info
Google Groups no longer supports new Usenet posts or subscriptions. Historical content remains viewable.
Dismiss
Moisture in Magnesium Oxide insulator
13 views
Skip to first unread message
Stephen Biddle
Jun 23, 2015, 10:55:56 AM6/23/15
to
Hi All
I work with electric heaters and have a problem with moisture getting into the element, causing the insulation resistance to drop. The BS spec for immersion heaters says it must be at least 2M ohm at 500V. If I power up the heater it can dry out and recover. Does anyone know the minimum insulation resistance that I need to turn it on without causing permanent damage. It seems to me that a leakage current could cause "tracking" and make the component useless.
Stephen
I work with electric heaters and have a problem with moisture getting into the element, causing the insulation resistance to drop. The BS spec for immersion heaters says it must be at least 2M ohm at 500V. If I power up the heater it can dry out and recover. Does anyone know the minimum insulation resistance that I need to turn it on without causing permanent damage. It seems to me that a leakage current could cause "tracking" and make the component useless.
Stephen
Andrew Gabriel
Jun 23, 2015, 6:23:54 PM6/23/15
to
In article <23291c15-87e7-40f8...@googlegroups.com>,
material breaking down and forming a conductor (or at least a partial
conductor), such as plastics breaking down and leaving a carbon track.
Magnesium Oxide will not breakdown, so you shouldn't be able to damage
it any further by turning it on. If there was lots of moisture in there,
you might get an arc right across that would leave vaporised metal, but
the heater has had it by that point anyway (the magnesium oxide should
be under enough pressure to quench any such arc unless the case is burst).
I don't have the PAT test guidelines to hand at the moment, but they
used to allow you to operate mineral insulated heaters to drive off
condensation before performing the insulation test. I just can't recall
if that's still in the current version of the IEEE in-service inspection
and testing document.
Obviously, it's important to check the casing is properly earthed. If
there's an RCD in the circuit, that may prevent you operating the
heater to dry it, but if it's leaking somewhere over 15mA (as may trip
a 30mA RCD), then it's probably got too much water in to be considered
still OK.
I would also say if you have an earth leakage and are contemplating
leaving the heater in service, you should inspect the surface for
damage, as the usual cause nowadays is that a hot-spot has formed and
punctured the case, so it may not last much longer anyway. Given that
you have to take the heater out to do this, is it really worth putting
an old one back in?
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
Stephen Biddle <tanner...@gmail.com> writes:
> Hi All
> I work with electric heaters and have a problem with moisture getting into the element, causing the insulation resistance to drop. The BS spec for immersion heaters says it must be at least 2M ohm at 500V. If I power up the heater it can dry out and recover. Does anyone know the minimum insulation resistance that I need to turn it on without causing permanent damage. It seems to me that a leakage current could cause "tracking" and make the component useless.
Tracking that results in permanent damage is caused by the insulating
> Hi All
> I work with electric heaters and have a problem with moisture getting into the element, causing the insulation resistance to drop. The BS spec for immersion heaters says it must be at least 2M ohm at 500V. If I power up the heater it can dry out and recover. Does anyone know the minimum insulation resistance that I need to turn it on without causing permanent damage. It seems to me that a leakage current could cause "tracking" and make the component useless.
material breaking down and forming a conductor (or at least a partial
conductor), such as plastics breaking down and leaving a carbon track.
Magnesium Oxide will not breakdown, so you shouldn't be able to damage
it any further by turning it on. If there was lots of moisture in there,
you might get an arc right across that would leave vaporised metal, but
the heater has had it by that point anyway (the magnesium oxide should
be under enough pressure to quench any such arc unless the case is burst).
I don't have the PAT test guidelines to hand at the moment, but they
used to allow you to operate mineral insulated heaters to drive off
condensation before performing the insulation test. I just can't recall
if that's still in the current version of the IEEE in-service inspection
and testing document.
Obviously, it's important to check the casing is properly earthed. If
there's an RCD in the circuit, that may prevent you operating the
heater to dry it, but if it's leaking somewhere over 15mA (as may trip
a 30mA RCD), then it's probably got too much water in to be considered
still OK.
I would also say if you have an earth leakage and are contemplating
leaving the heater in service, you should inspect the surface for
damage, as the usual cause nowadays is that a hot-spot has formed and
punctured the case, so it may not last much longer anyway. Given that
you have to take the heater out to do this, is it really worth putting
an old one back in?
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
Stephen Biddle
Jun 24, 2015, 7:52:07 AM6/24/15
to
Rheilly Phoull
Jun 24, 2015, 11:03:07 PM6/24/15
to
"Stephen Biddle" wrote in message
news:23291c15-87e7-40f8...@googlegroups.com...
I have noticed that many of the cheaper Asian built units had crap sealing
on the ends of the elements.
As said before, it's difficult to heat them up to dry out the insulation but
once that is done resealing the element ends
with hi-temp silicon or whatever is your pleasure, usually corrects the
problem. Assuming you have meggered the repair
(during and after) to check for element damage.
Prior to heating dig out the old sealant with a scriber or whatever, this
has to be done anyway and allows the moisture escape easier.
news:23291c15-87e7-40f8...@googlegroups.com...
on the ends of the elements.
As said before, it's difficult to heat them up to dry out the insulation but
once that is done resealing the element ends
with hi-temp silicon or whatever is your pleasure, usually corrects the
problem. Assuming you have meggered the repair
(during and after) to check for element damage.
Prior to heating dig out the old sealant with a scriber or whatever, this
has to be done anyway and allows the moisture escape easier.
samaneh
Jun 20, 2022, 2:15:06 PM6/20/22
to
> TraHello friends
We are active in the field of pipe thermal elements.
thank you
For full context, visit https://www.polytechforum.com/electrical/moisture-in-magnesium-oxide-insulator-73886-.htm
We are active in the field of pipe thermal elements.
thank you
cking that results in permanent damage is caused by the insulating material breaking down and forming a conductor (or at least a partial conductor), such as plastics breaking down and leaving a carbon track. Magnesium Oxide will not breakdown, so you shouldn't be able to damage it any further by turning it on. If there was lots of moisture in there, you might get an arc right across that would leave vaporised metal, but the heater has had it by that point anyway (the magnesium oxide should be under enough pressure to quench any such arc unless the case is burst).
> I don't have the PAT test guidelines to hand at the moment, but they used to allow you to operate mineral insulated heaters to drive off condensation before performing the insulation test. I just can't recall if that's still in the current version of the IEEE in-service inspection and testing document.
> Obviously, it's important to check the casing is properly earthed. If there's an RCD in the circuit, that may prevent you operating the heater to dry it, but if it's leaking somewhere over 15mA (as may trip a 30mA RCD), then it's probably got too much water in to be considered still OK.
> I would also say if you have an earth leakage and are contemplating leaving the heater in service, you should inspect the surface for damage, as the usual cause nowadays is that a hot-spot has formed and punctured the case, so it may not last much longer anyway. Given that you have to take the heater out to
--
> I don't have the PAT test guidelines to hand at the moment, but they used to allow you to operate mineral insulated heaters to drive off condensation before performing the insulation test. I just can't recall if that's still in the current version of the IEEE in-service inspection and testing document.
> Obviously, it's important to check the casing is properly earthed. If there's an RCD in the circuit, that may prevent you operating the heater to dry it, but if it's leaking somewhere over 15mA (as may trip a 30mA RCD), then it's probably got too much water in to be considered still OK.
> I would also say if you have an earth leakage and are contemplating leaving the heater in service, you should inspect the surface for damage, as the usual cause nowadays is that a hot-spot has formed and punctured the case, so it may not last much longer anyway. Given that you have to take the heater out to
For full context, visit https://www.polytechforum.com/electrical/moisture-in-magnesium-oxide-insulator-73886-.htm
0 new messages