Experiencing volt-drop within household

[bridav]

Hi All,

I am not a qualified electrician - please be gentle!

I had renovation done to my house last October which included a complete refitted kitchen. The new kitchen included a new Neff double oven in which has been working like a charm since last it was installed (including both ovens being on at the same time!).

Suddenly, yesterday the double oven has decided to stop working, checked the distribution board and nothing has tripped. I have tried getting in touch with the electricians that did the installation, but has failed to get back in touch. Therefore, decided to investigate the matter further. I put my multi-meter over the live and neutral terminals on the oven and it read 150V AC, I have checked the outgoing voltage at the MCB which read 240V AC. I thought I may either have:

1. a bad switch
2. a bad MCB
3. a bad connection
4. may be an earth leak

I have tried changing the switch and the MCB, no change to the volt reading [whilst disconnected from the oven]. I have tried tightening the terminals within the distribution board in case of loose connections, no such joy!

Other observations, I noticed that the cable exiting the oven is BLUE and BROWN whereas the cable leaving the distribution board is RED and BLACK. I cannot find the join for this cable as I fear it may be tucked behind the newly plastered walls and ceilings!

Any assistance or information on how to rectify the above volt drop without punching holes about the house would be much appreciated.

Many thanks,
Brian

 

[Darkwood]

Welcome to the forum

 

[Pete999]

Did the "Electrician" leave you with any certification, did the company belong to any of the Schemes NICEIC,NAPIT STROMA? it could be that the "Electrician" was in fact Kev the Kitchen fitter, ergo not an Electrician. I could be that he connected your oven / cooker to a cable that is far to small for the intended use you require at present, I'm not saying this is the case, as I'm only going on the information you have given.

If the company doing the renovations were allied to any of the schemes, your first port of call would be to whichever scheme they belonged to, if not, then call a local registered Electrical Contractor and ask them for an assessment of your problem. Good luck with your investigations I hope it turns out to be a minor problem easily rectified.

 

[gazdkw82]

Is it on a fused switch which should be in the wall somewhere? If so check all terminations are good and check fuse.

The oven itself may have a fuse.

sounds like power to the cooker is good

always make sure you cut the supply at the cu via the mcb or better switch the main power switch off if you don't have the correct tools to make sure supply is in isolated.

 

[Octopus]

You need to locate a local competent spark.

Where are you based?

 

[gazdkw82]

How on, you've changed an mcb?

if your not competently experienced I wouldn't suggest taking on work like that. It can kill you

 

[David M]

Its best you get a qualified sparky in to check it out for you. The oven worked fine for a short period, then just suddenly stopped working properly and you are certain its not the oven?

If its definitely not the oven then there must be a fault that's appeared on the circuit supplying it. If all else is ok, to get such a dramatic voltage drop can only indicate a fault of some kind.

No offense, but a decent spark will be able to verify your voltage drop, do other fault finding tests and then proceed to try and find the culprit of the problem. But be prepared as it may indeed require some disruption. Unfortunately this may mean searching for and "digging" out any hidden joints.

 

[7029 dave]

Is it on a fused switch which should be in the wall somewhere? If so check all terminations are good and check fuse.

The oven itself may have a fuse.

sounds like power to the cooker is good

always make sure you cut the supply at the cu via the mcb or better switch the main power switch off if you don't have the correct tools to make sure supply is in isolated.

Not at 150v it's not.

 

[gazdkw82]

True.

how did he measure the voltage? Line to earth? Neutral to earth? Just the neutral? Just the line?

 

[7029 dave]

True.

how did he measure the voltage? Line to earth? Neutral to earth? Just the neutral? Just the line?

Looking at his post he measured across L N of cooker.

 

[Richard Burns]

A usual case (though this may not be your case) for an oven or cooker is a loose connection overheating and causing a partial or complete disconnection.
The location of this overheated connection is normally obvious as the accessory also starts to melt or discolour.
The normal run of cable would be from MCB to cooker isolator switch (on kitchen wall or in kitchen cupboard) to cooker outlet point (behind cooker) to flex or twin and earth to cooker.
It is possible that your cooker is supplied form a socket circuit (which it should not be) if there was only a single oven there before.
The different colours of cables could be because the cooker circuit from MCB to switch was not changed but the part after the cooker isolator was changed.
Correct identification of the circuit involved and safe isolation of the circuit are critical to safety.
It is generally best to test the resistances of a circuit whilst it is totally disconnected from the power supply and not to attempt to monitor voltages on a live circuit. Professional assistance should help in this regard.
A logical approach is also useful and just changing items, whilst it may cure a problem, means the reason for the problem is not known and can cause a repetition later.
Being alive is more important than a non working oven, so ensure safety at all times.

 

[Marvo]

Be very careful, from what you say it could be an open circuit neutral in which case the neutral wire will be at a high voltage with respect to earth so in laymans terms you could get a shock from the neutral wire as easily as you could get a shock from the live.

 

[bridav]

Is it on a fused switch which should be in the wall somewhere? If so check all terminations are good and check fuse.

The oven itself may have a fuse.

sounds like power to the cooker is good

always make sure you cut the supply at the cu via the mcb or better switch the main power switch off if you don't have the correct tools to make sure supply is in isolated.

The power to the oven is not good, it is currently reading 150V AC between the live and neutral terminals. The MCB [granted is an older type Crabtree SB6000 type 1] outgoing terminals is still reading 240V AC between the live and neutral terminals.

You need to locate a local competent spark.

Where are you based?

Glasgow.

How on, you've changed an mcb?

if your not competently experienced I wouldn't suggest taking on work like that. It can kill you

I would say that I am academically experienced and had previous experience in control panel / LV & MV switchgear panel building for various industries, now an instrumentation commissioning engineer whereas I rarely touch anything over 24V DC!

Its best you get a qualified sparky in to check it out for you. The oven worked fine for a short period, then just suddenly stopped working properly and you are certain its not the oven?

If its definitely not the oven then there must be a fault that's appeared on the circuit supplying it. If all else is ok, to get such a dramatic voltage drop can only indicate a fault of some kind.

No offense, but a decent spark will be able to verify your voltage drop, do other fault finding tests and then proceed to try and find the culprit of the problem. But be prepared as it may indeed require some disruption. Unfortunately this may mean searching for and "digging" out any hidden joints.

Certainly not the oven no, I have disconnected the oven from the switch [after isolating the mains supply and proving dead!] and tested between the live and neutral terminals and it read 150V AC. I am now starting to feared the worse that I may need to start bashing holes about the house looking for phantom cable joint(s).

A usual case (though this may not be your case) for an oven or cooker is a loose connection overheating and causing a partial or complete disconnection.
The location of this overheated connection is normally obvious as the accessory also starts to melt or discolour.
The normal run of cable would be from MCB to cooker isolator switch (on kitchen wall or in kitchen cupboard) to cooker outlet point (behind cooker) to flex or twin and earth to cooker.
It is possible that your cooker is supplied form a socket circuit (which it should not be) if there was only a single oven there before.
The different colours of cables could be because the cooker circuit from MCB to switch was not changed but the part after the cooker isolator was changed.
Correct identification of the circuit involved and safe isolation of the circuit are critical to safety.
It is generally best to test the resistances of a circuit whilst it is totally disconnected from the power supply and not to attempt to monitor voltages on a live circuit. Professional assistance should help in this regard.
A logical approach is also useful and just changing items, whilst it may cure a problem, means the reason for the problem is not known and can cause a repetition later.
Being alive is more important than a non working oven, so ensure safety at all times.

Very true, nobody has received an electric shock from the oven - I have in the meantime isolated the MCB until the problem has been rectified. Curious though, if there was to be a fault in the circuit, wouldn't it have tripped the MCB or the RCB?

Be very careful, from what you say it could be an open circuit neutral in which case the neutral wire will be at a high voltage with respect to earth so in laymans terms you could get a shock from the neutral wire as easily as you could get a shock from the live.

I recall an electrical engineer telling me the exact same thing, that you could potentially receive a bigger belt from the neutral than the live!

Thank you all for the responses, very much appreciated.

To date, I have contacted Scottish Power to ensure that there was no fault at their end, this was confirmed as there are no faults! I have managed to get a hold of the electrician in question however he informed me that the wiring of the oven was done by his workmate. I told him that I am not looking for a blame game but to rectify the problem and safely and then worry about the financial impact(s). I will report the result should we ever find one....!!

Thanks again,
Brian

 

[NDG Elecs]

Try testing the voltage at oven between L-CPC. If that's 240V it's likely a poor neutral connection somewhere. If it's reading 150V then it's possibly a poor live connection.

Is the double oven on its own cct? It should be. And is there a local isolator in the kitchen for the oven; not mandatory but I would always fit one, and if there is then that would be a good place to test also.

Just to add. If the oven is not on its own cct, and you received no certificate of any kind I would start to question whether the original installer is competent and possibly be reluctant to have them back.

Also, have you put up any pictures or drilled holes etc in the vicinity of where the cables might be?

 

[bridav]

The oven in question "should" be fed from its own MCB from the board, I haven't noticed anything else switched off after isolating the MCB! The oven also has its own local isolator (I called it a switch in previous posts!)

Is it mandatory in Scotland to receive certification(s) for household electrical works?

 

[Midwest]

As others have said, you should get an electrician in . In the meantime, if you know the layout of your old kitchen and where the old cooker location was, you could start looking in that area for your suspect joint (keep ringing matey boy up, 'cos they'll know). Kitchen fitter 'electricians' tend to burry their joint boxes in walls under tiles! Or you might be lucky, and it's in the ceiling void.

 

[NDG Elecs]

Not sure of Scottish requirements. Try the live to earth voltage test etc I mentioned, at all points including the incoming and outgoing sides of the switch. As Mid says, keep ringing because they may be the only person who knows if there is some hidden joint buried somewhere.

 

[polo1]

Just came across this thread. Requirements re certification - there's no equivalent to Part P, but the Scottish Building Regs do set out some requirements. Scheme member or not, every electrician worth his/her salt should certify the work they do.
If the o/p is still having problems, PM me and I'll have a look.

 

[TJ Anderson]

At least we got to know the outcome of this one........ Oh yeah, we didn't lol

 

[bridav]

Just came across this thread. Requirements re certification - there's no equivalent to Part P, but the Scottish Building Regs do set out some requirements. Scheme member or not, every electrician worth his/her salt should certify the work they do.
If the o/p is still having problems, PM me and I'll have a look.

Finally got a hold of the electrician that did the initial works, the fault was a "damaged cable" apparently caused by the joiner 8 months ago, although I remain a little skeptical about this! However that said luckily the damaged cable was hidden behind the plasterboard within close proximity of the oven isolator and the cable was re-jointed and the oven is now working again. Although I am curious to why the RCB or MCB did not trip.

I was working when the electricians did the works but did instruct the wife to query with them about the certificates, they did a Billy Whizz (from the Beano) in and out before questions were asked and said to the wife "aye I will be having words with the joiner" then left.

At least we got to know the outcome of this one........ Oh yeah, we didn't lol

Well, continuous sunshine in Scotland is rare, took the advantage while I could before the Scottish winter settles back in (in about 10minutes from now!)

 

[Octopus]

Finally got a hold of the electrician that did the initial works, the fault was a "damaged cable" apparently caused by the joiner 8 months ago, although I remain a little skeptical about this! However that said luckily the damaged cable was hidden behind the plasterboard within close proximity of the oven isolator and the cable was re-jointed and the oven is now working again. Although I am curious to why the RCB or MCB did not trip.

I was working when the electricians did the works but did instruct the wife to query with them about the certificates, they did a Billy Whizz (from the Beano) in and out before questions were asked and said to the wife "aye I will be having words with the joiner" then left.






Well, continuous sunshine in Scotland is rare, took the advantage while I could before the Scottish winter settles back in (in about 10minutes from now!)

So were you given a MWC to confirm the cable repair and the tests conducted?

 

[bridav]

No, just a brief explanation to the wife that the cable was damaged, now fixed thanks again cheerio.

 

[Lucien Nunes]

I thought I may either have: ...4. may be an earth leak

Although I am curious to why the RCB or MCB did not trip.

Why would you expect a high resistance connection or severed conductor do that? Unless the result was a general meltdown that destroyed the insulation and caused a short, probably revealing itself in the process with escaping smoke?

As an instrumentation engineer - you'll be aware of the input resistance of your DMM, in which case you can calculate the resistance of, and power dissipation in, the point of high resistance. Most likely, it did get hot at one stage, but soon burnt itself O/C. I am skeptical of the explanation given though!

I recall an electrical engineer telling me .... that you could potentially receive a bigger belt from the neutral than the live!

Go on, explain!

 

[Octopus]

No, just a brief explanation to the wife that the cable was damaged, now fixed thanks again cheerio.

Imho you should have.

 

[bridav]

Imho you should have.

I know, I may pester the builder that hired the sparks to see what he has to say!

Go on, explain!

I cannot recall what he said other than something along the lines of volt drop and the resistance of the person touching the neutral...debatable?!

 

[richy3333]

Not sure of Scottish requirements.

Certification as per BS7671 and in certain circumstances a Building Warrant could be required.

no certificate for work done and a balder-dash explanation makes you wonder if they were sparks?

 

[EastAnglian]

Although I am curious to why the RCB or MCB did not trip.

If the dodgy joint was simply providing a high resistance, which would explain the drop in measured voltage under load then (a) the MCB would not trip because the current being drawn would be well within the rated current of the device and (b) the RCD would not trip because its not a fault current to earth.

BS7671 says all work must be documented and there are model forms therin for various types of work. You should have received a certificate when the work was done originally and also when the corrective work was undertaken.

If the repair to the cable is "not accessible for inspection" (i.e buried in the wall) then the method of jointing cannot have screw terminals which can work loose. The most common forms of maintenance free joints are crimps or suitably rated push-fit connectors with sprung-loaded terminals. The joint must be contained in a box providing mechanical protection and it should have strain relief clips on the incoming and outgoing cables.

 

[Risteard]

I would say that it is obviously a loose connection as it would be an achievement to undersize cables enough at a great enough distance to lose 90V in a house!

You need to get an Electrician to sort this out urgently as it is a fire hazard.