Am i being cynical, or co-incident of failure....

[-Matt]

I work in coach building, mostly motorsport artic trailers.

These usually have a 32A 3PH supply.

I fit these with a phase correct relay, to stop some numbnuts mixing phase and neutral up on a hook-up (landline) cable.

We have just had one back with some issues including:
Phase relay faulty, so they bypassed it via the main contactor.
A/C units broken (seems the main pcb board has failed)
hydraulic system not working (a timing relay has failed)

On testing, the phase relay all works fine.


So would i be overly cynical in thinking what has really happed is this:

No power as their hook-up cable was wired wrong (phase-neutral reversed?), they have then bypassed the phase protection, then powered up putting 400V through components only designed for 230V, then bring it back as faulty.

However if this did happen, im surprised all the lights didn't blow.

Or has there been a coincidental component failure all at once......

What do we think?

 

[davesparks]

If the phase failure relay is working correctly then I would say the most likely explanation is that there was a supply issue, could be polarity, phase rotation, poor neutral connection or low voltage on one phase.

As you say you would normally expect more damage but without knowing exactly what happened and testing the supply it is hard to explain.

I would have thought that you are covered from a warranty point of view, they have tampered with the equipment and bypassed a safety feature designed to prevent damage and damage has occurred.
I wouldnt speculate about what happened in your communications with them, just stuck to the known, provable, facts. They bypassed a protection system, equipment was damaged.

 

[Lucien Nunes]

My thoughts exactly. It's difficult to prove a causal link to the bypassed relay, but both defects have arisen during their use of the equipment.

There might be overwhelming circumstantial evidence that the two are related if an autopsy can be done on the failed electronics, as overvoltage usually results in some recognisable failure modes. The effects of neutral loss can be much more subtle than a solid reversal of one phase and neutral, hence a limited amount of evident damage. There might be more concealed problems, such as stressed electrolytic capacitors in PSUs, that will take time to manifest. I always state this in the case of suspected overvoltage events; as the future cost in downtime due to reduced lifespan might far exceed the cost of replacing the completely failed items.

To minimise future temptation for people to bypass the relay(s) it would be worth reviewing the settable parameters, to ensure that they do not lock out supplies that are out-of-spec but still safe to use in practice. E.g. that the symmetry and overall voltage limits are not too stringent or the response too fast. Over-zealous protective devices can cause untold headaches when one is trying to deliver a show.

 

[marconi]

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