3 Phase Dis Board Incomer

[nandrews87]

Having a quick discussion in work with regards to sizing the main incomer of a three phase dis board. Can someone please tell me how the correct way to size the main incomer of a three phase board or single phase for that matter

Cheers

Folks

 

[Plonker 3]

Well it's switch so what do think it needs t be capable of doing?

 

[MDJ]

Having a quick discussion in work with regards to sizing the main incomer of a three phase dis board. Can someone please tell me how the correct way to size the main incomer of a three phase board or single phase for that matter

Cheers

Folks

um,no, you first what do you think?

 

[Darkwood]

More details please! You have given us no info to the set-up and whether its domestic, commercial or industrial and what is the nature of the systems it supplies.

 

[MDJ]

Well it's switch so what do think it needs t be capable of doing?

It might be able to make the tea or even tell the time lol

 

[gnuuser]

if you know the current requirements of the equipment it will be supplying its simple math and use of ampacity tables.
and its a matter of getting the proper hardware too
you should already be able to figure this out.

 

[nandrews87]

Its a three phase board so clearly commercial/industrial. Board would supply 8kw heater, 15kw cooker, 2 x 32amp socket circuits, 4 x lighting circuits and 3 x 32 amp commando sockets. its my opinion that a 125amp breaker would be enough based on previous experience but what I want is the theory/calculations to making such decisions.

 

[Plonker 3]

Why do you think a 125 amp BREAKER is what is needed?

 

[nandrews87]

As I have already said from previous experience working on 3 phase dis boards, What would you recommend Dillb?????????

 

[Sintra]

I would be looking at what type and rating of protective device is feeding the board.

 

[Plonker 3]

Then choose a switch accordingly.

 

[trev]

Its a three phase board so clearly commercial/industrial.

I've seen houses with 3 phase boards.

 

[Guest55]

maths ? your kidding right ?

just size your main switch to be = or > than the current rating of the upstream device.
you cant go wrong using that.

 

[Plonker 3]

You know what the next question is going to be now don't you?

 

[nandrews87]

Sintra the board in question is the example giving in an assignment question to someone I work with so that info is not included.

 

[Plonker 3]

No but the loading of the new DB is.

besides, what was there answer to the said question?

 

[nandrews87]

This is the rule of thumb I normally use but giving this info is not available I presume there must be a method to work it out based on the load on the board

 

[Plonker 3]

Of course it is,that's how you always work out a OCPD isn't it?

 

[nandrews87]

No but the loading of the new DB is.

besides, what was there answer to the said question?

There answer was to tally up total current from other loads and size main breaker on that number, I dont believe this to be right as it doesnt allow for things such as diversity factor. My approach is to size it based on device that provides protection upstream of the dis board in question but in this instance that info is not available.

 

[Plonker 3]

We'll apply diversity and you will have your answer.

 

[Darkwood]

edit ...deleted my page was stuck in the past so missed several post which answered what i was asking.

 

[nandrews87]

We'll apply diversity and you will have your answer.

What would your approach be? Seems u have lots of knowledge

 

[MDJ]

Having a quick discussion in work with regards to sizing the main incomer of a three phase dis board. Can someone please tell me how the correct way to size the main incomer of a three phase board or single phase for that matter

Cheers

Folks

Don,t exceed the rating of the actual distribution board, in other words if the db is 100 amp rated then that's the maximum switch rating, if you have more load than that then you allow for a larger rated db yes?

 

[nandrews87]

3ph is no different from 1ph (you weigh up the loading on each phase)- your front end device should be rated for the load of the DB and Protected against overload of the supply cable, sorry but Im not really following what your asking exactly.

Are you asking how to determine loading of 3ph equipment like motors etc or how to balance loads .... hence more info i requested. Your question is too wide field to answer.

I am aware its not giving alot of info, Basically question is from an assignment giving to a lad I work with. Info giving is KW rating of 3 circuits, then asked to size sub circuit protection which is not an issue, also asked to size main incoming device and explain reasons why, thats where I feel more info is required.

 

[MDJ]

Is the lad you work with yanking your chain a bit ?

 

[Plonker 3]

Well you know the size of loads being connected to the DB, so your OCPD has to exceed them after diversity has been applied. Use the guides in the OSG for more info. Then simply use the equivalent or next size up main switch for the DB, not that difficult is it?

 

[Darkwood]

Thanks for educating me - 'Clearly, this is commercial or Industrial as its a 3ph board' .... don't get me wrong here we are the experienced educated members here.

Three phase boards thus supplies are found in domestic too ive done several over the years, we are trying to help you here so try not be so quick to denounce a question you are asked it was relevant to your query... on that note im out of here! Happy Learning.