SWA long 140M run please help!!

[FCC5206]

Evening all
I have been asked what size cable will be required for a long run. I know there are heaps of threads on here from people too lazy to do their homework but I have and am still lost so sorry if this has been covered i just cant find the answer.
The run is to power a stable block which the customer has told me needs power equivalent to a 2 bed house!!
The length of the run is 140 meters!
Taking into consideration max demand and diversity after doing my voltdrop calcs i come up with a 2 core 95mm2 to achieve the required 5% drop!! I know this is absurd and was wondering if anyone could point me in the right direction

Thanks

Chris

 

[jeremy]

It wasn't suggested to save money, but for ease of installation. I'm not sure why it's idiotic. To try and terminate 95mm cable, or 2 cores of 50, in a confined space isn't so easy.Sizing up and down again in a resin joint is easy. This method is used on UK Highways for long runs.

 

[jeremy]

I thought it referred to running 2 smaller csa cables in parallel, instead of 1 larger one. In the case of a TT installation, 2 cores of a 4 core can be line, the other 2 neutral. Is this incorrect? If so can you tell me what it does refer to? Thanks!

 

[JD6400]

It wasn't suggested to save money, but for ease of installation. I'm not sure why it's idiotic. To try and terminate 95mm cable, or 2 cores of 50, in a confined space isn't so easy.Sizing up and down again in a resin joint is easy. This method is used on UK Highways for long runs.

Bear in mind that those joints will be ( from memory ) around £100 each , and will take around 1 hr each to make off .

 

[jeremy]

That's a fair point!! I never paid for them, just fitted them where I was told!

 

[JD6400]

Also if you were to go down the parallel route then as far as i am aware it would be against the regs for there to be a joint in them ?!

 

[jeremy]

I can't find anything in selection and erection precluding joints (523.7) but that doesn't mean there isn't! Is my understanding of a parallel feed correct?

 

[JD6400]

If you mean the ability to down size the individual csa's in each cable and make it a lot easier to handle then yes this is a good reason alone .

 

[Engineer54]

It wasn't suggested to save money, but for ease of installation. I'm not sure why it's idiotic. To try and terminate 95mm cable, or 2 cores of 50, in a confined space isn't so easy.Sizing up and down again in a resin joint is easy. This method is used on UK Highways for long runs.

NO it's not!! on highway lighting installations the CSA area of cables are reduced along the cable run according to the load that part of the cable installation is supplying, ...and will always be a fixed and known load . And it's never reduced at the origin of the cable run either!! A sub-mains supply is a completely different kettle of fish, ALL the load will originate at the END of the cable run!!

There are various means of terminating two smaller cables at the source and destination, without too much of a hassle. It's the larger single sized cables that will cause all the problems!!

You still haven't answered why you are providing more CSA of copper conductor in a parallel cable circuit, than is required installing a single cable??

 

[jeremy]

I've done quite a lot of work on UK Highways, none of it soley on lighting, but supplying power to traffic measurement, comms, detection and enforcement, cctv, gantry lighting. This is controlled by cabinets that the company I work for manufacture. Each cabinet is powered from a Electrical Incoming pillar which holds up to 4 fuses. Each fuse has a max rating of 40A. Each cable from here has a max size of 25mm. The cabinet could be 800m+ away from the EI pillar. The cable from the EI is fed to an "A" chamber, upsized if necessary according to the distance needed, this is run in ducting to a chamber local to the gantry or cabinet, then downsized to enter the cabinet , if necessary, where it enters a PDU which is then subdivided into circuits. That long cable is a sub main I believe. I don't see how this method differs from what I've suggested for the stable block. I apologise if I appear stupid, but I'm only translating a method from work, to a domestic situation, to try and make the install easier.
With regards to the parallel question, to provide equal CSA, I went with 2x50's as its the closest coupling to 95 that would ensure equal loading. If I'm barking up the wrong tree, please enlighten me, as I obviously don't have the grasp of it that I thought I had. Thanks!!

 

[Engineer54]

I've done quite a lot of work on UK Highways, none of it soley on lighting, but supplying power to traffic measurement, comms, detection and enforcement, cctv, gantry lighting. This is controlled by cabinets that the company I work for manufacture. Each cabinet is powered from a Electrical Incoming pillar which holds up to 4 fuses. Each fuse has a max rating of 40A. Each cable from here has a max size of 25mm. The cabinet could be 800m+ away from the EI pillar. The cable from the EI is fed to an "A" chamber, upsized if necessary according to the distance needed, this is run in ducting to a chamber local to the gantry or cabinet, then downsized to enter the cabinet , if necessary, where it enters a PDU which is then subdivided into circuits. That long cable is a sub main I believe. I don't see how this method differs from what I've suggested for the stable block. I apologise if I appear stupid, but I'm only translating a method from work, to a domestic situation, to try and make the install easier.
With regards to the parallel question, to provide equal CSA, I went with 2x50's as its the closest coupling to 95 that would ensure equal loading. If I'm barking up the wrong tree, please enlighten me, as I obviously don't have the grasp of it that I thought I had. Thanks!!

That was the point i was making, when using parallel supply cabling you can reduce the CSA of the parallel supply cables to roughly a third (and sometimes less), of the size of a complying single cable, obviously depending on installation method and length of run to meet VD requirements. So in the case of a 95mm, you would start looking at 35mm to meet your requirements...

As to your other comments, you seem to be talking about comms and other low power systems, rather than actual highway lighting strings etc. In that respect you may well be correct in the way things are done. But you can't compare Highway lighting strings to a sub-main supply. They are two very different animals!!

 

[Guest55]

Also if you were to go down the parallel route then as far as i am aware it would be against the regs for there to be a joint in them ?!

eh ?
maybe you should tell that to the highways agency who have been down-jointing motorways power cables for the last 30 years.
ever tried terminating a 95mm swa in a steel cabinet thats 2 ft tall ?

 

[Guest55]

NO it's not!! on highway lighting installations the CSA area of cables are reduced along the cable run according to the load that part of the cable installation is supplying, ...and will always be a fixed and known load . And it's never reduced at the origin of the cable run either!! A sub-mains supply is a completely different kettle of fish, ALL the load will originate at the END of the cable run!!

complete rubbish.
ever worked for the highways agency ?
i have and i personally rewired parts of the M58 and M65.

 

[Engineer54]

complete rubbish.
ever worked for the highways agency ?
i have and i personally rewired parts of the M58 and M65.

Really!!, perhaps you can enlighten us all then!!

 

[Guest55]

Really!!, perhaps you can enlighten us all then!!

i did , with post #56.
no cable size bigger than 25mm is terminated above ground although most motorway feeds go upto 120mm
hence down jointing before entering any surface structure.

 

[Engineer54]

i did , with post #56.
no cable size bigger than 25mm is terminated above ground although most motorway feeds go upto 120mm
hence down jointing before entering any surface structure.

Tell me, when and where have i said that joints are not used?? Generally there will be a Tee joint by every post (or pair of posts etc) to supply that posts power, which will be sized accordingly. As you go further along the string, cable sizes will reduce, according to the distance and remaining posts being supplied!! Never and i'll repeat never, have i seen a reduced cable size being used at the supply end feeder pillar....