Control/Dimming 208 volt on 2P&G?

[STEVETERRY]

Actually you said:

This is where we apparently disagree.

To DMXpro (actually, a somewhat unfortunate user name when considered in this thread):

I think (in fact, I insist) that you need to listen to people who know far more than you on this thread. Hopefully, a significant change in your world-view will occur before you seriously hurt yourself or others.

Sorry if this offends the sensibilities of any CB'ers, but there you have it.

ST

 

[MPowers]

To DMXpro (actually, a somewhat unfortunate user name when considered in this thread):

I think (in fact, I insist) that you need to listen to people who know far more than you on this thread. Hopefully, a significant change in your world-view will occur before you seriously hurt yourself or others.

Sorry if this offends the sensibilities of any CB'ers, but there you have it.

ST

Well said Mr. Terry. And thank you for saying it. Far more diplomatic than my Irish Temper would have allowed.

 

[DMXpro]

Actually you said:

This is where we apparently disagree.

Well, the last thing I want to do is start an internet argument, so I think I should clear this up.
I don't think I worded my posts very carefully, but I do agree with you. There is no situation where using 208V service on NEMA 5-15 is acceptable. The purpose of this whole thread was me asking how 208V works on stage pin (or any connector with only three conductors).

 

[danTt]

I think you are still confusing three phase power with 208v power. They are very different things. An L6-20 has only three connectors, 2 hots and a ground, and carries 208v. A L21-30 3 phase plug has 5 connectors, (3 Hot, 1 neutral, and 1 ground) and "carries" both 120v and 208v.

 

[TimMiller]

Movers that use 208 or 240 use 2 hot legs and a ground. So two of the prongs of a plug called x and y are hot the third is always ground.

To clear up the 208/240. In our power distros we have 3 phase service comming in but movers only use 2 of the 3 legs. They are typically fed off of a 2 pole 20 amp breaker. There are many variations of 3 phase power, they most common in theaters is 120/208. If you meter from any of the 3 legs to ground you get 120. If you meter between any of the three legs you get 208. The only time all 3 legs together are used is to drive motors and they use a 4 wire plug. 3 hots and ground. If you search around on here there are discussions on the different types and voltages of 3 phase systems.

 

[ProgrammerInTraining]

since the thread came back, i got something regarding nema 5-15's acceptable voltage..
what about 277V on a nema 5-15? I've seen a funky setup where lights from a prg shop in europe were sent and they needed one 277V hot leg, neutral and ground. a transformer was sent that took the 120/208v camlock and output 277v hot to neutral and 480v hot to hot on the cams. note that I did not set it up it was prg ml techs, I was the electric supplying power. they plugged the 277/480v into a dadco distro that had edison outs, ran an 5-15 cable from the disto to the light and put the proper adapter to it.I thought it was unsafe but it worked.

 

[RickR]

It will work until the over taxed part fails. Not IF it fails, WHEN it fails.

 

[TJCornish]

since the thread came back, i got something regarding nema 5-15's acceptable voltage..
what about 277V on a nema 5-15? I've seen a funky setup where lights from a prg shop in europe were sent and they needed one 277V hot leg, neutral and ground.
...
I thought it was unsafe but it worked.

Being unsafe but working are not mutually exclusive.

The NEMA 5 series plugs/receptacles are rated for 120v ONLY. That holds true if an intern does it, if PRG does it, your boss does it, etc. The copper in the receptacle will pass the voltage, but it's still very wrong and dangerous.

Summing up the thread:

- 3-phase does not necessarily correlate with a specific voltage - i.e. it's not correct to speak of a plug/receptacle with two current-carrying conductors and a ground as a 3-phase device, even if it happens to be sourced from a 208-volt 3-phase service - it's still a single phase device running at 208 volts, and in almost all cases related to lighting equipment, that same fixture will be perfectly happy running at 240 volts.

- NEMA 5 series devices are 120v ONLY - one hot, one neutral, one ground.
- NEMA 6 series devices are single phase 208/240 volts only (listed as 250 volts) - two hots, one ground.
- NEMA 14 series devices are single phase 208/240 volts (listed as 250 volts) with 4 wires - two hots, one neutral, one ground.
- NEMA 15 series devices are 3-phase 208 volts (listed as 250 volts) with 4 wires - three hots, one ground.

More NEMA types can be found here:
http://www.stayonline.com/reference-nema-straight-blade.aspx
and
http://www.stayonline.com/reference-nema-locking.aspx


- The NEMA keying system is to ensure that when an end user sees a receptacle that fits their device - i.e. a 5-15P on a hair dryer and a 5-15R or 5-20R on the wall somewhere - that it won't blow up on them by being the wrong voltage. It doesn't matter that the copper in the plug can handle a higher voltage.

- Just because something rigged up is "working", doesn't mean it's acceptable; it's just that the disaster hasn't happened yet.

- If you don't report a dangerous condition to your boss, steward, building official, etc. you potentially assume legal liability for an unsafe situation.

 

[n1ist]

In addition to using the correct plugs, you also must use the correct cable. 300V insulation won't cut it on either 277V or 480V.
/mike

 

[tdrga]

300V insulation won't cut it on either 277V or 480V.
/mike

Before someone asks this question, I'll throw it out as a learning opportunity:

480v is obvious, but why not 277v?

(hint: Peak voltage vs. RMS voltage)

-Todd

 

[PeteEngel]

Movers that use 208 or 240 use 2 hot legs and a ground. So two of the prongs of a plug called x and y are hot the third is always ground.

To clear up the 208/240. In our power distros we have 3 phase service comming in but movers only use 2 of the 3 legs. They are typically fed off of a 2 pole 20 amp breaker. There are many variations of 3 phase power, they most common in theaters is 120/208. If you meter from any of the 3 legs to ground you get 120. If you meter between any of the three legs you get 208. The only time all 3 legs together are used is to drive motors and they use a 4 wire plug. 3 hots and ground. If you search around on here there are discussions on the different types and voltages of 3 phase systems.

What I haven't seen here (please correct me if i'm wrong) is the difference between 208v 3 phase and 208v single phase on a connector like an L6-20. Given that an L6-20 connector has 2 hots and a ground, that doesn't preclude it's acceptance of and delineation for 3 phase power. requirements for some gear require 208v single phase (which has 2 hots from the same phase of power plus ground) and some gear requires 208v 3 phase (which has 2 hots from either the a/b, b/c, or c/a phases of a system, plus ground). Don't ever think that just because there are only 2 hots, that you are not using 3 phase power. Knowing what system you are utilizing, how your gear (lighting, sound and rigging) operates with said systems, and then appropriately loading all phases as equally as possible is kind of important.

 

[danTt]

I'm reading your post, and getting confused. If you have two hots coming from the same phase of power, you should meter 0 "between" them. If you are talking split-phase power, you should meter 240 volts between them. It's only when you meter between 2 different legs of a 3 phase system that you should see 208. That is, if I understand this correctly, which may or may not be entirely true. This Article does a good job of explaining it visually.

 

[TJCornish]

What I haven't seen here (please correct me if i'm wrong) is the difference between 208v 3 phase and 208v single phase on a connector like an L6-20.

There is no difference here, because there's no such thing as a single-phase 208 volt distribution source (the service panel), unless you're using a Variac to derate a 240 volt supply for testing, or something.

Given that an L6-20 connector has 2 hots and a ground, that doesn't preclude it's acceptance of and delineation for 3 phase power.

The L6-20 by definition IS a single phase device, period. The fact that it's often (probably the majority of the time) fed from a 3-phase service doesn't change this; the L6 series plugs provide a single phase circuit - only one current path.

Don't ever think that just because there are only 2 hots, that you are not using 3 phase power. Knowing what system you are utilizing, how your gear (lighting, sound and rigging) operates with said systems, and then appropriately loading all phases as equally as possible is kind of important.

Balancing loads between phases is indeed a good thing, and it is useful to know whether your distribution comes from a 3-phase or single-phase service, however I've never seen a device that couldn't work on either 208 volt or 240 volt power. Most require no modification to switch supplies as they're only about 10% different, and a few can be adapted by changing a buck/boost tap inside the device.

 

[TJCornish]

I'm reading your post, and getting confused. If you have two hots coming from the same phase of power, you should meter 0 "between" them. If you are talking split-phase power, you should meter 240 volts between them. It's only when you meter between 2 different legs of a 3 phase system that you should see 208. That is, if I understand this correctly, which may or may not be entirely true. This Article does a good job of explaining it visually.

The North American nomenclature is somewhat confusing. 208 volts implies that somewhere the power came from a 3-phase system (though that doesn't mean that your outlet is magically 3-phase if it only has 2 current carrying conductors), and 240 volts implies that the power was sourced from a single-phase system - one wire on the pole to a center-tapped step down transformer, which provides a single phase 240 volt circuit with a center tap allowing you to have two 120 volt circuits which happen to be 180 degrees out of phase with each other. Thinking from the point of the secondary of the step down transformer, it is indeed easier to think of this as two-phase power, however it all came from a single wire off the power pole, and thus is known as single-phase power.

 

[PeteEngel]

On the subject of 208v Single Phase, I will have to question the trade show electrical companies that offer me both 208v single phase or 208v 3 phase as a power option (see LDI 2012 exhibitor package). 208v Single phase is a bit of a misnomer. It is more like 220v as i understand, but that is for smarter people than me to explain. As for a lighting fixture that requires 208v and it gets fed 240v, try pushing 240v through a 208v magnetic ballast. The lamp will probably suffer early failure. Not sure what the long term effects will be on the ballast but I don't suggest trying it out. An electronic auto switching ballast should easily handle the difference since, as the name suggests, it reads all voltages and feeds the lamp what is required.

 

[danTt]

Another Place with some good information, taken from the split-phase page on the cb wiki.

 

[TJCornish]

On the subject of 208v Single Phase, I will have to question the trade show electrical companies that offer me both 208v single phase or 208v 3 phase as a power option (see LDI 2012 exhibitor package). 208v Single phase is a bit of a misnomer. It is more like 220v as i understand, but that is for smarter people than me to explain.

3-phase electricity requires all 3 phases to be called 3-phase power. Single phase power refers to a circuit with only one current path - either hot to neutral, or hot to hot. You can have 208 volt single-phase power in the sense that it's delivered via 2 legs from a 3-phase service, perhaps using an NEMA 6 or L6 receptacle.

The old 110/220 volt standard has been replaced in recent decades with the modern 120/240 volt standard for single phase services. You're unlikely to find 220 volts anywhere in the real world, apart from a Variac on your bench, anyway.

As for a lighting fixture that requires 208v and it gets fed 240v, try pushing 240v through a 208v magnetic ballast. The lamp will probably suffer early failure. Not sure what the long term effects will be on the ballast but I don't suggest trying it out. An electronic auto switching ballast should easily handle the difference since, as the name suggests, it reads all voltages and feeds the lamp what is required.

Do you have any examples of lights that cannot accept both voltages? I'm familiar with some older Martins that need to be manually switched via a jumper wire, but I'm unaware of any production lights ever made that cannot run on both voltages, either by having an automatic switching mechanism, universal power supply, or a manual switching mechanism?

 

[JD]

The old 110/220 volt standard has been replaced in recent decades with the modern 120/240 volt standard for single phase services. You're unlikely to find 220 volts anywhere in the real world, apart from a Variac on your bench, anyway.

Well, yes and no. There is actually very little standard to this "Standard." Your voltage is whatever the power company delivers to your door. Sometimes, it's 110, sometimes 115, sometimes 120, sometimes 130. If you complain the likely response will be "Yea, well."

Line voltage in OUR area is pretty tight in the 125 to 127 range. Each time the power company upgrades equipment, it is likely to climb a bit.

120, 208, 240, 277 etc., Good numbers to generalize on, but it is more the ratio between them that is important. If your 120 tracks high, so will your 208 or 240. (If 130v then 225 / 260) Yet, we still have to use SOME number!? So, why not use 120/208/240. If you average it out over the whole US, it is probably close to that.

Still, although off topic, the biggest problem with all of that is lamps. Generally, theater lamps come in 115 and 120 flavors. Dimmers are about 97% efficient, so 120 volt lamps are acceptable on 125 volt sources. Dimmers can often be calibrated to max out at 120 volts even if the line is up at 130.

As for magnetic ballasts, the saturation of the core provides some regulation. Usually there is a 208 and a 240 tap. I would still use the 208 tap even if it was running high at 225. Because of core saturation, you are not going to reduce the lamp life that much, where as on a fixed tap ballast, low voltage will cause drop-out problems. Auto-range E-ballasts eliminate the problem.

208 single phase: If all you are getting is two hots and no neutral, then there is no phase relationship to anything else and it could be considered "single phase." If you are getting 208 with two hots and a neutral, then you actually do have a phase relationship as there is 120 between each hot and the neutral, but 208 between your two hots. Does it matter? Not really. Even though dimmers are connected to multiphase power, they are single phase devices. Any 208 movers are single phase as well. Just be sure of your headroom on your neutral capacity.

 

[FMEng]

The old 110/220 volt standard has been replaced in recent decades with the modern 120/240 volt standard for single phase services. You're unlikely to find 220 volts anywhere in the real world, apart from a Variac on your bench, anyway.

They never were the standard. The reason for odd voltage numbers floating around over the years, like 110, 220, 115, 230, 200, etc., is from the electric motor industry. Motors can only provide the rated horsepower at some minimum applied voltage. The nameplates on motors list the MINIMUM rated voltage for that motor, NOT the NOMINAL voltage. If you see a motor that says it wants 230 Volts, then it is intended to go on a 240 V source, taking into account voltage drop in wiring and controllers that cannot drop it to less than 230 V during starting currents. This is a big deal in large buildings and factories where a long run of wire could result in too much voltage drop. Normally, in theater, we don't think much about voltage drop because a slightly dimmer lamp isn't a big deal. But a stalled motor can lead to a fire or other costly malfunctions.

 

[PeteEngel]

The fixtures I'm most familiar with are the RJ D'Artagnan profiles. The magnetic ballast operate at 208v 60hz, 230/245 50hz. They have a manual switch between the voltage options. Not for operation at 240v 60 hz. Guess this is a function of the choke design. Electronic Power Supplies are much more prevalent (and less expensive than in the past) in our industry for a number of fixtures so voltage variables across the world are less of an issue than with magnetic ballasts that needed to be designed to accept multiple voltages to cover various power systems. As for the single/3 phase questions, there is obviously a wide variation in the vocabulary across our industry, and much like lighting design, people can hold onto their electrical ideas to the exclusion of accepting new or additional information. As was stated earlier, there are some gaps in electrical knowledge in our biz (i admit my shortcomings). I do get questions from clients concerning operations on 220v systems, so it isn't as theoretical as one might seem.