More Phase Questions

[Shawncfer]

Okay okay so I know I've asked a lot of electricity questions lately. And I swear I'll stop pretty soon.

Just got three more for you right now

Okay. So First, can Arc flash happen just from you hooking up a dimmer rack to a disconnect? Or do you have to be doing repairs on it or something else for Arc flash to occur?

Second, Lets pretend youre on tour and you're using three phase on your tour. But then, you get to a building that has single phase only! How do you hook up to the disconnect? I mean if your rack can handle single phase. And if your rack cant handle single phase, do you just tell them you cant do the show or what?

Third, Let's pretend youre on tour and you're using single phase on tour. But then you find out your venue has three phase. So I know it's possible. But do you hook up two phases and nuetral and ground and leave the third phase un-used, or one phase, nuetral, ground and two phases un-used? And if you have one of the phases that you're not using, and it's not connected, is it bad if your disconnect is on but you have nothing plugged into one of the legs?

So a little more than three questions, sorry.

 

[photoatdv]

As for number 1, if for some reason what you were connecting the dimmers to was hot, then yes. This is why you DON'T do it hot.

 

[Shawncfer]

This is why you DON'T do it hot.

In other words, dont have the power on when I'm conencting?

 

[SteveB]

Second, Lets pretend youre on tour

But do you hook up two phases and nuetral and ground and leave the third phase un-used, or one phase, nuetral, ground and two phases un-used? And if you have one of the phases that you're not using, and it's not connected, is it bad if your disconnect is on but you have nothing plugged into one of the legs?

So a little more than three questions, sorry.

In theory, when you prepare to tour, you first determine the venues you'll be playing and find out their technical capabilities. If you find a venue that cannot support the event, you deal with that before you set out - I.E. bring it to the attention of whomever is booking the event, promoter, etc...

Some dimming systems can operate on single phase feed, but not the larger 48 to 96 dimmer sized systems. The control electronics on these systems will not work if they don't see 3 phase, so no amount of game playing with feeders is going to work. If you anticipate going to a venue without 3 phase, perhaps a different dimming system, such as a distributed pack system that can run on 20 amp Edison outlets, would be more appropriate.

And, NO, you do not do live tie-ins.

 

[Shawncfer]

So then how do you use a rack that can only use single phase on a three phase disconnect? And according to photoatdv, arc flash won't happen if the disconnect is off when hooking up the legs right? I mean its always off when nothings connected anyways, but an arc flash won't happen if I'm just connecting it like normal?

 

[STEVETERRY]

Okay okay so I know I've asked a lot of electricity questions lately. And I swear I'll stop pretty soon.

Just got three more for you right now

Okay. So First, can Arc flash happen just from you hooking up a dimmer rack to a disconnect? Or do you have to be doing repairs on it or something else for Arc flash to occur?

Second, Lets pretend youre on tour and you're using three phase on your tour. But then, you get to a building that has single phase only! How do you hook up to the disconnect? I mean if your rack can handle single phase. And if your rack cant handle single phase, do you just tell them you cant do the show or what?

Third, Let's pretend youre on tour and you're using single phase on tour. But then you find out your venue has three phase. So I know it's possible. But do you hook up two phases and nuetral and ground and leave the third phase un-used, or one phase, nuetral, ground and two phases un-used? And if you have one of the phases that you're not using, and it's not connected, is it bad if your disconnect is on but you have nothing plugged into one of the legs?

So a little more than three questions, sorry.

As to your second question: this is a fairly common scenario, and one that is anticipated by NEC section 520.53 (O)(1), which states:

Neutral Terminal. In portable switchboard equipment designed for use with 3-phase, 4-wire with ground supply, the supply neutral terminal, its associated busbar, or equivalent wiring, or both, shall have an ampacity equal to at least twice the ampacity of the largest ungrounded supply terminal.
Exception: Where portable switchboard equipment is specifically constructed and identified to be internally converted in the field, in an approved manner, from use with a balanced 3-phase, 4-wire with ground supply to a balanced single-phase, 3-wire with ground supply, the supply neutral terminal and its associated busbar, equivalent wiring, or both, shall have an ampacity equal to at least that of the largest ungrounded single-phase supply terminal.

What this means is that if a portable dimmer rack or pack does not have an internal method of switching between three-phase and single-phase (as most large racks do not), it must have a 200% rated neutral terminal.

Why? Because it is assumed that the road electrician, when confronted with a single-phase service for his three phase rack is not going to say "Gee, Mr. Merrick, we can't do a show tonight--we only have single-phase". He or she is going to take the two most lightly loaded phases of the dimmer rack and connect them to L1 of the single-phase service, while the third leg will get connected to L2 of the service. This is a classic "show must go on" event. This is fine, as long as the rack neutral terminal can handle the overcurrent caused by the imbalance. Any Listed rack will be able to do so.

For your third question, it is possible to connect a single-phase, 3-wire plus ground rack to a three phase service. You would simply not connect anything to the third phase of the service, as you would only have an L1 and L2 conductor on the dimmer rack. You would connect the neutral normally, as well as the ground.

As to your first question, there is a difference between arcing and arc-flash. Arcing can occur when a connector is made or broken under load. An arc-flash is the result of an arc being drawn between phase and ground, between two or more phases, or phase and neutral, where the full fault current of the source flows into the arc--which can be tens of thousands of amps or more. Both arcs and arc-flashes are bad, but the latter is catastrophic. An arc-flash has a number of causes that are outside the scope of this discussion. As an iron-clad safety rule, portable dimming equipment should never be connected or disconnected with the source energized.

Finally, please see the Glossary entry Qualified Person, per the NEC. Realize that the NEC section 520-53 (P)states:

Qualified Personnel. The routing of portable supply conductors, the making and breaking of supply connectors and other supply connections, and the energization and de-energization of supply services shall be performed by qualified personnel, and portable switchboards shall be so marked, indicating this requirement in a permanent and conspicuous manner.

Exception: A portable switchboard shall be permitted to be connected to a permanently installed supply receptacle by other than qualified personnel, provided that the supply receptacle is protected for its rated ampacity by an overcurrent device of not greater than 150 amperes, and where the receptacle, interconnection, and switchboard comply with all of the following:
(a) Employ listed multipole connectors suitable for the purpose for every supply interconnection
(b) Prevent access to all supply connections by the general public
(c) Employ listed extra-hard usage multiconductor cords or cables with an ampacity suitable for the type of load and not less than the ampere rating of the connectors.

ST

 

[SteveB]

Steve

Could you clarify that Sensor CEM's and CEM+'s will operate correctly on single phase (2 hots) feeders ?, as I was under the impression that the 24 and 48 module racks will not operate in that mode, due to the CEM's wanting to see 3 phase, and that the CEM itself operates off one of the phase feeds and that if you do indeed need to operate in 1 phase mode if allowed), make sure the CEM is getting powered.

 

[JD]

In the 80s we did a lot of small venues using a 86k EDI dimmer system. It consisted of 3 twelve channel 2.4k per chn. packs. Each of the packs was wired to run off of two legs. We simply carried two distros. The single phase distro simply supplied the packs in an AB AB AB layout. The three phase distro supplied the packs as AB BC CA. The packs themselves (Scrimmers) were laid out A 1,2,5,6, 9,10 / B 3,4,7,8,11,12. Depending on what we found, we simply grabbed the correct distro off the truck for that night. The old Scrimmers had a phase ramp generator on each 2 channel module, so it didn't really care one way or the other.

Load balance was a bit important as we rarely got the ampacity specified on the tech rider. (Often two 100a legs and a four leaf clover. System load was 48k so many scenes were modified on the fly.)

 

[STEVETERRY]

Steve

Could you clarify that Sensor CEM's and CEM+'s will operate correctly on single phase (2 hots) feeders ?, as I was under the impression that the 24 and 48 module racks will not operate in that mode, due to the CEM's wanting to see 3 phase, and that the CEM itself operates off one of the phase feeds and that if you do indeed need to operate in 1 phase mode if allowed), make sure the CEM is getting powered.

Both Sensor CEM Classic and CEM+ control modules do not care about the phase angle of the three phases feeding them. So, as long as all three phase inputs each have 120V applied to them with respect to neutral, it does not matter which phase the 120V comes from. This supports the A+B to L1 and C to L2 scenario in my earlier post.

ST

 

[derekleffew]

Both Sensor CEM Classic and CEM+ control modules do not care about the phase angle of the three phases feeding them. ...

Then why must the CEM be told whether the pack is being fed with single or 3Ø power?

 

[STEVETERRY]

Then why must the CEM be told whether the pack is being fed with single or 3Ø power?

In order to map the right zero-crossing circuit to the right dimmer.

Think of an SR6 layout for 3-phase and single phase

Dimmer............3 phase............Single Phase

1,2.................A.....................L1
3,4.................A.....................L1
5,6.................B.....................L1
7,8.................B.....................L2
9,10................C....................L2
11,12..............C.................... L2

So, in single-phase mode, one half of the dimmers are mapped to each zero-crossing circuit, while in 3-phase mode one third are mapped to each zero crossing circuit. This is done in software.

Note that in the unbalanced scenario where the racks stays in 3-phase mode but has A+B connected to L1 and C connected to L2--from my original post--this re-mapping is not needed because the right zero-crossing circuit is always on the right dimmer.

ST

 

[Shawncfer]

As to your second question: this is a fairly common scenario, and one that is anticipated by NEC section 520.53 (O)(1), which states:

Neutral Terminal. In portable switchboard equipment designed for use with 3-phase, 4-wire with ground supply, the supply neutral terminal, its associated busbar, or equivalent wiring, or both, shall have an ampacity equal to at least twice the ampacity of the largest ungrounded supply terminal.
Exception: Where portable switchboard equipment is specifically constructed and identified to be internally converted in the field, in an approved manner, from use with a balanced 3-phase, 4-wire with ground supply to a balanced single-phase, 3-wire with ground supply, the supply neutral terminal and its associated busbar, equivalent wiring, or both, shall have an ampacity equal to at least that of the largest ungrounded single-phase supply terminal.

What this means is that if a portable dimmer rack or pack does not have an internal method of switching between three-phase and single-phase (as most large racks do not), it must have a 200% rated neutral terminal.

Why? Because it is assumed that the road electrician, when confronted with a single-phase service for his three phase rack is not going to say "Gee, Mr. Merrick, we can't do a show tonight--we only have single-phase". He or she is going to take the two most lightly loaded phases of the dimmer rack and connect them to L1 of the single-phase service, while the third leg will get connected to L2 of the service. This is a classic "show must go on" event. This is fine, as long as the rack neutral terminal can handle the overcurrent caused by the imbalance. Any Listed rack will be able to do so.

Im not quite sure I understand.

And in single phase, are there two legs, a nuetral and a ground? Or just one leg?

Qualified Personnel. The routing of portable supply conductors, the making and breaking of supply connectors and other supply connections, and the energization and de-energization of supply services shall be performed by qualified personnel, and portable switchboards shall be so marked, indicating this requirement in a permanent and conspicuous manner.

So if Im doing lighting for a band on tour, but I dont have enough expereince to be ETCP certified, then I cant hook a rack to a disconnect?

 

[derekleffew]

... Note that in the unbalanced scenario where the racks stays in 3-phase mode but have A+B connected to L1 and C connected to L2--from my original post--this re-mapping is not needed because the right zero-crossing circuit is always on the right dimmer.

Sorry, I'm still not getting it. What's this zero crossing circuit of which you speak (and why does it matter)? Only dimmers 7,8 are different.

Think of an SR6 layout for 3-phase, single phase, and "unbalanced" (3Ø rack on 1Ø service)

Dimmer..........3Ø..............Single Phase...."unbalanced"
1,2.................A.....................L1...............L1
3,4.................A.....................L1...............L1
5,6.................B.....................L1...............L1
7,8.................B.....................L2...............L1
9,10................C....................L2...............L2
11,12..............C.................... L2...............L2

Hypothetically, given a Sensor SP6 pack, 12x2.4kW dimmers, set up for 3Ø operation,
when encountering a single phase or "split phase" service,
the user has two options:

A) Re-phase the pack by <following the manufacturer's directions> AND re-configure the CEM. Black cam into L1, red unused, and blue into L2.
OR,
B) "Cheat" with your "unbalanced" method by Cam-lok tee-ing the black and red together on L1 and the blue by itself on L2; and do nothing to the CEM.

Provided one had enough single phase power available, why would a user choose one method over the other?

Members of ControlBooth are ALWAYS encouraged to keep safety as a top priority. Forums are monitored by the CB Staff, but may not be able to react immediately. We reserve the right to edit or delete posts which we feel are unsafe, or discuss unsafe practices or materials. ControlBooth shall not be responsible for damage, injury or death resulting in any information posted on ControlBooth. When in doubt, always consult a qualified professional in person.

 

[derekleffew]

... So if Im doing lighting for a band on tour, but I dont have enough expereince to be ETCP certified, then I cant hook a rack to a disconnect?

Usually, you hand your Tails or the male ends of the Cam-Lok cables to the House Electrician or other venue personnel, and (s)he does the Tie-in. Next, you verify that the stagehands have run the Feeder appropriately. Mis-matched Cam-Lok colors should be a huge warning flag. Next, with all of your equipment off, you ask that the service be energized. Once it's hot, you meter the power to ensure the voltage is correct. (Always meter the power, every time! Trust no one. No one should be offended seeing you check his/her work.) Then and only then, do you turn on your touring equipment.

 

[STEVETERRY]

Sorry, I'm still not getting it. What's this zero crossing circuit of which you speak (and why does it matter)? Only dimmers 7,8 are different.

Hypothetically, given a Sensor SP6 pack, 2x2.4KW dimmers, set up for 3Ø operation,
when encountering a single phase or "split phase" service,
the user has two options:

A) Re-phase the pack by <following the manufacturer's directions> AND re-configure the CEM. Black cam into L1, red unused, and blue into L2.
OR,
B) "Cheat" with your "unbalanced" method by Cam-lok tee-ing the black and red together on L1 and the blue by itself on L2; and do nothing to the CEM.

Provided one had enough single phase power available, why would a user choose one method over the other?

There are effectively three dimming engines in a three-phase control module, each synced to the zero-crossing point of the three phases. Dimmers on each phase must be "told" which dimming engine to operate from. That's the 3-phase/single-phase setup in a CEM.

Don't forget that the NEC does not require a 200% neutral in cases where the rack is designed to be converted from single to three phase. In that case, the neutral only has to be as large as the largest phase conductor in single phase mode.

So, the "cheating" mode (as you call it) should not be used if the rack can be converted. If the rack cannot be converted, there is no choice, but the neutral will be 200%.

ST

 

[STEVETERRY]

Sorry, I'm still not getting it. What's this zero crossing circuit of which you speak (and why does it matter)? Only dimmers 7,8 are different.

Glossary entry Dimmer, zero crossing referenced covers the zero crossing circuit.

Actually, dimmers 5,6,7,8 move as the B phase dimmers are split between L1 and L2 (A and C when in 3-phase mode).

ST

 

[JD]

The zero cross detector (on digital control mods) starts a countdown that ends and restarts at the next cross point. The firing circuit calculates what the count should be when it fires the SSR.

If the wrong cross detector were selected for a specific dimmer mod, that dimmer would be on at 1/3 or 2/3 brightness with the dmx on that channel being at 0.

In true single phase, the setting would not matter as the cross point would be the same on all of the hot legs. However, in the real world, "single phase" may actually be two phase legs off of a 3 phase source. In this case, the cross detectors must be routed to the proper dimmer mods.

 

[Shawncfer]

Once it's hot, you meter the power to ensure the voltage is correct. (Always meter the power, every time! Trust no one. No one should be offended seeing you check his/her work.) Then and only then, do you turn on your touring equipment.

Okay, I know how to meter it. I just want to make sure Im understanding you correctly. So with the disconnect hot, are my cables not connected to the dimmers yet? Or distribution or whatever? How do I check voltage on the legs if theyre connected?

And Im still wondering. In single phase, are there two legs, a nuetral, and a ground? Or just one leg?

 

[MNicolai]

When connecting a distro to a company switch (or similar power source), you want the cables from the distro to the company switch to be connected properly before turning on the power source. Arcs, arc-flashes, and potential for other bad situations is reduced when the conductors are mated while they are not carrying electricity. When you flip the switch, power then should safely flow as far as your distro.

After the distro, it is dependent on your particular situation. Cables like camloks should always be connected before they are turned on, be it into a distro, a portable dimmer rack, a generator, or anything else you may be connecting these cables to. It's dangerous to mate connectors with so much raw power available.

Single-phase systems have two hots, a neutral, and a ground. Each hot is 180deg apart from the other, and conventionally at 120v (but can vary). A voltmeter measuring the potential difference between either hot and the neutral should read 120v, however the potential difference between both phases is 240v. Most single-phase systems are used in houses as 120v legs. However, the advantage of being able to tap into 240v is useful for motors and large appliances such as stoves and laundry machines.

Three-phase systems on a wye-configured 120/208v transformer have five wires. L1, L2, L3, neutral, and ground. The neutral and ground are bonded together, therefore having a potential difference of 0v between them. Each hot wire to neutral will read 120v, while between phases a voltmeter will read 208v.

 

[Shawncfer]

Okay so I wanna ask some questions with pictures

So power comes out a disconnect and into something like this right?

From there, the Camlocks daisy chain off to a dimmer rack correct? And then if there are two dimmer racks can the cam locks daisy chain off one rack into the other?

In the picture above theres a row of plus and it has A plug coming out but only one, and I have no idea where it goes. And the top row has one plug comming out, but once again I have no idea where it goes or what its for.

Then the two rows go out and connect to the sound equipment like this right?

What kind of cables are those?
Or the other two that I dont know what they're for?