Well-Known Member
And do we not expect the same from employees of Vari-Lite, Leviton, et al ?

2. It's not ETC equipment we're talking about modifying, is it?

The same would apply to nearly all companies these days. Especially when concerning electrical or other equipment that could result in injury, death, fire, etc. I just mentioned ETC specifically since it was their employees that you quoted. And odds are they were talking about modifications to their own products when you saw them speak against modifying modules.


Resident Curmudgeon
Senior Team
Premium Member
I just mentioned ETC specifically since it was their employees that you quoted. And odds are they were talking about modifications to their own products when you saw them speak against modifying modules.
As a matter of fact, they were NOT talking about modifying ETC dimmers. The only mention of that that I can recall is here:
As has been said, many reasons against doing this. The most pragmatic one is that it's not easy, if even possible, to bypass the SSR on a Sensor, as it is with other/older dimmer modules. *cough* CD80.
It's sorta possible, but you have to cut open the power cube and scrape away some potting compound to do it. Definitely not a good or correct approach to something that could start on fire and/or electrocute someone if it fails. Liability is a thing...

Also, the chokes in a dimmer module are an important part in determining how much fault current the rack as a whole can handle safely. In bypassing or removing those, you're creating something that looks the same in normal operation, but is potentially much more dangerous when something goes wrong. The proper CC20 modules achieve the same results by including fuses in place of the chokes. Those fuses have a higher rating than the breaker so a normal overload (like 30A on a 20A circuit) will just trip the breaker. In a more extreme failure, those fuses can react faster than the breaker can trip and that limits the total amount of energy released.

Oh, and in case anyone decides to be half-clever: leaving the chokes in is not a good solution because they're actually more likely to be the cause of problems than the SCR when powering things that don't like dimmers. That's especially true for higher rise-time modules like the D20AF since the chokes are bigger.


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Premium Member
If you look at a”factory” CONSTANT module, that is exactly how they are constructed. No SSR, no coils, just a short length of wire from the breaker to the output pin (two circuits per module=two lengths of wire, one from each breaker to the corresponding output pin). ... Again, look at a “factory” made CONSTANT module. That’s all they are… two breakers and two short wire leads, one from each of the breakers to each corresponding output pin.
What you've said is correct, but leads to more questions than answers. Please see and its following post for more discussion. The OP, @microstar , either negligently or being intentionally nefarious, failed to mention the brand in question, But I think it's obvious to many the form factor of that particular dimmer module. Other posts in the same thread are enlightening as well.

Was there ever a "factory" made CONSTANT module for the 1992-ish Strand CD80AE racks? ISTR back then all we wanted dimmer racks to do was dim.

EDIT: I'm reminded of some of the 1985 Colortran D192 rack's modules, which did have a mechanical switch to set dimming/non-dimming operation. I'm pretty sure LMI-L86 dimmers had similar. Not quite the same as an air-gap relay or constant circuit however.

I’ll refrain from trying to help from now on.
Please don't refrain. A cornerstone of ControlBooth is members helping other members. This includes helping a dumb ol' stagehand like me understand how to safely modify something a captain of the industry (and other respected members) says is a bad idea.


Well-Known Member
This issue has always revolved around fault current coordination, which is poorly understood by many people in our industry who are not electrical engineers. The previous advice surrounding bypassing of chokes and SSR's is manufacturer-agnostic. The only way to do it safely is via a fault current coordination study to determine the available fault current at the feeder to the dimmer rack. If that available fault current exceeds the native AIC rating of the module circuit breaker, a non-dim module (or conversion) must include a current-limiting fuse to maintain the safety of the installation. Realize that on a large high-density dimmer rack with feeders of 400A or larger, there is a high likelihood that the available fault current exceeds the typical 5,000A or 10,000A AIC rating of the module branch breaker.

How could the original module be listed without a fuse? The impedance of the choke and SSR provided inherent limiting of fault current. When they are removed from the circuit to create a constant circuit, so is their fault current limiting.

What kind of safety is compromised by omission of such a fuse where one is needed? The module breaker may not safely clear a short-circuit and may also self-destruct when a short-circuit occurs. If this results in injury or a property loss, the insurance company will no doubt be very interested in the details of any module modification.

BTW, any fault current coordination study would need to be performed by a licensed electrical engineer.

I think that covers it.

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Well-Known Member
Steve Terry's answer is (as usual) very thorough, but there's one aspect I feel could use a little further discussion. You might be wondering why we're making such a big deal about this when it's clear that many people have been doing their own homemade versions for years without any apparent problems. Some have suggested that it's just about manufacturers being over-cautious about liability, but that's not really the case. The real reason is that this modification doesn't--by itself--directly increase the odds of any part of the system failing. A modified module could go years or even decades without any apparent problem. However, if something else goes wrong, then the modified module can make that situation much more dangerous than it would be in an unmodified system. In other words, it takes this modification plus another failure before the real problem becomes apparent.

This is the case with a lot of things in our industry: you can often get away with taking shortcuts here and there, but when the sloppy choices stack up, you may end up killing or seriously injuring someone. Everything will seem perfectly fine right up until it isn't.


Active Member
I had a few colortran i96 dimmer modules converted to relay by steve short at lite trol. Not sure he does much cd80 or general strand stuff. He seems to work closely with johnson systems who do tons of strand stuff. Both companies should be able to provide more than enough information for you. Like most others here I would recommend against making your own constant modules. I would much rather pay someone else to make proper relay modules, or even to give me advice, than chance putting others in danger because of a module I modified/installed.

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