Distribution board

[Lc1]

We are replacing a single phase lighting DB with a 3 phase DB. We are also replacing the cable that goes from the substation to the DB.

This new DB will be used for lighting circuits( we will change existing for LEDs) and we will leave spare ways.
My question is how do we size this new cable from substation to DB to take into account future expansion.

The distance between the substation and DB is approx 200m. And the existing cable CSA is unknown.



Currently the existing board is single phase and is fed from panel 2 cubicle 1 of a 3phase switchboard. This cubicle also feeds another single phase board and has a spare way.


As panel 2 cubicle 1 split into 3 single phase loads, we cannot reuse the existing feed to our new board.

We have panel 5 cubicle 1 in the switchboard which is free. 160A/160A. So for rough pricing purposes we could use this to feed our new 3 phase board in the field and use 160A as a basis for cable sizing?

Thanks

 

[Pete999]

Hi, as a trainee should you be doing this sort of work? the description is a bit hap hazard to say the least. Get permission to join the Trainee forum, all the help you need you can find in there.
It still worries me that you are playing around with something that you are plainly not very sure of, or are you asking the question out of interest?

 

[Lc1]

Just asking out of interest. I think my question can be simplified. If we have a 3 phase switchboard cubicle.that is split into single phases say L1,L2,L3 and say L3 is powering a single phase DB in the field. then say we replace the single phase DB with a three phase DB, we cannot use L3 to power it, correct? Ie we would have to find another cubicle.

 

[Pete999]

Just asking out of interest. I think my question can be simplified. If we have a 3 phase switchboard cubicle.that is split into single phases say L1,L2,L3 and say L3 is powering a single phase DB in the field. then say we replace the single phase DB with a three phase DB, we cannot use L3 to power it, correct? Ie we would have to find another cubicle.

Maybe it's me but I still can't get to grips with what you are trying to do, the bit highlighted confuses the hell out of me

 

[cprfenom]

How can a single phase board power a 3 phase board and actually be 3 phase

 

[Lc1]

We have a switch board in a substation which is a 3phase switchboard. One of the cubicles is split into three single phases.
these power 2 single phase lighting db's out in the field and one of the ways is spare.

if we were to replace one of the single phase lighting db's out in the field with a new 3ph DB, we cannot use its current feed. We would have to find another cubicle to power this new DB, correct?

 

[Pete999]

We have a switch board in a substation which is a 3phase switchboard. One of the cubicles is split into three single phases.
these power 2 single phase lighting db's out in the field and one of the ways is spare.

if we were to replace one of the single phase lighting db's out in the field with a new 3ph DB, we cannot use its current feed. We would have to find another cubicle to power this new DB, correct?

Still not clear mate to feed a 3 phase DB you need a 3 phase supply L1.L2,L3 and a Neutral and Earth

 

[Lc1]

That answers my question.
the existing 3 phase cubicle is split into 3 single phase supplies. As mentioned these power 2 single phase db's. So if we were to replace one of these single phase dbs with a new 3 phase one it would need a new 3 phase supply and so we would have to find a new cubicle to power thre new db

 

[Pete999]

That answers my question.
the existing 3 phase cubicle is split into 3 single phase supplies. As mentioned these power 2 single phase db's. So if we were to replace one of these single phase dbs with a new 3 phase one it would need a new 3 phase supply and so we would have to find a new cubicle to power thre new db

Well whoopy do glad that's sorted

 

[amlu]

use a 3phase cable, connect it into your 3 phase switchboard.
or get someone competent to do it for you if you are not sure.

what those "cubicles" are... switch fuses? enclosures?
take a picture or make a drawing of existing arrangement to make it more clear...

 

[Lc1]

Our new 3 phase DB would need a new cable from a new cubicle of the switchboard. I have looked at the sld and it says panel 5 cubicle 5 has nothing connected,it says160A/160A. So would we use this current to size the new cable?

thanks

 

[Pete999]

Our new 3 phase DB would need a new cable from a new cubicle of the switchboard. I have looked at the sld and it says panel 5 cubicle 5 has nothing connected,it says160A/160A. So would we use this current to size the new cable?

thanks

You will need the length of run, the installation method, type of cable, anticipated max loading at the new DB and a copy of BS7671 to calculate the size of cable needed.

 

[Lc1]

The length is approx 200m. We do not know what the spare ways will be used for. We can only estimate the load of the lighting. Can we not use the 160A as a basis for the current?

 

[Plonker 3]

You could use that yes, but your volt drop will be considerably more than if you were to use the Ib, as you could also fuse the cable down accordingly.

 

[Deleted member 72666]

What's with the 'cubicle' bit?

 

[Deleted member 9648]

Is this actually a job or a 'hypothetical' question? Because if its a job you really-really want to make sure you get it right. Could be a VERY expensive mistake if you are relying on forum answers to very poorly phrased questions.

 

[Knobhead]

Just because you have a free 160A doesn’t mean it has to be used to capacity. If it’s a switch fuse, fit smaller fuses, a MCCB, change the MCCB.

This may sound ridiculous I found a board fed with a 25mm² 4c SWA. The nearest free distribution switch fuse was 800A. They left the 800A fuses in because that was what was fitted.

Work out your existing plus anticipated loading and then determine the OCPD. Don’t try to work the other way around.

 

[martinh89]

I completed my electrical apprentership but changed jobs to cable jointing. If the cable your talking about is coming out of a substation its either PILC or waveform and if you clean the cable back around 2meters it will state the size. Also if your changing lights to LED's your max load will decrease so why are you upgrading to a 3phase supply ? your load will dercrese

 

[sammyshooter]

My head hurts