Cable Calc Template.

[Guest123]

Evening all.

This has been in the arms for a while now and I meant to post it in the open forums ages ago but totally forgot.

It's the design template I created when I did my C&G 2400 design course (C&G 2391-20 in todays money). I have tweaked it a bit to update it, regs references etc but the fundamentals haven't changed at all.


Hope you find it useful.

:cyclist:

 

[silva.foxx]

Thanks Lenny.

It would be really handy as a spreadsheet :wink_smile:

 

[Guest123]

Thanks Lenny.

It would be really handy as a spreadsheet :wink_smile:

Funny you should mention that.

I started one, ages ago with hyperlinks to actual regs pages etc, and never have got round to finishing it. Who knows, maybe one day.........got this HNC thingy robbing me of all my spare time at the mo though.:smart:

 

[i=p/u]

always looked for one of these when didnt quite grasp it all... whats point 7 all about, would you max zs from circuit breaker??? cheers will save it anyway and print and pass on too i think appropriate

 

[Guest123]

always looked for one of these when didnt quite grasp it all... whats point 7 all about, would you max zs from circuit breaker??? cheers will save it anyway and print and pass on too i think appropriate

Point 7 is calculating wether or not the CPC would be large enough to cope with the magnitude of earth fault current that may flow under fault conditions, using the adiabatic equation.

 

[i=p/u]

so you would use, the breaker device max zs for the sum...... would you multiply by 0.8 before you find your fault current??? )

 

[johnboy6083]

no mate you wouldnt, asitsthe max fault current you are looking for, to ascertain if your protective devices have sufficient breaking capacity to contain the fault.

 

[i=p/u]

ok so point 7 is very clear in saying, thermal constraints i.e breaking capicty for that point ic circuit... i thought when done at the origin and devices selected along with this it would cover downstream ones as got less fault current....

but i think i know you still need to check when out in industry , where im on about domestic lol

 

[johnboy6083]

what your talking abput mate is called cascading, or back-up protection. It is permitted in industry too.

what usually happens is that you have a main board, that will be weither MCCB's or fuses, this will then feed smaller panelboards, or large machines. The panleboards will have MCCB's or fuses, and then your final ccts will be fed from a 3phDB that will be on MCB's.
this is because its very difficult to acheive discrimination with MCB'as feeding MCB's, but easier to use fuse's or MCCB;s to feed MCB's.

you will then in all likelyhood, if using large cables to feed you final 3ph DB, be using the MCCB or fuse on the feed as backup protection for short circuit and/or earth fault protection.

 

[i=p/u]

yes great page for someone like myself with ahaqlf a clue... black and white

 

[i=p/u]

i do think it should say at point 7 , Uo /Ze.... but im sure there is perfectly good reasn why... dont mind me

 

[Guest123]

i do think it should say at point 7 , Uo /Ze.... but im sure there is perfectly good reasn why... dont mind me

I suggest you investigate exactly what the adiabatic equation is and how it used in circuit design.

 

[i=p/u]

so does that mean you would use the max zs reading of the breaker for the design???? sorry

 

[i=p/u]

sorry at first point

 

[dingledong]

hmm i cant get it to open:ninja:

 

[Guest123]

so does that mean you would use the max zs reading of the breaker for the design???? sorry

No, the permitted device Zs doesn't come into the equation. The value used is the calculated theoretical of circuit Zs found by using the formula Zs = Ze+(R1+R2).

This theoretical Zs value is then used in a calc with the supply voltage to find the (I) component (which is the maximum earth fault current that could flow in a fault condition) of the adiabatic equation which is - S = sqroot of I squared x t divided by k.

The use of this equation with the correct information will then confirm wether or not the CPC of the proposed circuit is large enough to cope with the fault current that may flow in it.

 

[Guest123]

hmm i cant get it to open:ninja:

Seems to be ok, what browser are you using??

 

[i=p/u]

so is that why you say at top, the length and ze must be obtained... sorry for con fussin ya you

 

[jimmy_one_ball]

For step 6, would you take 80% of the Zs AND multiply the R1+R2 by 1.2? I thought it was one or the other?

 

[big willie]

I have been asked to connect a mobile home on a large transport site. The supply cable run is approx 250 meters. When I try to work out the voltage drop for the swa cable from size 25mm upwards there are three values in the regs book x,y,and z which shoul I use

Thanks anybody

 

[Guest123]

I have been asked to connect a mobile home on a large transport site. The supply cable run is approx 250 meters. When I try to work out the voltage drop for the swa cable from size 25mm upwards there are three values in the regs book x,y,and z which shoul I use

Thanks anybody

Upto 35mm, I continue to use the resistive (r) component for calculating the VD. By moving to the impedance (z) component you will end up with a pessimistically large conductor size.

Going above 35mm and bringing reactance & impedance in to play makes it all a bit more complicated as power factors (if known) and temperature corrections come into play.

Have a read from page 312 (new green book) onwards (appendix 4).

 

[krishcanag]

I can provide everyone with a excel automatic caluator butit is not a valid file extension to upload!!!

 

[spiders803]

hi krishcanag

was just wondering if you could email me a copy of ur excel cable calculator would be very helpfull, my email is [email protected]

many thanks

 

[adigear]

is that maximum allowable earth fault current is 1mA?
sorry i dont understand about Cg, Ci, Ca.....
thank you

 

[muneeb]

nice thing, helped me a lot during my trial period in a textile mill
thanx

 

[linetech]

Excellent, been meaning to knock one of these up for the back of my regs manual but aint had the time. A handy must to have a hard copy like this, especially the adibatic equation if you looking to save a few £££.. Why go large if theres no need!

Cheers

 

[ingflying]

a little complex,thanks:wings:

 

[Blue Whale]

Thank you Lenny for your time.

Very useful format.

Regards

Blue Whale.

 

[georges]

thanks lenny makes life really easy when your having a blonde moment

 

[astralis]

good job, Lenny!

 

[JUD]

Good job Lenny.

Hope you don't mind but I added a few bits and pieces that I thought could be useful.

See what you think...

 

[johnboy6083]

I like it JUD. I didn't see anything about ring final circuits though, or thermal withstand calcs for short circuit protection.Very good template though.

 

[ackbarthestar]

I like the clear layouts of both Lenny's and JUD's cable design templates

Just a couple of points

I would use U and Uo for the 3-phase and single phase voltages, respectively

JUD you have forgotten, in step 6, the Length of the final circuit being calculated.

Otherwise excellent stuff !

 

[brav]

thts brilliant len, thanks

In step 6, do i have to multiply it by 0.001 to get ohms? i.e 4.91mohm/m x 9 metres x 1.2 x 0.001 = 0.053 ohms?


Or have i got it confused with something else, cheers mate

 

[JUD]

thts brilliant len, thanks

In step 6, do i have to multiply it by 0.001 to get ohms? i.e 4.91mohm/m x 9 metres x 1.2 x 0.001 = 0.053 ohms?


Or have i got it confused with something else, cheers mate

Yep or divide by 1000 (4.91 ÷ 1000) x 9 x 1.2 = 0.053Ω

It's all the same thing.

 

[brav]

Yep or divide by 1000 (4.91 ÷ 1000) x 9 x 1.2 = 0.053Ω

It's all the same thing.

cheers mate

I enjoy doing cable calcs, so this is a perfect backup to make sure i'm always going in the right direction. cheers

 

[B16 Tom]

Brill but defo needs the spread sheet version! Thought it was the answer to all my prayers then :juggle2:

 

[JUD]

You're in luck

 

[Gman137]

Hi, I'm interested in seeing this spreadsheet as I'm doing cable calc's, trouble is all these books and tables are Blowing my mind. Can't seem to open it tho !! Any ideas ???

 

[Sherlock]

Hi

Where is the template from post #1, I dont see it.

Also, how do I contact Guest 123 to ask him for a copy???

Thanks.