ETC SR48 Dimmer Questions

[Repeater]

We have three SR48 racks installed in our church, each of course with it's own CEM. I am on a project to understand these racks better and to quickly deal with problems on a Sunday morning, should (when) it occur.

A. If one, or two, CEMs fail, does it affect only that rack(s), or the others too?

B. Can CEMs be pulled/plugged in with the rack hot? (Seems like I've done it under direction of ETC, but confirming).

More questions may follow, but this is a start.

Thanks!
Laryn

 

[JD]

Unless the DMX is being shorted, only the rack with the bad CEM would go down. Not a good idea to hot swap CEMs. Can't say it has never been done, but there is a chance of spiking the replacement and taking that out as well.
Rule of thumb- Always kill the rack (lock-out) when swapping anything out. I know rules get broken, and some may tell you that the dimmers are designed to be hot-swapped, but it really is a good rule to follow.

 

[jhochb]

Good Morning repeater

Is it a CEM (classic), CEM+ OR CEM3

The CEM brains ARE hot swappable. Each rack is controlled by its CEM. And the CEM from one rack can be put into another rack for testing or as a replacement.
If you swap the CEM you need to change its address (if it’s a CEM classic this would be the link #)
The CEM classic has been out of production for quite awhile now. The current model is the CEM3, they are not interchangeable.
but the rack can be upgraded.
If the church can find, afford a spare, that would be something to push for. ETC has a small number of LOANER modules but a spare on site is the best thing.
The SR racks are very sophisticated systems and can last for decades.
Find a local ETC dealer & get some training on it, even if you have to pay for it. You’ll be glad you did

 

[derekleffew]

...The CEM brains ARE hot swappable. ...

Just because they are, doesn't mean one should. From the wiki entry Lock-Out/Tag-Out (LOTO):

Even something as mundane and seemingly harmless as swapping a dimmer module [or control module] (a very common troubleshooting procedure) now requires completely powering down the rack.

...Because of NFPA 70E, and its regulations on arc flash potential, we [ETC] cannot recommend hot-swapping any dimmer module while the rack is powered on. We strongly recommend that you power off the rack before swapping modules to prevent the potential for an arc-flash incident.

 

[danTt]

Question, because it's really hard to actually read that document. Is the arc-flash incident potential when hot swapping a dimmer module similar to the arc flash potential when unplugging a stage pin under load? i.e., are these recommendations that etc makes driven by the need for legal safety? Or because of a likelyness of something happening.

 

[DavidNorth]

Question, because it's really hard to actually read that document. Is the arc-flash incident potential when hot swapping a dimmer module similar to the arc flash potential when unplugging a stage pin under load? i.e., are these recommendations that etc makes driven by the need for legal safety? Or because of a likelyness of something happening.

The arc flash potential when swapping a module might be much larger than when unplugging a stage pin under load. Unfortunately, ETC doesn't know what the incident energy available at the phase bars in the rack might be as that is specific to each installation. When removing a module from a rack, you are exposing potential to both electric shock and arc flash and we would like everyone to know that doing any electrical work live is neither safe nor recommended unless you have been trained to do so.

Let's be clear, because these questions have come up before. Sensor rack dimmer and control modules are designed to be hot swapped. You can either swap the modules while wearing the appropriate PPE and following your facility's electrical safety practices as designated by NFPA 70E, or you may simple choose to Lock-Out/Tag-Out the rack.

Also, while no incidents of swapping modules have created an electrically unsafe situation for a system owner, the likeliness of something happening cannot be predicted. Simply think about the possibility that someone has previously dropped a dimmer module which cracked the casting and then placed it back into the rack. The next person comes along to remove the module and that casting piece breaks off the module into the dimmer below or falls next to the phase bar. That's all it would take to potentially be a problem.

I do have stories of other electrical safety issues that have occurred over the years, but fortunately no one has been hurt. So to answer the last question....ETC is spreading this information, and training all their internal and contract technicians, because of legal issues AND our desire to keep everyone educated and SAFE.

Dimmer racks are high current power distribution devices. We need to respect them as such.

If there are additional questions about electrical safety, since I spend a good amount of time on this area, I would be glad to provide answers.

David

 

[Repeater]

Yes, I have since learned that we have CEM Classics. I am now pondering several scenarios that will give us a useful backup plan in case of CEM failure.

Thanks for the help.

Laryn

 

[chausman]

Someone please correct me if I'm wrong, but aren't CEMs generally the kind of thing where you don't normally keep spares?

 

[DuckJordan]

Tell that to my boss we have 8

 

[icewolf08]

Someone please correct me if I'm wrong, but aren't CEMs generally the kind of thing where you don't normally keep spares?

In a large multi-rack installation and in large professional venues, it would be prudent to have a spare. Even if you are in the biggest theatre city in the world, it is a lot easier to drop in a spare when something goes wrong and the audience is starting to walk in than it is to call your local shop! You probably don't need lots of spare, and in most places, one should be enough, but Personally I think that a spare CEM should be spec'd with all dimmer installations. The key is knowing how to swap it in on short notice if you need to. If you don't have someone who can do that, then it is superfluous to have a spare.