DOL starter and switches

[munga42]

your input and help is greatly received geoffa!

 

[geoffa]

there's no need to be like that munga42.
the reason i deleted the post was because i had spent a considerable time describing to you exactly how to wire the system up and what additional equipment you would need for the system to operate as you wish.
To write all that was taking a long time and as i was 3/4 of the way through it i pressed the save button accidentally.
I didn't have the time then to edit it without the post being read and it was incorrect as it was and would've been confusing or just obviously wrong depending on who was reading it.
So i decided it was better to delete it save it edit it and re-post when i had time.
If i had a way of drawing the circuit for you to see i would do that as it would be quicker.
What i will say is that i believe you need 2 float switches both having N/O and N/C contacts to gain control over the solenoid switching on and off to re-fill and the pump switching off and on as necessary. you will also need an additional relay to operate the solenoid.
Supply phase conductor connects to the N/C contacts on the stop button, overload, pressure switch and Low level float switch connect in series prior to the start button, retaining contact of the contactor, and the N/O contact of the High level float switch which all connect in parallel and feed the coil of the contactor.
Supply phase conductor connects to the N/C contact of the High level float switch then to the N/O contact of the Low level float switch and the N/O retaining contact of the control relay which are both connected in parallel which then feeds the coil of the control relay and and the coil of the solenoid.
Supply phase conductor connects to L1 of the contactor through the overload to the T1 terminal then back to the L2 terminal through the overload to the T2 terminal then to the pump. N conductor connects to L3 through the overload to T3 terminal and to the pump.
Reason for looping the L through the contactor twice is to get balanced current flowing through all 3 overload elements.

 

[silva.foxx]

Helpful post by Geoffa... diagram to supplement.

(disclaimer: not the finished article as to what Geoffa stated, but offers some visual)

.

 

[geoffa]

agree silva what you've represented so far is the same as i described. The only bit i find a bit confusing are the states of the float switches and that maybe it would've been better to show them assuming the water was midway in the tank so the Low level float would be shown as a N/C contact and the High level float shown as a N/O contact as they would be in reality.
If i had a scanner i'd attach the ladder diagram i've drawn for the control circuit. Can't afford the time to draw it with CAD.

The only problems i can see with the circuit i described is that the pump will not re-start until the tank is recognised as being full, this can be overcome by including a timer contact in parallel with the start button. (whether this would be necessary would depend on the output from the pump compared to the input of water through the solenoid valve and user preference. If the fill rate was greater than the drain rate then a timer contact would be ok to parallel across the Low level float contact and start button combined for the duration that Low level float took to return back to the N/C state)

The other problem is that if the tank was full and the pump was running it wouldn't be possible to switch the pump off until the High level float had dropped so that the contact in parallel with the start button had returned to the N/O state. There would be no way of dropping the retainer out otherwise.
The way around this is to have a D.O.L. starter with a twist to release mechanism, essentially an emergency stop button.

 

[geoffa]

it would be far better to abandon the D.O.L. starter altogether and build a small control panel for the job as there are other control components required.
That way it would be possible to have a control contactor operated in a D.O.L configuration which would then supply power to the circuit you have drawn so far.
It's far from ideal having a pump automatically starting up as soon as an emergency button is released.
A start button should be pressed to begin any control system from a safety point of view.
Maybe there's a simpler way to get the desired result.

 

[geoffa]

i'm interested to know munga42, if you are a qualified electrician, a plumber or a diy'er.
you didn't answer the question i posted in reply to your original post, and seem very defensive and attacking in response.
my point was that you are asking people how to do something which appears to be putting you out of your depth with capability, so, as i said before maybe it would be better / safer for you and anyone else in the environment of your proposed system, (assuming it's for personal use rather than a client as it sounded) to employ somebody who knows what they are doing to handle the elecrtrical control side.
i think that's a fair comment.

regardless of your apparent irritation with being suggested of this, i have spent some considerable time helping you although i doubt it will be understandable to you.

 

[munga42]

Geoffa, forgive me for sounding a bit off as your first 2 posts seemed a bit off. Apologies and i'm grateful for your input and thought in to my system.
You are correct that im not an electrician but I have done many different projects which I have been more than capable of carrying out with no issues. This is a more complex situation hence coming on this forum for expert advice. The advice I have had so far is invaluable! When it comes to wiring the system up I will probably ask a competent electrician to do the install. As this forum has shown me, everyone has a slightly different opinion on the setup. Thanks again. Jim

 

[geoffa]

no prob's
geoff

 

[geoffa]

Also munga42,
you say the overload is rated 17-25A
I suspect the motor on the pump is only a few Amps, so if i'm right that would need to be changed.
It's good practice to have a separate fuse for the power circuit and another fuse for the control circuit; as different currents are likely to be used. It would be better to have an anti-surge fuse protecting the motor, wheras a quick blow fuse for the control circuit would be safer.

 

[munga42]

the pump motor is 3kw with max 17 amps, I was told by an electrician to look for a contactor with a 17 to 25 amp rated overload.

 

[geoffa]

that be right then. big pump
definetly need separate protection for power and control to prevent fire in control panel e.g. coil on contactor overheating.