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https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl DIY Forum >> Electrical Questions >> 415v 3 phase motor starter https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1238792883 Message started by lozz on Apr 3^rd, 2009, 10:08pm

Title: 415v 3 phase motor starter
Post by lozz on Apr 3^rd, 2009, 10:08pm

i have a 415v jetwash wired into a dol starter box with a contactor and overload, i have a automatic pressure cut off valve which i need to wire in, the pressure switch has 3 wires red, blue, and brown ive been told by someone one is norm open, norm closed, and line. i was told to break the coil with the pressure switch, then told by somone else to wire the pressure switch in parallel with the on switch im not sure witch one to go by any help appreciated

Title: Re: 415v 3 phase motor starter
Post by Zambezi on Apr 3^rd, 2009, 11:42pm

I would say you want the pressure switch to kill the control circuit when it reaches a certain pressure. You would wire the normally closed and line wires of the pressure switch in series with the coil (control) circuit, so when the pressure gets too high the normally closed becomes open thus killing the power to the coil.

I will probably read this in the morning and wonder what I was trying to say, it is too late and I need to sleep...........

Title: Re: 415v 3 phase motor starter
Post by lozz on Apr 4^th, 2009, 12:08am

lol, if the control cut the power to the coil would the starter box need switching back on?

Title: Re: 415v 3 phase motor starter
Post by Y3 on Apr 4^th, 2009, 8:33am

You would have to manually switch it back on, thats the feature of a DOL starter.

Title: Re: 415v 3 phase motor starter
Post by Lectrician on Apr 4^th, 2009, 9:42am

What is the pressure switch actually doing?

You do say it is a 'cut off' pressure switch so I assuming that it is going to turn the compressor off when the hose or jet is closed and pressure rises. When a hose or jet is opened you want the compressor to run again.

You would be better with a 'plain boxed' DOL starter for this. One with no red/green buttons. You would then not wire a green start switch, and connect the pressure switch as a stop switch. The DOL starter should be set to the current of the compressor. If ever the pressure switch fails, the motor will labour when the presure gets too high and the overload will operate.

This DOL control starter would be best supplied via a second contactor which has a red/green stop/start and also some extra em stops dotted around if required.

Title: Re: 415v 3 phase motor starter
Post by Zambezi on Apr 4^th, 2009, 10:50am

wrote on Apr 4^th, 2009, 12:08am:

lol, if the control cut the power to the coil would the starter box need switching back on?

Yes, you would have to push start again. It would work similar to an emergency stop button.
As Lec said what is the purpose of the pressure switch? There will be different ways of wiring it depending on what the switch is supposed to do.