1756-ob16d

Am looking for advice on the 1756-OB16D.
Rockwell/Allen Bradley have just told me that the datasheet is wrong!!!

We have a site problem. A short on any output of an OB16D channel is tripping the fused supply to the OB16D module. This then takes out the supply to all the other 7 output channels (note: the OB16D requires 2 x fused supplies, 1 for each half of the module).

The datasheet states that each channel will supply a load of 2 Amps and a 4 Amp surge. We have therefore rated the fused supply to the half of the module to just above the 4 Amp surge plus the normally energised load of the other 7 output channels.

I assumed that in the event of a field short circuit the 'e' fuse inside the channel would trip and therefore 'protect' the upstream fused supply that is supplying the whole of the half of the module and also provide a short circuit indication. Rockwell are now telling me that this is not the case and that every output on the OB16D module needs to have a fused connection. That's a lot of fuses. 16 fuses per OB16D module and then no way of indicating a short circuit on the output.

Any ideas?

Thanks

The 1756-OB16D is a diagnostic and electronically fused module. It can detect open circuit, and report that, and it can indeed trip, but at 8 amps (for 180ms), or 10amps for 120ms.

The 1756-OB16E is the electronically fused module (only), (still in two groups of 8 points) that will trip if any output point exceeds just over 2amps. Each output channel is rated for 1 amp continuous.

True, the manuals on the actual functionality of those modules is a bit deceptive.

In any event, I still only fuse the overall module supply, and not individual outputs. Generally, I run all power through these things by Siemens.