Is there a safe connector for these limit switches?

[Plugger]

Hi,

Anybody know what kind of connector I might be able to plug right to these? I was originally going to solder a cable to them for 5VDC, but my electrical plans changed. Now, I might consider 120VAC to trip the main contactor coil and that means no soldering on the connections. They're rated at 5A, 250VAC. It seems too dangerous and that I might have to buy a different style.

These are .78 inches long.

Thanks!

[Al_The_Man]

Why would you consider solder unsafe? Unless you mean they have no protection.
Why not use them in a low voltage E-stop string or whatever they are controlling and use a small multi-contact control relay at the end of the string.
This relay could in turn open any contactor or power relay and also have an input to Mach or whatever controller to indicate an E-stop has occurred?
Al.

[Plugger]

Thanks Al!

Would you or anyone happen to know if those limit switches are acceptable according to NFPA79? It seemed to say they are acceptable if enclosed to protect from contamination and also from accidental operator tripping.

Also, I thought solder was generally not used for voltages above about 60VAC, 50VDC since NFPA79 mentioned not using solder inside the electrical enclosure. I reasoned that it would be generally good practice elsewhere too. I guess you have a good point; it has to get above 400 degrees F to melt most solders.

Good idea about the low-voltage control relay. My original goal was to put the limit swithes in series with the contactor coil to avoid an interposing relay. I was trying to make it as failsafe as possible. I guess I don't need too go that far though.

Thanks again!!

[Al_The_Man]

I have an older edition of NFPA79 but mine does not mention a voltage restriction in soldered connections?
Usually the recommendation for voltage is as long as the device is properly rated then the only other concern is to correct insulation for safety purposes.
Personally for out on the machine control circuitry my preference is low voltage.
Al.

[underthetire]

They did change nfpa rules last year for some of that. Think 40 volts and less, but must be covered even at 24 to prevent accidental contact. I try to never run anything over 24 volts for any logic circuit.

[neilw20]

I believe the solder consideration stems from the fact that when a multistranded flexible wire is soldered, at the junction where the solder stops and the strands can flex,
unless they are 100% supported they will fatigue and break at the solder/wire point -given repeated movement or vibration.

All wires, if soldered, should be mechanically stable before they are soldered.

The relay you show has posts, and the wire should be wrapped around the post before soldering.

The aim here, is that if there is excess heat -- maybe the contact burns internally, even if the solder melts the wire cant fall off.

[Plugger]

Great discussion guys! I really appreciate your input! I’ll try 5VDC shielded cables for my limit switches.

Al – I think you are correct!
Underthetire - I don’t remember seeing 40 volts mentioned, but it does make good sense.
NeilW20 – Very good point!!

In case anyone does not know, NFPA 79 is free at NFPA if you give them your e-mail, or it’s $43 to buy.


The following may clarify my prior comments a bit:

More than once, NFPA 79 mentioned voltages above 50VAC or 60VDC and then it went on to make some kind of criteria that “shall” be met. I concluded that I would follow the safest practices with any voltage approaching these values.


Clarification about soldering:

I believe NFPA 79 is referring to wiring practices inside the electrical enclosure that are for power and control and especially above 50VAC or 60VDC when it states the following:

“Soldered connections shall only be permitted where terminals are provided that are identified for soldering.” NFPA 79 - 13.1.1.5

“Means of retaining conductor strands shall be provided when terminating conductors at devices or terminals that are not equipped with this facility. Solder shall not be used for that purpose.” NFPA 79 – 13.1.1.8

I don’t find voltages explicitly stated in relation to these two criteria. So, I prefer not to use solder for 120VAC connections, but 5-24VDC seems obviously acceptable to me. I do not remember seeing solder mentioned elsewhere in NFPA 79.