I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

How quickly should the thermal trip reset itself? Not my problem, but at
the livery stables where my horse lives.

TIA

On 28/11/2017 14:49, newshound wrote:
I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

How quickly should the thermal trip reset itself? Not my problem, but at
the livery stables where my horse lives.

You seem to have an impressive horse. Have you thought of putting it on
the stage?


TIA

On 2017-11-28 14:49, newshound wrote:
I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

How quickly should the thermal trip reset itself?

It doesn't reset itself (unlike, e.g. the thermal trips in some model
railway power units). Both detection mechanisms trip the same switch.

You manually reset both mechanisms by operating the external switch
toggle (hopefully after looking for the cause of the trip).

This video of the insides of a mcb shows the solenoid for short-
circuit protection and the bimetallic strip for moderate overloads:

https://www.youtube.com/watch?v=JbyTHlx4tQM


--
Graham Nye
news(a)thenyes.org.uk

newshound wrote:

How quickly should the thermal trip reset itself?
Sometimes (may depend on make?) you have to operate the lever to "off"
manually, even though it's pointing at "off" from being tripped before
you can operate it back to "on".

On Tuesday, 28 November 2017 14:49:03 UTC, newshound wrote:

I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

How quickly should the thermal trip reset itself? Not my problem, but at
the livery stables where my horse lives.

TIA

the thermal element bends back to enable the mcb to be reset quite quickly. I've had times when it may take over 10 seconds before it'll reset, can't be more precise though, and can't guarantee it's not something else going on.

If you're getting repeating trips with failure to reset, that's 2 problems that need sorting.


NT

On Tue, 28 Nov 2017 14:49:00 +0000, newshound
coalesced the vapors of human experience
into a viable and meaningful comprehension...

I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

You are correct

How quickly should the thermal trip reset itself? Not my problem, but at
the livery stables where my horse lives.

TIA

Never. A normal MCB is not self-resetting irrispective the magnetic or
thermal operation. User intervention is involved, so some sort of
alarm would be a good idea.



--

Graham.
%Profound_observation%

On 28/11/2017 15:08, GB wrote:
On 28/11/2017 14:49, newshound wrote:
I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

How quickly should the thermal trip reset itself? Not my problem, but
at the livery stables where my horse lives.

You seem to have an impressive horse. Have you thought of putting it on
the stage?


TIA


Slightly confused. Must be missing something.

To go back to the problem, this turns out to be an RCBO of an obsolete
design (Square D type QOE).

Typically, it's an intermittent problem. When I arrived it was tripped
and would not reset even with all the load turned off. Whipped it out,
took it down to Screwfix only to find they don't stock old design.

Took it back, meggered the circuits (all fine), wired it back in and
powered up, not tripping with ~ 30 amp load (but didn't try overloading it).

So perhaps a tired device with a worn latch, but behaving after a
shake-up? Do they suffer random age failures?

On 28/11/2017 16:30, Graham. wrote:
On Tue, 28 Nov 2017 14:49:00 +0000, newshound
coalesced the vapors of human experience
into a viable and meaningful comprehension...

I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

You are correct

How quickly should the thermal trip reset itself? Not my problem, but at
the livery stables where my horse lives.

TIA

Never. A normal MCB is not self-resetting irrispective the magnetic or
thermal operation. User intervention is involved, so some sort of
alarm would be a good idea.



Sorry all, really bad wording in my original post (rushing a bit to get
there before dark). I know they need to be manually reset, I was
wondering how quickly they would cool down after a trip to permit a
reset. Having now looked at the diagram and seeing it is a bimetallic
strip carrying the current, the answer is (obviously) fairly fast. I
suppose I had in mind that perhaps they had something like a wax
thermostat to provide a reasonable delay, so that it might take a few
minutes for the accumulated heat to escape to the outside world.

newshound wrote:

I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

this turns out to be an RCBO of an obsolete
design (Square D type QOE).

OK, so you've got three trip mechanisms

Typically, it's an intermittent problem. When I arrived it was tripped
and would not reset even with all the load turned off.

Was anything unplugged or turned off (maybe via timer/thermostat)
between the time it wouldn't and later would reset?

No I did not get the joke either, so don't feel cheated.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"newshound" wrote in message
o.uk...
On 28/11/2017 15:08, GB wrote:
On 28/11/2017 14:49, newshound wrote:
I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

How quickly should the thermal trip reset itself? Not my problem, but at
the livery stables where my horse lives.

You seem to have an impressive horse. Have you thought of putting it on
the stage?


TIA


Slightly confused. Must be missing something.

To go back to the problem, this turns out to be an RCBO of an obsolete
design (Square D type QOE).

Typically, it's an intermittent problem. When I arrived it was tripped and
would not reset even with all the load turned off. Whipped it out, took it
down to Screwfix only to find they don't stock old design.

Took it back, meggered the circuits (all fine), wired it back in and
powered up, not tripping with ~ 30 amp load (but didn't try overloading
it).

So perhaps a tired device with a worn latch, but behaving after a
shake-up? Do they suffer random age failures?

On 28/11/2017 18:33, Andy Burns wrote:
newshound wrote:

I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

this turns out to be an RCBO of an obsolete
design (Square D type QOE).

OK, so you've got three trip mechanisms

Yes, hadn't noticed that when I first posted.


Typically, it's an intermittent problem. When I arrived it was tripped
and would not reset even with all the load turned off.

Was anything unplugged or turned off (maybe via timer/thermostat)
between the time it wouldn't and later would reset?

There is a washing machine, so the heater could be a good candidate. I
started it running when I finished this evening, it hadn't tripped by
the time I had loaded the tools but we will see when I get in tomorrow
at 7 am!

I've just remembered that there used to be a small heater in the loo at
the far end of the site, which was disconnected last year because it
kept tripping one circuit. Will check tomorrow if it is on the same
circuit, although from the geometry it probably isn't.

Being a stables, there are plenty of rats and mice, and being old farm
buildings means none of the wiring is mechanically protected, and mostly
just clipped to wooden beams. So there are *lots* off opportunities for
hard-to-locate damage to insulation.

Of course at the moment I don't know if it is an earth leakage or an
overcurrent fault. Could be both!

This 32A circuit might not be code compliant, there is a ring main with
sockets plus what seems to be an unfused spur running a small lighting
load. This starts off in 2.5 mm^2 and ends up away from the main
building in 1 mm^2. I suppose there might be a fuse at this point (but I
havn't even found the junction yet). I take some comfort in the thought
that an unprotected fault on the thin stuff would eventually take out
the RCD, but obviously there is a fire risk.

On 28/11/2017 20:38, newshound wrote:

havn't even found the junction yet). I take some comfort in the thought
that an unprotected fault on the thin stuff would eventually take out
the RCD, but obviously there is a fire risk.

As long as the circuit is not excessively long, even the 1mm^2 section
will *probably* be fault protected by the RCBO's fast over current
mechanism.

(earth leakage faults will be protected by its RCD functionality anyway)


--
Cheers,

John.

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

On 28/11/2017 15:29, Graham Nye wrote:
On 2017-11-28 14:49, newshound wrote:
I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

How quickly should the thermal trip reset itself?

It doesn't reset itself (unlike, e.g. the thermal trips in some model
railway power units). Both detection mechanisms trip the same switch.

You manually reset both mechanisms by operating the external switch
toggle (hopefully after looking for the cause of the trip).

I think he was suggesting that after a thermal trip, you may have
difficulty getting it to manually reset immediately, since you will need
to wait a short time for the bimetal strip to cool enough to permit it
to reset.


--
Cheers,

John.

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

On 29/11/2017 10:42, John Rumm wrote:
On 28/11/2017 20:38, newshound wrote:

havn't even found the junction yet). I take some comfort in the thought
that an unprotected fault on the thin stuff would eventually take out
the RCD, but obviously there is a fire risk.

As long as the circuit is not excessively long, even the 1mm^2 section
will *probably* be fault protected by the RCBO's fast over current
mechanism.

(earth leakage faults will be protected by its RCD functionality anyway)


Thanks!

*Some* (though not all) of the wiring looks as though it might have been
fitted by someone not over-familiar with the regs and calculations!
Apparently a proper "sparks" is coming out to look at it.

On Wednesday, 29 November 2017 11:42:36 UTC, newshound wrote:
On 29/11/2017 10:42, John Rumm wrote:
On 28/11/2017 20:38, newshound wrote:

havn't even found the junction yet). I take some comfort in the thought
that an unprotected fault on the thin stuff would eventually take out
the RCD, but obviously there is a fire risk.

As long as the circuit is not excessively long, even the 1mm^2 section
will *probably* be fault protected by the RCBO's fast over current
mechanism.

(earth leakage faults will be protected by its RCD functionality anyway)


Thanks!

*Some* (though not all) of the wiring looks as though it might have been
fitted by someone not over-familiar with the regs and calculations!
Apparently a proper "sparks" is coming out to look at it.

Cue a list of 'urgent' problems that aren't

On Tuesday, 28 November 2017 20:38:49 UTC, newshound wrote:
On 28/11/2017 18:33, Andy Burns wrote:
newshound wrote:

I know MCBs have two separate trips, a fast one for big faults and a
slower thermal trip for moderate over-current.

this turns out to be an RCBO of an obsolete
design (Square D type QOE).

OK, so you've got three trip mechanisms

Yes, hadn't noticed that when I first posted.


Typically, it's an intermittent problem. When I arrived it was tripped
and would not reset even with all the load turned off.

Was anything unplugged or turned off (maybe via timer/thermostat)
between the time it wouldn't and later would reset?

There is a washing machine, so the heater could be a good candidate. I
started it running when I finished this evening, it hadn't tripped by
the time I had loaded the tools but we will see when I get in tomorrow
at 7 am!

I've just remembered that there used to be a small heater in the loo at
the far end of the site, which was disconnected last year because it
kept tripping one circuit. Will check tomorrow if it is on the same
circuit, although from the geometry it probably isn't.

Being a stables, there are plenty of rats and mice, and being old farm
buildings means none of the wiring is mechanically protected, and mostly
just clipped to wooden beams. So there are *lots* off opportunities for
hard-to-locate damage to insulation.

Of course at the moment I don't know if it is an earth leakage or an
overcurrent fault. Could be both!

This 32A circuit might not be code compliant, there is a ring main with
sockets plus what seems to be an unfused spur running a small lighting
load. This starts off in 2.5 mm^2 and ends up away from the main
building in 1 mm^2. I suppose there might be a fuse at this point (but I
havn't even found the junction yet). I take some comfort in the thought
that an unprotected fault on the thin stuff would eventually take out
the RCD, but obviously there is a fire risk.

On 29/11/2017 14:33, wrote:
On Wednesday, 29 November 2017 11:42:36 UTC, newshound wrote:
On 29/11/2017 10:42, John Rumm wrote:
On 28/11/2017 20:38, newshound wrote:

havn't even found the junction yet). I take some comfort in the thought
that an unprotected fault on the thin stuff would eventually take out
the RCD, but obviously there is a fire risk.

As long as the circuit is not excessively long, even the 1mm^2 section
will *probably* be fault protected by the RCBO's fast over current
mechanism.

(earth leakage faults will be protected by its RCD functionality anyway)


Thanks!

*Some* (though not all) of the wiring looks as though it might have been
fitted by someone not over-familiar with the regs and calculations!
Apparently a proper "sparks" is coming out to look at it.

Cue a list of 'urgent' problems that aren't

As a followup, the sparks called me *after* doing his investigation,
which turned out to be exactly the same as mine: disconnect, megger the
wires, find nothing, then say "They might have had too much load on it".
Alternatively, a load device might be dying with a fault to earth.

At the moment it is all working fine.