Space heater requirement for the outdoor Junction Box 1

[krisys]

We have an outdoor power Junction Box (JB) in the offshore platform. Installed an year ago and was in service. It has hinged door. Recently the door was found to be bulged out. Immediately taken out of service, as it has 6.6kV cable inside.

This installation is in the Middle East region, where the ambient temperature goes above 50 deg C in the summer. Not to mention that the humidity of almost close to 100%.

The volume of the box is about 0.4525 cubic meter. There is a provision for space heater but it is found not connected. When opened the JB lot of salt deposit was observed. The JB has a breather also. It is suitable for the hazardous area Ex 'e' type and IP56 enclosure.

I wanted to know what is the criteria to provide the space heater for the JB? Is it based on the inside volume of the JB?
Because when the inside volume increases, the amount of air trapped is higher, thus the condensation will be more.

Any industry standard available for reference on this subject?
I need it to support my argument to take the space heater in service.

Also another question regarding the breather:
Will the breather prevent the moisture entry? or it will only restrict the free air movement.

 

[7anoter4]

See[for instance]:

https://www.brenclosures.com.au/anticondensation_heater.htm

for breather:

http://www.emersonindustrial.com/en...ng/haz-loc-drain-breathers/Pages/default.aspx

 

[krisys]

7anoter4,

Thanks for your quick response. But I did not get clue on the enclosure volume criteria to decide whether the space heater is required or not.

In my case the space heater is provided, but not connected. I want a back up to insist that the space heater is required to be connected and shall be in service.

 

[waross]

The breather does not restrict the slow movement of air. A breather in a classified area does restrict and cool the escape of hot gasses in the event of an internal explosion.
A two way pressure relief valve may act similar to a breather with the added feature that it allows an slight positive or negative pressure in the enclosure before allowing air to pass. This greatly reduces thermal pumping of moist air into the enclosure.
The criterea? If you have a problem with condensation than you need a heater.
A note on the action of an anti-condensation heater;
The heater acts to indirectly heat the enclosure surfaces and internal components so as to maintain them above the dew point during swings in ambient temperature and humidity. Moist air is not the direct issue. The problems arise when the moisture in the air condenses on cool surfaces inside the enclosure.
Often the current in the cables will generate enough heat in the enclosure so as to avoid condensation problems.
Condensation is more an issue with conditions of use than with volume.
Again. If you have an issue with condensation that is the indication that the heater is advised!
Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[cuky2000]

See if the enclosed calculator could help

https://www.stego.de/nc/us/support/calculation-tools/heater-calculation/

 

[krisys]

cuky2000,
Thanks for the link. It is quite useful.

Bill,
Thanks for your perspective.

 

[prc]

krisys, why a space heater is required for such an application? You said it is IP-56 class enclosure, correct, considering off shore service. I would go for the sealed construction with a dehydrating breather, like of transformer. It will prevent unnecessary air circulation, but dehydrate whatever air breathed in. I used to provide such arrangement in large air filled cable boxes of power transformers.

 

[ScottyUK]

The ATEX / IECEx certification might limit the choice of dehydrator-breathers but it's a fair solution. I think the dehydratant might need replacing fairly often given the day / night temperature cycle which is driving the enclosure breathing combined with the marine environment.

Another suggestion - if you can maintain certification - would be to bleed instrument air into the enclosure and allow it to exhaust through the breather. I'm not suggesting either the volume or the pressure required for Ex 'p' type enclosures, but a few mBar of positive pressure to keep the outside air, outside. I've done this on non-hazardous equipment (isolated phase bus duct on a generator) with success but have never looked closely at the hazardous area certification aspects; this idea could be a complete non-flier from that point of view.

 

[prc]

There is an industry standard for Control cabinets for Power Transformers -IEEE C57.148-2011. Clause 5.10 ask for a ventilation louver near to top of cabinet wall and a 12 mm minimum dia drain hole at bottom with adequate screens to prevent entry of insects. Clause 5.22 gives the heater requirements.
Calculations for heater wattage can be deduced from the annexure to IEC 60076-16-2014 Transformers for wind turbines where calculations for ventilation requirements of transformer chamber is given.
But I believe a cabinet described as above will not be very good for off shore platforms due to salty mist, but may work to prevent condensation.