Melting rcd

[daniel hill]

Afternoon, had a fault this afternoon at a property that one of my lads rewired 12 month ago. The property in question has a 11 kw in line heater that warms a tank up for the domestic hot water and also the central heating. The heater draws close to 50 amp so we fitted a separate consumer unit, tails, henley block ect. The rcd was a Wylex 80A 30mA with a 63A type b mcb. The circuit is wired in 16mm t+e all surface mount and no signs of burning on the cable ect. The problem that I have is this afternoon I have fitted a new rcd consumer unit (Schneider electric) with again a 80A rcd 30mA and 63a mcb fitted. After half a hour I started feeling heat on the rcd and the smell of burning. I have isolated and had to remove as needing to think what is causing the heat. I made sure that all the connections were tight. The voltage of the install is 243V tncs. Have the amp meter on and is only drawing 46A so it's not overload. Any one got an idea of the cause of the burning. Hope you can help, thanks Danny

 

[1shortcircuit]

Was the RCD fuctioning correctly on tests before energising?

 

[GLENNSPARK]

Bad batch of RCDs with the wrong CCC stamped on em?

 

[Engineer54]

Duff internals on the RCD unit, Seen this a good few times i'm afraid!!!

 

[GLENNSPARK]

Duff internals on the RCD unit, Seen this a good few times i'm afraid!!!

well i suppose i got it half right lol.....

 

[1shortcircuit]

Duff internals on the RCD unit, Seen this a good few times i'm afraid!!!

Would this not have shown on testing before energising?

 

[Specialist]

Hi Danny: What was wrong with the Wylex ? had that burnt out as well ?

 

[Engineer54]

Would this not have shown on testing before energising?

It's certainly Possible, but when testing, your basically testing the sensing circuit, not the main internal contacts...

 

[GLENNSPARK]

When testing, your basically testing the sensing circuit, not the main internal contacts...

yeah it aint maximum let through......just the imballance bit....the coil......

 

[GLENNSPARK]

mA...not Amps.....

 

[daniel hill]

mA...not Amps.....

Where have I put that ?

And the Wylex on totally melted and the new Schneider one started to melt after half a hour but only drawing 47A I just don't understand .

 

[daniel hill]

I carnt understand why 2 different manufactures are doing they same. I just don't no what else I can do

 

[GLENNSPARK]

Where have I put that ?

And the Wylex on totally melted and the new Schneider one started to melt after half a hour but only drawing 47A I just don't understand .

was in reply to RCD testing mate as in mA....not rated amps capacity.... bad contacts as eng says inside and you said all terminations tight....did you retighten em after you brought/banked the cables into position as stranded can come loose again after being manipulated......

 

[GLENNSPARK]

Have you got the ends IN the termination clamps on the rcd or BEHIND em? can happen this ....especially if its been a long day....seen it a few times at places we`v been to where the rcd either wont stay in or theres evidence of scorching on mcb terminations etc......

 

[nickblake]

test the circuit insulation etc and increase the curent of the RCD , although the current drawn is below the rated current if the contacts are slightly weak then it can over heat at high currents , i would always go for the higher rated RCD in situations like this so go for either 80 or 100 amp RCD dont forget these are not overload devices they are RCD's basically an isolator with RCD protection

 

[GLENNSPARK]

test the circuit insulation etc and increase the curent of the RCD , although the current drawn is below the rated current if the contacts are slightly weak then it can over heat at high currents , i would always go for the higher rated RCD in situations like this so go for either 80 or 100 amp RCD dont forget these are not overload devices they are RCD's basically an isolator with RCD protection

yep. any imballance over 30mA and it will go (if its working ok)..lol........

 

[GLENNSPARK]

you`v got a 63A MCB for overcurrent protection here and any signs of overheating there?.....If thats happy then it has to be crap contacts within that RCD......like Nick says..go up a size......give it every chance.....

 

[daniel hill]

Yep have checked all the cables were in the clamp, tightened up by 2 electricians and a test engineer, am going to try a 100A rcd tomorrow and also going to take a thermal image camera. I just carnt understand why a rcd rated at 80A is running warm when the load is 47A a load difference of 33A under maximum current draw.

 

[Engineer54]

Yep have checked all the cables were in the clamp, tightened up by 2 electricians and a test engineer, am going to try a 100A rcd tomorrow and also going to take a thermal image camera. I just carnt understand why a rcd rated at 80A is running warm when the load is 47A a load difference of 33A under maximum current draw.

That's a good and wise idea to make use of a thermal imaging camera. It will certainly show you, if and/or where there is any high resistance causing your overheating. Try it first, with the existing RCD in place, before moving on to the higher rated unit, if just to confirm where the problem lays. Check the whole of supply side of things too!!

 

[Knobhead]

It’s no reflection on you Daniel.
It’s the usual cost cutting by manufacturers. If they can shave a gram off the contacts they will. They work on the basis that the loading won’t be anywhere near the nominal maximum.

A sad state of affairs but to undercut the competitors, quality goes out of the window.