New to site - anywhere to ask questions about dimmer racks?

Hi Derek

I have forwarded a link to your post to Steve Terry who can probably provide some insight. Can you post your situation?

Or email sterry@etcconnect.com with your situation.

David Lincecum

David,

 a long time since my original post - I have put a fix in place but I wanted to follow up to find out about other options to addess the situation.

 The configuration in question has 3 no. SN48N+ racks rated with 800A (120VAC rating) supplied from the same LV switchboard.  A fourth load connected to the same LV switchboard is a non-dimmed lighting control panel.  These 4 loads are protected by Reyrolle electromagnetic induction disc relays for OC & EF.

During a particular maintenance programme with turns all the lights on to 15% power to identify burnt out lamps, THD at the supply switchboard was measured at over 30%.  During this maintenance programme the EF protection to the 4th load (the non-dimmed control panels) would operate, even in situations where the load was disconnected from the non-dimmed control panels. 

In normal show operation - where there was no turn on of all light circuits programmed - there was no spurious trip on the other load.

The settings for the EF protection were all plugged at the minimum setting - 10%.

To attempt to "tune" the EF settings, they were stepped out to 15% - the spurious tripping stopped, although THD is still at over 30%.

 Question are:

a. have you seen this type of EF proteciton spurious operation in other installations?

b. in situations where there is a heavy dimmer load connected to a single source, what approaches are commonly used to address the / prevent high THD content?

or

c. should the loads have been split across different load buses

Regards

Derek

Derek,

Adam Bennette and I have had a chat about your situation and have a few comments and questions after which I think we should talk over the phone in order to get into more details of your installation.

When you measured THD at 30% was this a voltage or current reading?  We would expect this as apossibility for current but would need to discuss this if it is voltage.

Since you have SR48N+ racks I am assuming that you are also running D20AFG modules.  Is this correct?  If so, what is the reason for having a GFCI feed breaker in adition to the GFCI dimmers?  Oh, and what facility are these installed in please so that I may look up your information.  What type of loads are running on the dimmers.  Any ballasts or low voltage transformers by chance?

It is possible that one or more of the circuits or fixtures may have compromised insulation but more than likely the issue is that the harmonics generated by the dimming system are not tolerated by the feed breaker.  You know, I have also seen situations where different length feeder wire from a feed breaker and split to different racks would cause a false trip as well.  With the setting on the breaker can you tell me what the trip level equates to in milliamps?

Please give me a call to discuss or email me when you get a chance.

David

888-908-2142

dnorth (at) etcconnect.com