Wiring Color

Hello Gents,
Just a quick one ....what is the fixed mains 230v ac wire color for a panel. What is the mains control color for 230V AC in new zealand.

Thanks

Star Point

Hello Gents

I just finished a job on a ship.....I got involved with the generators and an interesting observation was made. There is no neutral on the generator...this is due to a chemical/electrical action (electrolysis).

I was discussing this with one of the ships engineers and he was telling me that this is maritime law and aluminium ships will corrode within 2 years if there is a neutral to the deck but steel ships are OK.

Does anybody care to comment?

Regards
Carl

Inrush Current

Hello Gents,
I’m at a stage of developing the circuit art work for an AC squirrel cage motor. I’ve just noticed that I have no inrush limiter.
The route I’ve chose is a resistor in parallel with a normally open relay.

1 I have 3x 450v 330uF Capacitors in parallel for the bus
2 I’m targeting a 1Kw three phase 220v star connected motor
3 I have a single phase input with a 10A fuse.
4 I’m going to be monitoring the bus voltage via a resistor voltage divide network.
5 Can’t remember the input bridge rating, but have an idea its about 15 amps

My concern at the moment is the actual resistance value and wattage rating of the inrush resistor. I don’t want to stress the bridge and obviously I don’t want to be blowing fuses. I plan to switch the bypass relay on with a uProcessor after the bus voltage has reached a value of ??

I’m not concerned about the target motor size at this point; I just want to see the thing come alive. I’ll most likely load it up with some light bulbs.

q/ what should the resistor be rated at?
q/ what would the be the voltage point to switch the bypass relay in ?
q/ Is there anything wrong with this design approach
q/ Are there any other point that I should be considering.

Thanks in advance

Rotor time constant

hello Forum

Q/ What is the realtionship between the rotor time constant and the pwm switching frequency. Is there a point where an increase in the carrier frequency has no point. For some reason the figure of 8 switching points comes to mind??
I realise there is a limit to the power device frequency as every switched edge causes heat.
I also appreciate that there is an audio content at lower switching frequencies
The assumption is the higher the carrier frequency the better the AC "form" of the current wave............but is this correct when it comes to motors??

Capacitor inrush

Hello

I’m looking at limiting the inrush current for the dc bus in a bank of capacitors on an inverter.
The methods that I’m aware of are resistor and contactor
Solid state control of the bridge rectifier.
There is another one and that is using a ntc this method I find interesting it looks cheap to and it seems simple….does it work on the principle of having a high resistance on inrush and a low resistance on running current……seems to good to be true.
If it’s that simple why bother with all the other methods??