L5508D1A dimmer Failures

Hi there

My system has been installed since 2011 and working fine overall.

I have a system power requirement of 550ma and a power availability of 600ma. This comes from three L5508D1A dimmers.

About 6 months ago one of these dimmers appeared to fail and continuously tripped the 240v input breaker. No output shorts or other failures could be identified and the dimmer was replaced. All went well until last week when the exact same thing happened on the same dimmer. None of the 1A output breakers tripped at any time and even with all 8 breakers manually tripped off, the input breaker still would not reset. The dimmer appeared normal temperature and a new dimmer has been ordered again but I don't want to install it until I find the cause of the problem. Strangely, I found that the following morning the dimmer would reset and I left it like that (but with the output circuits isolated) because without it the Cbus power is insufficient for the control side and the entire system is compromised. However it tripped again a few hours later with the output circuit still isolated. I now wonder whether the original dimmer was permanently failed or if it too may have reset after a while.

My questions are threefold:

1). What could possibly be going on to cause the input breaker to trip without any obvious output problem, that then resets after a period? Surely any internal protection would not cause the input breaker to trip?

2). There is not a huge margin between Cbus power required and available. The loss of any power supply causes the entire system to go down. Would it be a good idea to purchase a standalone power supply (5500PS) to provide redundancy support?

3). Could this lack of margin be a factor in the dimmer "failure"?

Thanks for you thoughts.


Duncan

 

Unless there was a garden hose pointed at the dimmer I'd be very surprised it is going to take out a 10A breaker but still this has happened twice.
Is the input breaker for the dimmer power supply an RCBO/ safety switch?
Your 8 channel dimmer has 2 sources of 240v supply.
Are they fed by the same breaker?
If so I suspect you probably have a neutral to earth fault somewhere or something taking out the RCD.

For my installations I have a standard breaker for the CBus power supply side of the dimmer and a separate RCBO to supply and protect the channel outputs.
Note from the instructions that they should be on the same phase.

If you have separate breakers for the built in CBus power supplies then they are isolated from other circuit faults and I don't think you need to worry about standalone CBus power supplies.

As far as total power supplies goes 2000mA is the max you can have on the network.
You could take it up towards 2000mA to give some redundancy but I don't think that is the cause of your problems.

If you have enough power supplies for your CBus devices calculated load then there is nothing to worry about with regards to causing a failure.

 

Thank you for that. Very useful! I had forgotten that the dimmer power and Cbus power supply could be separated! That has not been done in my installation but it would be a good idea to retrofit. Certainly cheaper than a standalone power supply and it would solve the problem of one issue taking down the entire system.

Yes, it is a RCBO that protects the power input and I have been thinking overnight that I should look at non Cbus related faults but I had, annoyingly, been called abroad for a few days.

Very glad that you think the issue unlikely to be internal Cbus. That may save me $xxxxs.

I'll check it out and report back.

Thanks so much


Duncan

 

Yup, it seems as though the problem is NOT Cbus related.

I have disconnected the power input and am now just powering the Cbus control PS. All has been running smoothly for a couple of hours. I have swapped a functioning dimmer module with the old one I replaced 6 months ago and it works fine, too. I guess I might now swap the offending RCBO and see what happens.

Question: can you tell me what MCB you use to protect the Cbus control power supply on these units? I will do as you suggest and separate them from the main 10A input supply.

Many thanks

Duncan

 

I've always used standard Hager MCB but it couldn't hurt to use a single RCBO for the CBus power supply side too.
It's not going to trip ever but it would offer a higher level of safety.
Since you are in UK I can't help much with advice for your regulations.

 

Ok thanks

Would you suggest a 1A, or less?

 

I could not find any specs for the recommended circuit protection for the CBus power supply side of din rail units on CIS web site.
I've always used a 10A breaker to protect the 1.5mm cable.
The actual load will be much less.
You will need to check what you do complies with local standards and the device specifications.

I'd like to ask other forum members or anyone from CIS to clarify CBus power supply circuit protection due to no specification.
I also invite comment or discussion on the merits or otherwise of RCD protection for CBus power supplies.

 

I will call CIS Tuesday and post their answer.

 

Hi adgilcan
You could swap the RCBO but I think you should also test the outgoing circuits to see which one might be causing the fault.

 

CIS tech support did not supply a specification but suggested for a CBus power supply a smaller breaker is also suitable.
As far as circuit protection goes your existing setup had a 10A RCBO powering both 240V supplies on the dimmer.
If you want to keep the circuit protection as it was but separate the CBus power supplies from outgoing circuit faults you could use a separate 10A RCBO to protect CBus power supply side of the dimmer.

 

Hi

Thank you for your continued help.

I was thinking that the control MCB could be a 1A breaker? Those are way more expensive than the larger ones but should provide greater protection?

I have swapped the dimmer module itself, the 10A RCBO and have bypassed the wiring from the RCBO to the dimmer module. None of these changes affect the fault. In addition I have turned off ALL 1A output MCBs whether related to the dimmer or not and switched them on again individually. The point at which the RCBO trips appears to be random and not connected to any one circuit but it does seem to be related to the output circuits in general. Certainly there appears to be no fault lying within the electrical intake cabinets.

I have an electrician coming round at the beginning of May to investigate further as my knowledge and experience stalled 25 years ago following a career change. May I ask what your next steps would be in the investigative process?

Many thanks

Duncan

 

Hi Duncan
You should call the electrician.