Weird Electrical Service (What am I working with?)

[BenTev28]

Hello Control Booth geniuses! So, I'm doing in an install in an old theater, and I came across the electrical service in the attached image. As you can see, it has 3 hots in, as you might expect, with lugs after the fuses. What's weird is that it has nothing at all run to the neutral bus. I tested, and I've got 125VAC across each leg to the ground.... Obviously it would be completely unsafe and incorrect to treat the ground as a neutral, but I'm hazy on how this box is meant to be tied into. My best guess is that it's intended as a 4-Wire 208V service - 2 loads and a ground to equipment, no neutral necessary. Is this correct? Is there an existent distro for this kind of tie-in? Is it possible to connect it to something that will give me 115-120V on the other end, or can it only go out to 208V?

I'm sure this can't be an uncommon power feed, but it's strange to me.... please advise.

Thanks,
Ben Tevelow

 

[mstaylor]

This an equipment disconnect. It is made to run a motor of some type. I rent motor distros from one company that has no nuetral. You will need an electrician to modify it into anything useful for theatre.

 

[Footer]

This an equipment disconnect. It is made to run a motor of some type. I rent motor distros from one company that has no nuetral. You will need an electrician to modify it into anything useful for theatre.

Agreed. This type of disconnect is pretty common in many theatres that regularly do automated scenery. Odds are it is fed with no more then 50 amps. I have seen this type of disconnect put in so that the audio and lighting guys won't steal the automation power.

 

[BenTev28]

Jerks! I want to steal it for audio! It sounds like there's no safe way to do that, but if anyone has a brilliant idea, please share.

 

[mstaylor]

That's why you need an electrician. He can look at your setup and see if there is a way to pull a nuetral in. There is another possibility but I think it would violate the TOS to detail it.

 

[BenTev28]

Thanks mstaylor ... Yeah, I thought of that way but it's just such a bad idea I can't bring myself to do it. The main panel is very close, I'll look into having IBEW run a neural over

 

[JD]

Looks like an old run for HVAC to me. As long as it's Wye, an electrician should be able to fix things up. Sounds like Wye, but confirm the 208. (Untapped Deltas can sometimes fake you out.)

 

[Footer]

Jerks! I want to steal it for audio! It sounds like there's no safe way to do that, but if anyone has a brilliant idea, please share.

TD's aren't morons, they know your types! Now, if this is the only disconnect onstage, thats a bit of a jerk move. Odds are it is possible to pull a neutral into that disconnect. Depending on how its fed you could also convert it over to a single phase disconnect. Get an electrician in there to take a look and see if they can make it a bit more usable.

 

[BenTev28]

TD's aren't morons, they know your types! Now, if this is the only disconnect onstage, thats a bit of a jerk move. Odds are it is possible to pull a neutral into that disconnect. Depending on how its fed you could also convert it over to a single phase disconnect. Get an electrician in there to take a look and see if they can make it a bit more usable.

The jerk comment was totally a joke.... How would the conversion to a single phase work? I'm sure it's something I'd need an electrician for, I'm just curious about theory at this point.

 

[Footer]

The jerk comment was totally a joke.... How would the conversion to a single phase work? I'm sure it's something I'd need an electrician for, I'm just curious about theory at this point.

If the panel that feeds the disconnect has a neutral bus, you could just pull a hot and a neutral over, instead of 3 hots. You would lose a conductor and would lose 208 and your capacity would be divided by 3, but it would be a single phase disconnect that you could actually use. It all depends though on the panel feeding the disconnect. Your best bet is to pull a neutral over, but if cost was an issue this solution could be done if code allows it and you had an installer that would do it.

 

[derekleffew]

I want to steal it for audio! It sounds like there's no safe way to do that, but if anyone has a brilliant idea, please share.

Many audio companies carry an isolation transformer that generates its own neutral. I just used one this past weekend. A 400A that measured about 3'x4'x4' and weighed 920 lbs.

The box pictured has provision for a neutral in the upper left; pulling a neutral is really the best course of action. I'd also be concerned about lack of bushings in the knockouts on the bottom of the box.

This thread is already on very thin ice. From the CB Safety Policy:

The members of ControlBooth, in a effort to police themselves, have evolved the following: No discussion of "how-to" of rigging, pyrotechnics, human flight, stunt falls, weapons and electrical will be permitted. Our stock answer to these questions is always "Consult a qualified professional."

 

[mstaylor]

I was thinking about switching a hot to a nuetral but was afraid I would step over the TOS. Any solution is going to require an electrician.

 

[SHARYNF]

Do it the right way get an electrician to pull a neutral to the unit it is simple, and that box supports it. Making any other changes is going to be dangerous and will cost the same. This way from the disconnect with a proper neutral you can get e 120 feeds or a 208 feed or a three phase feed.
it is a simple thing for the electrician to do

Sharyn

 

[Chris15]

You're going to require the services of a qualified electrician to tie in to this box anyway, so they are really the best person to be asking.

You can safely connect a delta wired load to a supply without neutral, and that may be the input of a transformer, but doing anything wye is not going to be safe without addition...

 

[cdub260]

Pulling a neutral with the existing wiring is likely to be a code violation as the conduit is probably sized for the existing wire run. Adding a neutral may exceed the 40% fill capacity allowed by the NEC. A qualified electrician could determine whether this is the case quite easily.

 

[Dionysus]

Chances are to make this work for 120v you'll have to replace much of it. It CAN be made singlephase without replacing the conduit and wires but you'd have to change the guts of the switch, etc among other things. It's something that must be done PROPERLY. As an Electrician I say "Call an electrician".

If you still want all phases present, plus a Neutral you'd likely have to replace the conduit, add a conductor, replace the entire switch, etc.

For flexibility you want all phases to remain present, for if you may one day hook up a heavy load, or a motor.

It'll cost a bit.

Or you can leave it as-is for future motor loads.

 

[Footer]

If you still want all phases present, plus a Neutral you'd likely have to replace the conduit, add a conductor, replace the entire switch, etc.

If the conduit is not sized properly, you would have to replace the conduit, but what is your reasoning to replace the entire switch?

 

[journeymanjohn]

My first question, as an electrician, is what are you going to use it for??

You still have to provide proper overcurrent protection for the wire and load to be fed from this. Going to set another switchboard / breaker box ??

Secondly, what size is the wire?? And what size is the conduit??

 

[SHARYNF]

Looking at the picture, which clearly shows 3 fuses, if these are selected for the correct rating based on the wire being used in the feed FROM this unit then why would you need additional protection? I would have thought that the purpose of this box and fuses was to provide this protection


Sharyn

 

[JD]

The nipple on the end of the conduit and the tape around the wires may be throwing what I think I see off. It looks like 3 pieces of #4. What bothers me is the ground lug being mounted on the nipple. It also appears this is only a frame ground as I see what looks like both ends of the ground line (one cut off near the knockout.) Looks a lot like #12 ! Love the shredded wire strands laying about the bottom of the box! You need to call someone in big time.