New installation

[leatherneck]

Hi,

I am a time served Electrician (industrial) serving my time with British steel,

I am still working for Corus (formerly British steel) as shift Electrical engineer, working on a wide range of equipment and plant.

I have done some domestic wiring over the years, I am now doing a self-build for my family I am doing the wiring and as a result will have some basic questions that will be easily answered by most of the boards members.

As I said I am doing the electrics, and as part of a building notice I do not need to be Part "P" accredited, but still need to provide a commissioning certificate to the building inspector. I have dowloaded a certificate that indicates what tests are required, including earth loop impedance.

Not ever having completed an earth loop impedance test before I decided to have a look into it. The result showed that this needs to be done on an energised system, with a dedicated tester.

I now have a small problem, I have a date for my new supply to be installed, but I have been informed from EDF that they will not connect the meter until second fix is completed and the job signed off.

How can the job be signed off without an earth loop impedance test?

Is there a method of calculating without the need of a dedicated tester?

Regards.,

 

[sparkytim]

Hi

They ask for an EIC with all " Dead test" results. i.e. R1+R2 + IR for all circuits

In practice the Meter guy who comes is not really interested in seeing it and all he will check is Bonding is in place and will check correct polarity when powered up.

Just had a Test and connect last week and the only Test equipment the SEIMANS METER Guy used was a Neon screwdriver to check polarity and stuck a warning sticker on saying "Installation connected but NOT tested, advise getting Electrical Contractor to Test installation is safe".

Bit of a joke really as I stood there, but He "had to fit it to cover his butt".

 

[NozSpark]

Do all dead tests and take your Ze from the BRB...

then calculate all your readings and fill out your EIC... that should keep him happy.

once it's powered up do full dead and live testing and fill out a proper EIC

 

[steptoe]

where in the country are you leatherneck.?

 

[steptoe]

Do all dead tests and take your Ze from the BRB... then calculate all your readings and fill out your EIC... that should keep him happy.

once it's powered up do full dead and live testing and fill out a proper EIC

doesnt always work,

I did a job last week,

TNS

where hardly anything would meet the max Zs

certainly not the 32A + anyway

 

[leatherneck]

Middlesbrough.

 

[NozSpark]

doesnt always work,I did a job last week,

TNS

where hardly anything would meet the max Zs

certainly not the 32A + anyway

must have been pushing it close on the design!

 

[leatherneck]

"Do all dead tests and take your Ze from the BRB..."

BRB ???

 

[tom1]

do you know what earthing system your getting?

tn-s

tn-c-s

or are you providing your own earth TT

each system will have a maximum ze this is external loop impedences

tn-c-s is 0.35 ohms

tn-s is 0.80 ohms

tt you need to get below 200 ohms

your circuits will have a zs value this is internal loop impedences this value must be lower than the calculated figurs in the brb. this is based on the size and type of the protective device ie mcb or fuse. the bigger the fuse the lower the zs needs to be.

zs can be caluclated by adding r1+ r2 +ze

so if your getting a tn-c-s supply add 0.3 to your r1 +r2 value and thats your zs.

 

[JUD]

"Do all dead tests and take your Ze from the BRB..." BRB ???

Big Red Book (BS 7671 17th Edition)

 

[ProDave]

I have a date for my new supply to be installed, but I have been informed from EDF that they will not connect the meter until second fix is completed and the job signed off.

All I can say is I'm glad i'm not in a area "served" by EDF as they seem to put obstacles in the way all the time.

Have you asked for a "building supply" from them?

Normal practice up here in Scottish & Southern energy land, is they will provide a supply and connect it as long as there's a CU and ONE circuit to energise.

So I just fit the CU and one double socket wired as a 32A radial in 6mm right next to the CU and they are happy to energise the supply.

That gets you a supply in the building as soon as it's wind and water tight so the builders, and you, have a supply to work from while completing the build and wiring.

Can you not do the same, just connect a single circuit and issue a EIC for that to get the supply energised?

 

[initforthemoney]

I dont understand what the problem is.

I would say installation dead tests are more important than live tests.

Just do the dead tests and when connected you can finish off.

Also, are you familiar with circuit design?

Safe zones?

Part L, M etc etc??

 

[steptoe]

must have been pushing it close on the design!

No, was a void council house, (card meter) but with TNS at 0.8ohms doesnt give you much to go on before you hit 1.15ohms

do you know what earthing system your getting?tn-s

tn-c-s

or are you providing your own earth TT

each system will have a maximum ze this is external loop impedences

tn-s is 0.35 ohms 0.8 ohms

tn-c-s is 0.80 ohms 0.35 ohms

tt you need to get below 200 ohms

your circuits will have a zs value this is internal loop impedences this value must be lower than the calculated figurs in the brb. this is based on the size and type of the protective device ie mcb or fuse. the bigger the fuse the lower the zs needs to be.

zs can be caluclated by adding r1+ r2 +ze

so if your getting a tn-c-s supply add 0.3 to your r1 +r2 value and thats your zs.

me RED

 

[green-hornet]

I think he just made the crossover mistake, often seen with late night posts.

 

[tom1]

me RED

thanks steps

I think he just made the crossover mistake, often seen with late night posts.

spot on there mate will go back and correct

:coat

 

[Sidewinder]

Peeps,

The values in the above posts are NOT the maxium allowed, the DNO does NOT have to comply with these, their constraint is normally "volt drop" from the local HV transformer.

Both Phase & CNE legs combined.

They will NOT guarantee these values in most areas, they are "typical".

As I have said before, I am lucky with my DNO guys locally.

However, on conventional supplies it is doubtful these will go above these values.

Certain supplies will though end of line some others. HOWEVER, DNO SHOULD be able/willing to advise.

PFC & Ze may not correlate directly doe to DNO fault current limiting.

Paul