Electric Heaters Insulation Resistance

I would call that unacceptably low.

I would run it for a while then recheck....

From a manufacturer's instructions:

"...The refractory material used in heating elements may absorb some moisture during transit, periods of storage, or when subjected to a humid environment. This moisture absorption results in a cold insulation resistance of less than twenty (20) megohms. If this heater has been subjected to the above condition, each heating element must be checked for insulation resistance before energizing. A low megohm condition can be corrected by removing the terminal hardware and baking the element in an oven at 350°F -700°F for several hours or until the proper megohm reading is obtained..." There's more info if you read through the whole thing.

I don't know how large your vessel is, but most marine electrical systems are ungrounded to minimize corrosion/electrolysis problems (the vessel is the earthing conductor, not the neutral/return conductor). If this is the case then the there shouldn't be too much current flow from the elements to the sheath; however, IF (notice that it's a big "if") there's a fault anywhere else you could have problems. Proceed at your own risk and peril.

I'd ask the manufacturer to put his hand on the heater wall or pipe when you power it up.

Ramconsult

Thanks for comments. We have powered up 2 heaters & warming up 3rd with low volt dc supply to improve insulation. Have overcurrent protection which should trip. You are right there is no earth leakage at the moment - & may be risky with 2nd fault. Will monitor while running & see if there is improvement. Anyway it is uncomfortable situation. Like to state the manufacturer here is Sandvik with their Kanthal range of heaters.

Anant

We did lamp heating at terminal box of heater. For two heaters the IR improved from 0.1Mohm to 0.6 Mohm. third heater it is 0.12 Mega ohm. Since there was good improvement with lamp heating( 20 mins) I understand the moisture is usually at the terminal end. This is the reason probably we had slow improvement with dc current injection into coils. For immersion heaters this MGO powder being hygroscopic is an issue. Will do final check on monday. Hope to recover to min 10Megaohm.

Consider ensuring the ends are unsealed (if possible) to allow the moisture somewhere to escape during heating. Also if the humidity is high or room temperature fluctuates consider adding heaters to heat the surrounding air to speed up the drying out process.

Unfortunately there is really no quick way to dry these elements out, so take your time before powering up with full supply voltage.

If you connect a heater of 0.1 Mohm earth resistance then current drawn to earth will be Iph/R i.e. 250/100000=0.0025A i.e. 2.5 mA which is a very safe amount. You can use the heater with a ROCB/ELCB of 30 mA leakage current very safely.

Hi all,

Would like to provide further feedback. After 2 weeks of running the IR value improved between 1.7mohm to 7 Mohm. We have 3 heaters whose starting sequence is based on load. Since at present the load is not much heaters run 2 hrs per day.

However have noticed running heaters record low IR value while standby heaters have higher value. If the starting sequence is changed the heater 1st in line records low IR ( 0.7Mohm) while standby heaters ( 3-4 mohm).

We have checked individual heating element IR value & it varies between 0.5Mohm to 27mohm. ( FYI as stated in 1st post the elements are grouped in delta together to form 3 heater groups of 35 kw, 27.5kw, 27.5kw respectively.

Does above means the heater has manufacturing defect - seals are not good allowing the heater(MGO powder) to breath moisture ?

Appreciate your feedback & comments. Some of the dealers of watlow informed me this is common problem in Singapore & there could also be manufacturing defect.

Unfortunately Manufacturer - Sandvik india has not been supportive & I had to take this to their M.Director today.

Really frustrating as my client says they will not accept heater unless the IR value is 10Mohm atleast.

Thanks in advance

Anant

Hi all,

Would like to provide further feedback. After 2 weeks of running the IR value improved between 1.7mohm to 7 Mohm. We have 3 heaters whose starting sequence is based on load. Since at present the load is not much heaters run 2 hrs per day.

However have noticed running heaters record low IR value while standby heaters have higher value. If the starting sequence is changed the heater 1st in line records low IR ( 0.7Mohm) while standby heaters ( 3-4 mohm).

We have checked individual heating element IR value & it varies between 0.5Mohm to 27mohm. ( FYI as stated in 1st post the elements are grouped in delta together to form 3 heater groups of 35 kw, 27.5kw, 27.5kw respectively.

Does above means the heater has manufacturing defect - seals are not good allowing the heater(MGO powder) to breath moisture ?

Appreciate your feedback & comments. Some of the dealers of watlow informed me this is common problem in Singapore & there could also be manufacturing defect.

Unfortunately Manufacturer - Sandvik india has not been supportive & I had to take this to their M.Director today.

Really frustrating as my client says they will not accept heater unless the IR value is 10Mohm atleast.

Thanks in advance

Anant

Perhaps there is still moisture sealed in the heater. Try unsealing the ends and running it (along with perhaps dehumidifiers in a sealed room to control air moisture levels) to allow moisture to evaporate out then seal the ends up to prevent moisture being absorbed back in when the heater is off.

If it is anything more perhaps it is a manufacturing defect.

<...Unfortunately Manufacturer...has not been supportive & I had to take this to their M.Director today....>

Exactly the right course of action.

Hello Mr.anant

I hope the ussue is resolved by now. If not then . Pls follow this process and you need to have a oven big enough to fit that 90 kw flange heater inside a oven

Mostly your heater size would have been 400 NB ANSI flange with length of the ehater around 1200mm

Soyou will beed a 1.2 meter oven

1. Remove all the terminals nuts of the heater elements ... Mostly this is M4 nuts from terminals

2. Remove the ceramic bush

3. Remove any rtv sealent if it provides and completely cleane it with a pointer and blow compressed air to remove and clear it from any forigh materials. You should see white mgo crust

4. Keep/ place the heater standing position facing the terminals upwards. if possible of other wise horizontal position will also do.

5. In this position place it inside the oven and heate the complete bundle upto 400 deg.C

And maintain it for 2 hours atleast

6. Remove it from oven . If you check the IR value now you will see lower megger values. But as the tube cools down this vales will imporove greately

However dont wait for the heater to cool down as the mgo which is very highly hygroscopic materilal will absorb atmospheric moisture. So when you remove it from the oven. At that temperature with gloves on hands . Do the RTV silicon sealing. We do different kind of sealing as we are manufacturers and have facility . But in site this is whatyou could getbthe best .. a RTV silicon sealing 280deg C grade and sealing should be done properly and see after sealing you reinstall those ceramic bushes on the tube ends

And fasten a small nut tightly. While doing so. You will see som red RTV puffs out on edge of bush and tube.. let it be like that..

Once the heater bundle cools down ... you can check the IR valelues to be improved for sure. And if the process is done correctly

can provide you further assistance if required

Let me know.

A1) <...normal...> is irrelevant. Acceptability must be the criterion. The acceptability boundary may be found in local electrical codes.

A2) Open a dialogue with <...Hubble heaters...>. Telephone?