Cable size

[uksparks]

Hi,

I am going to be connecting an out door power supply, away from the building, its all metal casing.

The supply is 10mm, I am using a 3 core SWA for part of the run, the inside part was going to be in twin and earth, but then I was just thinking, going on table 54.8 section 544.1, am I looking into this too much or does it need to have a 10mm earth as its extraneous metal which is fixed into the ground?

In which case I was just thinking of running 3x 10mm inside the building so the earth is 10mm too to them comply with min size of bonding conductor.

I am right to make it 10mm throughout the entire run aren't i?

 

[uksparks]

I think if I just disconnect the main earth and then take a wonder lead either from the MET to the steel or the steel bond and see what IR I get, if its above 23,000 ohms, then thats good is it not? and surely that confirms that its a good enough earth?

 

[Engineer54]

WPD don't even record it, I have spoken to them about lost neutrals before and they say there is more chance of finding a needle in a haystack.

That is my opinion too....
But tell that to some here that reckon they have seen it happen on numerous occasions. When what they really mean is, they have heard 3rd hand stories from others that know others that have seen a broken neutral. lol!!

Generally long before a neutral joint breaks, it will go high resistance, and it's normally during this time the faults are noticed and rectified

 

[Engineer54]

I think if I just disconnect the main earth and then take a wonder lead either from the MET to the steel or the steel bond and see what IR I get, if its above 23,000 ohms, then thats good is it not? and surely that confirms that its a good enough earth?

I think you'll find it'll be the other way round, ....if it's over 23K then the structure isn't considered extraneous. The betting is that you'll be very lucky indeed to find a steel structure such as you have, that won't be extraneous. I'm betting it'll at the most a low single figure!!

 

[telectrix]

then again, last year i had a call-out to an elderly disabled gentleman... no power. volt tester into CU on incomer. L-N 0V. L-E 245V. SP came out @ 6 p.m. dug up road. open circuit N joint due to corrosion by infill materials. estate only built 15 years ago.

 

[uksparks]

I think you'll find it'll be the other way round, ....if it's over 23K then the structure isn't considered extraneous. The betting is that you'll be very lucky indeed to find a steel structure such as you have, that won't be extraneous. I'm betting it'll at the most a low single figure!!

Thats what I meant, sorry, so if its a low single figure as you put it, whats the problem is using that as the source of additional earthing?

 

[Dan]

I'm just bumping some of the older threads in the general electrical forum that had a lot of replies. They might not be current topics, if they're not, just ignore them and they'll soon drop off the list. If you DO wish to add a reply and get the conversation going again, feel free to do so. Your input might help somebody else in the future.