Turning High Amp Equipment Using Low Amp?

audiobull · Feb 24, 2014

Hi i am going to install a new air compressor. It suggests installing onto a 30 amp supply. I have a 30 amp supply.

The air compressor will be controlled by a float switch in a water tank which is about 60 meters away. The float switch is only rated at 10-15amp so my question is what can i use to connect the float switch to the compressor to turn it on and off?

Is there a contactor or a starter of some sort that i can wire in line for this?

The float switch is only a 2 wire switch so i think it used in line of the live wire. live goes in, through the float and back out to turn whatever on and off. Sorry if i have missed anything out.

SLIPSHOD & SLAPDASH · Feb 24, 2014

A contactor would be used here. This would be fixed near the compressor with a smaller cable running to the switch. Have you checked the spec for the compressor , they have high start up current but drop to lower when running. You probably need a C curve breaker and an additonal smaller fuse/breaker for the control wiring. What is this project.

audiobull · Feb 24, 2014

thanks for the fast reply. I install well and borehole pumps but sometimes the well or borehole have very high iron or sand content so normal metal submersible pumps fail very quickly.

I have started using a new air driven pump with 1 moving part inside called a brumby pump. all plastic so does not corrode. Usually i only use a small compressor on a timer but this one requires a larger compressor and fills a large tank for irrigation.

From what i remember it is a 14amp motor.

There is already a motor rated fuse installed and there is a 16amp standard fuse spur. Can i use the 16amp for the control?

Is there a specific contactor i need to get for this? I do not usually do the electrical side but as the breakers and fuse spurs/rotary isolators are already there all i need to do is wire into them plus it gives me a little more experience.

NozSpark · Feb 24, 2014

Given your situation, that you are doing this as a business and that you admit that you are unsure as to what you'd be doing, then I'd get someone in to do the elrctrical side as you have a duty to ensure that this is done safely and I doubt that you have the equipment to test your work

ProDave · Feb 24, 2014

If you just turn the power on and off, there will be a delay as the compressor builds up to pressure, and when you turn it off, there will be a delay as the pressure runs down. not very elegant. then there's the issue of the stop start circuit, a non starter (literally) if the compressor has a no volt release.

So Is this a better suggestion:

Leave the compressor on all the time. It's own controls will stop it when it gets up to pressure.

Use your flow switch to turn on a solenoid air valve, to supply air to the pump only when the flow switch calls for it.

Simple and elegant.

audiobull · Feb 24, 2014

Prodave. you are an absolute legend. That is soo simple and elegant like your good self. Why did i not think of that! That has just saved a few £££ and a hell of a lot of hassle too.

a solinoid valve costs £30 and i work with them a lot of the time.