NCD? (Neutral current diversion?)

What sector are you in, what earth arrangement do you have  and I'd like to know how you found this and what made you look? Did you clamp the main earth and find current there? Not doubting, just interested.

Kind Regards

Tatty

With a PME system, diverted neutral currents are almost inevitable and not in my view anything to comment upon. The suppliers CNE conductor carries appreciable current with a voltage drop in proportion. Metallic services and structural steelwork provide a parallel earth path and will therefore take some of this current.

Thanks for your response, I am an electrician that does residential, commercial & industrial works. In this instance I have a PME supply into a clients property, we recently received a bulletin post from SELECT which started about the increase in NCD and how we should proceed with works on a PME supply. Due to this I thought as a measure to check before starting works on the main earth with a clamp meter. With the installation isolated as we should expect there was no current but when load was increased such as a shower I was reading between 10 to 15A passing back through the main earth and finding a path to the transformer through the bonding ( gas & water)

Thank you for your response & I also agree to a certain degree, but what current would you say would be acceptable to find within the main earth when the property is under load. In this case I had between 10 to 15A?

I have reservations about ..

diverted neutral currents are almost inevitable and not in my view anything to comment upon

Only up to the point that the bonding  conductors etc are man enough, I  hope you'd comment if the green and yellow plastic was dripping off, and the pipe clamps were too hot to touch.

Perhaps ignore only up to a reasonable fraction of the total supply..
Mike

what current would you say would be acceptable to find within the main earth


It may be worth a call to the DNO - as they will know the layout of their supplies, and can comment intelligently about what is is reasonable for that particular substation or whatever.

You need to get past the 'have a nice day' girls to reach someone technical, but they certainly will have someone who understands.

Mike

mapj1 said:

Only up to the point that the bonding  conductors etc are man enough

Given that the minimum size is 10 mm² (Table 54.8), one might assume that the diverted neutral current could be considerable. Table 4D1A permits 65 A for clipped direct SP.

I would only be concerned if the main earthing conductor, or anything connected thereto was getting warm or if the diverted neutral current exceeded the supply capacity.

60 amp cut out fuse, and 70 amps diverted neutral current would be bit concerning and might warrant investigation.

Main earthing conductor warm to the touch=concern, hot to the touch=alarming.

Quite, and at that level I'd be thinking may be broken neutral in the street and calling the DNO. At 10A on a 100 supply I probably would not, but if it was 100% of my local  load it could be my neutral that was off ... say 5A CPC current on a  street cabinet with 5A of kit in it - that would still be a worry.
 I was really saying 'its normal and OK' does have an upper  limit, and its when it compares to local load.
Mike

Another consideration is the direction of flow. Is it my neutral which is being diverted down the gas pipe to next door, or theirs which is going in the opposite direction?