3PH MCB's

[Jay]

Hi All,

Can anyone help me out with a problem I have.

I have to install 2 extra 3ph industrial sockets on a circuit which already has 2 existing on it.

The 3ph MCB protecting the existing 2 is rated at 32A so could it hold an additional 2.

The circuit will be protecting / supplying 4 industrial heaters rated at 9kW - is this too much for a 32A MCB.

The main sw. fuse is rated for 125A which supplies 6 single phase MCB's (1x20A, 3x16A, 1X10A, 1x6A) aswell as the 400V socket circuit.

Thank You.

 

[Engineer54]

The circuit will be protecting / supplying 4 industrial heaters rated at 9kW - is this too much for a 32A MCB.

You tell us if a 32A MCB is suitabley sized for a 36KW load ??

 

[Jay]

Obviously not - What shall I do though redesign the incoming power to accomodate this extra load?

 

[Knobhead]

What calculation have you done?

 

[Jay]

Im trying to find out suitable MCB Rating for the additional two 3ph sockets.

The formula that I'm using to calculate the current is - Watts / √3 Line Voltage × cos Power Factor Angle

which gives me 18000/√3 x 400V × 0.95 (guesstimate!!!) = 27A therefore a 32A would suffice but i'm worried about the main sw. fuse

blowing with too much loaded on it.

What do you think?

Thank you for replying

 

[Knobhead]

With heaters there was no need to include PF so it will drop a bit more.

As for the main supply:
The first question is will all the heaters be on at any one time, IE thermostats, etc. If yes you can apply diversity.
(Not that you need to)

 

[Engineer54]

Im trying to find out suitable MCB Rating for the additional two 3ph sockets.

The formula that I'm using to calculate the current is - Watts / √3 Line Voltage × cos Power Factor Angle

which gives me 18000/√3 x 400V × 0.95 (guesstimate!!!) = 27A therefore a 32A would suffice but i'm worried about the main sw. fuse

blowing with too much loaded on it.

What do you think?

Thank you for replying

That's a bit different to asking if 4 X 9KW on a 32A breaker is suitable, ...isn't it?? lol!! So now it's just 2 heaters!!

 

[Jay]

sorry i knew i phrased that wrong just as i sent it.

No there will be 4 heaters in total on the board but i just need to accomodate the extra 2.

Thats why I am asking if you think the Main Sw. Fuse will hold the additional 2.

 

[Engineer54]

Well as the Main Switch is rated at 125A, i don't think you'll have much of a problem there. you haven't exactly got that much else on that DB have you..

 

[Knobhead]

Read what's in the () in #6

 

[Jay]

The main sw. fuse is rated for 125A which supplies 6 single phase MCB's (1x20A, 3x16A, 1X10A, 1x6A) aswell as the 400V socket circuit(32A).

I just dont want to install it and then have to increase cable / mcbs down the line .

What do you think?

 

[Jay]

Tony I dont understand what youre trying to say.

I thought diversity only counts if you dont have everyhting running at the same time.

In my case all circuits will be running continuosly.

 

[Knobhead]

Then you can't apply diversity, but as I put in #6 (Not that you need to).

 

[Jay]

ah ok now i understand.

Do you think I should install an extra circuit though or should I redesign the incoming supply?

 

[Engineer54]

The main sw. fuse is rated for 125A which supplies 6 single phase MCB's (1x20A, 3x16A, 1X10A, 1x6A) aswell as the 400V socket circuit(32A).

I just dont want to install it and then have to increase cable / mcbs down the line .

What do you think?

This is a 3 phase DB, so you have in effect 3 X 125A!! Are you still worried?? ...lol!!

 

[Jay]

Thank You i'm a bit rusty lol

 

[Jay]

Thank You for being so clear... Im a bit rusty LOL...!!!