From time to time, some of you describe yourselves as “Jobbing Electricians” or “Jobbing Engineers”. Does this mean that you are self-employed and move across the US from project to project? It is a job title that has not crossed the Atlantic.
I am replacing three wye/delta 30kW motor starters. The existing starters are closed transition with a small resistor bank. The client wants to take out the the resistor bank because it frequently burns out and repairs are difficult and expensive. What are the implications of fitting an open...
I have an electric motor of European manufacture with 6 leads coloured, yellow, brown, green, black, blue and white.
The green wire is not earth, there is a green/yellow wire which is connected to the frame of the motor.
The motor is dual voltage, 230 or 380V depending upon if it connected in...
I am to build a small electrical control panel which is to use a 230 volt control circuit supply. The incoming supply is a 480 volt: 3 phase 60 Hz: three wire system (no neutral). I have proposed a double wound transformer: 480/230 volt for the control circuit and other small single phase...
I recently went to witness the testing of a small electrical control panel on behalf of one of my clients. The control panel contained a small electronic temperature controller, two MCBs, a contactor and thermal overload relay and 4 plug-in relays. The specification called for the insulation to...
I have a project to build a control panel for a ship. The incoming supply is 440 V: 3 phase: 3 wire: 60Hz. I need a 220 volt supply for the control circuit and some little single phase motors and other small single phase loads. I shall fit a double wound transformer to obtain the 220 volt...
I design and build electrical control panels for refrigeration systems. Very often the refrigeration compressor has a part wind start using two star connected, electrically separate windings. Each winding carries about 50% of the total running current of the compressor. One winding is energised...
In air conditioning systems there are small motors opening and closing water valves, dampers etc.. These motors often have a permanent 24 volt AC supply and a variable 0 - 10 volt DC supply. By altering the DC supply the motor opens or closes the valve. At 0 volts the valve is closed and at 10...
