Please help me out with a wiring issue

[Jeff7]

Really, no lawsuits.

Backstory: I was presented with an old press-brake with a servo-controlled backstop, the latter of which was acting up by rapidly ramming itself into the rear of the pressing die. This apparently happened repeatedly throughout the life of the backstop mechanism, which was designed in the late 70s. This had been tripping a breaker, but it was finally too much, and some circuitry blew out.

I have repaired the circuitry, but a switch anomaly caused the servo to again misbehave, though it did no damage. The switch anomaly likely resulted from the door switch on the "enclosed box" (where all the electronics are housed) being rapidly cycled on and off, when the door partly opened up.

The servomotor has not acted up since, so I really think that switch issue was the problem. The servo amp is rather simplistic, and likely not good at dealing with such disruptions.

Anyway, I decided that I wanted something more for safety, so I'm installing limit switches which will cut all power if the backstop carriage moves out of range.

Here's a very nicely drawn diagram of what I have in mind.

The question: Should I have the limit switches wired in series with the hot or neutral wire?
The breakers in the electronics box are wired in series with the hot wire, but they're fully enclosed, and thus don't present any risk of operator harm, should they go on the fritz.

The wire to the limit switches would be somewhat more exposed; while not in the way of the operator, it may be accessible to someone doing maintenance.
So would it therefore be better to have the neutral going to the limit switches?



(Dammit Jim, I'm a mechanical engineer, not an electrician!)

 

[iGas]

Limit switch would work on hot or neutral wire. But normally limit switch is on the hot leg to cut off the power completely so that no power exist in the device that being switch off.

 

[boomerang]

IMO you need a relay that breaks the hot if the limit switches trip. A little more wiring involved though.

I have to tell you though that my experience with industrial equipment from an electrical perspective is minimal.

 

[Jeff7]

That did come to mind; I guess my concern is about having a few feet of hot wire "out and about" - they'd be outside of the enclosed electronics box, in what is most definitely a non-standard installation.
These limit switches are to be mounted on small plates I custom designed just this morning, and they then attach to some freshly drilled and tapped holes on the base of the backstop.


I did consider using relays, but yes, that would be more wiring, and these switches were used because they are a standard item, in that they are used in several other pieces of equipment in the workshop, so there were some of them on hand.

 

[boomerang]

Well, there is flexible armored conduit you could use that you could affix to the framework or underpinnings. You'd want to keep it out of harms way to keep it from being damaged. But perhaps you're on a budget?

My thoughts is the life of the limits. Are they rated to handle the current? Regardless, I think best practice dictates that these circuits be isolated from each other.

But I really shouldn't be commenting in the thread. It's not my area of expertise. I'm not being snide with that comment, it's the truth.

 

[Jeff7]

Yes, I am on something of a budget, both money and time. I'd wanted this thing finished yesterday, but then I had the idea of these limit switches, so that added more than a day to design fixturing for them, get the fixturing made (done in-house), and then fuss around with the wiring and limited resources on hand.

The limits are well-equipped. 125VAC load, at 3 amps. The limit switches are rated to 15A.

These are normally-closed switches, and I plan to wire them in series - if either one gets tripped, the circuit is broken, and the electronics shut down.