Safety Relay Help

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CEDEng

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Can anyone point me at a reliable source that shows a safety relay NOT using the external K1/k2 and monitoring?

If the load is not great - a few amps or less - there is no reason to include these parts, and the safety relay itself is self-monitoring...why complicate things?

This is entirely "legal" and within the capabilities of these devices - I don't know why it's not more often shown.

Anyway - I need a piece of info as ammo - no one here believes me and I can't find a source. Ordinarily, that's because I'm wrong, but this time, I'm not.

Probably.
 
CEDEng said:
Can anyone point me at a reliable source that shows a safety relay NOT using the external K1/k2 and monitoring?

If the load is not great - a few amps or less - there is no reason to include these parts, and the safety relay itself is self-monitoring...why complicate things?

This is entirely "legal" and within the capabilities of these devices - I don't know why it's not more often shown.

Anyway - I need a piece of info as ammo - no one here believes me and I can't find a source. Ordinarily, that's because I'm wrong, but this time, I'm not.

Probably.
Click to expand...

Well, for one, you cannot use a safety relay AS a load switching device, it is not rated for that. A Safety Relay is the control circuit interface interface TO a load switching device. So with that being the case, what ARE you going to be controlling if not a load?

Can you describe your application? Sounds like maybe you are a little confused about what a Safety Relay is and what it is for.
 
Jraef said:
Well, for one, you cannot use a safety relay AS a load switching device, it is not rated for that. A Safety Relay is the control circuit interface interface TO a load switching device. So with that being the case, what ARE you going to be controlling if not a load?

Can you describe your application? Sounds like maybe you are a little confused about what a Safety Relay is and what it is for.
Click to expand...

where does it say that in the instructions?

the output ratings tend to be pretty low on safety relays so whatever loads are switched would need to be relatively light.

in any case, I have seen AB safety relay diagrams showing them switching loads like solenoid valves.
 
Presumably the safety relay can handle the load of any external contactor coil, right? So if my load is less than that, it doesn't seem sensible to add complexity.

In this case, for instance, it's just serving as the interlock relay on a power supply. Practically no current, and low voltage.
 
The inclusion of K1/K2 into the discussion implied moving machinery, which is what Safety Relays are all about. If there is none, and the load is below the ratings of the contacts, I suppose it's fine. But a Safety Relay ahead of a power supply? That's kind of odd but if you are using it as part of an Emergency Shut Down procedure that requires removal of ALL energy sources, I suppose so. If that's the case however, why not kill the control power to the entire panel with a Safety Contactor?

The reason is, one aspect of this that might be troublesome is that a Safety Relay is really about the safety LOGIC, the checks and double checks necessary for the entire SYSTEM to meet the necessary safety categories. One of those logic checks is that the relay has a feedback circuit FROM a contactor, so the Safety Relay can tell IF the contactor changed state when told to. What kind of feedback can it get from the power supply? I'm not saying it couldn't work, it's just not something I've ever seen implemented and I don't know how it would.
 
I have to respectfully disagree with motion and motors sentiment.

For instance, if you work with laser marking or welding equipment, a safety relay is required to monitor all the (movable) guarding and so forth before the laser can operate.

If you do high-voltage destructive or impulse testing, a safety relay can be required to monitor your safety gates and fences, and prevent operation if violated.

And if you're using a solid state power supply to test things on a small table behind a light curtain, then the light curtain may use a safety relay to keep things ...safe.

There are endless instances of applications that require or could benefit from a safety relay that are not moving parts.

So imagine that the laser power supply has two safety interlocks built in. These interlocks must be shorted together, or the thing won't work. Using the safety relay contacts directly to tie those locks together is completely OK. The safety relay itself serves as the monitoring device - if its own contacts weld shut (they are in series internally, two per channel typically), then it won't allow a reset. Those external K1/K2 aren't needed until your load exceeds the contact rating (4 amps is typical).
 
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