3 phase dimmers on 1 phase service??

[lightingguy1]

Hi guys,


I have been designing a local community show that has rented 2 24 Sensor dimmer racks, ETC Instruments, and a Express 250. They have turned an (make that REALLY) old african american school into a theater.

I was talking with the somewhat head electrician the other day, and he said that the dimmers are operating on single phase power. When I went to visit the dimmer room/supply closet, I saw the 2 racks and 3 phase camlok connectors connecting power to the dimmers.

Now, why would there be 3 phase camlok connectors in a single phase system?? In the garage/shop, There is a main panel, and then off of that is a service disconnect box. 5 Cords( L1,L2,L3,Neu.,Ground) come out from there and then go on to the Dimmer room.



I will try to get pics uploaded on monday.
Thanks!
-Lightingguy1

 

[techieman33]

sounds like the "head electrician" doesn't understand what he's talking about, or someone did some extremely creative wiring in that box.

 

[lightingguy1]

naharnahekim,

The problem with that is, these dimmers arn't the SP6 or the SP12 model.

To all of the thread,

On the service diconnect box, I want to say that there are 6 breakers physically connected to one another, so you can't turn one off by itself.

 

[mstaylor]

That definitely needs a picture. It is possible to run lights off single phase and do what they call faking a phase. It isn't a great thing to do because you are pulling two legs off one side.
Take pictures of the disconnect and dimmer setup.

 

[bishopthomas]

he said that the dimmers are operating on single phase power. When I went to visit the dimmer room/supply closet, I saw the 2 racks and 3 phase camlok connectors connectting power to the dimmers.

5 Cords( L1,L2,L3,Neu.,Ground) come out from there and then go on to the Dimmer room.

Quite simply, your janitor is an idiot.

 

[David Ashton]

At this point it may be worth mentioning that all individual dimmers are single phase, the 3 phase is only the power distribution to the dimmers.You can run a 3 phase dimmer on single phase, all you need to do is triple the size of the neutral.Having said that there is one model of dimmer I worked on which took control volts across 2 phases, but as far as I know that was unique.

 

[JD]

At this point it may be worth mentioning that all individual dimmers are single phase, the 3 phase is only the power distribution to the dimmers.You can run a 3 phase dimmer on single phase, all you need to do is triple the size of the neutral.Having said that there is one model of dimmer I worked on which took control volts across 2 phases, but as far as I know that was unique.

This is true. In fact, the CEM is only concerned with which dimmers are connected to which phase leg; L1, L2, or L3. When the rack is changed from Single Phase to Three Phase, (or the other way) buss arrangement is changed. If it were set for single phase and the power was actually three phase, the phase of firing circuit for a given dimmer would be wrong and with all controls set at 0, 1/3 of the rack would be on 33% and 1/3 would be on 66%.

However, if you took L1, L2, and L3 and connected them all to one hot leg, the three ramps would be the same for either configuration and the dimmer rack would work fine in theory. (In practice, the CEM software may flag an error, never tried it on an ETC.)

Often, when benching road racks for service, that is exactly what I would do as I didn't have three phase available in my shop. If you actually used a rack this way for a show, the big issue would be the cable sizing and OCPD size, although I have no idea why you would want to.

Most likely, bishopthomas is probably correct! (Although it is not impossible.)

 

[derekleffew]

This is true. In fact, the CEM is only concerned with which dimmers are connected to which phase leg; L1, L2, or L3. When the rack is changed from Single Phase to Three Phase, (or the other way) buss arrangement is changed. If it were set for single phase and the power was actually three phase, the phase of firing circuit for a given dimmer would be wrong and with all controls set at 0, 1/3 of the rack would be on 33% and 1/3 would be on 66%. ...

I've never seen dimmers output anything other than 0V when CEM phase settings are incorrect. A more common symptom is some of the dimmers (the "middle" ones, IIRC) not having dimming capability.

 

[JD]

I've never seen dimmers output anything other than 0V when CEM phase settings are incorrect. A more common symptom is some of the dimmers (the "middle" ones, IIRC) not having dimming capability.

Oh yea. Might be inhibited on the ETC, never tried it, but used to see it often on other systems. The ramp generator is getting ZVD at the wrong time. The dimmers that are in sync run fine, the dimmers on leg two are at 33% and go to 100% at about 2/3ds (liner) then wink out and come back up to 1/3rd at full brightness, and leg three is the same, but start at 66% etc.

The old, old analog dimmers like TTI and EDI did not have a problem because there was an individual ramp generator built into each channel card.

EDIT: Memorable occurrence:
Did a club job, two stages. The other stage was being set up for Frank Stallone (brother of Sly.) About an hour before show time heard a lot of yelling coming from the other stage. Wasn't long before someone grabbed me to look into their "strange problem." Rack was set up with first generation non-analog EDI and was wired for single phase. (HHNG) About 1/2 of their lights were on even though the board was blacked out. I moved the dimmer through its range and had my "ah-ha" moment. Source looked like single phase but was actually two legs of three phase wired into a single phase breaker panel. Hadn't had much experience with digital back then, but suspected it had little to do with the digital part. Since they had sufficient capacity on their feeder, and the supply OCPD was large enough, I swapped everything onto one leg. Everything worked fine. Was their third show out and first time they ran into this. I assured them it would not be their last and told them to contact their vendor who will remain nameless.

 

[mstaylor]

We have done the fake the leg trick on road racks when three phase isn't available but we do it with small rigs, 25 or 30k total. That way we don't go over our nuetral rating.

 

[lightingguy1]

Hi guys,


So I went and took some pictures of the dimmers and power situation today after rehersal. As it turns out, when I was authoring this thread at 2 AM in the morning, I was assuming that all of the Camlok connectors were connected to the racks - You know what they say about assuming things, right? - Well, The Red Camlok connector was nowhere to be found!

......See pics below/Attached.......

 

[DuckJordan]

It looks like a single phase setup to me, that or a two phase which I'm not sure its possible to use on dimmer racks I know some higher horsepower electric motors can use two phase.

 

[mstaylor]

That is definitely a single phase set-up. I assume that the buses inside the dimmers can be changed to split the dimmers to two 110v legs instead of three. I know we used to do it with old TTI racks but never opened any ETC dimmers.

 

[robartsd]

That is definitely a single phase set-up. I assume that the buses inside the dimmers can be changed to split the dimmers to two 110v legs instead of three. I know we used to do it with old TTI racks but never opened any ETC dimmers.

I have seen the ability to do this listed on some ETC spec sheets.

 

[JD]

Someone doesn't like red I guess. Usually, blue is the color left behind. Single phase it is. (or two of three)

Most packs can be set up both ways. That's why the number can usually be divided by two or three, such as 6, 12, 24, 48, 96. Although many require you to relocate feeds coming off of the pack's main lugs.

 

[soundlight]

Also, those are SP12 racks - the 12 refers to the number of modules. The modules are double density (2 dimmers to a module) so 12*2=24. The SP12s can be changed to single phase inside by reconfiguring the buss bars, as stated before, so that's definitely what happened if the dimmers are running properly.

 

[mstaylor]

Someone doesn't like red I guess. Usually, blue is the color left behind. Single phase it is. (or two of three)

Most packs can be set up both ways. That's why the number can usually be divided by two or three, such as 6, 12, 24, 48, 96. Although many require you to relocate feeds coming off of the pack's main lugs.

I started to mention the blue/red thing but thought it was just me being picky.

 

[JD]

I started to mention the blue/red thing but thought it was just me being picky.

Yea, can't say too much on that. I am guilty of sometimes leaving black behind just because I think it is a boring non-color.

 

[lightingguy1]

Ok - Thanks guys!

I still have a few questions that have stayed unawnsered, so here is one of them,

If it is single phase then why do we have the 2nd leg attached? And how does this Faking a leg work?


Thanks!
Btw, I never really did understand ETC's 2 Dimmers on one module thing. Thanks Soundlight!


-Lightingguy1

 

[derekleffew]

... If it is single phase then why do we have the 2nd leg attached? ...

split-phase - ControlBooth

See also the thread http://www.controlbooth.com/forums/lighting-electrics/20234-more-phase-questions.html .