Earth Leakage, concerns and solutions - Shower

[1shortcircuit]

Good evening all, Happy Weekend

Just thought I'd post another thread as I have given my earth leakage clamp meter an outing today and need to learn a little more about the results I am receiving.

Firstly, 16th Edition board - RCD - Shower, Cooker, Sockets, Sockets, Sockets and then two lighting circuits on the unprotected side.

Called to a job because everytime they turn on the shower the RCD trips. No loose terminals in entire board or shower unit. Checked the isolator switch to find that one of the terminals on the neutral had a snapped screw. This could be undone with long nose pliars and the copper had turned an almost silver colour so I thought I was onto a solution. I replaced the switch with a new MK type after I had IR'd on a 250 and 500v test, both supply and load cable came back with maximum readings. Refitted everything ensuring all connections were tight and fired up shower again.

The shower pulls 34.6 amps on a 40A breaker.

On packing up my tools and after running shower for approx 20 minutes, TRIP! Damn, wasn't that then lol

Clamped my earth leakage meter onto the shower circuit cpc and obtained very high readings, high as in exceeding 30mA high on one instance.

Now, I have left the circuit isolated because like I explained to the client I could remain there for the rest of the day testing and looking for faults BUT all it will do mostly is rack up the hourly charges and I still believe the fault is related to the shower.

When clamping the main earth even with the shower running I couldn't get a reading over 10mA (100A main fuse)

The shower is now running for much longer as originally it would trip everything immediately before (although it did not trip immediately on arrival).

My thoughts are that I could move this shower circuit onto an unprotected way and use a 40A RCBO thus reducing issues with the rest of the property being affected if the circuit trips. Can anyone say that they see any concerns with this proposal giving the high earth leakage that was detected? I've read that an installation should not exceed 10mA earth leakage if protected with 100A fuse, can anyone shed any light on this matter that will aid me making a decision? It's too easy to say your shower has had it you need to spend a couple of hundred quid to swap it when swapping in a 20 quid RCBO may resolve the issue or at least make the installation far safer.

What would be the maximum earth leakage you would expect to see on something like this? I have seen that a cooker max should be approx 5mA?

It's great having these fancy bits of kit but useless if you cannot read the results correctly.

Any assistance would be much appreciated, it would also be great if someone could point me to some literature that would benefit me as I want to understand this issue.

This is an ongoing fault finding exercise, which is why the shower remains isolated to try and eliminate/prove the where the fault is without running up too much expense in labour.

Kind Regards

1SC

 

[spark 68]

Originally Posted by Engineer54
Trying the RCBO approach as an initial fix, is probably the best way to go!!

I would do this anyway, to prevent the shower from tripping most of the installation out, in the event of a fault (just like this one).

Also to provide some load balancing at the CU, as the shower is on the same side as the cooker and RFC's at the moment, there are only lighting circuits on the other side of the board.

 

[Engineer54]

well i`m sorry eng ..but as someone who looks on RCDs somewhat dubiously...i find this post strange.....

Nothing wrong with RCD's mate, .....When there working!!

It's when they don't, and your totally relying on them for your earth fault protection, you need to start worrying...lol!!!

 

[MarkieSparkie]

Almost certainly leakage from element(s) to heater tank. A hot element-tank IR test should confirm this. Replace the heater tank or complete shower unit. Once an element starts to breakdown it will only get progressively worse.

 

[1shortcircuit]

Thank You very much to everyone that has provided assistance regarding this matter. I'm pleased that it seems my line of thought is correct.

1SC

 

[HandySparks]

Clamped my earth leakage meter onto the shower circuit cpc and obtained very high readings, high as in exceeding 30mA high on one instance.

Coming to this one a bit late, I know, but if you can get your current clamp around both the line and neutral supplying the shower, set to the mA range, you will see exactly the same differential current from that circuit that the RCB sees. This should be a more accurate picture of the situation than just clamping the cpc (although it's a good start) which can be affected by parallel earth paths through pipework.

 

[1shortcircuit]

Thanks for your input HandySparks. I will have to try this method on the next opportunity:thumbsup

Received an update this afternoon. No tripping since shower circuit has been isolated

 

[GLENNSPARK]

Thanks for your input HandySparks. I will have to try this method on the next opportunity:thumbsup

Received an update this afternoon. No tripping since shower circuit has been isolated

yes because the difference between the 2 is the imballance that the RCD senses.....and a ramp test will tell you at what point it lets go....giving you a max value difference before it lets go.....

 

[GLENNSPARK]

but dont forget that accumilated earth leakage will play a part here so you could ramp the RCD...with all final circuits/connected loads fed by that RCD on......that will take into account accumilated earth leakage the higher they are...the lower your ramp should be