Square D starter/contacter help needed

[mt92]

I am trying to wire a Hem metal saw that I got in pieces. I have a Square D nema size 1 contacter. The numbers on it are:
Type sc03
form s
series a


The problem is when I energize the 120v coil to start the motor I lose the 120v to my control.
Any help would be appreciated.
Thanks Mike.

[Al_The_Man]

The description of what is happening is too vague, is the contactor staying in but the control voltage disappears?
If so, the control may be going through NC contact on the SqD.
Did you wire it from the original or did you come up with the control circuit? What picks up the contactor?
I would imagine it is a standard push button start across a retaining contact on the SqD and a stop button in series?
Sometimes a trip switch drops out the motor when the saw is down.
More is required and preferably how you wired it.
Al.

[mt92]

The 120v is lost for the control when the blades comes on and then as soon as the blade stops the control voltage is there again. I think that it is the way I have the 120 coil on the starter wired?

[Al_The_Man]

Unfortunately, without detail as to how you wired it it is sheer speculation.
If you can post the wiring connections then maybe help can be offered.
Al.

[One of Many]

Here is a standard 3 wire motor control circuit that should work. The only difference would be the source of power, either direct from L1, L2, N or through a step down control transformer. The contactor itself for the most part makes no difference what it controls, with the exception of ratings and overload protection.

The type of contactor you have should include an auxiliary contact that is NORMALLY OPEN for the latching of the coil across the start button. Another one that is NORMALLY OPEN, but HELD CLOSED by the overload holding mechanism.

What you need to see, is that if any of the contacts that maintain the power to the coil is interrupted, the M1 coil drops out.

Compare this to what you have to see if it makes more sense or resolves your troubles.



DC

[Mike Nash]

Not to be picky, but you're more likely to see it as below, simply because it's easier to tie the aux contact to the coil. In a multi starter situation, you don't have to tie L1 to the starters at all, just the pusbuttons.

And how did you get the thumbnail in your post?

[Al_The_Man]

Control wise, there also could be more going on here, depending on whether it is a simple reciprocating saw or a Hem Vertical band saw, where the contactor control is tied in to other control items.
Also, although for many years the OL has been wired this way, it is now considered safer to wire it in the 'Hot' side of the coil when a grounded neutral exists.
The old way, If a ground occurs between the coil & OL, the OL is defeated.
Al.

[One of Many]

If it weren't for someone being picky, the rest of us would never know how fast posting mis-information can be corrected with better ways(with good reason) to do the same thing. Although I have seen it drawn both ways, I sincerely appreciate the reasoning behind why and how it is done otherwise.

To get an image inside the post. I right click the uploaded image attachment link to get an address. Copy that address, now click the mountain scene icon above this post reply window and paste the copied address into its pop-up address bar.

DC

[Mike Nash]

Thanks DC. I tried that, but it wasn't showing up in the preview for me, so I figured I was doing it wrong.

And I agree Al on the O/L location. I've always hated the neutral side wiring. I wonder where that convention got started?

I've also run into situations where the stop pushbutton was in the seal in around the start pushbutton. This allows the contactor to be pulled in even while the stop is being held! Lawsuit waiting to happen.

[One of Many]

Originally Posted by Mike Nash I've also run into situations where the stop pushbutton was in the seal in around the start pushbutton. This allows the contactor to be pulled in even while the stop is being held! Lawsuit waiting to happen.

The OEM I used to work for did it this way in order to have a jog function. Several other machines I ran in the steel wire industry while in electronics Tech school, had this also. And I cannot tell you how many times the contacts welded on the main motor contactor with no way to shut it off on the operator side. The element of danger is ever present, but certain modes of failure may be unpreventable. Redundant contacts might be a fail safe?

DC

[Mike Nash]

You should look into safety relays and circuits. Dual contactors, in series, force operated contacts, redundant safety checks (that can't simply be duplicates.) It can get crazy.

[Al_The_Man]

Originally Posted by Mike Nash You should look into safety relays and circuits.

They are slowly appearing in N American equipment, Europe has used them extensively for some years now.
I believe Piltz was one of the first producers of safety relays. There is quite a combination available that covers safety and internal controlled shut down timers etc.
Al.