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High earthing conductor current at a house

Chris Pearson

In the discussion on a similar topic concerning a bridge, JP kindly wrote:

Chris

An urgent investigation is required.

You don't say how much current is flowing in your protective conductors?

The symptoms of a lost neutral,  or a high resistance neutral, on a PME installation are ...

I can only measure to the nearest 10 - 20 mA. The current in the earthing conductor, which matches the difference between line and neutral, is highly variable, but seems to be between 10% and 15% of the line current. There are currents of a few tens of mA in the gas and water main bonds. They do not sum to the value in the earthing conductor. Even though the water supply is plastic, there may be a connexion between gas and water in the CH boiler.

Turning off the main switch reduces the current in the earthing conductor to zero. Turning off all the breakers also reduces it to zero. No one MCB abolishes the current: instead, the greater the number of closed breakers, the greater the current.

Stainless steel garden fork to kitchen sink or gas cooker gives about 0.15 V. Met to garden fork gives about 0.3 V.

Zs to a convenient socket was 0.57 Ω.

If there is a N-E fault in the installation, I suspect that it is in a ≈ 10 m length of SWA which goes from a switch-fuse adjacent to the meter, under the floorboards, to the main DB.

Investigations will continue tomorrow.

Parents

  • That's better!

    The 'needle' barely flickered on a whole board IR N-E. (The supply cable and sub-main boards were fine.)

    Problem now narrowed down to one of the downstairs socket circuits, which I have disconnected. Unfortunately, the circuit supplies my workshop, so further investigation is a priority.

  • in reply to Chris Pearson

    further investigation is a priority.

    Oddly I am reminded of one time that power was lost to the circuit supplying the kitchenette with the tea urn, and the speed with which temporary supply cables were laid in down the corridor from an adjacent zone within the building, compared to 'normal' speed response to a works ticket.

    Some services can tolerate an interruption of some duration, others really have quality of life impact and move higher up the list. 

    As the owner of a lathe and a selection of dangerous toys, I feel your pain.

    Have you considered laying in redundant supplies to the workshop?

    Mike.

  • in reply to mapj1
    mapj1 said:
    As the owner of a lathe and a selection of dangerous toys, I feel your pain.

    Mike, thank you for your empathy.

    I found it! I always consider it very satisfying to find the cause of a problem and fix it.

    Neutral cable nipped by a socket back box. It may have been like that for 40-odd years.

Reply
  • in reply to mapj1
    mapj1 said:
    As the owner of a lathe and a selection of dangerous toys, I feel your pain.

    Mike, thank you for your empathy.

    I found it! I always consider it very satisfying to find the cause of a problem and fix it.

    Neutral cable nipped by a socket back box. It may have been like that for 40-odd years.

Children
  • in reply to Chris Pearson

    A good exercise in fault finding and no doubt pleased with your efforts.

    I have a workshop with a Myford lathe, pillar drill and woodworking machinary which is my man cave. Needs a serious tidy up and a re-organisation but a mug of tea and the radio on cleaning and sharpening tools is very theraputic. 

    JP

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