Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • Replies 15 replies
  • Subscribers 38 subscribers
  • Views 355 views
  • Users 0 members are here
Options
You may also be interested in

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

  • Try looking for the many 'vampire' electronic circuits that are likely to have EMC / EMI / RFI filters within them..

    Chris Pearson said:
    No one MCB abolishes the current: instead, the greater the number of closed breakers, the greater the current.

    Things like TVs and digital boxes on standby, mobile phone chargers, PCs, displays, printers, laptops and their charger / PSUs, along with establishing which circuits they are on. Likewise the boiler circuit and central heating timers, microwaves and cookers, fridge and freezer. Solar inverters and car chargers (and electric bicycle chargers) are also possible leakage sources (all especially so when in standby mode).

    It's a veritable maze of appliances and circuits of power wasters (££) and leakage providers.

    I don't know which is worst, to find a cable fault, or to realise it's all normal current wastage ?  Grimacing

  • in reply to Philip Oakley
    Philip Oakley said:
    It's a veritable maze of appliances and circuits of power wasters (££) and leakage providers.

    Philip, I couldn't agree with you more. We recently had a smart meter installed and this shows a background consumption of about 120 W. Broadband router and its booster are always on. Then tellies, printer, phones, iPad and 'phone chargers, clocks (on boilers), microwave with its own little clock, fridge-freezers with their temperature displays, all with little LEDs, etc. Even the smart meter display draws a few mA!!!

    However, it does not account for 1/2 A to 1 A down the earthing conductor.

  • in reply to Chris Pearson

    is your incomer TNC ? if so if it  is all 'in house' I'd expect the earth current to scale with the load - as your fault will be one resistance in parallel with the NE split which is another. Both are largely constant & resistive.

    If you are looking at an amp or so, while main current is a few tens of amps, then the two resistances are in the ratio of say 10 to one or whatever the current split is. Such a significant fault cannot be load side of a working RCD, or you'd never keep the thing held in.

    Not sure if that helps focus attention on a reduced area?

    Mike.

  • in reply to Chris Pearson
    Chris Pearson said:
    We recently had a smart meter installed and this shows a background consumption of about 120 W.

    Our discovery was more that we'd had solar and battery installed, and even with a full battery charge (5kWh) we'd find that it was hit or a miss about the battery supplying all trickle loads through the night. The fridge & freezer were the main load.

    Chris Pearson said:
    does not account for 1/2 A to 1 A down the earthing conductor

    Getting a clean reading can be tricky. We've an overhead supply (1ph) from a 3 phase pole distribution in the other corner of our garden. Our only mass-of-earth is via the water pipe / plumbing bond, so I think I some times get part of the 3ph out of balance via the DNO neutral supplying the MET point.

    I have noticed that I can get different / fluctuating results from the simple clamp meter depending on positioning within the internal cabinet, the tails and the CPC lead, i.e. imperfect sensing current's magnetisation into the 'CT' of the clamp meter.

    The overall 500mA+ reading does sound high for the 'normal' additive leakage currents - that's a lot of real power trying to create RF balanced conductive emission leads! 

Reply
  • in reply to Chris Pearson
    Chris Pearson said:
    We recently had a smart meter installed and this shows a background consumption of about 120 W.

    Our discovery was more that we'd had solar and battery installed, and even with a full battery charge (5kWh) we'd find that it was hit or a miss about the battery supplying all trickle loads through the night. The fridge & freezer were the main load.

    Chris Pearson said:
    does not account for 1/2 A to 1 A down the earthing conductor

    Getting a clean reading can be tricky. We've an overhead supply (1ph) from a 3 phase pole distribution in the other corner of our garden. Our only mass-of-earth is via the water pipe / plumbing bond, so I think I some times get part of the 3ph out of balance via the DNO neutral supplying the MET point.

    I have noticed that I can get different / fluctuating results from the simple clamp meter depending on positioning within the internal cabinet, the tails and the CPC lead, i.e. imperfect sensing current's magnetisation into the 'CT' of the clamp meter.

    The overall 500mA+ reading does sound high for the 'normal' additive leakage currents - that's a lot of real power trying to create RF balanced conductive emission leads! 

Children
  • in reply to Philip Oakley

    Philip, thank you again. I forgot the toothbrush chargers.

    The whole thing does not seem quite right, but there must be a lot of householders in a similar position who have measured nothing.

Community Rules & Guidelines