Power Distribution Help

[adaguy]

So a venue I'm going to be running a tour through has confused me quite a bit. Correct me where I'm wrong but, typical 3 phase power has 208 volts hot to hot (except the high leg) and single phase would have 240v. so when looking at the disconnect in the venue I assumed it was single phase based on the lack of a third phase line in the box. (H-H-N-G connections)
i did some multimeter tests N-H was 120v but as I said the H-H was 208v not 240 v so it seems the contracting electrician left the high leg out. how would I go about connecting a distro to this as I have 208v moving lights to power and normally I would rent 3 phase distros at 208v, but this is neither single or 3 phase kinda half half from what I can understand. (by how would "I" i mean the electritian that comes in to tie in power i just rent and handle the equipment)

 

[Footer]

240v power is only seen in split phase residential systems or delta systems where a high leg or "wild leg" is present. This systems are extremely rare.... and when you do see them they are labeled as such. This is not one of those situations.

A typical 3-phase company switch disconnect has three hots, one neutral (sometimes two), and one ground. Hot to hot you should see 208v and hot to neutral or ground you should see 120v. In a single phase system hot to neutral should always be 120v. All that happened here is you have two legs of a 3 phase system. You can tie in a standard distro, just turn the breakers off on any circuit using the leg that you don't have connected. Most distros label this type of thing.

 

[adaguy]

Okay that's great to know about the split and delta being so uncommon, and yea that's why I was thrown off when it only had 2 hots a neutral and a ground.

now in terms of renting that. Would I just go with an ordinary 3 phase system and avoid the channels on that phase, given that, wouldn't a single phase system work for this set up as it just divides power amongst the 2 phases instead of 3.

Lastly how would 208v distro handle connecting 2/3 phases on a 3 phase system and avoiding the certain breakers.

The original set up rented is camlock to MLD Main with 6 c5 outs to 3 208v MLD and 1 120 MLD that have twist out. ("Christie lights" in Toronto,ON is where I was looking at renting for a show in Sudbury,ON)

Thanks for all the help its greatly appreciated.

 

[Scenemaster60]

It's most likely that the venue has three-phase Y service at the service entrance and for running motors and compressors but in order to save money, some of the distribution panels only get 2 phases. It's not great practice but it's legal. If it were my venue, I would have labeled that panel as 120/208 phases (n) & (n) only.

This is why it's so important to ALWAYS take your meter and check voltages before connecting ANYTHING in a strange venue.

 

[Footer]

Call Christie and tell them the kind of power you have and see what they can do for you. Because they use CEE-Form connectors it could get a bit hairy. You would be wasting a lot of copper that way and might not end up with enough power at each sub distro.

What is your total load? Can the moving lights you are getting run on 120v or do they have to have 208v? How much power is the disconnect in question capable of?

 

[adaguy]

Call Christie and tell them the kind of power you have and see what they can do for you. Because they use CEE-Form connectors it could get a bit hairy. You would be wasting a lot of copper that way and might not end up with enough power at each sub distro.

What is your total load? Can the moving lights you are getting run on 120v or do they have to have 208v? How much power is the disconnect in question capable of?

Christie said they won't do that but are gonna try to find another local company that will. Lighting load isn't all that crazy 6 750 source fours, 4 martin 700 profiles, 9 quantum wash. The moving lights can do 120 just need Christie to re fuse them for rental. The disconnect is 100 amp so from the understanding of power I'm getting that means I can only put about 90 amps per phase, correct?

 

[JD]

80 amps if it is a continuous load. Of course, stage lighting is rarely a "continuous" load, so you should have no problems. As long as you don't have any equipment that requires 240 volts (rare), just treat the thing like you would a single-phase disconnect, as each leg is 120 volts to neutral.

As for the "high leg", that is known as tapped delta, which is usually 240 between any two of the hots. The problem on this form of delta is that two legs are 120 volts to neutral, but the third "wild leg" of "high leg" is 208 to neutral. It is very rare that you see this pop up in stage lighting, just nice to know that it is out there should you ever run into it. Wye is 3 hots, each of which is 120 volts to neutral, and 208 between any two hots.

 

[adaguy]

80 amps if it is a continuous load. Of course, stage lighting is rarely a "continuous" load, so you should have no problems. As long as you don't have any equipment that requires 240 volts (rare), just treat the thing like you would a single-phase disconnect, as each leg is 120 volts to neutral.

As for the "high leg", that is known as tapped delta, which is usually 240 between any two of the hots. The problem on this form of delta is that two legs are 120 volts to neutral, but the third "wild leg" of "high leg" is 208 to neutral. It is very rare that you see this pop up in stage lighting, just nice to know that it is out there should you ever run into it. Wye is 3 hots, each of which is 120 volts to neutral, and 208 between any two hots.

Yes i get that what i was asking is if the distros i looked at on Christie Lites was gonna work for the 208v lights but from what you're saying it seems like it would be easier to use only 120v lights spread across two of the 3 phases by turning off the breakers for the 3rd phase on a 120v distro.

 

[Footer]

Yes i get that what i was asking is if the distros i looked at on Christie Lites was gonna work for the 208v lights but from what you're saying it seems like it would be easier to use only 120v lights spread across two of the 3 phases by turning off the breakers for the 3rd phase on a 120v distro.

Won't even have to turn off the breakers... the outputs just won't work. You are going to be right at capacity for that switch to be careful how you load up each phase. You only have 200 amps to play with and you have a 190 amps of load.

 

[JD]

from what you're saying it seems like it would be easier to use only 120v lights spread across two of the 3 phases by turning off the breakers for the 3rd phase on a 120v distro.

Yes, run them at 120 and you only have 1/3 of breakers not putting out. At 208, 2/3 of your breakers won't put out. (Norm outputs; A-B, B-C, C-A but only A-B will work on 208 since C is missing.)

 

[danTt]

Now, missing one leg means that two thirds of your 208 outputs won't work, Assuming XYZ phases, and X-Y, X-Z, and, Y-Z 208 outputs, any dropped leg will result in anything relying on that phase to misbehave.

 

[JD]

One other thing- Don't forget to "cap or strap" the unused leg! You don't want a male connector hanging around that may have a back-feed voltage on it.

 

[MikeJ]

Delta is actually fairly common in industrial buildings, but should be uncommon in performance spaces. Its good to be aware of the possibility especially for old buildings that have been converted for theaters and concert venues.

None of your fixtures should need to have any fuses changed to run on 120v (the Mac 700 is a little older so I would have to double check), most fixtures these days are "auto ranging." There are many PD's that have 4 Main breakers to allow for 3 phase, or single phase use, depending on the breakers that are switched on. It is also possible to double up on a leg with a jumper from y-z on your inputs, but this will still yield every third output of a 208v soca to have zero volts across the hots, because they are both the same leg. You must be aware of easily overloading one leg, and need to load balance accordingly.

 

[adaguy]

Call Christie and tell them the kind of power you have and see what they can do for you. Because they use CEE-Form connectors it could get a bit hairy. You would be wasting a lot of copper that way and might not end up with enough power at each sub distro.

What is your total load? Can the moving lights you are getting run on 120v or do they have to have 208v? How much power is the disconnect in question capable of?

Okay so Christie after hassling finally got back to me and said they could offer "24x2.4K Sensor Dimmer Pack" set to single phase. Will this work to spread the power across the 2 phases as at 120v we have almost 180A and its a 100A breaker but 2 phases.

Thanks for your help everyone i'm used to pre existing set ups and this is the first time i've had to find my distro solution for the electrician.

 

[Footer]

Okay so Christie after hassling finally got back to me and said they could offer "24x2.4K Sensor Dimmer Pack" set to single phase. Will this work to spread the power across the 2 phases as at 120v we have almost 180A and its a 100A breaker but 2 phases.

Thanks for your help everyone i'm used to pre existing set ups and this is the first time i've had to find my distro solution for the electrician.

As long as they install constant power modules or relay modules it will work fine.

 

[adaguy]

As long as they install constant power modules or relay modules it will work fine.

Okay perfect then they said they will put the breaker modules in. So on the back I'd use phase 1 and 3 in correct? Then ground and neutral obviously.

 

[petercav17]

Okay perfect then they said they will put the breaker modules in. So on the back I'd use phase 1 and 3 in correct? Then ground and neutral obviously.

Any 2 legs will work. 1&2, 2&3. 3&1, it doesn't matter. But the way that you worded that reminded me: ALWAYS tie in your ground first and untie the ground last!

 

[Wood4321]

Any 2 legs will work. 1&2, 2&3. 3&1, it doesn't matter. But the way that you worded that reminded me: ALWAYS tie in your ground first and untie the ground last!

This isn't true, when a sensor rack is configured for 2 phase operation, the 3rd phase is not connected inside the rack.
There are metal plates that are moved, to buss together half the dimmers on 1 phase, and the other half on the other.
That being said I don't recall which phase is disconnected. (I want to say its the B/Y phase, but could be remembering incorrectly)

 

[derekleffew]

Any 2 legs will work. 1&2, 2&3. 3&1, it doesn't matter.

Incorrect. When a Sensor portable pack is set up for 120/240V single phase operation, the center hot terminal (red Cam-Lok) on the pack is unused.

 

[petercav17]

Sorry guys, I was a bit unclear. I was talking about the two legs coming from the disconnect, not the inputs into the rack. Although that comment doesn't apply as he only has 2 legs from the disconnect to begin with. Disregard the first part of my previous comment!