Assessment time again

[m4tty]

Hi,

Ive got my assessment coming up soon and looks like im going to change by board indoors as jobs ive done have all been too far away to show assessor.

I live in a maisonette which is concrete. Walls floors and ceilings. All wiring in conduit using conduit as earth. Its TNS 60A mainfuse. The CU is underneath the immersion heater so water bonding wont be a problem.

The gas bonding is going to be a problem as the gas meter is on wall outside and there is no easy route. It is already bonded in 6mm buried in the floor.

The gas meter is outside and the only gas pipe in the house goes through wall directly into back of boiler thats it. So no pipes can possibly be touched.

I normally upgrade MEC to 16mm and MPBCs to 10mm as the norm but wanted to know how to do the calculation to see whether my 6mm gas bond complies?

Thanks in advance

Matt:Salute

 

[Andy™]

if you use a 10mm

 

[S60TEM]

How big are the tails?

MEC needs to be equal to or half the CSA of the Tails so 25mm tails would require 12.5mm MEC which as we know we cant get so 10mm is too small hence we use 16mm.

If your tails are 16mm then a 10mm MEC will be sufficient and as Andy has said, 6mm then complies.

 

[m4tty]

16mm tails so all good. Cheers

 

[jaykala]

man i scarde

 

[Andy™]

man i scarde

???

 

[sparky b]

man i scarde

Scarde of what........M4tty?? :run

 

[TonyCE]

Line conductor 16mm, gives Earthing conductor required as 16mm, and main protective conductor 10mm according to OSG table 4.1 (TNS/TNCS)

 

[m4tty]

Line conductor 16mm, gives Earthing conductor required as 16mm, and main protective conductor 10mm according to OSG table 4.1 (TNS/TNCS)

Anyone comment on Tonys comment please. Cheers

 

[Andy™]

OSG is just that, a guide.

 

[TonyCE]

A guide which is based on the regulaions.

This is for your assessment so I think you need to be able to justify any variations from the guide yourself: "Earth conductor size is for conductors not buried or buried protected against corrosion / mechanical damage" - that is probably your escape route.

Worth checking with the DNO as well as "The distributor may require a min.m size of 16mm for TNxx supplies",

 

[Apache]

Does ELECSA not have a helpline you can ring/email? Get it from the horses mouth (take a person's name). If you can email and get answer in writing you are home and dry.

 

[S60TEM]

if we use the Adiabatic equation then for the installation to get the required calculated size of the bonding conductor:

equation is S= (square root)I2t/k

V=IxR to get the PFC

230v = ? x 0.8ohms (for TNS - assumed although it could be less thus increasing the possible fault current)

230/0.8 = 287.5A PFC

so.........

S= (sq root) 287.5x287.5 x t / k

= (sq root) 82,656.25 x t / k

so for a 60A assumed BS1361 main fuse on a distribution circuit exceeding 32A would be a disconnection time of 5 sec.

= (sq root) 82,656.25 x 5 / k

so k for an insulated protective conductor of less than 300mm in copper would be 143 (table 54.2 BRB)

=(sq root) 413,281.25

=642.870 / 143

=4.49mm

Doesn't seem right does it that when calculated 230v on a TNS system with a max Ze of 0.8ohms will produce 287.5A PFC. Ran through the equation comes out at just a 4.49mm required CSA CPC but we all know that that conductor wouldn't take 287.5 A! Also, using the fig 3.1 page 244 in the BRB, a BS1361 fuse of 60A could take a fault current of 287.5A for approx 8 - 10 secs!

Can someone else do this calculation also to see what they come up with as reg 543.1.1 states by

i) calculation in accordance with 543.1.3 or

ii) selected in accordance with 543.1.4

I think I must have calculated it wrong like, it's been a while since I did one of these calcs! LOL

---------- Post Auto-Merged at 12:48 ---------- Previous post was made at 12:38 ----------

Either way, your 6mm Gas bonding would still be sufficient

 

[ian932]

if we use the Adiabatic equation then for the installation to get the required calculated size of the bonding conductor:equation is S= (square root)I2t/k

V=IxR to get the PFC

230v = ? x 0.8ohms (for TNS - assumed although it could be less thus increasing the possible fault current)

230/0.8 = 287.5A PFC

so.........

S= (sq root) 287.5x287.5 x t / k

= (sq root) 82,656.25 x t / k

so for a 60A assumed BS1361 main fuse on a distribution circuit exceeding 32A would be a disconnection time of 5 sec.

= (sq root) 82,656.25 x 5 / k

so k for an insulated protective conductor of less than 300mm in copper would be 143 (table 54.2 BRB)

=(sq root) 413,281.25

=642.870 / 143

=4.49mm

Doesn't seem right does it that when calculated 230v on a TNS system with a max Ze of 0.8ohms will produce 287.5A PFC. Ran through the equation comes out at just a 4.49mm required CSA CPC but we all know that that conductor wouldn't take 287.5 A! Also, using the fig 3.1 page 244 in the BRB, a BS1361 fuse of 60A could take a fault current of 287.5A for approx 8 - 10 secs!

Can someone else do this calculation also to see what they come up with as reg 543.1.1 states by

i) calculation in accordance with 543.1.3 or

ii) selected in accordance with 543.1.4

I think I must have calculated it wrong like, it's been a while since I did one of these calcs! LOL

---------- Post Auto-Merged at 12:48 ---------- Previous post was made at 12:38 ----------

Either way, your 6mm Gas bonding would still be sufficient

Looks spot on to to me can't confirm your value for 't' as my van is off for new brakes with the BRB in it so no access to time-current characteristics.

 

[Sidewinder]

Got mine Tuesday next week too!

 

[ian932]

Got mine Tuesday next week too!

Just had my DI to AC today was bricking it, but past with no departures or actions required, feel totally mentally drained now though. Good luck to anyone who is due for theirs I don't envy you

 

[Sidewinder]

No mate mine is not a transfer assessment it is my annual AC assessment!

Have not even looked at anything with regard to it yet!

I am busy all day tomorrow & all weekend.

The only prep time I have is Monday unless a breakdown comes in!!!