3 phase consumer unit - quick question

[Stevenf]

Hi,

I have a 125a C/unit
I have two sub-mains to go from this board.

how can I connect to the busbar?
is there essentially a MCB without a rating/switch

if so, what is this called please???

or is it best to protect the cable???!!

thanks

 

[Leesparkykent]

Hi Stevenf, are you an electrician? As on your profile it just says farm. If you are not then it would probably be best to get an electrician in as it's no really the type of work you should be attempting without the knowledge.

 

[telectrix]

each sub main feed cable must be protected ... MCBs or fuses. best taking lee's advice and employ a qualified electrician who will be able to deign, install, test, and certificate..... safe job.

 

[Stevenf]

My sparky advised going off the busbar and I can't find the appropriate hardware - (mcb without switch / protection)

im I buying all the materials for him to install. I was unsure of his advice.

 

[Leesparkykent]

My sparky advised going off the busbar and I can't find the appropriate hardware - (mcb without switch / protection)

im I buying all the materials for him to install. I was unsure of his advice.

how far is the sub board going to be from the board you want to tap off?

 

[Stevenf]

45 metres

 

[Leesparkykent]

45 metres

The sub mains are going to need protection. It's not ideal though to feed another board off an mcb due to discrimination issues between circuits on new sub board and the mcb feeding the sub board.

 

[Stevenf]

I am replacing switched fuses with a board to gain additional circuits.
not sure of a better way / options.

sub main going to a New 125a board
i should just protect sub-main cable with a 63a type D mcb (as there is motors running off sub main board)
will discrimination be an issue?

 

[Darkwood]

My sparky advised going off the busbar and I can't find the appropriate hardware - (mcb without switch / protection)

im I buying all the materials for him to install. I was unsure of his advice.

Piggy backing submains of existing 125amp distribution board as you explain in your opening post is poor design and will have drawbacks, if you are really stuck for any alternative then I would suggest fitting a 200amp busbar chamber to the wall and the supply feeding your existing distribution board is removed and fed into an Isolator which then feeds this new busbar chamber. From there you fit 3 outgoing sw/f isolators :-

1 - feeds existing board
2 - feeds sub-mains one
3 - feeda sub-mains two

This all has to be designed on site and it will need to be confirmed that the existing feed to your existing board has the capacity for the extra submains.

Voltage drop will also need to be calculated all the way back to the origin of your supply to the end of the sub mains you propose.

If you are advised to run the submains off mcb's in the existing board then this would be poor advice as it is poor design and a fault in you new submain circuits may equally take out the submain mcb thus losing all the power to all submain circuits as oppose to just the circuit at fault.

It would be almost impossible to design or advice you over a chit chat on a forum and I would strongly advise you get qoutes and designs from 3 or 4 recognised registered companies... this is not a job for a mate you know down the pub unless they are well seasoned and competent, its also not a job for anyone who only has experience in domestic.

We try our best to advice but sometimes its just not possible without seeing the installation and the proposed submains... your profile says farm and if this is correct then extra measures of safety need to be incorporated into the design so how ever tempting it maybe - don't cut corners (just a word of advise and I'm not suggesting you would cut corners).

You say you are running motors of the submains... this adds a complexity to the design, if they are small <5.5Kw then not too much of a worry but if we have larger motors then start up current will need to be calculated to ensure any upstream device including the front end for the existing cable will not trip out.

 

[Leesparkykent]

It's hard to give an opinion without seeing it but a busbar chamber and switch fuses for the new sub boards maybe an option.

edit: posted same time as darkwood, he has given you some good advice.

 

[Stevenf]

That is v. Sound advice - appreciated.

I think a second or third opinion is needed

just trying to get a new 60a machine up and running without up rating All the electrics (which I intend to in the future)
not cutting corners will pay Iagree

Thanks for taking time on my dilemma

 

[Darkwood]

That is v. Sound advice - appreciated.

I think a second or third opinion is needed

just trying to get a new 60a machine up and running without up rating All the electrics (which I intend to in the future)
not cutting corners will pay Iagree

Thanks for taking time on my dilemma

Your appreciation and taking of our advice is our reward ... please feel free to click the Thanks and/or likes

If the machine is 60amps and incorporate a large motor then I feel you will be best asking an Electrician or Electrical Engineer competent in running factory machinery supplies, please ask any company if they have experience in this area to save you alot of time and effort, I seen professionals make a mess of such installs because they think they know what they are doing but they are clearly working out of their comfort zone and experience.

All the best.