Immersion

KOWBUOY

I have an immersion heater tripping an RCD. I have measured the resistance between earth and the two elements and between the 2 elements (20ohms and 30ohms and open circuit respectively) I have by passed the switch and reset the RCD it still trips. The immersion is the only circuit on the MCB (which is not tripping) I have turned off the Immersion reset the RCD which does not trip until I hit either the on/off or bath/sink switch. Any ideas?????????

mikehammer67

hmm what are you testing with ? a multimeter?

what did you bypass?


the first thing you do is confirm whether the immersion is faulty

if not you can check for faults in the fixed wiring, rcd etc.

KOWBUOY

Yea a multimeter on low ohms. I bypassed the isolation switch next to the water cylinder incase it was faulty. The rcd controls a number of other circuits and they are fine. The mystery thickens ?????

KOWBUOY

PS the elements appear fine

mikehammer67

you can 't confirm anything with the multimeter unfortunately


except for heater resistance and stat continuity

you need a megger

KOWBUOY

Why a megger to test what ?

mikehammer67

what?

KOWBUOY

mikehammer67 wrote: »

you can 't confirm anything with the multimeter unfortunately


except for heater resistance and stat continuity

you need a megger

What would a megger do that a multi meter cannot,(im not being smart i genuinely dont know) Surely the only things I need to measure are heater/element resistance and stat continuity, no?

mikehammer67

no the megger tests for insulation faults at a higher voltage

Diggerdunne

maybe the immersion is leaking a little to earth that is putting the RCD over its 30ma limit... you cud put the immersion on its own rcbo and see if it still trips.....
other appliances in the house cud also be leaking a little to earth and the immersion is the one thats putting it over the edge...

mikehammer67

Diggerdunne wrote: »

maybe the immersion is leaking a little to earth that is putting the RCD over its 30ma limit... you cud put the immersion on its own rcbo and see if it still trips.....
other appliances in the house cud also be leaking a little to earth and the immersion is the one thats putting it over the edge...

i don't think he should do that if he's having difficulty troubleshooting tbh

Diggerdunne

I agree but get an electrician to do it 4 him...

brightspark

It's odd he is working on two immersions?

I'm guessing he's either an apprentice doing homework, or else just a troll.

frankmul

The op stated that he was getting 20 & 30 ohms resistance between the elements and earth in their original post. Is that not the problem, shouldn't here be a very high resistance to earth? Something is shorting to earth!

Bruthal

frankmul wrote: »

The op stated that he was getting 20 & 30 ohms resistance between the elements and earth in their original post. Is that not the problem, shouldn't here be a very high resistance to earth? Something is shorting to earth!

I'd say he meant 20 ohms for bath element resistance, and 30 for sink. For 3 and 2 kw they would be 17 and 26 ohms respectively. And open circuit for each element to earth.

Bruthal

mikehammer67 wrote: »

you can 't confirm anything with the multimeter unfortunately


except for heater resistance and stat continuity

you need a megger

A multimeter will usually show up earth faults on immersions. But the op said they had the multimeter on low ohms settings. An earth fault of 6k ohms live to earth as an example, would trip an RCD. The low ohms setting will show anything above 200 ohms as open circuit on my one. Or at least out of range, which the op might assume means open circuit or very high ohms, as expected from element terminals to earth.

It needs to have its range put in the high ranges, and reduced from each range that shows a reading, or increased from the low ranges that show open circuit , to get decent readings. Not just a low range setting reading showing open circuit, and take that as meaning no earth fault.

Bruthal

brightspark wrote: »

It's odd he is working on two immersions?

I'm guessing he's either an apprentice doing homework, or else just a troll.

2 elements I think he is saying.

Edit. 2 immersion jobs in different threads maybe?

brightspark

Yes Bruthal he has another thread

http://www.boards.ie/vbulletin/showthread.php?t=2056934543

The 20 and 30 ohm values make me think it is an exercise. But it's a long time since I did my exams so I can't be sure.

dupeters

Sounds likeone of the immersion coils is down to earth under load.
A MULTI METER WILL NOT FIND THIS TYPE OF FAULT ON LOW OHMS SETTING
I would get a megger and do an insulation resistance test on both coils to earth.From what i have read already you are not familiar with a megger so i would call a spark.
Or you could just change the immersion coils ,you already know the immersion is causing the problem.TURN OFF THE RCD FIRST THO!!

Bruthal

brightspark wrote: »

Yes Bruthal he has another thread

http://www.boards.ie/vbulletin/showthread.php?t=2056934543

The 20 and 30 ohm values make me think it is an exercise. But it's a long time since I did my exams so I can't be sure.

Yea if measured with multimeter it will be 17 and 26 probably. 20 and 30 is very sort of rounded up alright.

Bruthal

dupeters wrote: »

sounds like the immersion coil is down to earth under load.
A MULTI METER WILL NOT FIND THIS TYPE OF FAULT

Really? You can say that beyond all doubt?

If a multimeter can accurately measure megaohm resistors, chances are it can detect a 17 ohm heating element in contact with its copper jacket, even if only due to moisture into split in element.

Also, you said the op has already shown the immersion is causing the problem, and try changing the elements. But an item tripping an RCD does not prove that is the faulty item. It probably is, but its not proven.

Edit I see you said the multimeter won't find this fault on low ohms setting. Yea your right there, I did,t see that bit

dupeters

I dont know brutal.
From experience i know that you need voltage to find certain earth faults.
a low ohm meter will not find a fault better than a decent insulation resistance meter any day of the week(even weekends)
i have had faults that would only arise under applied voltage.Put an ordinary ohm meter on the fault and it wouldn't even read low.

Bruthal

dupeters wrote: »

I dont know brutal.
From experience i know that you need voltage to find certain earth faults.
a low ohm meter will not find a fault better than a decent insulation resistance meter any day of the week(even weekends)
i have had faults that would only arise under applied voltage.Put an ordinary ohm meter on the fault and it wouldn't even read low.

Yes, I didn't see your mention of the low ohms setting on multi meter. I edited last post.

On earth faults where there is contact, even if fairly high resistance contact, a multimeter will show it. Water based elements will show them. But not usually on low ohms settings as I said myself earlier, and you say yourself.

A meggar is a better fault finder because it has high voltage obviously, because the voltage they operate at can show faults when there is no direct contact, such as a nail through a twin and earth that is not quite touching both conductors, because the voltage can jump or break down the much weakened insulation.

But the nature of faults on elements that cause RCD trips, will usually show on multimetets, but often not on low ohm settings

Dotsie~tmp

Experience tells me some element earth faults only occur as the element begins to heat up, expand and allow water to enter. Disconnect the elements from the switch and if it holds it needs replacing.

Bruthal

Dotsie~tmp wrote: »

Experience tells me some element earth faults only occur as the element begins to heat up, expand and allow water to enter. Disconnect the elements from the switch and if it holds it needs replacing.

The type of fault that causes that delayed trip can be down to how far along the element the fault is. If water gets in, the nearer to the neutral end it is, the less leakage current there is.

But elements usually trip rcd's long before the outer copper jacket fails, and is due to the element conductor failing with open circuit, then beginning to arc, and this burning reaches the inside of the copper jacket through the mineral type insulation. This can have a delayed tripping too, each time the RCD is reset.

Immersions not on rcd's were often seen with outer copper jacket split wide open and still staying on, with inner element conductor completely exposed to the water.

KOWBUOY

Thanks eveyone. Cheers digger that worked

mikehammer67

KOWBUOY wrote: »

Thanks eveyone. Cheers digger that worked

what worked?

Bruthal

mikehammer67 wrote: »

what worked?

Probably put immersion on its own RCbo. Cumulative leakage possibly.

dupeters

Bruthal wrote: »

Probably put immersion on its own RCbo. Cumulative leakage possibly.

If that is true i would still change the immersion as the leakage can only get worse. is he not just prolonging the inevitable??
The old rcd saw this fault and tripped for a reason (cumulative or not). i have never known an earth fault to improve only worsen with time.

Bruthal

dupeters wrote: »

If that is true i would still change the immersion as the leakage can only get worse. is he not just prolonging the inevitable??

But if it works fine now if its on its own rcbo, why replace now?

Most if not all circuits have leakage to some degree, although usually infinitely small in most cases. But elements will have some small leakage.

Put enough circuits onto a single RCD, and the nuisance tripping risk increases, even with normally operating devices.

The old rcd saw this fault and tripped for a reason (cumulative or not). i have never known an earth fault to improve only worsen with time.

No, it saw a cumulative leakage of over 30ma, assuming the RCD itself is OK.

If the immersion now works on the rcbo, its fine to use IMO. Why change it?

Maybe other items were leaking 25ma, and switching on immersion added another 5. What then, replace everything in the house?

dupeters

Maybe bruthal,
but what if it the element has a fault of 28mA? And it was causing the rcd to trip? along with say 3mA of cumulative?
Adding it to its own rcbo would be ok for now.

i think for safety sake (and because it is a cheap purchase/remidy) that changing the whole immersion coil would be the right way to continue.
I know if it was my house with my kids using hot water every day i couldn't sleep knowing my immersion had a fault which i had not repaired but transferred to another device?