125 kva supply cable calc

tom20 · May 20, 2016

Hi,

We are undertaking quite a big job for an extension at a school and as it is a little out of our experience i was hoping to run it by a few of you kind folk before we have another meeting with the client on Tuesday.
I've read through the forum at cable calc questions and i know they can come across a little lazy! so i will show as much info and what i have come up with so far.

The job is an extension for a new kitchen / dining room at a school and the client require a new 125 kva supply. XLPE/LSF/SWA/LSF 4core with separate earth underground in a 150mm duct. the run is to be 300m from a sub station located on the edge of the grounds.

We have so far come up with 180A required (per phase?) with 5% volt drop Which brings us to requiring a 95mm 4core swa cable.

does this seem correct? or a little too excessive? and lastly what would be expected in terms of terminating this in the new intake room before MCCB main dist board

Thank in advance and please let me know any other info required.

tom

ian.settle1 · May 20, 2016

I have to ask why you have taken the work on when you clearly have admitted by your post that you do not know what you are doing.

SheffSimon · May 20, 2016

tom20 said:
Hi,

We are undertaking quite a big job for an extension at a school and as it is a little out of our experience i was hoping to run it by a few of you kind folk before we have another meeting with the client on Tuesday.
I've read through the forum at cable calc questions and i know they can come across a little lazy! so i will show as much info and what i have come up with so far.

The job is an extension for a new kitchen / dining room at a school and the client require a new 125 kva supply. XLPE/LSF/SWA/LSF 4core with separate earth underground in a 150mm duct. the run is to be 300m from a sub station located on the edge of the grounds.

We have so far come up with 180A required (per phase?) with 5% volt drop Which brings us to requiring a 95mm 4core swa cable.

does this seem correct? or a little too excessive? and lastly what would be expected in terms of terminating this in the new intake room before MCCB main dist board

Thank in advance and please let me know any other info required.

tom

Surely you must have costed up the job based on the cable required?

You need to get somebody to do this calc properly, not just asking on a forum. Where are the building designers/architects in all this?

Amp David · May 20, 2016

Another quality job getting done.

Hawk · May 20, 2016

No job too small

tom20 · May 23, 2016

the company is doing all of the works not just the electrical. Therfore yes my Directors have taken on the job and priced etc, really without giving myself or the other electrical supervisor sufficient initial warning regarding the electrical specification. I dont accept or decline jobs as that is in the directors hands. The metal clad, conduit & 3 phase etc is no problem inside the build, we have plenty of experience with that but i have openly admitted that a new intake is not something myself or my college have overseen before. We have already recommended to the directors subing particular parts of the specification out because of it.

It isnt very often you calculate a run of 300 meters which is why i was after some expertise. We have calculated the current required along with volt drop and have come up with 95mm or possibly one size up to be sufficient, it is something We are going over again. It will hopefully make more sence when we meet the gut tomorrow who designed all parts of the spec as we haven't met anyone yet ourselves.

I read through the forum every now and then and i get it irritates some when questions are asked but dont see the need to mock/judge peoples integrity or workmanship. I take a lot of pride but my experince is limited in some areas, i thought i could use the forum for some help and awareness would but it seems not so much. If im not comfortable with something i wont oversee it. Which is why inrecommended solubbing this part of the works.

SheffSimon · May 23, 2016

tom20 said:
the company is doing all of the works not just the electrical. Therfore yes my Directors have taken on the job and priced etc, really without giving myself or the other electrical supervisor sufficient initial warning regarding the electrical specification. I dont accept or decline jobs as that is in the directors hands. The metal clad, conduit & 3 phase etc is no problem inside the build, we have plenty of experience with that but i have openly admitted that a new intake is not something myself or my college have overseen before. We have already recommended to the directors subing particular parts of the specification out because of it.

It isnt very often you calculate a run of 300 meters which is why i was after some expertise. We have calculated the current required along with volt drop and have come up with 95mm or possibly one size up to be sufficient, it is something We are going over again. It will hopefully make more sence when we meet the gut tomorrow who designed all parts of the spec as we haven't met anyone yet ourselves.

I read through the forum every now and then and i get it irritates some when questions are asked but dont see the need to mock/judge peoples integrity or workmanship. I take a lot of pride but my experince is limited in some areas, i thought i could use the forum for some help and awareness would but it seems not so much. If im not comfortable with something i wont oversee it. Which is why inrecommended solubbing this part of the works.

None of which anybody on this forum knew from your first post.

Either way, you seem clear that you need some help to do the required calcs. I would stand your ground with your directors, and get the design of this cable run subbed out.