Direct online starter with overload wiring help

[moosey86]

Hi guys, I was looking for a bit of help on wiring up a direct online starter with overload and stop start for an ancient bandsaw located in a workshop I'm working in. The band saw has a really old overload contactor intergrated into it. Basically the usuall 3 phases in and 3 phases out, but it also has door switches to shut down the machine when they are not closed.

The way it's currently wired is that the out going wire of the first door switch is connected to a rusty old terminal on the existing overload, goes up to the switch, comes back down and is linked to the outgoing wire of the second door switch, goes up to the switch, then comes back down and is connected into another rusty old terminal on the overload.

How do I implement this into the new direct online starter I have?

L1 is prewired to A1

L3 has a prewire long enough to go into NO contacts 98, 97 or NC contacts 95, 96

From there there is a prewire going into NO 14 of the contactor

Out of there into the start switch

Out the other side of the start switch into NO 13 of the contactor

And out of there into A2 effectively energising the contactor.


I can see that I could break into that sequence with the door switches either before or after the overload but I didn't know whether this was the 'right' way of doing it? If it's not then I'd appreciate some guidance on how to go about it properly.


Cheers guys

 

[Knobhead]

Break in to whatever line the stop P/B is in.

 

[BlueToBits]

Each door contact (stop switch) should be wired in series with the overload relay NC contacts, stop button (NC) and the start button (NO). This 'loop' should be wired between L2 and A2 with the contactor aux NO contacts wired in parallel with the start button. In practical terms additional connectors or free terminals may be required inside the contactor enclosure marked by the 2 black rectangles on the sketch. Only the control wiring is shown. I hope I haven't made any errors. I'm sure someone will point out if I have.

 

[moosey86]

View attachment 16178
Each door contact (stop switch) should be wired in series with the overload relay NC contacts, stop button (NC) and the start button (NO). This 'loop' should be wired between L2 and A2 with the contactor aux NO contacts wired in parallel with the start button. In practical terms additional connectors or free terminals may be required inside the contactor enclosure marked by the 2 black rectangles on the sketch. Only the control wiring is shown. I hope I haven't made any errors. I'm sure someone will point out if I have.

Ok thanks very much that explains how to wire it but why did the on line starter come pre-wired in reverse to that diagram? Does it not matter? By reverse if you just swap A2 and L3 around on the diagram this is what I mean.

Cheers

 

[mr murdock]

I was sent this link resently for a job - if it helps?

 

[BlueToBits]

OK. You need to be happy you have got your head around this before powering up, but it's just a simple switch circuit at the end of the day.

If you follow the circuit round, A2 is connected to L3 via the switches. That is exactly the same as connecting L3 to A2 via the switches. It's really that simple. The factory fitted links are probably confusing the situation. It doesn't matter which order the switches are in. They just need to break the circuit to the contactor coil. It may be convenient for the manufacturer to pre-wire one particular way, and that's the only reason it may be done like that. There are many different applications for these devices, all require different wiring. You will probably want to come to your own decision about which is best for you. They almost certainly won't come pre-wired for external stop buttons anyhow.

Just to be 100% clear, and this is simple stuff. There's nothing hidden or complicated about it. I'm sure you already know it.

• L1 L2 and L3 and the 3 incoming phases (no neutral)
• There is 400V between any 2 of these 3 incoming phases
• It is convenient to use L1 and L3 in this example but we could get our 400 volts from L1 & L2 or L2 & L3
• A1 and A2 are the connections to each end of the electromagnet coil that pulls in the main contactor.
• The contactor coil is rated at 400v
• The coil is not polarised and can be connected either way round.
• The motor will not be reversed by swapping wires to A1 and A2, or the OUTGOING wires from L1 & L3 but will be reversed by changing the INCOMING wires to L1 and L3.
• Connecting any 2 of our incoming phases across the coil will energise the coil and pull in the contactor.
• Connecting any of our switches directly across L1 and L3 will cause a bang, damage and possible injury.

So in this example we are connecting L1 directly to A1 with nothing else. This way we can't make a mistake and connect anything directly across our incoming supply. We are left with L3 & A2 which we will connect together through our switches. You could think of this as L1 to A1 is our 'neutral' and L3 - A2 is our 'live'.

Ignoring the start button for the moment, some of our switches are normally open, some are normally closed. Because they are all in series they behave like a single switch. If any one of them is open the single switch effect is OFF. If they are all closed the single switch effect is ON. So if the motor overloads, a door is opened, or the stop button is pressed the circuit is broken and the motor stops and won't re-start until the issue is rectified.

One of these switches is the auxiliary contact on the contactor. When the contactor is NOT energised the auxiliary switch is off. This means that the motor can never start because the contactor coil can not be energised as this switch is always open when the contactor at rest (off). To energise the contactor we need to temporarily short out this auxiliary switch. We do this by bridging a push 'start' button across this switch. When all the other switches are closed, this allows power to the coil which brings in the contactor. Once the contactor is in, we can let go of the start button as the auxiliary switch is now closed. Of course, all the doors will have to be closed first, the overload relay will need to be set and the stop button released before this can happen.

To add to an already lengthy post:
The overload relay rating and setting is important. It should allow enough current to keep the motor running under full load conditions, but be able to break the current if the motor is overloaded to prevent it overheating, burning out and preventing mechanical damage to whatever it is turning. The setting needs to be the same as the manufacturer's data full load current for the motor, or some other point that will prevent damage to the equipment the motor is turning. You will also need to decide if you want the overload relay to automatically re-set itself after tripping off, or if it should require someone (skilled, authorised, key-holder etc) to manually re-set the relay following an overload incident. I would say that 90% of burned out motors and a lot of damaged machinery can be attributed to incorrectly set overload relays.

I hope that explains it.

 

[BlueToBits]

I was sent this link resently for a job - if it helps?

Use Diagram 2 (I assume 3 phase 400v)
Paragraph 2 : Three Phase supply 415 Volt Coil - see wiring diagram .The following links are pre-fitted to the starter; 13 - 17 with a flying lead to be connected to Overload terminal 95; A2 - 14 - 18; Contactor terminal 1 - A1; Contactor terminal 5 via flying lead to Overload terminal 96. All other control and power connections have to be made by the installer.

SO: I would do it like this:
Leave the pre-fitted links as they are. Connect one external switch between 95 and 13.
connect the other external switch between 5 and 96.
This way, no internal connector is necessary, all the switches are in series. Note that the wires crossing above A1 in the diagram are not connected.
Robert is your aunt's husband.

 

[clematis432]

Cracking post from bluetobits, very knowledgeable and explained well. Only thing I could maybe add is that in 240V coil circuits (rather than your 400V one) the o/l contact normally came first in circuit from the live side, maybe reasoning for that was that if the o/l tripped, there would be no voltage to any interlocks or control gear. Maybe that was in your thinking ?

 

[moosey86]

Bluetobits that was awesome, it's exactly what I was looking for. I'd of been able to do it with minimal guidance and get it working but I prefer to actually know why it's working not just be glad that it did. It's so simple now you explain it like that