Machine Safety Circuit: Fuse Integration Query

[DSS139]

Hello Everyone,

I have a technical question that I hope someone can help clarify.

We're currently facing an odd issue with a machine equipped with a safety relay and interlocks. The interlocks have been failing, seemingly due to an unstable or 'dirty' power supply. While the ideal solution would be to improve the power supply quality, I'd like to explore an alternative interim solution: integrating a fuse into the circuit.

This fuse would be placed in line with the interlock, between the power supply and the interlock itself. I believe this could potentially prevent the interlocks from failing and could be a more cost-effective and simpler fix than frequent interlock replacements.

I've reviewed the following standards:

• BS EN ISO 13849-1-2015
• BS EN 60204-1-2018
• BS EN ISO 13850-2015

None of these standards seem to explicitly state that including a fuse into the safety circuit would be problematic, given that the circuit already has a safety relay and interlock.

The only foreseeable downside would be the inconvenience of replacing the fuse every time this issue arises. However, this still seems to be a lesser burden than replacing the interlocks themselves.

I appreciate any insights or experiences you can share on this proposed solution. Are there any potential issues I may have overlooked, or any alternative solutions you can suggest?

Thank you

 

[James]

Not really enough info to go on but, interlock switches rarely fail due to a power supply issue.
a short circuit on the control circuit could overload the rating of the switch, generally speaking, the control circuit would normally be protected by a fuse or circuit breaker anyway.
can you post a wiring diagram?

 

[Lucien Nunes]

In what way are these devices failing? What is the source of power that is thought to be 'dirty' and in what way? I find it hard to imagine that a fuse will prevent damage, other than perhaps preventing failure due to VDRs that are breaking over on transients and then destroying the module.

 

[Marvo]

As above, I'd be interested to know more about the nature of the failures and why you conclude that the power supply is at fault and why additional fusing could be an effective remedy.