Building Control

[carl9254]

Hello, got my Elecsa assessment on 4th january, going to change the cu in my house and use that as assessment job, its simple as only 3 circuits, sockets, lights and shower. But shall i tell building control?? Elecsa said upto me, they dont request it but they will let building control know once ive done the job. it will cost £107 if i do.

Also supply into house is TN-S so should get away with 6mm bonding which it looks like, but i just want to make sure by doing the adiabatic equation on page 128 of regs book, can anyone shed any light on easiest way of doing this??

Thanks.

 

[adam.h]

I was told by building control to update to 10mm when I changed mine.

 

[roukel01]

also just a board change might not be enough for them to see, they usually like to see some installation work. I always try and take them to a full rewire

 

[carl9254]

Elecsa have said board change is fine and 6mm is fine aslong as supply is TN-S and that formulaworks out correct. Help on the formula would be good??

 

[Guest123]

Hi.

You cant use an adiabatic equation to size a bonding conductor, it's only for CPC's.

 

[carl9254]

So will 6mm be ok for a TN-S spply??

 

[Guest123]

Well I would say as it's an existing scenario then you may be able to check the suitability of the existing bonding conductors by taking into account the PFC and size of the main fuse almost like doing an adiabatic but not really as it's not the main earthing conductor.

Obviously you would need to know the PFC (by testing it), rating of main service fuse, time/current characteristics, and K value. All these can be found in the regs book.

Probably best to install new 10mm for the assesment. You could show him that you used the equation to check, make you look good then too.

 

[carl9254]

Im new to testing so just checking if done right.

I got 1.37kA for my L-E reading. 1200A for my t reading and 143 for my k reading.

Does that look right and will the answer be 11.49??

Anyone?

 

[Guest123]

Hi.

I squared you have there.


(T) comes from APP 3 of ol red. (K) comes from table 43.1 of ol red. (S) must be equal to or greater than the result of the sum.

(S) = the square root of ((I) squared x (T)) divide by (K).

 

[carl9254]

So if i stick a 16mm in it will be fine.

 

[Guest123]

Mate, you dont need to put in a 16mm bonding conductor 10mm is more than adequate.

I didn't wat to do the calc for you as I believe working stuff out yourself is the best way of learning.


Ok so the fault current is 1370A

We'll assume a 0.1 disconnection as ol'red is in the van and it's belting down!!!

The K value we'll take as 115.

1370 squared = 1876900, x 0.1 = 187690

187690 square root = 433.2

433.2 / 115 = 3.76mm.

 

[carl9254]

Mate, you dont need to put in a 16mm bonding conductor 10mm is more than adequate.

I didn't wat to do the calc for you as I believe working stuff out yourself is the best way of learning.


Ok so the fault current is 1370A

We'll assume a 0.1 disconnection as ol'red is in the van and it's belting down!!!

The K value we'll take as 115.

1370 squared = 1876900, x 0.1 = 187690

187690 square root = 433.2

433.2 / 115 = 3.76mm.

Why did you do 0.1 disconnection and not 0.4?? Also why 115 for the k and not 143?? Tryin to learn

 

[Guest123]

0.1 comes form the time current table in ol'red. The 0.4 value is the max value that circuits must disconnect under.

With the fault current known you go to the graph in ol'red with a ruler and plot a line from the fault current you have to where it meets the time/current curve for your particular protective device. I dont know what you have so i was making an educated guess as the fault current you have, i think is past the curve for most devices so you assume a 0.1 disconnection.

The 115 value is for 70 degrees thermoplastic cable with copper conductor.


Right I went out in the MONSOON to get ol'red....turns out I was right so I got wet for nowt.

 

[carl9254]

Its a 1361 100A, so am i right in sayin it meets around the 0.3-4 mark??

I took my last k reading from the 30 deg table, are most 70 deg??

 

[Guest123]

Its a 1361 100A, so am i right in sayin it meets around the 0.3-4 mark??

Yes I think so too.

Put 0.3 into the equation then and see what you get.

 

[carl9254]

I get 6.525, so 10mm would be good, thanks for that so this equation is used to determine earth size from met to cu??

Ill do the job tomoz.

 

[Guest123]

You use to check that a CPC of any circuit complies.

 

[carl9254]

So the k reading would generally be 115?? Because housing cable is copper pvc 70 deg??

So if i wanted to work out this for my downstairs sockets circuit for example where would i stick my probes for the I reading??

 

[Guest123]

You wouldn't need to.

Fault current (I) = Uo/Zs So 230V/the Zs for that circuit = your fault current.