ECN Forum Forums Code Related Discussion NEC & other Code issues Crestron Home Automation

Does anyone have any knowledge about Crestron diming modules? For example- Can you control multiwire branch circuits or must all of your circuits on the module be on the same side of the line?

George:

Most dimming modules used by both Crestron and AMX require separate neutrals for the lines and loads, and are not recommended for multi-wire circuit use. They speak of "SCR crosstalk" as the main reason.

My field experience when they were wired in multi-wire is that the different circuits suffer from irregular dimming, flickering and undesired operation.

OOPS, now I read that differently. If you're talking about feeds on different legs, IIRC each module can be fed on its own leg. Sharing neutrals is still a no-no.

edited to add "lines and" , spelling
edited again for opps...

[This message has been edited by mxslick (edited 02-18-2006).]

[This message has been edited by mxslick (edited 02-18-2006).]

Thanks mxslick - for the fast response. Further question- Would it be a problem using both sides of the line as long as they have their own neutral? Or as Crerstron says "hot and ground". They seem to get neutral and ground confused.

Yeah, I believe there's no problem there.

To clarify what I've run into: AMX (and Crestron) usually place anywhere from two to eight "modules" or as I prefer to call them, "Channels" into a given enclosure. If the channels each have their own hot and neutral, circuit feed and load wise, no problems. If say, you were to wire Ch 1 and Ch 2 as a multi, (A phase, B phase, common neutral) that's when the trouble starts. (Line or load.)

Some installers would wire (depending on loads) say, 1&2 on A, 3&4 on B, or 1&3 on A and 2&4 on B. I've also seen all channels powered on the same circuit (if the load totals are withing circuit capacity) but that's just lazy work. If any of the channels fails you pop the breaker and lose everything.!

Be sure to watch your grounding (enclosure and channels must be grounded as per spec) and the control line shield should NOT be bonded at the dimmer end, only at the controller end.

How can these controls know where the service or feeder stops and the branch circuit starts? Saying that they can’t be supplied but multi-wire circuits is nonsense. The panel supplying these branch circuits is fed by a multi-wire circuit.

Curt

I have never used Crestron but I have used Vantage and they will tell you NO multiwire anywhere, line or load side of modules. The reality is they are protecting themselves from warranty issues. If you are controlling only incandescent loads ( a rarity but possible) you would encounter no troubles with multiwire on either side of the modules. But throw in electronic ballasts, low voltage lighting, motorized draperies, pumps, pool covers etc. etc., and you will wish you'd done it their way. Even if your wiring method is not the cause of trouble, if you didn't do it as recomended they are off the hook and you are on it.

Nothing personal, but now I must rant:

We've beaten this dead horse extensively in many threads here. In addition to Gregtaylor's response, I'll repeat and expand on the same points I made in the multi-wire thread:

1: The impedance of the neutrals at feeders and panel buss are (electrically) significantly lower than the #12 or #10 branch circuit wiring thus allowing any noise or harmonics to be "absorbed" (Not exactly the right word I'm wanting, but you get the idea);
2: ANY electronic load of ANY kind is far more sensitive to power quality issues than incandescant lighting or pure resistive loads like heating devices;
3: Electronic dimming controls of any make or style are VERY noisy (just take a portable AM radio near any of those things and you'll see what I mean.);
4: Most of these systems are extremely expensive and sophisticated in their control schemes and do not take kindly to noise issues on incoming power (not to mention the risks of a lifted neutral frying everything); and
5: Candidly, and this is not directed at any specific person, but I have a real problem with the attitude of trying to save a few bucks in copper on such high-end work!

Finally, if the manufacturer says don't do it, then don't do it! There are reasons for such instructions.

This issue really gets me going, and like I said, it's not personal but c'mon, how much does one really save on these jobs by using multi-wire?

O.k., rant off.