open neutral problem please hlep

[beresford]

Hi,
I have an open neutral problem within CU from the main-power supply to FCU (3A) to boiler. The voltgages of L(brown) and N(blue) on my boiler both appears as 238 v against earth. I tried to find where the neutral is open. I disconnected the three main-power lines (one red supposed to be live, one black supposed to be neutral and the yellow/green supposed to be earth) on the FCU (the other three lines to boiler also disconnected from FCU). I checked the voltage of these three lines from main power against the other earth which is grounded by connection to the metal panel of the boiler in the end.

Red the live against earth on boiler: 238
Black the neutral against earth on boiler: 147
yellow/green the earth from main-supply against earth on boiler: 178

Black against yellow/green the earth from main-power: 18
Black against red: 51
Red against yellow/green the earth from main-power: 36


I did some more tests. I connected both earths in FCU together and grounded it by connection to the metal panel of boiler.

Red against earth: 238
Red against black: 174
Black against earth: 37

I get confused now. Is the lines from main-power to FCU ok? Does the test suggest a short cut between the live and neutral somewhere from the air-switch box? why the voltage between the two earths isn't 0? Does it mean the earth from main-power isn't grounded?

Please help me. Thank you so much

 

[lamb]

Turn the power off to this circuit and fault find by using dead tests.
You cannot identify a short by measuring voltages on an energized circuit, and lack of continuity is much easier to test using dead tester.

 

[Spazz]

Just a thought

Is your switch for your boiler on or off?
If its off then its switching N, turn the switch on and test again!

Otherwise turn all power off and do a continuity check between boiler and CU.


That will tell you what the situation is with the cables.

If the cable is broken you need a spark in to replace the cable between your boiler and CU.

If your Boiler has a 13A Plug and plugged into a Socket then check the plug, incase the wire has come off - same as the switch if its hard wired into a switch.



Looking at earth and earth
TURN IT OFF AND UNPLUG IT!

Get a spark out NOW and dont mess with it!

It will kill you if you come into contact with the earth!


So we know are you a sparky?

Also post your location on here so one of us in your area might be able to help!

 

[telectrix]

isolate from supply. disconnect both ends, all 3 conductors. if you haven't got a wander lead, short all 3 at 1 end, then meter for continuity across the 3 at other end. all should read as short. then part the shorted ends and IR test.

 

[beresford]

Thanks for all. I did a bit more tests and edited my poster on top.
My boiler is off. I already took the pcb out after someone told me i have an open neutral problem. I am triing to find whether the broken happended between main-suppler-air-switch to FCU or between FCU to Boiler. I only connected the earth to the metal panel on boiler now.
I am so confused why the voltage of red against black isn't '0' if the neutral is broken happened between main-supply-air-switch and FCU or '238' if the CU between main-supply-air-swict and FCU is ok (174 and 51 dependant on the two earths connected or not).
I am aslo confused why the voltage between two earths is '178'. I am sure one earth is grounded.
I have not checked thecables on the main-power-supply-air-swich end.

 

[SPARTYKUS]

I really think you should seek a professionals assistance.

Where are you roughly in the country?

 

[Des 56]

You seem to have a urge to use a voltmeter to verify continuity
As said a continuity test should be a straightforward simple task to find this open neutral suggestion

Given you are sticking with this voltage detection,disconnect the neutral from the load on the fused spur,switch on or short out any switching in the circuit and test to earth,you should read mains voltage between the live and any reference earth and check for 230-e at the disconnected neutral

 

[SPARTYKUS]

Are you near Shropshire. I 'd love to find the fault for you

 

[beresford]

Thanks for Spartykus and everyone. sorry for reply so late. a very busy day.
I actually live in Cardiff.
I did the continuity for the cables between the boiler and FCU using a multimeter. The cables are fine. I connected the boiler to alternative power from a wall socket (I changed the 13 A fuse to 3A) and am very happy to find that the boiler still work although I already paid £100 for the parts that I won't use any more.

I have not done the continuity test for the cables between FCU and main-power-supply. I opened the air-switch box in the main-power-junction-box and have no idea why the colour of cables is different (red, black green, don't spot any loose coonection) from the colour in FCU-switch-on/off (red, black, yellow&green). I guess there is another juntion hidding somewhere for the cables between the FCU and main-power-supply. The neutral cable may be loose there.
I do have to find a professional to solvent the problem now.

Are you near Shropshire. I 'd love to find the fault for you

 

[beresford]

Thanks. Could you please tell me what is spark? Is it used to conntect two wires? I tried to google information but no success.

Just a thought

Is your switch for your boiler on or off?
If its off then its switching N, turn the switch on and test again!

Otherwise turn all power off and do a continuity check between boiler and CU.


That will tell you what the situation is with the cables.

If the cable is broken you need a spark in to replace the cable between your boiler and CU.

If your Boiler has a 13A Plug and plugged into a Socket then check the plug, incase the wire has come off - same as the switch if its hard wired into a switch.



Looking at earth and earth
TURN IT OFF AND UNPLUG IT!

Get a spark out NOW and dont mess with it!

It will kill you if you come into contact with the earth!


So we know are you a sparky?

Also post your location on here so one of us in your area might be able to help!

 

[Andy 7671]

Spark = Electrician

 

[Des 56]

Spark-shortened version of Sparky
Used as a slang term for electrician on building sites esp

Probably started on ships to refer to the radio operator

 

[beresford]

Godnees, I once thought it in a completely wrong way

Spark = Electrician

Spark-shortened version of Sparky
Used as a slang term for electrician on building sites esp

Probably started on ships to refer to the radio operator