A designer is saying to me you can use an onload device (it s a rail application), but to me it clearly staes it has to be an off load device.

If you're thinking because you want the ability to lock off in the on position, it needs to be an off-load device, then i think you're reading it backwards. To me it reads, if you have a device that can only safely be opened when no current is flowing, then you should take precautions against it being opened when it shouldn't be. It doesn't read the same vice-versa.

   - Andy.

Hi Andy, the regs say

537.2.5   Provision shall be made for securing off-load isolating devices against unwanted or unintentional opening. This may be achieved, for example, by locating the device in a lockable space or lockable enclosure or by padlocking. Alternatively, the off-load device may be interlocked with a load-breaking one.

Its saying you can only lock on an off-load switch, AC-20 rating , the switch is in a public area hence the locking on, im totaly against it, I would just put on on-load isolator in a box.

Alex Cooper said:

Its saying you can only lock on an off-load switch, AC-20 rating , the switch is in a public area hence the locking on, im totaly against it, I would just put on on-load isolator in a box.

No, Andy is correct ... where is the word 'only' used in Regulation 537.2.5.

The Regulation requires you to make sure that off-load isolators can't be switched off unintentionally (because there is a risk to a person who switches off an off-load isolator when current is flowing through it). You can achieve the requirement with a padlock, or locating the isolator in a suitable enclosure, for example.

This does not preclude other isolators from being locked 'on', and there are many applications in which this is done.

Provided anyone needing to use he isolator for safety reasons, such as maintenance, has a key to unlock the isolator, and uses another (unique) key to secure it in the off position when required, there is no problem. This is merely an operational issue for the owner/operator of the installation.

After all, there's not much difference between locking a larger-rated isolator "on" from using a security-switched fused connection unit or 20 A security switch?

If, on the other hand, a suitably-rated isolator were intended as an emergency switching device, it should not be locked in the "on" position, for obvious reasons ...

I can see it does not say “only”, but this is the only reference to locking on an isolator in the whole 624 page document. I can see it is open to interpretation, but it specifically “only” mentions an offload device. Which to me means only an offload device.

An offload device is not designed to switch current.

I can see it does not say “only”, but this is the only reference to locking on an isolator in the whole 624 page document. I can see it is open to interpretation, but it specifically “only” mentions an offload device. Which to me means only an offload device.

Yes, only off-load devices MUST have locking, but still on-load devices MAY have locks - it says nothing to preclude that.

  - Andy.

I can see it does not say “only”, but this is the only reference to locking on an isolator in the whole 624 page document. I can see it is open to interpretation, but it specifically “only” mentions an offload device. Which to me means only an offload device.

Yes, only off-load devices MUST have locking, but still on-load devices MAY have locks - it says nothing to preclude that.

  - Andy.