115 volt AC to 220 volt AC

[Chris15]

Chris, from a quick glance it appears that the top-left relay is redundant. The top-right relay can't energise if there's no voltage on the top incoming line anyway.

This would probably be true, I did a rough design and neglected the system optimisation phase...

Depending on how you built this in terms of perhaps involving low voltage in the control systems, there may still be advantage in involving the dual step relays if there is a supply cap that would hold a charge and not disconnect quickly enough...

You could also expand the design for a three phase system, but all of this relies on being able to get the relevant phases of supply in the space you need them...

Oh and to solve the issue in a safe and compliant manner, use either a step up transformer (bearing in mind the reduced amount of current) or to have a qualified electrician install the relevant circuit for your needs.

 

[JD]

Bridging the neutrals is not cool either. There is no guarantee that two random outlets will be fed by the same load panel. In this case, you would be bonding two panels with a piece of #12 or #14 wire. In the case of our building, there are 5 load panels. Although voltages on neutrals due to drop tend to be small, the current can be massive. Need to keep distribution in a "Star" topography.

 

[Chris15]

Bridging the neutrals is not cool either. There is no guarantee that two random outlets will be fed by the same load panel. In this case, you would be bonding two panels with a piece of #12 or #14 wire. In the case of our building, there are 5 load panels. Although voltages on neutrals due to drop tend to be small, the current can be massive. Need to keep distribution in a "Star" topography.

Neglect to bridge them and you can easily kill your gear because of those very neutral currents...

I hope by now people have worked out that this discussion is purely academic. The compliant method I mentioned at the end of my last post...

 

[CBR372]

Getting 200-240VAC with 120VAC Pigtails.

So I have a question. This is all hypothetical as my theatre's don't have access to any movers that require 200-240VAC or any constant or relay dimmer modules.

Lets say I want to run some 200-240VAC moving lights on my 120vac 3-phase dimmer system. If I put a relay module lets say dimmer 1 which is on Phase A and then another relay in dimmer 2 which is on Phase B. Then I built a reverse 2fer (2 males, one female) and that took those two circuits at the pigtail end and took both hot leads from the 2 circuits and only one neutral and both grounds, would that create 200-240vac? I've been really confused reading other posts about how the difference between phases is 208 or 240 as it doesn't really explain how to make 200-240vac.

Thanks guys!

Again I just want to know this so i can stop trying to wrap my head around it!!!

 

[Sean]

Re: Getting 200-240VAC with 120VAC Pigtails.

Well....

First of all this is a bad idea from a safety standpoint: you'd have a hot MALE connector.

Electrically you'd have two hots, and a ground. Voltage between the two hots would be ~208v.

The way you really do this is to get a Power Distro (PD) that is "tied-in" to the building's power, usually at a company switch.

Again, DO NOT do what you're suggesting. It's a really bad idea.

 

[tyler.martin]

Re: Getting 200-240VAC with 120VAC Pigtails.

That would not "make" 240V. potentially very dangerous. Get an electrician in to see if there are any 208 lines in your building

Splitting a fixture across phases is bad IIRC.

 

[ajb]

Re: Getting 200-240VAC with 120VAC Pigtails.

Splitting a fixture across phases is bad IIRC.

Any 208V fixture connected to a 120/208 Y system is "split" across phases. . .phase-to-phase is the only way to get 208V in such a system.

To the OP: What you describe would, in fact, do what you're after, but doing it safely is a bit more complicated than you've described. For one thing, you'd need a very specific interlock arrangement to ensure that with a load plugged into the female and one male plugged into a live receptacle that the other male did not wind up at line voltage, and that the load only gets either both phases or none. For another, the NEC requires that any multiwire branch circuit (which is what you're creating by combining those two separate 120V circuits) be equipped with an overcurrent protection device that simultaneuously interrupts all line conductors--in other words, a single two-pole common trip breaker, or two single pole breakers with the handles mechanically tied together. This is not something that is easily accomplished in an off-the-shelf dimming system. It may be possible to place an OPD somewhere within the device that joins the two circuits that will satisfy your AHJ, but that would require some close reading of the NEC and/or local codes--and more importantly, you'd have to convince an inspector that it's safe and compliant, which would possibly be the hardest part.

 

[mrb]

Re: Getting 200-240VAC with 120VAC Pigtails.

Hubbell and one or two other manufacturers make a device that does this safely with necessary interlocks. Theyre used in marine applications. Too costly for it to make sense for this application, just have an electrician install the circuits you need, or get the proper distro if you have a company switch to connect to.

as others have said, DO NOT do what you propose. It is very dangerous.

 

[derekleffew]

Re: Getting 200-240VAC with 120VAC Pigtails.

Furthering what's been said, note that products exist to go from one 3Ø to three 1Ø outlets:
(one example)

PowerFLEX™ Cable Assemblies: 3Phase 3Fer | Lex Products

but NOT the reverse (not legally, at least).

If one were so inclined, one could likely find pictures at various "wall of shame" sites. Pictures depicting bad, illegal, or unsafe practices are frowned upon here at ControlBooth.

 

[CBR372]

Re: Getting 200-240VAC with 120VAC Pigtails.

Thanks guys! I'm just trying to understand how 208 is made from 120v. our building doesn't have a company switch, so "legally" the only way to do this whould be to have an electrician install a few 208-240 circuits around the grid? (these would be a black box application).

 

[derekleffew]

Re: Getting 200-240VAC with 120VAC Pigtails.

For explanation of single-phase and three-phase circuits, see Single-phase power systems : POLYPHASE AC CIRCUITS and the pages that follow.

Correct, the only way to obtain 220V or 208V circuits is to have a licensed electrician install them.

 

[n1ist]

Re: Getting 200-240VAC with 120VAC Pigtails.

One other way would be to use a 110V non-dim circuit feeding a step-up transformer. It may be a cheaper solution for a 1-off rental. For permanent use, I'd get the correct circuit installed.
/mike

 

[jjkool]

Re: Getting 200-240VAC with 120VAC Pigtails.

I bet if you were to get a proper rating on your system it isnt @ 120v its more then likely @ 208v

 

[ajb]

Re: Getting 200-240VAC with 120VAC Pigtails.

I bet if you were to get a proper rating on your system it isnt @ 120v its more then likely @ 208v

huh?

If the OP's nominally 120V circuits are actually running at 208V, then there's something seriously wrong. . . and they'd probably have noticed issues already.

If you're suggesting that the OP's building infrastructure is wired with 3Ø 120/208V Y distribution. . . well, that was a given in the opening post, and the resulting discussion was entirely based on that fact.

 

[derekleffew]

Re: Getting 200-240VAC with 120VAC Pigtails.

Hubbell and one or two other manufacturers make a device that does this safely with necessary interlocks. ....

A post on SML has reminded me of this device: Voltage Converter: 220 230 240 Volt Power from 110 115 120 Volt Outlets, which we discussed here: http://www.controlbooth.com/forums/lighting/19720-115-volt-ac-220-volt-ac.html.

 

[kicknargel]

Re: Getting 200-240VAC with 120VAC Pigtails.

huh?

If the OP's nominally 120V circuits are actually running at 208V, then there's something seriously wrong. . . and they'd probably have noticed issues already.

If you're suggesting that the OP's building infrastructure is wired with 3Ø 120/208V Y distribution. . . well, that was a given in the opening post, and the resulting discussion was entirely based on that fact.

I think what he's getting at is the 208V can probably be installed with no new wiring, just modifications at the breaker and a new outlet. By a licensed electrician of course, but maybe not too expensive.

 

[SalvatoreDelorean]

Pulling 240v from two 120v circuits

I'm lighting a small corporate event in an office building, and I have a few Mac 575s I was hoping to use. They run on 200-240v, but there aren't any accessible 240v circuits in the building. I was talking to the building electrician, however, and he told me it would be possible to pull from the hots of two normal 20a 120v circuits, make an adaptor, and wind up with 208/240v. I've heard of things like this, and it makes sense to me in theory, but seems incredibly sketchy. Is this safe, and if so, how would I go about doing this?

My first instinct would be to do something like wire up a twofer in reverse with two male edisons to plug into the 120v wall circuits, and a female L6-20 on the other end, but that just seems like a bad idea. In my experience, jury-rigged solutions like this rarely end up working well, so I'm wondering if this is a more common practice than I'm aware, or if this building electrician happens to be an idiot.

It also doesn't seem like it can be that simple. Would drawing from two 20a 120v circuits give you 40 amps of 120v, or 20 amps of 240v? Would a transformer of some kind be needed to step up the voltage?

 

[LavaASU]

Re: Pulling 240v from two 120v circuits

Ok, not quite. An actual electrician should be able to get you 208 or 240V (depending on if the building is single or 3 phase), but it needs to be run through a panel with appropriate double pole breakers. 2 20A circuits on the same phase would get you 40A of 120V. 2 20A circuits of a different phase would get you 20A of 208/240. You would not need a transformer in this case.

 

[ProgrammerInTraining]

Re: Pulling 240v from two 120v circuits


like this?

 

[derekleffew]

Re: Pulling 240v from two 120v circuits

View attachment 8444
like this?

I thought we had set you straight when you originally posted that picture in this thread: http://www.controlbooth.com/forums/lighting-electrics/27159-120-208-240v-questions.html .
.