Sound Issue Connecting Blu-ray player

[Steve Guttag]

I'm guessing you are referring to your findings in Canada and are perfectly believable and consistent. In my area of the US (Middle Atlantic region), I typically find 120V in the suburbs of DC but a bit lower within DC however...there are exceptions to that rule too. It can also depend on how the electrician taps a step down transformer as often the power coming into a building is 277/480 in commercial spaces. If the electrician measuring the incoming, and taps the transformer correctly, you end up with nominal 120/208...if not it can indeed be low or high. I had one theatre that tended towards 125V and others that tended towards 115.

In a suburb in Maryland, I was on a government owned facility and found that the voltage was tending towards 115V and caused all of the current to run a bit higher on the rectifiers/ballast as they were tending towards only 200VAC L-L. I asked for the transformers to be retapped for 120V L-N and you'd think I asked for the moon and the stars despite the transformer(s) having the taps that clearly identified what should be used based on incoming voltage. In some of the systems we were running 6KW lamps and the low-bid breakers/load centers would get VERY warm to the touch and would false-trip. Still they refused retap the incoming to attain 120V L-N 208 L-L. I guess the manufacturer of the transformer put those extra taps in for show.

[Stefan Scholz]

I can just tell for my home in Europe.
Some networks are the old threephase distribution networks, like in Berlin Center where I live. Those are star connection 220 V, grounded starpoint, delta threephase 380 Volts. They use a mid voltage network, that is 10 kV. Rarely exceeding 223 Volts in singlephase.
The theatre is in a newer distribution structure, mid voltage is 24 kV, with transformer feed at 242 Volts star connected to ground, and 420 Volts in threephase delta.
On sunday mornings, with a lot of wind powering the crappy wind electricitry, the singlephase voltage goes up to 259 Volts, which I consider excessive. A switchoff would occurr at 264 Volts.

Even though the world wide rated voltage for singlephase is 230 Volts, in the US domestic this means grounded center tap, modern distribution tends to end up on the high end. With switchmodes, it doesn't really matter. They have to be designed to withstand 265 Volts input, and accept wide range lower inputs.

[Sean McKinnon]

Many higher power digital cinema projectors require 240 volt single phase power. It is very important in these installations NOT to use the 208 volt high leg and a leg from the center tapped transformer for the power connections.

I have installed plenty of Digital Cinema projectors including "higher power" ones on 208v circuits and have never ever had any issues. In fact the 208Y/120 configuration is by far the most common in my experience.

[Steve Kraus]

Regarding clothes dryers, it wasn't two hots and a ground but rather two hots and a neutral with the chassis "grounded" to the neutral. If hot should somehow contact the machine you get a short and the breaker blows. That aspect is fine. Chassis cannot go above a few volts.

Certainly the light bulb, and timer motor, etc, were across one hot and neutral. Very possibly the motor, too, with only the heating element spanning the two hots for 240V.

The danger was if neutral was broken for some reason. Then because of the 120V components, the body of the machine becomes hot at 120V. Newer setups use 4 pin plugs with a proper ground. Lots of old stuff out there with three pin cords, grandfathered in. My washer / dryer stack was and remains 3 pin. I'm too lazy to bother to replace cord and plug but I did break the neutral to chassis connection and hard wired a ground from the body to the outlet. I can't say what the code says about that but I do know having a real ground is safer.

There would be no issue if all the components were 240V. Then no neutral would be needed and that third pin could be a real ground. Then again even it was still a neutral being used as a ground, if it broke the body would not go hot without any 120V components.

I've never had an electric range but they might be similar.

[Scott Norwood]

The first theatre where I worked had 125v at the booth wall outlets. The biggest problem at that place was that light bulbs didn't last very long--we were always replacing light bulbs there. A solution for this is to switch to 130v bulbs (which appear orange-ish if used on 120v power, but which last longer at higher voltages), but they don't (or didn't) make colored bulbs designed for the higher voltage.

[Paul Finn]

Steve K.: "and hard wired a ground from the body to the outlet". I hope I assume correctly that you mean to the outlet mounting box which should be grounded? The outlet (receptacle) itself would only be three pin with a neutral but no ground.

The DP manufactures' voltage and current data listed earlier herein is missing one critical piece of information. Are the numbers applicable to single or three phase power requirements?? I seem to remember seeing Christie(?) literature having both single and three phase power wiring options for some models, depending on what electric source is available. Clearly the voltage range indicated (200-240) puts the projector to be installed in a nominal 208Y/120V electrical system in the USA , using either single or three phase connections as required. If there is a choice, I would always use a three phase connection. If the only electrical source available is from a 120/240V single phase service, the 240V with the normal plus or minus 5% tolerance makes this source unacceptable for a DP installation application. Some adjustment method of voltage range correction/modification would be required, which is outside relevance of this discussion.

My earlier comments about 240delta/120V systems, were to give a heads-up that they may be encountered in retrofit installations. They were commonly used into the 1970s in numerous facilities like churches, schools, THEATERS, and commercial spaces where both single and three phase power was required but the installation did not justify separate services. Detroit for example, has hundreds of these installations yet today and I know of at least five theaters here in Michigan with them. Older versions of these services were based on the 230delta/115V standard of the times. The feeder and branch circuit conductors of the "high" leg in these systems should have orange insulation on only these wires for identification. However, orange insulated conductors may NOT be found in these older electrical installations. And, these delta services may not be usable for DP installations without modification due to the DP manufacturers' specified voltage range tolerances. ANSI C84.1 defines electrical system voltages and tolerances in use today in the USA and also proper designation nomenclature of the various electrical services.

Paul Finn

[Steve Guttag]

A big clue walking into a high-leg panel is the breaker layout. When the majority of the panel is missing every 3rd breaker...even before the panel cover comes off, you pretty much know the deal. If installing electrician taped the feeds then yes, more often than not, the high leg will have the orange tape (some have used yellow).

As for projectors having choices of single or 3-phase, most do not give the option. Those that use 4000W or smaller lamps typically only work with single phase. Those that have larger lamp capabilities, typically only accept 3-phase.

Barco, on their 32B systems did/do offer some choices on wiring based on one's native country. There is the typical US configuration with 3-hots and ground (NEMA15), which they call "Delta" even if we have a neutral referenced to ground and 120V L-N...it does not come into play for this model. The wye system they are referring to would be in a European country where it is nominally 230V Line to Neutral and 400V nominally leg-to-leg. One, using a set of links configures the input for the type of incoming. Without even looking at the schematic I'd be willing to wager, since Barco uses three separate supplies in the 32B system that for 208 Delta systems they wire each supply L-L such that one supply is A+B, the next is A+C and the third supply is B+C phases since each supply is a single phase supply. However, if in a country with 230V Line to Neutral, that each supply gets its own phase and neutral. Perhaps it is this model of projector where you are getting the impression that they are expecting 230V rather than 208V. I can assure you, the individual power supplies that comprise this projector work JUST FINE with lower voltages. They're switch mode and will take whatever is coming in and then convert it to what it needs. All that is really going to change based on the incoming voltage is the current.

The new Barco SP4K-C series are the only ones I know where you get choices of single or 3-phase. The SP4K series are designed to no only go into new installations but to replace whatever came before it and are therefore designed to be as accommodating as possible. They are laser and draw significantly less current than their xenon counterparts (seriously...they draw, at most 14A single phase at 200V even while outputting up to 23,500 lumens. Wiring the unit as 3-Phase only drops the current to 11A...which is not as good a savings as one would expect on a linear supply (like a rectifier for film based systems). The only advantage I can see to wiring 3-phase in this application is A) that is what was there and you are replacing a projector, B) you are really trying to balance the load on the panel and somehow going single phase will significantly tip your balance. From a cost standpoint, 3-Phase breakers and plugs are going to be more expensive than their single phase counterparts as single phase is used in both commercial and residential and single phase is significantly more prevalent. Unlike i a linear rectifier, where 3-phase significantly lowers the ripple on the DC output, for a switch mode supply, it is of little consequence on the output.

Steve Kraus, you are correct, it is two hots and a neutral and the neutral is attached to the chassis. It was/is NEMA 10 and it was used on dryers and ranges. And yes, it does have safety issues if things become loose. NEMA 14 replaced it and it is a 4-wire (L-L-N-G).

[Harold Hallikainen]

Since this started as an audio discussion, has anyone used "balanced power" where a typically 120VAC line with one side grounded (neutral) is converted to two 60 VAC lines? The balanced line substantially reduces the "touch current" or the current through the ground conductor due to EMI filter Y capacitors. This gets the chassis of equipment closer to ground since the current through the safety ground conductor is decreased. This reduces audio hum problems.

If 240VAC single phase (in the US, where the center tap of the transformer secondary is neutral and grounded), it seems that we could just power equipment that has a universal power supply on 240VAC and get "balanced power" that way. Has anyone done this as a way of reducing hum?

Harold

[Steve Guttag]

You'll find that sort of thing in recording studios and, as some of my Navy friends have told me...on ships. When working on balanced power 120V...things have to be VERY clearly identified cause common presumptions no longer apply and people could get hurt. One has to label things extensively (including any splices in junction boxes). See article 647 of the NEC.

[Sean McKinnon]

Paul Finn you may be looking at the difference between the lamp and electronics on some DC projectors. Some will require 200-240 single phase or 3 phase for the lamp and 100-120 or 200-240 single phase for the electronics. Usually there are internal jumpers to provide this power internally but for using a UPS these can be powered as separate feeds.

[Marcel Birgelen]

The new Barco SP4K-C series are the only ones I know where you get choices of single or 3-phase. The SP4K series are designed to no only go into new installations but to replace whatever came before it and are therefore designed to be as accommodating as possible. They are laser and draw significantly less current than their xenon counterparts (seriously...they draw, at most 14A single phase at 200V even while outputting up to 23,500 lumens. Wiring the unit as 3-Phase only drops the current to 11A...which is not as good a savings as one would expect on a linear supply (like a rectifier for film based systems). The only advantage I can see to wiring 3-phase in this application is A) that is what was there and you are replacing a projector, B) you are really trying to balance the load on the panel and somehow going single phase will significantly tip your balance. From a cost standpoint, 3-Phase breakers and plugs are going to be more expensive than their single phase counterparts as single phase is used in both commercial and residential and single phase is significantly more prevalent. Unlike i a linear rectifier, where 3-phase significantly lowers the ripple on the DC output, for a switch mode supply, it is of little consequence on the output.

Since there are no large moving parts in those projectors, it doesn't really make sense to connect such a machine to three phases, unless the infrastructure is already there. Balancing can easily be done by connecting projectors in other rooms to other phases, given there are other rooms.

I still think I'd always consider to go for a single-phase model, even if there is 3-phase infrastructure, since this allows for more flexibility to use the projector for other purposes.

[Steve Guttag]

It is pretty typical here to "match" the load centers so if breaker 1 and 3 are the projector, that is the case in every panel (presuming one panel per screen). The SP4K are not ordered by single or 3-phase...they are installed that way. By changing the straps, one sets up the power inputs to suit the available power.