Breaker type

[wade88]

Hi guys,

Just had a bit of a tidy up at work regarding the circuitry of a few bits and bobs.

I have recently just put in a new TPN 6 way and want to move one of the machines on to this board and take it off the current tp&n switch fuse. Each phase is currently protected by a BS88 32amp 80KA 415v fuse and the machine in question is run with (now this is where the issue is) what ibelieve to be an 11kw motor. Ohm's law calcs suggest to me it is 11kw not the 14kw it was also suggest it might have been but due to the protective device ratings it has operated on all this time [as 11kw @ 415v would be drawing 26amps pp] i believe it to be 11kw. There is no spec plate so i cant even denote it from any given HP values.

But going on the knowledge it is drawing 26amps or there abouts, a type C 32amp would suffice correct.

Cable supplying feed is 6mm 4 core SWA, new sub board [lets call it DB2 for now] is fed with 10mm 4 core SWA and protected with a type D 63A at the main board DB1

Ben

 

[wade88]

I have also told a lie - The motor will not be removed from the switched fuse i plan to leave it on that switch, but connect the switch to the new board.

This is somewhat irrelevant as it will not affect the rating of the PD at the board any differently so same question applies

 

[Knobhead]

What was the original protection to the switch fuse?
I don’t agree with protective devices in series, the protection should be at the source. My normal practice would be to remove the fuses and fit copper links.

I’m curious how your working out the rating of the motor, you say it’s supposed to be 14KW, but you get 11 KW.

 

[johnboy6083]

i agree with tony. Also your MCB's will not discriminate on short circuit, so any machines fed from the same protective device anywhere along the chain could be lost in the event of a fault. Fuses do discriminat between other fuses and MCB's. A rule of thumb is that the downstream device should be half the value of the upstream device, but im aware that the ratio is 1.6 to be more accurate. So a 160 A fuse can feed a 100A fuse, and it will discriminate on overload and short circuit.

 

[Wazzajnr]

The fuses are only protecting the cables anyhow, not the motor so the fuse size should be sized to protect the cable

 

[plugsandsparks]

Couple of things that might help.
Are the fuses motor rated,someone may be able to compare the fuse type to the breaker, but if motor rated i would have put in a D breaker but actually have never compared graphs.
Also does the motor have to start on full load or is it lightly loaded against its actually capacity.
Have you managed to clamp it to see what you get when its supposed to be working hard.
hope this helps

 

[wade88]

No the motor is 11kw - But that is information that has been handed down to me through a third party but i have no actual proof of this.

The MCB at DB1 is a 63amp type D, but i am removing this and changing it for 63amp type B and feeding a sub board from this MCB. Within DB1 there are no other circuits.

From this type B i am feeding a new TPN board i installed yesterday with a piece of 10mm 4 core SWA and using this new board to supply the motor in question. in this new baord [DB2] i have a type C 32 amp which is protecting a 2 meter length of 6mm 4 core SWA which is terminated into a 32amp MEM switch fuse - where the motor is connected. Each phase is protected by a 32amp 80KA 415v rated BS88 fuse.

a further piece of 6mm 4 core then terminates into an 11kw inverter which then finally feeds into the machine.

I shall tajke some photos no and put them up, im making a right pigs ear of explaining this and you will all be scratching your heads cursing away. All i wanted to know is, what is the suitable MCB type to install in the new TPN board downstream of the switch fuse and the inverter.

 

[plugsandsparks]

Ha ha, inverter .... grab the pdf doc from inverter supplier quick...... they tend to be very specific in what protection devices are used both before the inverter and after. You may end up keeping those pesky fuses.... cheers

 

[wade88]

Well im keeping the fuses - in fact thinking about it, im jjust being a total donut, because im not rerally changing anything about this set up at all aside from the fact there use to be two motors that were split from a 63amp switch fuse, down to two seperate 32amp switch fuses - one for each motor. But one has been been taken out of service, so i have removed the 63amp switch, and the obsolete 32amp switch and now just have the one 32amp switch supply and one motor to run, so i was planning on just running it straight to the board. But i want the switchfuse in as an added means of isolation (as the new TPN board is in the adjacent warehouse seperated by a foot of concrete block.

Allow me to take some photos - makes my morning a little less dull that way anyway. :drunk:

 

[wade88]

Ah the photos files are too large

 

[wade88]

apparently not that one however....this is DB1 lol ill try get the rest up hang on

 

[wade88]

how do i compress a file lads? taken the photos on my iphone they are coming out at between 2.3-3 megabytes each but this file size is too large for the up loader on here so how can i compress it to get it uploaded?

 

[plugsandsparks]

It may help to just think about the inverter, this is what you are supplying. The inverter generally has lots of protection for the motor and cable between. Did a 11KW ABB inverter a few weeks ago and used 25A general purpose fuses for the supply to the inverter.

 

[wade88]

My problems are a little more severe now it would appear. Just went to fire the board up and see where i was at, and the RCCB just blew and showered sparks everywhere......absolutely no idea why. Please someone correct me where i may have gone wrong here.

new TPN board supplied with 4 core 10mm SWA approx 15 meter run from main supply board. 100A 100MA RCCB incomer kit. All terminations are correct, Neutral is linked, board is earthed, cabled is earthed. lives are all correct. im stumped

 

[wade88]

False alarm - found the fault.

 

[Knobhead]

Don’t keep us in suspense, what was it?

That does seem a big board to feed off a 63A way. You’ll soon be asked for other supplies off it. It’s one thing I always found, no matter how big the board is it will always be to small a couple of years down the line.

 

[wade88]

Im a little embarrassed Tony to be honest im not sure i want to explain in detail what had happened....its all fine now though, no need for concern :blush5:

Well it was only intended to feed this mixer at circa 26 amps, then a 3p+e socket ring in an adjacent room - these sockets will only be powering a labelling machine and a lazy susan turn table so minimal draw.

 

[plugsandsparks]

Ha, he who never makes mistakes , never does anything etc etc.

I am sure you are in good company, wasn't that black wire again was it...lol

 

[wade88]

Ha, he who never makes mistakes , never does anything etc etc.

I am sure you are in good company, wasn't that black wire again was it...lol

.......oh no, you haven't been reading past posts of mine have you....

 

[plugsandsparks]

No believe it or not my brother and i, who started out in the 80s, were just talking about colours and has it been a good thing going for the new colour scheme. When you spend all week / month working on RYB and Bl and then suddenly you get a job and its BrBlGr and Blue - one little slip with the old brain and it all goes pear shaped.......tee hee