New submain from existing TT supply.

[safedepth]

Evening all,

Went to look at a job today and found the following.

Existing service head in meter cupboard adjacent to properties gate, immediately next to it is a second meter cabinet housing a switched fuse and single henly block.

Property is approximately 5 meters from meter boxes. 25mm tails out of head cab and into second cab and switched fuse. 16mm swa glanded at second cab, phase and neutral off to property, earth terminated into the henly. No earth rod at cab's. CU in property is rodded at point of entry.

Please correct me if necessary but I'm thinking the swa needs an earth at the service head end and a 100mA RCD, all to protect the swa.

I haven't been in the property, I was called in to look at putting a new supply into a different building no more than 15 meters from the supply cabinet.

I was going to run a new swa submain from the second box, via a 100mA RCD and switched fuse into the new building, rod again and fit a small CU with 30mA RCD's.

Sorry it's long winded and a beer for all those who have stayed with me.

 

[Evans Electric]

Would the rod at the house end be earthing the armouring on the SWA ?

 

[NozSpark]

You say the earth is going into a henly,,, what henly?

What is the supply type at the suppliers meter?

 

[safedepth]

Deke,

"Would the rod at the house end be earthing the armouring on the SWA ?"

Yes I expect so, but is it not best earthed at the supply end rather than the load?

You say the earth is going into a henly,,, what henly? What is the supply type at the suppliers meter?

The SWA earth conductor is in a henly block, nothing else is connected to it.

It's a TT supply out of the service head, phase and neutral from meter go via T&E into adjacent meter cabinet into a Switched fuse. Phase and neutral from that switched fuse are 2 of the 3 cores in a swa submain going to the house. The 3rd core, correctly identified as the earth conductor is terminated into a henly block. The customer remarked that the original sparks who installed it all joked with him about how it looked odd to have that henly there and doing nothing.

I just feel, (rightly or not) that the submain should be earthed at source. Am I wrong?

 

[kme]

I`d want it that way, too - though I don`t have the regs book here, so its more a case of "feels wrong" than a specific reg.

That`s not much help; but I believe it needs a rod at the cabinet, as you`ve suggested.

KME

 

[safedepth]

I spent some time with my nose in the book but couldn't pin down a specific reg on it. Such a big book with so many long words;-)

 

[kme]

Awwww, bless :run

 

[safedepth]

Awwww, bless :run

Is that what sympathy looks like, I've been married so long I've forgotten?

 

[kme]

No - its more pathology nowadays . . . . ( hope Mrs. don`t read this :Spam2 )

 

[apprentice87]

Hi all,

I have read somewhere [cannot remembver where though] that a cable must be earthed at the supply end, this is only a matter of common sense, as other wise if the cable got cut in half or disconnected at the "other end" it would then possibly be live, or become live with no way of the ADS working...

Anyway, Lets start at the beginning.... There is a submain; ; Yes?? This submain needs protective devices to protect it against both overcurrent and shock hazards.

So, you say;

"Please correct me if necessary but I'm thinking the swa needs an earth at the service head end and a 100mA RCD, all to protect the swa"

And you are of course completely right!! Time delay rcd perhaps though might be better..

There is very definitely a reg that says a cable must be earthed in the installation that contains the assoiciated protective device, so, do as you say, you are perfectly correct!!!

john..

 

[safedepth]

Quick update.

Had my assessment today and spoke with my assessor on this subject. We both feel it requires a time lag RCD. Just wish I could pin down a reg to show the customer.

Many thanks for your input on this subject gents, much appreciated.

 

[Sidewinder]

Quick scenario to think about.

Main property is to be refurbed.

All cables disconnected for removal whilst isolated and made safe, so all ends are now isolated from each other including the SWA.

Supply at origin is re-energised.

Refub contractor sticks pick through SWA, what caused circuit protective device to operate?

This IS WRONG, however, I have stuff to do & don't have time, sorry!