electrical wiring

[teamparel]

Dear Sir,

We have a (difficult to access) underground room where we are planning to install a small ventilation fan (single phase,200 watts).The present electrical load in this room is a three phase pump with its remote starter(DOL) of capacity 3 h.p. three phase.

Now for the new load since it is difficult to lay a new cable(making a peneteration on the concrete wall,waterproofing,right of way, etc..) ,can we wire it on the pump incoming cable??.The scheme will be as follows:

The incoming cable will be routed thro a distribution board having

1. Incoming Isolator where the 3 phase cable from the remote DOL starter will be terminated.

2. After the Isolator the supply scheme will fork into two parts.One part(3 phase) going to a Motor protection breaker(this will provide o/c and s/c protection to the motor),as I will be cancelling the thermal overload in the remote DOL starter.The second part will go to a transformer with 415 volt primary and 230 volt secondary,which will then feed single phase to the ventilation fan in question.

Ofcourse I will be providing dp rccb for fan and fp rccb for pump in the distribution board for earth fault protection.

Is this scheme OK.What will be spec for transformer ,300 va single phase 415 volt (primary) and 230 volt(secondary)- is this ok??

One problem which I can visualise is that the fan will be ON only when pump is running , but I can live with it.!!

 

[jro]

Re: electrical wiring

It seems to me that you are going to spend a lot of money for a fan that only pulls less than 2amps ,assuming the fan is 120v you could tie into an exsisting receptacle circuit, asumming there is 120v inside this room, also some of your terminology is difficult to understand, and please dont use so many abbreviations, as somtimes only the person typing knows what these mean, also include voltages for the equipment that you will be installing, but your question is very intresting to me.

 

[hurk27]

Re: electrical wiring

this sounds like this is being installed in europe and they dont have 120 volts. so an inexpansive transformer could be used 300va is not that much as most power converters that consumers use to convert us appliances to 220v european style are 300 va or more
Ok I went back and reread the post I now see that the fan is 230 volt and I think he wants to tap off a motor starter for a pump thats 415 volts I'm not sure as to why he wants to defeat the motor protection over loads as this does not sound good all you have to do is install a small fusable disconect on the line side of the motor starter and use a fuse close to the rating of the fan. then to a transformer that will drop to 220 volts then to fan?

[ June 08, 2003, 05:02 PM: Message edited by: hurk27 ]

 

[teamparel]

Re: electrical wiring

Dear Friends,
Sorry for using so many abbreviations.Firstly, I will expand the abbreviations:

1) DOL: Direct On Line Starter

2) o/c and s/c : Over current and Short circuit protection.

3) dp rccb : double pole residual current circuit breaker.(similiar to GFCI)

fp rccb : four pole residual current circuit
breaker(similiar to GFCI)

4) Voltages: we do have 415 volts three phase, 50 hertz and 230 volts single phase ,50 hertz power supply.

5) Fan currents: 0.8 amps starting current
: 0.4 amps running current
Fan voltage: 230 volts single phase.

Pump voltage : 415 volts three phase.


Now as Jro had pointed out,we thought about doing the same but alas there being no receptacle didn't work.

Further I need to bypass the thermal overlaod provided in the remote DOL starter of the pump because I am tapping off a supply down stream ie.,after the thermal overload for deriving power for the fan and hence if i retain the thermal over load it is bound to malfunction due to unbalanced loading .

Anyhow I will be providing a additional motor circuit breaker which has over current(adjustable trip setting) and short circuit protection near to the pump after the tap -off.

Please advice regarding the wiring practice in question and the transformer specification.Thanks in advance for all the inputs.

 

[hurk27]

Re: electrical wiring

teamparel
there are some alternatives to this without changing the overloads one is if there is any auxiliary contacts on the load side of the contactor before the ol's this would give you the necessary control for the fan. the other one is what is the coil voltage of this starter if it 230 the extra .80 amps would not hurt a thing. as for the taping off the load side of the o/l's the .4 amps should not ever give you any problems as there is this much and more unbalanced current in a motor to start with and the overloads should have some head room or you would be experiencing premature tripping now the addition should not be a problem. and as for the transformer goes a 100 v/a will work just fine even a 50 v/a would work which is not much more than a furnace transformer.

 

[hbendillo]

Re: electrical wiring

Do you have lighting in the room? How is the lighting powered? Can you tap that circuit for the fan?