Unable to to get a direct measurement reading for shower Zs

[onfire25]

Hi guys,

Would be greatful if i could pick a few brains.

Scaniro.

You get a call re shower not working so pop over.....take pull coard down and can see that the supply netural has overheated and started to melt the PVC!

On the pull coard terminal for the netural supply you can clearly see that it too has started to overheat!

Re made the cable off and connected back to a new 45A pull coard.

Test results

R1+R2=0.04
IR = >299Mohms L-E, N-E, L-N
RCD @ x1=43.7ms
RCD @ x5=11.8ms
Zs = TRIP

I'm using a Megger MFT1552 and it was set on no trip.

The shower is a Gainsborough 9 or 9.5Kw
Cable is 10mm
45A 60898-B MCB

The length of run of cable is about 13M

The RCD (80A 30mA) for that side of the board keeps tripping whilst trying to do the Zs at the pull coard.

Ramp test on RCD tripped at 25mA so not to worried about the RCD.....but would appreciate some thoughts re overheating netural and why i am not able to undertake a direct measurement of Zs.

I have taken a Ze reading and done Zs by calc but really want to do a direct......peace of mind and all that.

Any thoughts would be appreciated.

 

[Dan the spark]

Possibly the supply neutral terminal had not been tightened up enough or come loose and had been arcing away when shower was in use

 

[onfire25]

Will agree with that reason.....where im not able to get a direct measurement of Zs im probably over-reading that bit.

Any thoughts though re the Zs bit and tripping?

 

[bigspark17]

did you try a ZS test on any other circuit RCD protected.?

 

[sparks1973]

well you`v got an R1+R2....so whats your problem?....go to the incomer and get yourself a Ze....then just calc it....

 

[trev]

If it absolutely refuses to hold on the Zs test why not prove your CPC continuity with a wander lead between the shower and the MET, then as said enter the calculated figure on the SoTR.

 

[onfire25]

did you try a ZS test on any other circuit RCD protected.?

Yeah.....tested Zs at cooker socket protected by same RCD......and that was fine

 

[onfire25]

well you`v got an R1+R2....so whats your problem?....go to the incomer and get yourself a Ze....then just calc it....

I got a Ze of 0.19 therefore by calc Zs=0.23......which is fine......call it ---- but i just want a direct measurement or know a logical reason for not being able to get one on a straight run of cable with no joints!

 

[Dcf]

Some rcds seem to require a bit of resistance for some reason.connect about 1 metre of 1.5 flex at the circuit breaker disconnect shower circuit and see if the meter will do a loop test at the board.if you have the luxury of another meter cross reference the two. My megger likes some rcds better than my metrel and vice versa