks ancient and only has live and neutral, so I guess I'm
ok? It's also oil rather than gas; does that make a difference?

In situations that require it, how is it achieved?

For pump over-run to work, there must always be a flow path open for the
water to follow. A 3-port valve always has at least one port open. A 2-port
valve doesn't - and all (2 or 3) could be closed when all demands are
satisfied. You would then need a by-pass circuit - preferably using an
automatic by-pass valve - to provide that flow path.

I've heard of these bypass valves. Do you also use them if TRVs are on
all radiators? I've always left TRVs off the hall rad (thermostat) and
bathroom (towel rad) hoping that would be sufficient for whent he
other TRVs close. Do I need a bypass in addition or is that enough?

Thanks again.

In an earlier contribution to this discussion,
Sam wrote:


My boiler looks ancient and only has live and neutral, so I guess I'm
ok? It's also oil rather than gas; does that make a difference?

I don't know much about oil-fired boilers - but imagine that some *do* need
pump over-run. If yours is old, and holds a lot of water, it probably
doesn't. Especially since it only appears to have a switched live.

In situations that require it, how is it achieved?

Invariably the pump is connected to some dedicated pump control terminals on
the boiler, and the boiler decides when the pump needs to run - quite
independently of what the external timers and stats are doing. The actual
logic varies from boiler to boiler. Mine has a thermostat and, in addition
to running the pump whenever the external 'call for heat' demand is on, also
runs it whenever the boiler temperature is above a certain value - until
such time as it has cooled sufficiently. Some simply have a timer which
continues to run the pump for a specified time after the demand is removed -
similar to a bathroom fan remaining on for a while after switching off the
light. As I said in an earlier post, the boiler needs a permanent live so
that it *can* power the pump even when the external (switched live) demand
is off.


I've heard of these bypass valves. Do you also use them if TRVs are on
all radiators? I've always left TRVs off the hall rad (thermostat) and
bathroom (towel rad) hoping that would be sufficient for whent he
other TRVs close. Do I need a bypass in addition or is that enough?


From what you say, your boiler doesn't need a pump over-run - so the pump
stops when the demand is removed, and the water doesn't need anywhere to go.
Systems which have TRVs on *all* radiators (not recommended!) and which use
a boiler which needs pump over-run may well need a by-pass - even when using
a 3-port valve because in CH-only mode with all TRVs closed there would
otherwise be no flow path.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!

In article ,
writes:
On 10 Jan,
(Andrew Gabriel) wrote:

I use a 3-port valve to switch separate upstairs and downstairs
heating zones. I put downstairs on A and upstairs on B, on the
basis that if it broke I can still heat downstairs, and that
indirectly heats upstairs to some extent. Also, downstairs is
heated more than upstairs, so the valve spends more time powered
off than powered up with the synchronous motor stalled.

I did that for about 5 years (together with a preceding one for HW/CH) until
I got fed up with replacing micro switches.

Funny, I see a few reports on here of unreliability of these
things, but we've never had one fail in mine or any of about
3 other family member's systems yours truely ends up maintaining.
They're all 3-port mid position units. Just checked one of them
which is at least 8 years old and it claims to be a British Gas
one (rebadged I'm sure, but don't know who from). One I fitted
in a new system about 6 years ago was Landys and Steaefa and
going very cheap as old stock. Don't know about the others as
I've never had to pay them any attention.

Since changing to 3 two port valves I haven't had to change anything in the
last 8 years (although I should get round to fixing a slight leak on the
spindle of one of the valves one of these days).

For some reason the micro switches in the 3 port valves seem much less
reliable than in 2 port valves, perhaps the valves hunt slightly with mains
volts when in the mid position. I can't think of any other reason.

In the system I designed, I don't use the microswitch as the
valve is driven by a computer, not one of the conventional
circuit arrangements. (I did use it to confirm the valve was
working initially, but I needed that computer input back for
something more important.) There is a second microswitch which
is used internally to lock in mid position.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Sam wrote:

On Thu, 10 Jan 2008 16:05:49 -0000, "Roger Mills"
wrote:

The actuator of a 3-port valve has more components (extra microswitch,
diode, etc) than the 2-port equivalent and is more prone to failure. Mine
last about 2 years on average.

That's not very long. It's not very reassuring.

Might be worth considering what sort of load you are switching with the
microswitch. Often people don't bother fitting snubber circuits when
they are controlling inductive loads. This can lead to premature wear on
the microswitch contacts.

They also have the disadvantage that
they can only control 2 zones - usually one HW and one CH - whereas you can
have multiple zones with 2-port valves just by adding more valves.

Couldn't you have a 3-port for CH or HW, with the CH port connected to
another 3-way for upstairs (A), downstairs (B), or both (A+B)?

You could...

Someone else mentioned this "pump over run". What is it and how do I
find out if I have it?

Most modern boilers will control the pump. As a result they have the
option of running the pump for a period of time after the boiler has
ceased firing. This helps extend the life of the heat exchanger and is a
little more energy efficient since it does not leave the HE full of hot
water.

Older systems with "dumb" boilers would probably have had the pump
controlled directly from the valve. Hence as soon as the call for heat
from the stat was taken away both the pump and the boiler would be
turned off.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Fri, 11 Jan 2008 15:14:04 +0000, John Rumm
wrote:

Might be worth considering what sort of load you are switching with the
microswitch. Often people don't bother fitting snubber circuits when
they are controlling inductive loads. This can lead to premature wear on
the microswitch contacts.

Sorry, what is a snubber circuit?

Sam wrote:
On Fri, 11 Jan 2008 15:14:04 +0000, John Rumm
wrote:

Might be worth considering what sort of load you are switching with the
microswitch. Often people don't bother fitting snubber circuits when
they are controlling inductive loads. This can lead to premature wear on
the microswitch contacts.

Sorry, what is a snubber circuit?

A circuit that helps dissipate the big spike of voltage that is
generated when you switch an inductive load. At its simplest it can be a
metal oxide varistor suppression type device (cheap at maplin).

There is an example of a more sophisticated circuit used for protecting
the relatively delicate contacts of a reed switch shown he

http://wiki.diyfaq.org.uk/index.php?...nk#Flow_Switch

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Sat, 12 Jan 2008 06:13:16 +0000, John Rumm
wrote:

Sorry, what is a snubber circuit?

A circuit that helps dissipate the big spike of voltage that is
generated when you switch an inductive load. At its simplest it can be a
metal oxide varistor suppression type device (cheap at maplin).

If they are cheap, why don't the valve manufacturers fit them as
standard?

In article ,
John Rumm writes:
Sam wrote:

Sorry, what is a snubber circuit?

A circuit that helps dissipate the big spike of voltage that is
generated when you switch an inductive load. At its simplest it can be a
metal oxide varistor suppression type device (cheap at maplin).

A MOV is the wrong device to use for this, as the energy it
absorbs uses it up, until it runs out of capacity to absorb
any more and stops working. It's good for one-shot protection
or a small number of smaller incidents, but not for something
which is routinely expected.

All you need for a contact snubber is something which allows
the current to carry on flowing when the contacts open until
the reactive energy is safely dissipated. This is normally
done with a resistor which allows current flow and dissipates
the energy, in series with a small capacitor which blocks the
current flow at 50Hz.

e.g. [fixed width font]

| |
--/\/\/\---| |--
| | | |
| |
| / |
| / |
---------/ -------------


This is so common you can buy the resistor and capacitor
combined in one component (looks like a capacitor, e.g.
Maplin part RG22Y).

There is an example of a more sophisticated circuit used for protecting
the relatively delicate contacts of a reed switch shown he

http://wiki.diyfaq.org.uk/index.php?...nk#Flow_Switch

I would say that's a rather dubious circuit. The snubber isn't
protecting anything, but there isn't anything in that circuit
which needs protecting with a snubber anyway (except possibly
the triac, but a snubber across a triac is for a completely
different reason).

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andrew Gabriel wrote:
In article ,
John Rumm writes:
Sam wrote:
Sorry, what is a snubber circuit?
A circuit that helps dissipate the big spike of voltage that is
generated when you switch an inductive load. At its simplest it can be a
metal oxide varistor suppression type device (cheap at maplin).

A MOV is the wrong device to use for this, as the energy it
absorbs uses it up, until it runs out of capacity to absorb
any more and stops working. It's good for one-shot protection
or a small number of smaller incidents, but not for something
which is routinely expected.

All you need for a contact snubber is something which allows
the current to carry on flowing when the contacts open until
the reactive energy is safely dissipated. This is normally
done with a resistor which allows current flow and dissipates
the energy, in series with a small capacitor which blocks the
current flow at 50Hz.

e.g. [fixed width font]

| |
--/\/\/\---| |--
| | | |
| |
| / |
| / |
---------/ -------------


This is so common you can buy the resistor and capacitor
combined in one component (looks like a capacitor, e.g.
Maplin part RG22Y).

There is an example of a more sophisticated circuit used for protecting
the relatively delicate contacts of a reed switch shown he

http://wiki.diyfaq.org.uk/index.php?...nk#Flow_Switch

I would say that's a rather dubious circuit. The snubber isn't
protecting anything, but there isn't anything in that circuit
which needs protecting with a snubber anyway (except possibly
the triac, but a snubber across a triac is for a completely
different reason).

Snubber are for arc suppression when switching inductive loads like pumps.

Andrew Gabriel wrote:
In article ,
John Rumm writes:
Sam wrote:
Sorry, what is a snubber circuit?
A circuit that helps dissipate the big spike of voltage that is
generated when you switch an inductive load. At its simplest it can be a
metal oxide varistor suppression type device (cheap at maplin).

A MOV is the wrong device to use for this, as the energy it
absorbs uses it up, until it runs out of capacity to absorb
any more and stops working. It's good for one-shot protection
or a small number of smaller incidents, but not for something
which is routinely expected.

(I was not suggesting it was a particularly good solution - just one
that you see quite commonly used).

I was not aware that MOVs had a particularly limited number of cycles,
or were you just referring a limited energy dissipation per use?

I was thinking of the mains rated devices like:

http://www.maplin.co.uk/module.aspx?...=12m1#overview


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/