Trapped Key Isolation Failure

[Shaun_H26]

Hi all.

Can someone point me in the right direction for the current regulations on control panel isolation for machinery (industrial) if possible please?

An issue arose with a machine trapped key system failing, allowing an individual to remove the key, but the machine staying live and running.

It was discovered that the trapped key isolation mechanism had failed allowing it to be turned off for the key to be removed, but not disengaging the electrical breaker mechanism unfortunately.

My concern is that the trapped key system is being used as a separate supply isolation system rather than being incorporated into the existing safety system (PILZ etc) so if it fails, there is no redundancy.
Any help much appreciated !

 

[netblindpaul]

As far as standards go, the latest versions of these will give you a start, there will I have no doubt probably be more you will need to refer to.
BS EN 60204-1 £282
BS EN ISO 13849-1 £234
BS EN ISO 13849-2 £244
For example if the machiney is CE marked, also
BS EN ISO 12100 £244
Your legal references are
PUWER
MHSWR
EAWR
HASAWA

 

[Cadgey123]

Hi all.

Can someone point me in the right direction for the current regulations on control panel isolation for machinery (industrial) if possible please?

An issue arose with a machine trapped key system failing, allowing an individual to remove the key, but the machine staying live and running.

It was discovered that the trapped key isolation mechanism had failed allowing it to be turned off for the key to be removed, but not disengaging the electrical breaker mechanism unfortunately.

My concern is that the trapped key system is being used as a separate supply isolation system rather than being incorporated into the existing safety system (PILZ etc) so if it fails, there is no redundancy.
Any help much appreciated !

You shouldn’t rely on a control circuit for primary means of isolation.
Is there not another means of isolation? Does the main panel not have a Isolator which breaks the electrical supply to all the machine & can be locked out?

 

[David Prosser]

Any chance of a picture. I have an ongoing issue with a well know supplier of circuit breakers that have been allowing the castel interlock key to be removed with out tripping the breaker.

 

[netblindpaul]

Any chance of a picture. I have an ongoing issue with a well know supplier of circuit breakers that have been allowing the castel interlock key to be removed with out tripping the breaker.

A trapped key interlock should not "trip" a circuit breaker.
That is not how the system should work if it is to comply with statute law regulations.

 

[netblindpaul]

You shouldn’t rely on a control circuit for primary means of isolation.
Is there not another means of isolation? Does the main panel not have a Isolator which breaks the electrical supply to all the machine & can be locked out?

Is the trapped key for isolation, or is it part of a functional safety system, this is the issue, the OP has not made things clear.

 

[David Prosser]

A trapped key interlock should not "trip" a circuit breaker.
That is not how the system should work if it is to comply with statute law regulations.

Quite right not sure what I was typing there (was trying to reply while doing two other jobs) the issue I have is that the key can be removed with the breaker still closed.

 

[Shaun_H26]

The trapped key is used as a form of isolation, interrupting the power supply to the machine panel and the control circuit supply transformer.

My concern was that it was in effect powering down the PILZ unit when used due to cutting both the control supply and main supply for the panel.

I've got no pictures to hand unfortunately but it's a well known manufacturer for trap key systems that failed.

 

[netblindpaul]

The trapped key is used as a form of isolation, interrupting the power supply to the machine panel and the control circuit supply transformer.

My concern was that it was in effect powering down the PILZ unit when used due to cutting both the control supply and main supply for the panel.

I've got no pictures to hand unfortunately but it's a well known manufacturer for trap key systems that failed.

Shaun,
I am more than familiar with trapped key systems, EN 60204-1, EN 13849 & EN 62061, amongst others, as well as BS7671.
The trapped key should not be implementing isolation, so there is your systems first failing.
What is the PLr required of the system?
Shutting down the functional safety system on the machine is fine, as long as the system doing this is at the same or greater PLr as the functional safety system on the remainder of the machine, as you describe it the Pilz unit.
As long as power is not required to keep the safety functions and systems on the machine keeping the machine in a safe state.
e.g. are the electromagnets holding stuff up in the air, which will release when the trapped key system is utilised.
This is not as simple as it seems, and there is statute law involved, and that means prison sentences are possible if it goes wrong.

 

[Shaun_H26]

Thanks for your replies all of you.

The original isolation method was a simple isolation handle on the panel such as like Cadgey said. However over time, a trapped key system was added to allow access via keyed doorways into the machine.

This trapped key system main panel was added in-between the supply to the main panel as a isolator interrupt so in effect simulates turning it off at the panel. (simple on off isolator switch with two removable keys)

However with this mechanism failure not interrupting the supply to the main panel, I felt like it was worth bringing up that the system doesn't seem correct in it's modification design. Unfortunately my knowledge in such practices and regulations is lacking to back that 'hunch' up to others.