voltage drop in a circuit

[searley]

i got this last year and can`t find the answer to 10mm two-core mineral insulated cable with copper conductors and sheath and an overall covering of pvc. i have got the 17th onsite guide could the answer been of the old regs 16th ed ?

question

a single phase circuit is wired 10mm two-core mineral insulated cable with copper conductors and sheath and an overall covering of pvc.if the design curent (ib) is 65A AND THE LENGH of the cicuit is 40m. calculate the voltage drop in the curcuit ?

4.2x65x40/1000 = 10.9v

where does 4.2 come from ?

 

[NozSpark]

It's the voltage drop in mV per meter for your cable..

Volt drop = (mV per meter) x (design current) x (length of circuit) / 1000 (factor to get it back to volts)

 

[Andy™]

obviously not quick enough tonight!

 

[searley]

can`t find what i am supposed to be looking for ?

is there an answer in there somewhere ?

 

[Andy™]

can`t find what i am supposed to be looking for ?is there an answer in there somewhere ?

dont think VD tables are in OSG. you need the regs for that. there are a few pages with VD for various cables

 

[searley]

how about this one then.

a 3kw load is supplied from a 230v, 50hz supply.the circuit is protected using bs 3036 (rewirable) fuse and is situated 15m away from the db .it is run with.it is run with one other circuit and is buried within the buliding material of the intallation.the temp within the installation can be assumed to be 25c.determine the volt drop ?

 

[Andy™]

you need to work out what the amps will be (I= P/V)

the 3036 has no use in this

nor does the temperature (you need that for current carrying capacity calcs)

then use the formula

VD = mv*A*m /1000

you havent said what cable your using, so ill assume pyro as in first question. also assume its 2L2.5

VD= 17*13*15 / 1000 = 3.315V

 

[searley]

did you get the 17mv from the regs if not where ?

are is it you just clever

 

[NozSpark]

With questions like this they are putting a lot of info that is not required for the specific question.. you find this a lot with C&G exams.

The info you need for volt drop is..

Length of circuit

Demand of circuit (Amps)

CSA of L & N conductors

So for this question, you are missing some info --- cable size!!

 

[Robojin]

how about this one then.a 3kw load is supplied from a 230v, 50hz supply.the circuit is protected using bs 3036 (rewirable) fuse and is situated 15m away from the db .it is run with.it is run with one other circuit and is buried within the buliding material of the intallation.the temp within the installation can be assumed to be 25c.determine the volt drop ?

Damm Andy I think you need a new nick "Speedy"

I was assuming 2.5mm (since you don't quote)

18*13*15 /1000 = 3.52v

 

[Andy™]

did you get the 17mv from the regs if not where ?are is it you just clever

1: from regs

2: clever because i know where in the big red (or in this case, brown - red book is in van)

 

[Andy™]

18*13*15 /1000 = 3.52v

where did you get the 18 from? has the VD changed between 16th and 17th?

its too cold to go get the red book out to compare it to the brown book i have infront of me

 

[Robojin]

did you get the 17mv from the regs if not where ?are is it you just clever

BS7671 pages 274-317 cover cable VD (did I get this before Special Applaud Smiley)

 

[Robojin]

where did you get the 18 from? have the VD changed between 16th and 17th?

Sorry Andy should have said PVC T+e, I'll look up pyro, but likely your correct

 

[Apache]

BS7671 pages 274-317 cover cable VD (did I get this before Special Applaud Smiley)

you did but it's an unfair advantage as he's not online ATM!

 

[NozSpark]

You get these figures from the tables in appendix 4

4D5 for T&E (column 8)

4G1B PVC coated pyro (column 3 for 2 core)

 

[Robojin]

where did you get the 18 from? has the VD changed between 16th and 17th? its too cold to go get the red book out to compare it to the brown book i have infront of me

Yup Pyro is 17

I guess buried is a red herring too!!

 

[Andy™]

Yup Pyro is 17I guess buried is a red herring too!!

like most of the info! just to confuse you into thinking its harder than it actually is. bit like use asking the vet a question on a dog and giving some info from a horse

 

[searley]

the question i put on was of a collage paper.it does not say what cable to use.

collage lecturers. why dont they just make it easy then try`ing to confuse. a--- holes

 

[Andy™]

the question i put on was of a collage paper.it does not say what cable to use.collage lecturers. why dont they just make it easy then try`ing to confuse. a--- holes

if they dont put what cable to use, or what size cable it is, you cannot answer the question.