100V across immersion - no hot water

[PHILatHOME]

Seem to have developed a problem that I am only measuring 100V L to N across pair at switch to thermostat/heater element. I measure 230V L to E but also 150V N to E. All measurements with switch open (no supply to heater). Do these measurements indicate an earth fault between N/E.

I am not sure where that cable runs to as chased down wall!! I'm wondering if I can take a lead (temporary to verify immersion) from a socket to the heater, not sure how many amps these elements pull. Any thoughts would be appreciated! Cheers

 

[stardanny]

Hi PhilatHome.

Best to ask in Electric UK.

Regards

Dan.

 

[onlyfitidealboilers]

take it you have not got an RCD? if so even if you get a few volts on the earth it trips there very sensitive sounds like a faulty immersion your picking the 150v between N/E off the neutral i think.

 

[Spark123]

Sounds like you could have a loose connection in the neutral somewhere, possibly in the isolation switch or the consumer unit. It could also be a faulty switch.

 

[onlyfitidealboilers]

how many volts can you expect on a neutral before it will blow the fuse?

 

[Spark123]

It will never blow the fuse, even with 240v on it.
In a healthy circuit the neutral should be at about 0v with respect to earth.
If the return path via the neutral isn't healthy then the voltage on it will increase, up to 240v and the equipment won't function properly.

 

[PHILatHOME]

Thanks Spark123...what you say makes sense....I guess I need to chase the cable! Was thinking to switch ease RCD at the consumer unit to find which feed it comes from and see if there are any joint boxes. The consumer unit is in the garage and I know there are a few JB's on the roof of the garage (no berating as all electrics as fitted when I moved in, hence not fully sure about the feed!!!! ...thanks though, gives me something to look at/think about.

 

[onlyfitidealboilers]

does confuse me electrics some times!!!!!!!

if you put water on a Live an it spreads to neutral that will blow the fuse yes?

just like on a faulty piece of wire if the insulation was faulty an the live touched the neutral it would blow?

same with a faulty component ie a fan if the winding are faulty an worn an the L Hits N Blow again..

 

[Spark123]

A fuse will blow if too much current flows through it.
If you have a short circuit the fuse will blow. If you have water tracking across L-N then it may blow the fuse, it depends how good the path via the water is current to flow (i.e. the resistance of the fault path.)
A dead short should blow the fuse yes
Faulty components - again depends on how good the path is.

Open circuit faults such as described above will have either no current flowing in the circuit or a reduced current will not result in the fuse blowing, that is until the heat causes another fault and bang!

 

[onlyfitidealboilers]

thanks spark123 il press the button

 

[PHILatHOME]

Not an electrician myself but I think its the current that blows the fuse not the voltage, hence why when we connect live to neutral in a kettle 9or in my case an immersion) the fuse doesn't bow as the 'coil' has a high enough resistance to lower the current.

However, sparks comments about perhaps a loose cable in the neutral does confuse me, is either the connection made and I get a circuit or broken and I don't get a circuit...how does a loose connection allow me to see 150v between N & E?

 

[ricicle]

does confuse me electrics some times!!!!!!!

if you put water on a Live an it spreads to neutral that will blow the fuse yes?

just like on a faulty piece of wire if the insulation was faulty an the live touched the neutral it would blow?

same with a faulty component ie a fan if the winding are faulty an worn an the L Hits N Blow again..

Any fault deliberate or otherwise between L and N or L and E will cause the protective device to operate. The smaller the resistance of the fault the quicker the device will operate (subject to mechanical components on circuit breakers)

If you don't fully understand electrics then it would be worthwhile educating yourself before you attempt to work on it....

 

[ricicle]

If a Neutral connection is poor somewhere the joint will have a resistance. This resistance will cause a voltage drop across it, which is why the voltage is lower between L and the N of the other side of the heater.
If you remember Ohm's law it will like be having two resistors in series - the heater with 100V across it and the bad joint with 150V across it (which is being measured to earth, which in turn is the same potential as Neutral)

 

[onlyfitidealboilers]

i aint got 4 years to go an do another apprenticship, already done 4 years on the gas just a few pointers will do i hope!

 

[PHILatHOME]

Ricicle, I'm sure I must be being thick but my post described two points, the first that the isolation switch is open and therefore there is zero volt drop across the heater and second that, with this switch open (no load) I measure 150V between N and E. Because you say that N should be the same potential as E then, even with a faulty connection in this N how is the cicuit being made (where is the loop?)