Testing a heating element

honda boi

Hi all,

My partner got a steamer that is used for steaming horse hay.

Now it didn't work when she got it and I was entrusted to fix it.

I first measured the resistance of the element, got around 18ohms which is normal to me. Power wattage is 2.9kw , so 18ohms isn't far off what it should be.

Checked the thermostat and it was toast, so replaced that ,

Turned it on and it worked for about 15mins, then tripped the RCD. Now as soon as I turn it on it trips!

First thought was earth leakage. So I tested between live/neutral to earth.

Both times to earth , when I set my meter to 200kohms I was getting a reading that started around 20 that just keeps increasing as I measure.

To me I just want to make sure that the element is fried? I don't have a megger so can't do an insulation resistance test.

The element is still reading 18ohms which I thought If there was a leakage to earth it would read as an open connection or I'd get a different result to the 18ohms ?

Needles73

My thoughts. The element is probably faulty and giving an earth fault when hot and when you measure it’s cool or cooling hence the resistance to earth keeps increasing as you measure ?

Slightly Kwackers

I assume the element is a steel encased device with the case bonded to ground?

If the heater was not in use for some time and stored in damp conditions the insulation can absorb moisture and lead to tripping.

An Ohmeter or DMM is not the most suitable test item for the leakage to earth. You need a Megger or some other high Voltage sourced instrument really.

You would need to identify that the leakage to ground is via the element and then run the element somewhere secure with no access to anyone and apply power without a ground connection until the leakage clears.

The technique is not normally advisable or permitted on industrial premises, when I was confronted with the problem on site, I would remove the element and use the clients oven or dryer to clear the problem. For a long element this can take hours.

Of course if you replaced the thermostat, then the element should not cost much more, so just see if removing the live and neutral from the element stops the tripping and order a replacement.

kirk.

As above if element is in fact damp not faulty, I did that recently with an electric pizza oven to clear the damp fault

Extreme caution needed if you decided to do that ..

Realistically you need a Megger for testing insulation faults

10-10-20

You only need a resistance of 7600 ohms for 30mA @230v to pass through to cause the RCD to trip, so you seeing 20k ohm at a DVM would indicate moisture alright and that resistance would decrease at 230v AC causing the short to earth.

Is the device clean and dry internally and can you see any damage to the wires at all? Disconnect the heater element at the L and see if it still trips.

honda boi

Thanks for the replies.

Regarding the dampness issue, if it was damp from being left for a prolonged time surely it wouldnt of worked as intended when I powered it on for the first time?

It ran for at least 15 mins and heated the water up and did what it was supposed to.

Yep the element is inside a steel casing bonded to earth.

Am I right in reading to get rid of the moisture I take out the element and just leave it in the oven at a low temperature?

I haven't taken the element out or checked the actual insides of the steel enclosure, just been going by the readings.

All wires are fine.

When I plug it in with the switch off, it doesn't trip but I'll disconnect the L and see if it trips.

10-10-20

https://www.boards.ie/discussion/comment/120053254#Comment_120053254

Moisture's odd. You can drive the moisture further into the element as it boils off and then cools. It may now have collected at a point where there was damage to the ceramic insulator. I'd guess that drying it in an oven would improve the resistance - obviously it should be fully open in terms of resistance between the element L and the external case.